slru.c File Reference

#include "postgres.h"
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
#include "access/slru.h"
#include "access/transam.h"
#include "access/xlog.h"
#include "access/xlogutils.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/fd.h"
#include "storage/shmem.h"
#include "utils/guc.h"

Include dependency graph for slru.c:

Go to the source code of this file.

Data Structures
struct	SlruWriteAllData

Macros
#define	MAX_WRITEALL_BUFFERS   16
#define	SLRU_BANK_BITSHIFT   4
#define	SLRU_BANK_SIZE   (1 << SLRU_BANK_BITSHIFT)
#define	SlotGetBankNumber(slotno)   ((slotno) >> SLRU_BANK_BITSHIFT)
#define	INIT_SLRUFILETAG(a, xx_handler, xx_segno)

Typedefs
typedef struct SlruWriteAllData	SlruWriteAllData
typedef struct SlruWriteAllData *	SlruWriteAll

Enumerations
enum	SlruErrorCause {   SLRU_OPEN_FAILED , SLRU_SEEK_FAILED , SLRU_READ_FAILED , SLRU_WRITE_FAILED ,   SLRU_FSYNC_FAILED , SLRU_CLOSE_FAILED }

Functions
static int	SlruFileName (SlruCtl ctl, char *path, int64 segno)
static void	SimpleLruZeroLSNs (SlruCtl ctl, int slotno)
static void	SimpleLruWaitIO (SlruCtl ctl, int slotno)
static void	SlruInternalWritePage (SlruCtl ctl, int slotno, SlruWriteAll fdata)
static bool	SlruPhysicalReadPage (SlruCtl ctl, int64 pageno, int slotno)
static bool	SlruPhysicalWritePage (SlruCtl ctl, int64 pageno, int slotno, SlruWriteAll fdata)
static void	SlruReportIOError (SlruCtl ctl, int64 pageno, TransactionId xid)
static int	SlruSelectLRUPage (SlruCtl ctl, int64 pageno)
static bool	SlruScanDirCbDeleteCutoff (SlruCtl ctl, char *filename, int64 segpage, void *data)
static void	SlruInternalDeleteSegment (SlruCtl ctl, int64 segno)
static void	SlruRecentlyUsed (SlruShared shared, int slotno)
Size	SimpleLruShmemSize (int nslots, int nlsns)
int	SimpleLruAutotuneBuffers (int divisor, int max)
void	SimpleLruInit (SlruCtl ctl, const char *name, int nslots, int nlsns, const char *subdir, int buffer_tranche_id, int bank_tranche_id, SyncRequestHandler sync_handler, bool long_segment_names)
bool	check_slru_buffers (const char *name, int *newval)
int	SimpleLruZeroPage (SlruCtl ctl, int64 pageno)
void	SimpleLruZeroAndWritePage (SlruCtl ctl, int64 pageno)
int	SimpleLruReadPage (SlruCtl ctl, int64 pageno, bool write_ok, TransactionId xid)
int	SimpleLruReadPage_ReadOnly (SlruCtl ctl, int64 pageno, TransactionId xid)
void	SimpleLruWritePage (SlruCtl ctl, int slotno)
bool	SimpleLruDoesPhysicalPageExist (SlruCtl ctl, int64 pageno)
void	SimpleLruWriteAll (SlruCtl ctl, bool allow_redirtied)
void	SimpleLruTruncate (SlruCtl ctl, int64 cutoffPage)
void	SlruDeleteSegment (SlruCtl ctl, int64 segno)
static bool	SlruMayDeleteSegment (SlruCtl ctl, int64 segpage, int64 cutoffPage)
bool	SlruScanDirCbReportPresence (SlruCtl ctl, char *filename, int64 segpage, void *data)
bool	SlruScanDirCbDeleteAll (SlruCtl ctl, char *filename, int64 segpage, void *data)
static bool	SlruCorrectSegmentFilenameLength (SlruCtl ctl, size_t len)
bool	SlruScanDirectory (SlruCtl ctl, SlruScanCallback callback, void *data)
int	SlruSyncFileTag (SlruCtl ctl, const FileTag *ftag, char *path)

Variables
static SlruErrorCause	slru_errcause
static int	slru_errno

Macro Definition Documentation

INIT_SLRUFILETAG

#define INIT_SLRUFILETAG	(		a,
			xx_handler,
			xx_segno
	)

Value:

( \
	memset(&(a), 0, sizeof(FileTag)), \
    (a).handler = (xx_handler), \
    (a).segno = (xx_segno) \
)

Definition at line 156 of file slru.c.

{
    SLRU_OPEN_FAILED,
    SLRU_SEEK_FAILED,
    SLRU_READ_FAILED,
    SLRU_WRITE_FAILED,
    SLRU_FSYNC_FAILED,
    SLRU_CLOSE_FAILED,
} SlruErrorCause;
 
static SlruErrorCause slru_errcause;
static int  slru_errno;
 
 
static void SimpleLruZeroLSNs(SlruCtl ctl, int slotno);
static void SimpleLruWaitIO(SlruCtl ctl, int slotno);
static void SlruInternalWritePage(SlruCtl ctl, int slotno, SlruWriteAll fdata);
static bool SlruPhysicalReadPage(SlruCtl ctl, int64 pageno, int slotno);
static bool SlruPhysicalWritePage(SlruCtl ctl, int64 pageno, int slotno,
                                  SlruWriteAll fdata);
static void SlruReportIOError(SlruCtl ctl, int64 pageno, TransactionId xid);
static int  SlruSelectLRUPage(SlruCtl ctl, int64 pageno);
 
static bool SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename,
                                      int64 segpage, void *data);
static void SlruInternalDeleteSegment(SlruCtl ctl, int64 segno);
static inline void SlruRecentlyUsed(SlruShared shared, int slotno);
 
 
/*
 * Initialization of shared memory
 */
 
Size
SimpleLruShmemSize(int nslots, int nlsns)
{
    int         nbanks = nslots / SLRU_BANK_SIZE;
    Size        sz;
 
    Assert(nslots <= SLRU_MAX_ALLOWED_BUFFERS);
    Assert(nslots % SLRU_BANK_SIZE == 0);
 
    /* we assume nslots isn't so large as to risk overflow */
    sz = MAXALIGN(sizeof(SlruSharedData));
    sz += MAXALIGN(nslots * sizeof(char *));    /* page_buffer[] */
    sz += MAXALIGN(nslots * sizeof(SlruPageStatus));    /* page_status[] */
    sz += MAXALIGN(nslots * sizeof(bool));  /* page_dirty[] */
    sz += MAXALIGN(nslots * sizeof(int64)); /* page_number[] */
    sz += MAXALIGN(nslots * sizeof(int));   /* page_lru_count[] */
    sz += MAXALIGN(nslots * sizeof(LWLockPadded));  /* buffer_locks[] */
    sz += MAXALIGN(nbanks * sizeof(LWLockPadded));  /* bank_locks[] */
    sz += MAXALIGN(nbanks * sizeof(int));   /* bank_cur_lru_count[] */
 
    if (nlsns > 0)
        sz += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr));    /* group_lsn[] */
 
    return BUFFERALIGN(sz) + BLCKSZ * nslots;
}
 
/*
 * Determine a number of SLRU buffers to use.
 *
 * We simply divide shared_buffers by the divisor given and cap
 * that at the maximum given; but always at least SLRU_BANK_SIZE.
 * Round down to the nearest multiple of SLRU_BANK_SIZE.
 */
int
SimpleLruAutotuneBuffers(int divisor, int max)
{
    return Min(max - (max % SLRU_BANK_SIZE),
               Max(SLRU_BANK_SIZE,
                   NBuffers / divisor - (NBuffers / divisor) % SLRU_BANK_SIZE));
}
 
/*
 * Initialize, or attach to, a simple LRU cache in shared memory.
 *
 * ctl: address of local (unshared) control structure.
 * name: name of SLRU.  (This is user-visible, pick with care!)
 * nslots: number of page slots to use.
 * nlsns: number of LSN groups per page (set to zero if not relevant).
 * subdir: PGDATA-relative subdirectory that will contain the files.
 * buffer_tranche_id: tranche ID to use for the SLRU's per-buffer LWLocks.
 * bank_tranche_id: tranche ID to use for the bank LWLocks.
 * sync_handler: which set of functions to use to handle sync requests
 * long_segment_names: use short or long segment names
 */
void
SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
              const char *subdir, int buffer_tranche_id, int bank_tranche_id,
              SyncRequestHandler sync_handler, bool long_segment_names)
{
    SlruShared  shared;
    bool        found;
    int         nbanks = nslots / SLRU_BANK_SIZE;
 
    Assert(nslots <= SLRU_MAX_ALLOWED_BUFFERS);
 
    shared = (SlruShared) ShmemInitStruct(name,
                                          SimpleLruShmemSize(nslots, nlsns),
                                          &found);
 
    if (!IsUnderPostmaster)
    {
        /* Initialize locks and shared memory area */
        char       *ptr;
        Size        offset;
 
        Assert(!found);
 
        memset(shared, 0, sizeof(SlruSharedData));
 
        shared->num_slots = nslots;
        shared->lsn_groups_per_page = nlsns;
 
        pg_atomic_init_u64(&shared->latest_page_number, 0);
 
        shared->slru_stats_idx = pgstat_get_slru_index(name);
 
        ptr = (char *) shared;
        offset = MAXALIGN(sizeof(SlruSharedData));
        shared->page_buffer = (char **) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(char *));
        shared->page_status = (SlruPageStatus *) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(SlruPageStatus));
        shared->page_dirty = (bool *) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(bool));
        shared->page_number = (int64 *) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(int64));
        shared->page_lru_count = (int *) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(int));
 
        /* Initialize LWLocks */
        shared->buffer_locks = (LWLockPadded *) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(LWLockPadded));
        shared->bank_locks = (LWLockPadded *) (ptr + offset);
        offset += MAXALIGN(nbanks * sizeof(LWLockPadded));
        shared->bank_cur_lru_count = (int *) (ptr + offset);
        offset += MAXALIGN(nbanks * sizeof(int));
 
        if (nlsns > 0)
        {
            shared->group_lsn = (XLogRecPtr *) (ptr + offset);
            offset += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr));
        }
 
        ptr += BUFFERALIGN(offset);
        for (int slotno = 0; slotno < nslots; slotno++)
        {
            LWLockInitialize(&shared->buffer_locks[slotno].lock,
                             buffer_tranche_id);
 
            shared->page_buffer[slotno] = ptr;
            shared->page_status[slotno] = SLRU_PAGE_EMPTY;
            shared->page_dirty[slotno] = false;
            shared->page_lru_count[slotno] = 0;
            ptr += BLCKSZ;
        }
 
        /* Initialize the slot banks. */
        for (int bankno = 0; bankno < nbanks; bankno++)
        {
            LWLockInitialize(&shared->bank_locks[bankno].lock, bank_tranche_id);
            shared->bank_cur_lru_count[bankno] = 0;
        }
 
        /* Should fit to estimated shmem size */
        Assert(ptr - (char *) shared <= SimpleLruShmemSize(nslots, nlsns));
    }
    else
    {
        Assert(found);
        Assert(shared->num_slots == nslots);
    }
 
    /*
     * Initialize the unshared control struct, including directory path. We
     * assume caller set PagePrecedes.
     */
    ctl->shared = shared;
    ctl->sync_handler = sync_handler;
    ctl->long_segment_names = long_segment_names;
    ctl->nbanks = nbanks;
    strlcpy(ctl->Dir, subdir, sizeof(ctl->Dir));
}
 
/*
 * Helper function for GUC check_hook to check whether slru buffers are in
 * multiples of SLRU_BANK_SIZE.
 */
bool
check_slru_buffers(const char *name, int *newval)
{
    /* Valid values are multiples of SLRU_BANK_SIZE */
    if (*newval % SLRU_BANK_SIZE == 0)
        return true;
 
    GUC_check_errdetail("\"%s\" must be a multiple of %d.", name,
                        SLRU_BANK_SIZE);
    return false;
}
 
/*
 * Initialize (or reinitialize) a page to zeroes.
 *
 * The page is not actually written, just set up in shared memory.
 * The slot number of the new page is returned.
 *
 * Bank lock must be held at entry, and will be held at exit.
 */
int
SimpleLruZeroPage(SlruCtl ctl, int64 pageno)
{
    SlruShared  shared = ctl->shared;
    int         slotno;
 
    Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
 
    /* Find a suitable buffer slot for the page */
    slotno = SlruSelectLRUPage(ctl, pageno);
    Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
           (shared->page_status[slotno] == SLRU_PAGE_VALID &&
            !shared->page_dirty[slotno]) ||
           shared->page_number[slotno] == pageno);
 
    /* Mark the slot as containing this page */
    shared->page_number[slotno] = pageno;
    shared->page_status[slotno] = SLRU_PAGE_VALID;
    shared->page_dirty[slotno] = true;
    SlruRecentlyUsed(shared, slotno);
 
    /* Set the buffer to zeroes */
    MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
 
    /* Set the LSNs for this new page to zero */
    SimpleLruZeroLSNs(ctl, slotno);
 
    /*
     * Assume this page is now the latest active page.
     *
     * Note that because both this routine and SlruSelectLRUPage run with a
     * SLRU bank lock held, it is not possible for this to be zeroing a page
     * that SlruSelectLRUPage is going to evict simultaneously.  Therefore,
     * there's no memory barrier here.
     */
    pg_atomic_write_u64(&shared->latest_page_number, pageno);
 
    /* update the stats counter of zeroed pages */
    pgstat_count_slru_blocks_zeroed(shared->slru_stats_idx);
 
    return slotno;
}
 
/*
 * Zero all the LSNs we store for this slru page.
 *
 * This should be called each time we create a new page, and each time we read
 * in a page from disk into an existing buffer.  (Such an old page cannot
 * have any interesting LSNs, since we'd have flushed them before writing
 * the page in the first place.)
 *
 * This assumes that InvalidXLogRecPtr is bitwise-all-0.
 */
static void
SimpleLruZeroLSNs(SlruCtl ctl, int slotno)
{
    SlruShared  shared = ctl->shared;
 
    if (shared->lsn_groups_per_page > 0)
        MemSet(&shared->group_lsn[slotno * shared->lsn_groups_per_page], 0,
               shared->lsn_groups_per_page * sizeof(XLogRecPtr));
}
 
/*
 * This is a convenience wrapper for the common case of zeroing a page and
 * immediately flushing it to disk.
 *
 * SLRU bank lock is acquired and released here.
 */
void
SimpleLruZeroAndWritePage(SlruCtl ctl, int64 pageno)
{
    int         slotno;
    LWLock     *lock;
 
    lock = SimpleLruGetBankLock(ctl, pageno);
    LWLockAcquire(lock, LW_EXCLUSIVE);
 
    /* Create and zero the page */
    slotno = SimpleLruZeroPage(ctl, pageno);
 
    /* Make sure it's written out */
    SimpleLruWritePage(ctl, slotno);
    Assert(!ctl->shared->page_dirty[slotno]);
 
    LWLockRelease(lock);
}
 
/*
 * Wait for any active I/O on a page slot to finish.  (This does not
 * guarantee that new I/O hasn't been started before we return, though.
 * In fact the slot might not even contain the same page anymore.)
 *
 * Bank lock must be held at entry, and will be held at exit.
 */
static void
SimpleLruWaitIO(SlruCtl ctl, int slotno)
{
    SlruShared  shared = ctl->shared;
    int         bankno = SlotGetBankNumber(slotno);
 
    Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
 
    /* See notes at top of file */
    LWLockRelease(&shared->bank_locks[bankno].lock);
    LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED);
    LWLockRelease(&shared->buffer_locks[slotno].lock);
    LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
 
    /*
     * If the slot is still in an io-in-progress state, then either someone
     * already started a new I/O on the slot, or a previous I/O failed and
     * neglected to reset the page state.  That shouldn't happen, really, but
     * it seems worth a few extra cycles to check and recover from it. We can
     * cheaply test for failure by seeing if the buffer lock is still held (we
     * assume that transaction abort would release the lock).
     */
    if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS ||
        shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS)
    {
        if (LWLockConditionalAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED))
        {
            /* indeed, the I/O must have failed */
            if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS)
                shared->page_status[slotno] = SLRU_PAGE_EMPTY;
            else                /* write_in_progress */
            {
                shared->page_status[slotno] = SLRU_PAGE_VALID;
                shared->page_dirty[slotno] = true;
            }
            LWLockRelease(&shared->buffer_locks[slotno].lock);
        }
    }
}
 
/*
 * Find a page in a shared buffer, reading it in if necessary.
 * The page number must correspond to an already-initialized page.
 *
 * If write_ok is true then it is OK to return a page that is in
 * WRITE_IN_PROGRESS state; it is the caller's responsibility to be sure
 * that modification of the page is safe.  If write_ok is false then we
 * will not return the page until it is not undergoing active I/O.
 *
 * The passed-in xid is used only for error reporting, and may be
 * InvalidTransactionId if no specific xid is associated with the action.
 *
 * Return value is the shared-buffer slot number now holding the page.
 * The buffer's LRU access info is updated.
 *
 * The correct bank lock must be held at entry, and will be held at exit.
 */
int
SimpleLruReadPage(SlruCtl ctl, int64 pageno, bool write_ok,
                  TransactionId xid)
{
    SlruShared  shared = ctl->shared;
    LWLock     *banklock = SimpleLruGetBankLock(ctl, pageno);
 
    Assert(LWLockHeldByMeInMode(banklock, LW_EXCLUSIVE));
 
    /* Outer loop handles restart if we must wait for someone else's I/O */
    for (;;)
    {
        int         slotno;
        bool        ok;
 
        /* See if page already is in memory; if not, pick victim slot */
        slotno = SlruSelectLRUPage(ctl, pageno);
 
        /* Did we find the page in memory? */
        if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
            shared->page_number[slotno] == pageno)
        {
            /*
             * If page is still being read in, we must wait for I/O.  Likewise
             * if the page is being written and the caller said that's not OK.
             */
            if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS ||
                (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS &&
                 !write_ok))
            {
                SimpleLruWaitIO(ctl, slotno);
                /* Now we must recheck state from the top */
                continue;
            }
            /* Otherwise, it's ready to use */
            SlruRecentlyUsed(shared, slotno);
 
            /* update the stats counter of pages found in the SLRU */
            pgstat_count_slru_blocks_hit(shared->slru_stats_idx);
 
            return slotno;
        }
 
        /* We found no match; assert we selected a freeable slot */
        Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
               (shared->page_status[slotno] == SLRU_PAGE_VALID &&
                !shared->page_dirty[slotno]));
 
        /* Mark the slot read-busy */
        shared->page_number[slotno] = pageno;
        shared->page_status[slotno] = SLRU_PAGE_READ_IN_PROGRESS;
        shared->page_dirty[slotno] = false;
 
        /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
        LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
 
        /* Release bank lock while doing I/O */
        LWLockRelease(banklock);
 
        /* Do the read */
        ok = SlruPhysicalReadPage(ctl, pageno, slotno);
 
        /* Set the LSNs for this newly read-in page to zero */
        SimpleLruZeroLSNs(ctl, slotno);
 
        /* Re-acquire bank control lock and update page state */
        LWLockAcquire(banklock, LW_EXCLUSIVE);
 
        Assert(shared->page_number[slotno] == pageno &&
               shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS &&
               !shared->page_dirty[slotno]);
 
        shared->page_status[slotno] = ok ? SLRU_PAGE_VALID : SLRU_PAGE_EMPTY;
 
        LWLockRelease(&shared->buffer_locks[slotno].lock);
 
        /* Now it's okay to ereport if we failed */
        if (!ok)
            SlruReportIOError(ctl, pageno, xid);
 
        SlruRecentlyUsed(shared, slotno);
 
        /* update the stats counter of pages not found in SLRU */
        pgstat_count_slru_blocks_read(shared->slru_stats_idx);
 
        return slotno;
    }
}
 
/*
 * Find a page in a shared buffer, reading it in if necessary.
 * The page number must correspond to an already-initialized page.
 * The caller must intend only read-only access to the page.
 *
 * The passed-in xid is used only for error reporting, and may be
 * InvalidTransactionId if no specific xid is associated with the action.
 *
 * Return value is the shared-buffer slot number now holding the page.
 * The buffer's LRU access info is updated.
 *
 * Bank control lock must NOT be held at entry, but will be held at exit.
 * It is unspecified whether the lock will be shared or exclusive.
 */
int
SimpleLruReadPage_ReadOnly(SlruCtl ctl, int64 pageno, TransactionId xid)
{
    SlruShared  shared = ctl->shared;
    LWLock     *banklock = SimpleLruGetBankLock(ctl, pageno);
    int         bankno = pageno % ctl->nbanks;
    int         bankstart = bankno * SLRU_BANK_SIZE;
    int         bankend = bankstart + SLRU_BANK_SIZE;
 
    /* Try to find the page while holding only shared lock */
    LWLockAcquire(banklock, LW_SHARED);
 
    /* See if page is already in a buffer */
    for (int slotno = bankstart; slotno < bankend; slotno++)
    {
        if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
            shared->page_number[slotno] == pageno &&
            shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS)
        {
            /* See comments for SlruRecentlyUsed() */
            SlruRecentlyUsed(shared, slotno);
 
            /* update the stats counter of pages found in the SLRU */
            pgstat_count_slru_blocks_hit(shared->slru_stats_idx);
 
            return slotno;
        }
    }
 
    /* No luck, so switch to normal exclusive lock and do regular read */
    LWLockRelease(banklock);
    LWLockAcquire(banklock, LW_EXCLUSIVE);
 
    return SimpleLruReadPage(ctl, pageno, true, xid);
}
 
/*
 * Write a page from a shared buffer, if necessary.
 * Does nothing if the specified slot is not dirty.
 *
 * NOTE: only one write attempt is made here.  Hence, it is possible that
 * the page is still dirty at exit (if someone else re-dirtied it during
 * the write).  However, we *do* attempt a fresh write even if the page
 * is already being written; this is for checkpoints.
 *
 * Bank lock must be held at entry, and will be held at exit.
 */
static void
SlruInternalWritePage(SlruCtl ctl, int slotno, SlruWriteAll fdata)
{
    SlruShared  shared = ctl->shared;
    int64       pageno = shared->page_number[slotno];
    int         bankno = SlotGetBankNumber(slotno);
    bool        ok;
 
    Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
    Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
 
    /* If a write is in progress, wait for it to finish */
    while (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS &&
           shared->page_number[slotno] == pageno)
    {
        SimpleLruWaitIO(ctl, slotno);
    }
 
    /*
     * Do nothing if page is not dirty, or if buffer no longer contains the
     * same page we were called for.
     */
    if (!shared->page_dirty[slotno] ||
        shared->page_status[slotno] != SLRU_PAGE_VALID ||
        shared->page_number[slotno] != pageno)
        return;
 
    /*
     * Mark the slot write-busy, and clear the dirtybit.  After this point, a
     * transaction status update on this page will mark it dirty again.
     */
    shared->page_status[slotno] = SLRU_PAGE_WRITE_IN_PROGRESS;
    shared->page_dirty[slotno] = false;
 
    /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
    LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
 
    /* Release bank lock while doing I/O */
    LWLockRelease(&shared->bank_locks[bankno].lock);
 
    /* Do the write */
    ok = SlruPhysicalWritePage(ctl, pageno, slotno, fdata);
 
    /* If we failed, and we're in a flush, better close the files */
    if (!ok && fdata)
    {
        for (int i = 0; i < fdata->num_files; i++)
            CloseTransientFile(fdata->fd[i]);
    }
 
    /* Re-acquire bank lock and update page state */
    LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
 
    Assert(shared->page_number[slotno] == pageno &&
           shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS);
 
    /* If we failed to write, mark the page dirty again */
    if (!ok)
        shared->page_dirty[slotno] = true;
 
    shared->page_status[slotno] = SLRU_PAGE_VALID;
 
    LWLockRelease(&shared->buffer_locks[slotno].lock);
 
    /* Now it's okay to ereport if we failed */
    if (!ok)
        SlruReportIOError(ctl, pageno, InvalidTransactionId);
 
    /* If part of a checkpoint, count this as a SLRU buffer written. */
    if (fdata)
    {
        CheckpointStats.ckpt_slru_written++;
        PendingCheckpointerStats.slru_written++;
    }
}
 
/*
 * Wrapper of SlruInternalWritePage, for external callers.
 * fdata is always passed a NULL here.
 */
void
SimpleLruWritePage(SlruCtl ctl, int slotno)
{
    Assert(ctl->shared->page_status[slotno] != SLRU_PAGE_EMPTY);
 
    SlruInternalWritePage(ctl, slotno, NULL);
}
 
/*
 * Return whether the given page exists on disk.
 *
 * A false return means that either the file does not exist, or that it's not
 * large enough to contain the given page.
 */
bool
SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int64 pageno)
{
    int64       segno = pageno / SLRU_PAGES_PER_SEGMENT;
    int         rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
    int         offset = rpageno * BLCKSZ;
    char        path[MAXPGPATH];
    int         fd;
    bool        result;
    off_t       endpos;
 
    /* update the stats counter of checked pages */
    pgstat_count_slru_blocks_exists(ctl->shared->slru_stats_idx);
 
    SlruFileName(ctl, path, segno);
 
    fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
    if (fd < 0)
    {
        /* expected: file doesn't exist */
        if (errno == ENOENT)
            return false;
 
        /* report error normally */
        slru_errcause = SLRU_OPEN_FAILED;
        slru_errno = errno;
        SlruReportIOError(ctl, pageno, 0);
    }
 
    if ((endpos = lseek(fd, 0, SEEK_END)) < 0)
    {
        slru_errcause = SLRU_SEEK_FAILED;
        slru_errno = errno;
        SlruReportIOError(ctl, pageno, 0);
    }
 
    result = endpos >= (off_t) (offset + BLCKSZ);
 
    if (CloseTransientFile(fd) != 0)
    {
        slru_errcause = SLRU_CLOSE_FAILED;
        slru_errno = errno;
        return false;
    }
 
    return result;
}
 
/*
 * Physical read of a (previously existing) page into a buffer slot
 *
 * On failure, we cannot just ereport(ERROR) since caller has put state in
 * shared memory that must be undone.  So, we return false and save enough
 * info in static variables to let SlruReportIOError make the report.
 *
 * For now, assume it's not worth keeping a file pointer open across
 * read/write operations.  We could cache one virtual file pointer ...
 */
static bool
SlruPhysicalReadPage(SlruCtl ctl, int64 pageno, int slotno)
{
    SlruShared  shared = ctl->shared;
    int64       segno = pageno / SLRU_PAGES_PER_SEGMENT;
    int         rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
    off_t       offset = rpageno * BLCKSZ;
    char        path[MAXPGPATH];
    int         fd;
 
    SlruFileName(ctl, path, segno);
 
    /*
     * In a crash-and-restart situation, it's possible for us to receive
     * commands to set the commit status of transactions whose bits are in
     * already-truncated segments of the commit log (see notes in
     * SlruPhysicalWritePage).  Hence, if we are InRecovery, allow the case
     * where the file doesn't exist, and return zeroes instead.
     */
    fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
    if (fd < 0)
    {
        if (errno != ENOENT || !InRecovery)
        {
            slru_errcause = SLRU_OPEN_FAILED;
            slru_errno = errno;
            return false;
        }
 
        ereport(LOG,
                (errmsg("file \"%s\" doesn't exist, reading as zeroes",
                        path)));
        MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
        return true;
    }
 
    errno = 0;
    pgstat_report_wait_start(WAIT_EVENT_SLRU_READ);
    if (pg_pread(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ)
    {
        pgstat_report_wait_end();
        slru_errcause = SLRU_READ_FAILED;
        slru_errno = errno;
        CloseTransientFile(fd);
        return false;
    }
    pgstat_report_wait_end();
 
    if (CloseTransientFile(fd) != 0)
    {
        slru_errcause = SLRU_CLOSE_FAILED;
        slru_errno = errno;
        return false;
    }
 
    return true;
}
 
/*
 * Physical write of a page from a buffer slot
 *
 * On failure, we cannot just ereport(ERROR) since caller has put state in
 * shared memory that must be undone.  So, we return false and save enough
 * info in static variables to let SlruReportIOError make the report.
 *
 * For now, assume it's not worth keeping a file pointer open across
 * independent read/write operations.  We do batch operations during
 * SimpleLruWriteAll, though.
 *
 * fdata is NULL for a standalone write, pointer to open-file info during
 * SimpleLruWriteAll.
 */
static bool
SlruPhysicalWritePage(SlruCtl ctl, int64 pageno, int slotno, SlruWriteAll fdata)
{
    SlruShared  shared = ctl->shared;
    int64       segno = pageno / SLRU_PAGES_PER_SEGMENT;
    int         rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
    off_t       offset = rpageno * BLCKSZ;
    char        path[MAXPGPATH];
    int         fd = -1;
 
    /* update the stats counter of written pages */
    pgstat_count_slru_blocks_written(shared->slru_stats_idx);
 
    /*
     * Honor the write-WAL-before-data rule, if appropriate, so that we do not
     * write out data before associated WAL records.  This is the same action
     * performed during FlushBuffer() in the main buffer manager.
     */
    if (shared->group_lsn != NULL)
    {
        /*
         * We must determine the largest async-commit LSN for the page. This
         * is a bit tedious, but since this entire function is a slow path
         * anyway, it seems better to do this here than to maintain a per-page
         * LSN variable (which'd need an extra comparison in the
         * transaction-commit path).
         */
        XLogRecPtr  max_lsn;
        int         lsnindex;
 
        lsnindex = slotno * shared->lsn_groups_per_page;
        max_lsn = shared->group_lsn[lsnindex++];
        for (int lsnoff = 1; lsnoff < shared->lsn_groups_per_page; lsnoff++)
        {
            XLogRecPtr  this_lsn = shared->group_lsn[lsnindex++];
 
            if (max_lsn < this_lsn)
                max_lsn = this_lsn;
        }
 
        if (XLogRecPtrIsValid(max_lsn))
        {
            /*
             * As noted above, elog(ERROR) is not acceptable here, so if
             * XLogFlush were to fail, we must PANIC.  This isn't much of a
             * restriction because XLogFlush is just about all critical
             * section anyway, but let's make sure.
             */
            START_CRIT_SECTION();
            XLogFlush(max_lsn);
            END_CRIT_SECTION();
        }
    }
 
    /*
     * During a SimpleLruWriteAll, we may already have the desired file open.
     */
    if (fdata)
    {
        for (int i = 0; i < fdata->num_files; i++)
        {
            if (fdata->segno[i] == segno)
            {
                fd = fdata->fd[i];
                break;
            }
        }
    }
 
    if (fd < 0)
    {
        /*
         * If the file doesn't already exist, we should create it.  It is
         * possible for this to need to happen when writing a page that's not
         * first in its segment; we assume the OS can cope with that. (Note:
         * it might seem that it'd be okay to create files only when
         * SimpleLruZeroPage is called for the first page of a segment.
         * However, if after a crash and restart the REDO logic elects to
         * replay the log from a checkpoint before the latest one, then it's
         * possible that we will get commands to set transaction status of
         * transactions that have already been truncated from the commit log.
         * Easiest way to deal with that is to accept references to
         * nonexistent files here and in SlruPhysicalReadPage.)
         *
         * Note: it is possible for more than one backend to be executing this
         * code simultaneously for different pages of the same file. Hence,
         * don't use O_EXCL or O_TRUNC or anything like that.
         */
        SlruFileName(ctl, path, segno);
        fd = OpenTransientFile(path, O_RDWR | O_CREAT | PG_BINARY);
        if (fd < 0)
        {
            slru_errcause = SLRU_OPEN_FAILED;
            slru_errno = errno;
            return false;
        }
 
        if (fdata)
        {
            if (fdata->num_files < MAX_WRITEALL_BUFFERS)
            {
                fdata->fd[fdata->num_files] = fd;
                fdata->segno[fdata->num_files] = segno;
                fdata->num_files++;
            }
            else
            {
                /*
                 * In the unlikely event that we exceed MAX_WRITEALL_BUFFERS,
                 * fall back to treating it as a standalone write.
                 */
                fdata = NULL;
            }
        }
    }
 
    errno = 0;
    pgstat_report_wait_start(WAIT_EVENT_SLRU_WRITE);
    if (pg_pwrite(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ)
    {
        pgstat_report_wait_end();
        /* if write didn't set errno, assume problem is no disk space */
        if (errno == 0)
            errno = ENOSPC;
        slru_errcause = SLRU_WRITE_FAILED;
        slru_errno = errno;
        if (!fdata)
            CloseTransientFile(fd);
        return false;
    }
    pgstat_report_wait_end();
 
    /* Queue up a sync request for the checkpointer. */
    if (ctl->sync_handler != SYNC_HANDLER_NONE)
    {
        FileTag     tag;
 
        INIT_SLRUFILETAG(tag, ctl->sync_handler, segno);
        if (!RegisterSyncRequest(&tag, SYNC_REQUEST, false))
        {
            /* No space to enqueue sync request.  Do it synchronously. */
            pgstat_report_wait_start(WAIT_EVENT_SLRU_SYNC);
            if (pg_fsync(fd) != 0)
            {
                pgstat_report_wait_end();
                slru_errcause = SLRU_FSYNC_FAILED;
                slru_errno = errno;
                CloseTransientFile(fd);
                return false;
            }
            pgstat_report_wait_end();
        }
    }
 
    /* Close file, unless part of flush request. */
    if (!fdata)
    {
        if (CloseTransientFile(fd) != 0)
        {
            slru_errcause = SLRU_CLOSE_FAILED;
            slru_errno = errno;
            return false;
        }
    }
 
    return true;
}
 
/*
 * Issue the error message after failure of SlruPhysicalReadPage or
 * SlruPhysicalWritePage.  Call this after cleaning up shared-memory state.
 */
static void
SlruReportIOError(SlruCtl ctl, int64 pageno, TransactionId xid)
{
    int64       segno = pageno / SLRU_PAGES_PER_SEGMENT;
    int         rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
    int         offset = rpageno * BLCKSZ;
    char        path[MAXPGPATH];
 
    SlruFileName(ctl, path, segno);
    errno = slru_errno;
    switch (slru_errcause)
    {
        case SLRU_OPEN_FAILED:
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not access status of transaction %u", xid),
                     errdetail("Could not open file \"%s\": %m.", path)));
            break;
        case SLRU_SEEK_FAILED:
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not access status of transaction %u", xid),
                     errdetail("Could not seek in file \"%s\" to offset %d: %m.",
                               path, offset)));
            break;
        case SLRU_READ_FAILED:
            if (errno)
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not access status of transaction %u", xid),
                         errdetail("Could not read from file \"%s\" at offset %d: %m.",
                                   path, offset)));
            else
                ereport(ERROR,
                        (errmsg("could not access status of transaction %u", xid),
                         errdetail("Could not read from file \"%s\" at offset %d: read too few bytes.", path, offset)));
            break;
        case SLRU_WRITE_FAILED:
            if (errno)
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not access status of transaction %u", xid),
                         errdetail("Could not write to file \"%s\" at offset %d: %m.",
                                   path, offset)));
            else
                ereport(ERROR,
                        (errmsg("could not access status of transaction %u", xid),
                         errdetail("Could not write to file \"%s\" at offset %d: wrote too few bytes.",
                                   path, offset)));
            break;
        case SLRU_FSYNC_FAILED:
            ereport(data_sync_elevel(ERROR),
                    (errcode_for_file_access(),
                     errmsg("could not access status of transaction %u", xid),
                     errdetail("Could not fsync file \"%s\": %m.",
                               path)));
            break;
        case SLRU_CLOSE_FAILED:
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not access status of transaction %u", xid),
                     errdetail("Could not close file \"%s\": %m.",
                               path)));
            break;
        default:
            /* can't get here, we trust */
            elog(ERROR, "unrecognized SimpleLru error cause: %d",
                 (int) slru_errcause);
            break;
    }
}
 
/*
 * Mark a buffer slot "most recently used".
 */
static inline void
SlruRecentlyUsed(SlruShared shared, int slotno)
{
    int         bankno = SlotGetBankNumber(slotno);
    int         new_lru_count = shared->bank_cur_lru_count[bankno];
 
    Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
 
    /*
     * The reason for the if-test is that there are often many consecutive
     * accesses to the same page (particularly the latest page).  By
     * suppressing useless increments of bank_cur_lru_count, we reduce the
     * probability that old pages' counts will "wrap around" and make them
     * appear recently used.
     *
     * We allow this code to be executed concurrently by multiple processes
     * within SimpleLruReadPage_ReadOnly().  As long as int reads and writes
     * are atomic, this should not cause any completely-bogus values to enter
     * the computation.  However, it is possible for either bank_cur_lru_count
     * or individual page_lru_count entries to be "reset" to lower values than
     * they should have, in case a process is delayed while it executes this
     * function.  With care in SlruSelectLRUPage(), this does little harm, and
     * in any case the absolute worst possible consequence is a nonoptimal
     * choice of page to evict.  The gain from allowing concurrent reads of
     * SLRU pages seems worth it.
     */
    if (new_lru_count != shared->page_lru_count[slotno])
    {
        shared->bank_cur_lru_count[bankno] = ++new_lru_count;
        shared->page_lru_count[slotno] = new_lru_count;
    }
}
 
/*
 * Select the slot to re-use when we need a free slot for the given page.
 *
 * The target page number is passed not only because we need to know the
 * correct bank to use, but also because we need to consider the possibility
 * that some other process reads in the target page while we are doing I/O to
 * free a slot.  Hence, check or recheck to see if any slot already holds the
 * target page, and return that slot if so.  Thus, the returned slot is
 * *either* a slot already holding the pageno (could be any state except
 * EMPTY), *or* a freeable slot (state EMPTY or CLEAN).
 *
 * The correct bank lock must be held at entry, and will be held at exit.
 */
static int
SlruSelectLRUPage(SlruCtl ctl, int64 pageno)
{
    SlruShared  shared = ctl->shared;
 
    /* Outer loop handles restart after I/O */
    for (;;)
    {
        int         cur_count;
        int         bestvalidslot = 0;  /* keep compiler quiet */
        int         best_valid_delta = -1;
        int64       best_valid_page_number = 0; /* keep compiler quiet */
        int         bestinvalidslot = 0;    /* keep compiler quiet */
        int         best_invalid_delta = -1;
        int64       best_invalid_page_number = 0;   /* keep compiler quiet */
        int         bankno = pageno % ctl->nbanks;
        int         bankstart = bankno * SLRU_BANK_SIZE;
        int         bankend = bankstart + SLRU_BANK_SIZE;
 
        Assert(LWLockHeldByMe(SimpleLruGetBankLock(ctl, pageno)));
 
        /* See if page already has a buffer assigned */
        for (int slotno = bankstart; slotno < bankend; slotno++)
        {
            if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
                shared->page_number[slotno] == pageno)
                return slotno;
        }
 
        /*
         * If we find any EMPTY slot, just select that one. Else choose a
         * victim page to replace.  We normally take the least recently used
         * valid page, but we will never take the slot containing
         * latest_page_number, even if it appears least recently used.  We
         * will select a slot that is already I/O busy only if there is no
         * other choice: a read-busy slot will not be least recently used once
         * the read finishes, and waiting for an I/O on a write-busy slot is
         * inferior to just picking some other slot.  Testing shows the slot
         * we pick instead will often be clean, allowing us to begin a read at
         * once.
         *
         * Normally the page_lru_count values will all be different and so
         * there will be a well-defined LRU page.  But since we allow
         * concurrent execution of SlruRecentlyUsed() within
         * SimpleLruReadPage_ReadOnly(), it is possible that multiple pages
         * acquire the same lru_count values.  In that case we break ties by
         * choosing the furthest-back page.
         *
         * Notice that this next line forcibly advances cur_lru_count to a
         * value that is certainly beyond any value that will be in the
         * page_lru_count array after the loop finishes.  This ensures that
         * the next execution of SlruRecentlyUsed will mark the page newly
         * used, even if it's for a page that has the current counter value.
         * That gets us back on the path to having good data when there are
         * multiple pages with the same lru_count.
         */
        cur_count = (shared->bank_cur_lru_count[bankno])++;
        for (int slotno = bankstart; slotno < bankend; slotno++)
        {
            int         this_delta;
            int64       this_page_number;
 
            if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
                return slotno;
 
            this_delta = cur_count - shared->page_lru_count[slotno];
            if (this_delta < 0)
            {
                /*
                 * Clean up in case shared updates have caused cur_count
                 * increments to get "lost".  We back off the page counts,
                 * rather than trying to increase cur_count, to avoid any
                 * question of infinite loops or failure in the presence of
                 * wrapped-around counts.
                 */
                shared->page_lru_count[slotno] = cur_count;
                this_delta = 0;
            }
 
            /*
             * If this page is the one most recently zeroed, don't consider it
             * an eviction candidate. See comments in SimpleLruZeroPage for an
             * explanation about the lack of a memory barrier here.
             */
            this_page_number = shared->page_number[slotno];
            if (this_page_number ==
                pg_atomic_read_u64(&shared->latest_page_number))
                continue;
 
            if (shared->page_status[slotno] == SLRU_PAGE_VALID)
            {
                if (this_delta > best_valid_delta ||
                    (this_delta == best_valid_delta &&
                     ctl->PagePrecedes(this_page_number,
                                       best_valid_page_number)))
                {
                    bestvalidslot = slotno;
                    best_valid_delta = this_delta;
                    best_valid_page_number = this_page_number;
                }
            }
            else
            {
                if (this_delta > best_invalid_delta ||
                    (this_delta == best_invalid_delta &&
                     ctl->PagePrecedes(this_page_number,
                                       best_invalid_page_number)))
                {
                    bestinvalidslot = slotno;
                    best_invalid_delta = this_delta;
                    best_invalid_page_number = this_page_number;
                }
            }
        }
 
        /*
         * If all pages (except possibly the latest one) are I/O busy, we'll
         * have to wait for an I/O to complete and then retry.  In that
         * unhappy case, we choose to wait for the I/O on the least recently
         * used slot, on the assumption that it was likely initiated first of
         * all the I/Os in progress and may therefore finish first.
         */
        if (best_valid_delta < 0)
        {
            SimpleLruWaitIO(ctl, bestinvalidslot);
            continue;
        }
 
        /*
         * If the selected page is clean, we're set.
         */
        if (!shared->page_dirty[bestvalidslot])
            return bestvalidslot;
 
        /*
         * Write the page.
         */
        SlruInternalWritePage(ctl, bestvalidslot, NULL);
 
        /*
         * Now loop back and try again.  This is the easiest way of dealing
         * with corner cases such as the victim page being re-dirtied while we
         * wrote it.
         */
    }
}
 
/*
 * Write dirty pages to disk during checkpoint or database shutdown.  Flushing
 * is deferred until the next call to ProcessSyncRequests(), though we do fsync
 * the containing directory here to make sure that newly created directory
 * entries are on disk.
 */
void
SimpleLruWriteAll(SlruCtl ctl, bool allow_redirtied)
{
    SlruShared  shared = ctl->shared;
    SlruWriteAllData fdata;
    int64       pageno = 0;
    int         prevbank = SlotGetBankNumber(0);
    bool        ok;
 
    /* update the stats counter of flushes */
    pgstat_count_slru_flush(shared->slru_stats_idx);
 
    /*
     * Find and write dirty pages
     */
    fdata.num_files = 0;
 
    LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
 
    for (int slotno = 0; slotno < shared->num_slots; slotno++)
    {
        int         curbank = SlotGetBankNumber(slotno);
 
        /*
         * If the current bank lock is not same as the previous bank lock then
         * release the previous lock and acquire the new lock.
         */
        if (curbank != prevbank)
        {
            LWLockRelease(&shared->bank_locks[prevbank].lock);
            LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
            prevbank = curbank;
        }
 
        /* Do nothing if slot is unused */
        if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
            continue;
 
        SlruInternalWritePage(ctl, slotno, &fdata);
 
        /*
         * In some places (e.g. checkpoints), we cannot assert that the slot
         * is clean now, since another process might have re-dirtied it
         * already.  That's okay.
         */
        Assert(allow_redirtied ||
               shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
               (shared->page_status[slotno] == SLRU_PAGE_VALID &&
                !shared->page_dirty[slotno]));
    }
 
    LWLockRelease(&shared->bank_locks[prevbank].lock);
 
    /*
     * Now close any files that were open
     */
    ok = true;
    for (int i = 0; i < fdata.num_files; i++)
    {
        if (CloseTransientFile(fdata.fd[i]) != 0)
        {
            slru_errcause = SLRU_CLOSE_FAILED;
            slru_errno = errno;
            pageno = fdata.segno[i] * SLRU_PAGES_PER_SEGMENT;
            ok = false;
        }
    }
    if (!ok)
        SlruReportIOError(ctl, pageno, InvalidTransactionId);
 
    /* Ensure that directory entries for new files are on disk. */
    if (ctl->sync_handler != SYNC_HANDLER_NONE)
        fsync_fname(ctl->Dir, true);
}
 
/*
 * Remove all segments before the one holding the passed page number
 *
 * All SLRUs prevent concurrent calls to this function, either with an LWLock
 * or by calling it only as part of a checkpoint.  Mutual exclusion must begin
 * before computing cutoffPage.  Mutual exclusion must end after any limit
 * update that would permit other backends to write fresh data into the
 * segment immediately preceding the one containing cutoffPage.  Otherwise,
 * when the SLRU is quite full, SimpleLruTruncate() might delete that segment
 * after it has accrued freshly-written data.
 */
void
SimpleLruTruncate(SlruCtl ctl, int64 cutoffPage)
{
    SlruShared  shared = ctl->shared;
    int         prevbank;
 
    /* update the stats counter of truncates */
    pgstat_count_slru_truncate(shared->slru_stats_idx);
 
    /*
     * Scan shared memory and remove any pages preceding the cutoff page, to
     * ensure we won't rewrite them later.  (Since this is normally called in
     * or just after a checkpoint, any dirty pages should have been flushed
     * already ... we're just being extra careful here.)
     */
restart:
 
    /*
     * An important safety check: the current endpoint page must not be
     * eligible for removal.  This check is just a backstop against wraparound
     * bugs elsewhere in SLRU handling, so we don't care if we read a slightly
     * outdated value; therefore we don't add a memory barrier.
     */
    if (ctl->PagePrecedes(pg_atomic_read_u64(&shared->latest_page_number),
                          cutoffPage))
    {
        ereport(LOG,
                (errmsg("could not truncate directory \"%s\": apparent wraparound",
                        ctl->Dir)));
        return;
    }
 
    prevbank = SlotGetBankNumber(0);
    LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
    for (int slotno = 0; slotno < shared->num_slots; slotno++)
    {
        int         curbank = SlotGetBankNumber(slotno);
 
        /*
         * If the current bank lock is not same as the previous bank lock then
         * release the previous lock and acquire the new lock.
         */
        if (curbank != prevbank)
        {
            LWLockRelease(&shared->bank_locks[prevbank].lock);
            LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
            prevbank = curbank;
        }
 
        if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
            continue;
        if (!ctl->PagePrecedes(shared->page_number[slotno], cutoffPage))
            continue;
 
        /*
         * If page is clean, just change state to EMPTY (expected case).
         */
        if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
            !shared->page_dirty[slotno])
        {
            shared->page_status[slotno] = SLRU_PAGE_EMPTY;
            continue;
        }
 
        /*
         * Hmm, we have (or may have) I/O operations acting on the page, so
         * we've got to wait for them to finish and then start again. This is
         * the same logic as in SlruSelectLRUPage.  (XXX if page is dirty,
         * wouldn't it be OK to just discard it without writing it?
         * SlruMayDeleteSegment() uses a stricter qualification, so we might
         * not delete this page in the end; even if we don't delete it, we
         * won't have cause to read its data again.  For now, keep the logic
         * the same as it was.)
         */
        if (shared->page_status[slotno] == SLRU_PAGE_VALID)
            SlruInternalWritePage(ctl, slotno, NULL);
        else
            SimpleLruWaitIO(ctl, slotno);
 
        LWLockRelease(&shared->bank_locks[prevbank].lock);
        goto restart;
    }
 
    LWLockRelease(&shared->bank_locks[prevbank].lock);
 
    /* Now we can remove the old segment(s) */
    (void) SlruScanDirectory(ctl, SlruScanDirCbDeleteCutoff, &cutoffPage);
}
 
/*
 * Delete an individual SLRU segment.
 *
 * NB: This does not touch the SLRU buffers themselves, callers have to ensure
 * they either can't yet contain anything, or have already been cleaned out.
 */
static void
SlruInternalDeleteSegment(SlruCtl ctl, int64 segno)
{
    char        path[MAXPGPATH];
 
    /* Forget any fsync requests queued for this segment. */
    if (ctl->sync_handler != SYNC_HANDLER_NONE)
    {
        FileTag     tag;
 
        INIT_SLRUFILETAG(tag, ctl->sync_handler, segno);
        RegisterSyncRequest(&tag, SYNC_FORGET_REQUEST, true);
    }
 
    /* Unlink the file. */
    SlruFileName(ctl, path, segno);
    ereport(DEBUG2, (errmsg_internal("removing file \"%s\"", path)));
    unlink(path);
}
 
/*
 * Delete an individual SLRU segment, identified by the segment number.
 */
void
SlruDeleteSegment(SlruCtl ctl, int64 segno)
{
    SlruShared  shared = ctl->shared;
    int         prevbank = SlotGetBankNumber(0);
    bool        did_write;
 
    /* Clean out any possibly existing references to the segment. */
    LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
restart:
    did_write = false;
    for (int slotno = 0; slotno < shared->num_slots; slotno++)
    {
        int64       pagesegno;
        int         curbank = SlotGetBankNumber(slotno);
 
        /*
         * If the current bank lock is not same as the previous bank lock then
         * release the previous lock and acquire the new lock.
         */
        if (curbank != prevbank)
        {
            LWLockRelease(&shared->bank_locks[prevbank].lock);
            LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
            prevbank = curbank;
        }
 
        if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
            continue;
 
        pagesegno = shared->page_number[slotno] / SLRU_PAGES_PER_SEGMENT;
        /* not the segment we're looking for */
        if (pagesegno != segno)
            continue;
 
        /* If page is clean, just change state to EMPTY (expected case). */
        if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
            !shared->page_dirty[slotno])
        {
            shared->page_status[slotno] = SLRU_PAGE_EMPTY;
            continue;
        }
 
        /* Same logic as SimpleLruTruncate() */
        if (shared->page_status[slotno] == SLRU_PAGE_VALID)
            SlruInternalWritePage(ctl, slotno, NULL);
        else
            SimpleLruWaitIO(ctl, slotno);
 
        did_write = true;
    }
 
    /*
     * Be extra careful and re-check. The IO functions release the control
     * lock, so new pages could have been read in.
     */
    if (did_write)
        goto restart;
 
    SlruInternalDeleteSegment(ctl, segno);
 
    LWLockRelease(&shared->bank_locks[prevbank].lock);
}
 
/*
 * Determine whether a segment is okay to delete.
 *
 * segpage is the first page of the segment, and cutoffPage is the oldest (in
 * PagePrecedes order) page in the SLRU containing still-useful data.  Since
 * every core PagePrecedes callback implements "wrap around", check the
 * segment's first and last pages:
 *
 * first<cutoff  && last<cutoff:  yes
 * first<cutoff  && last>=cutoff: no; cutoff falls inside this segment
 * first>=cutoff && last<cutoff:  no; wrap point falls inside this segment
 * first>=cutoff && last>=cutoff: no; every page of this segment is too young
 */
static bool
SlruMayDeleteSegment(SlruCtl ctl, int64 segpage, int64 cutoffPage)
{
    int64       seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1;
 
    Assert(segpage % SLRU_PAGES_PER_SEGMENT == 0);
 
    return (ctl->PagePrecedes(segpage, cutoffPage) &&
            ctl->PagePrecedes(seg_last_page, cutoffPage));
}
 
#ifdef USE_ASSERT_CHECKING
static void
SlruPagePrecedesTestOffset(SlruCtl ctl, int per_page, uint32 offset)
{
    TransactionId lhs,
                rhs;
    int64       newestPage,
                oldestPage;
    TransactionId newestXact,
                oldestXact;
 
    /*
     * Compare an XID pair having undefined order (see RFC 1982), a pair at
     * "opposite ends" of the XID space.  TransactionIdPrecedes() treats each
     * as preceding the other.  If RHS is oldestXact, LHS is the first XID we
     * must not assign.
     */
    lhs = per_page + offset;    /* skip first page to avoid non-normal XIDs */
    rhs = lhs + (1U << 31);
    Assert(TransactionIdPrecedes(lhs, rhs));
    Assert(TransactionIdPrecedes(rhs, lhs));
    Assert(!TransactionIdPrecedes(lhs - 1, rhs));
    Assert(TransactionIdPrecedes(rhs, lhs - 1));
    Assert(TransactionIdPrecedes(lhs + 1, rhs));
    Assert(!TransactionIdPrecedes(rhs, lhs + 1));
    Assert(!TransactionIdFollowsOrEquals(lhs, rhs));
    Assert(!TransactionIdFollowsOrEquals(rhs, lhs));
    Assert(!ctl->PagePrecedes(lhs / per_page, lhs / per_page));
    Assert(!ctl->PagePrecedes(lhs / per_page, rhs / per_page));
    Assert(!ctl->PagePrecedes(rhs / per_page, lhs / per_page));
    Assert(!ctl->PagePrecedes((lhs - per_page) / per_page, rhs / per_page));
    Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 3 * per_page) / per_page));
    Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 2 * per_page) / per_page));
    Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 1 * per_page) / per_page)
           || (1U << 31) % per_page != 0);  /* See CommitTsPagePrecedes() */
    Assert(ctl->PagePrecedes((lhs + 1 * per_page) / per_page, rhs / per_page)
           || (1U << 31) % per_page != 0);
    Assert(ctl->PagePrecedes((lhs + 2 * per_page) / per_page, rhs / per_page));
    Assert(ctl->PagePrecedes((lhs + 3 * per_page) / per_page, rhs / per_page));
    Assert(!ctl->PagePrecedes(rhs / per_page, (lhs + per_page) / per_page));
 
    /*
     * GetNewTransactionId() has assigned the last XID it can safely use, and
     * that XID is in the *LAST* page of the second segment.  We must not
     * delete that segment.
     */
    newestPage = 2 * SLRU_PAGES_PER_SEGMENT - 1;
    newestXact = newestPage * per_page + offset;
    Assert(newestXact / per_page == newestPage);
    oldestXact = newestXact + 1;
    oldestXact -= 1U << 31;
    oldestPage = oldestXact / per_page;
    Assert(!SlruMayDeleteSegment(ctl,
                                 (newestPage -
                                  newestPage % SLRU_PAGES_PER_SEGMENT),
                                 oldestPage));
 
    /*
     * GetNewTransactionId() has assigned the last XID it can safely use, and
     * that XID is in the *FIRST* page of the second segment.  We must not
     * delete that segment.
     */
    newestPage = SLRU_PAGES_PER_SEGMENT;
    newestXact = newestPage * per_page + offset;
    Assert(newestXact / per_page == newestPage);
    oldestXact = newestXact + 1;
    oldestXact -= 1U << 31;
    oldestPage = oldestXact / per_page;
    Assert(!SlruMayDeleteSegment(ctl,
                                 (newestPage -
                                  newestPage % SLRU_PAGES_PER_SEGMENT),
                                 oldestPage));
}
 
/*
 * Unit-test a PagePrecedes function.
 *
 * This assumes every uint32 >= FirstNormalTransactionId is a valid key.  It
 * assumes each value occupies a contiguous, fixed-size region of SLRU bytes.
 * (MultiXactMemberCtl separates flags from XIDs.  NotifyCtl has
 * variable-length entries, no keys, and no random access.  These unit tests
 * do not apply to them.)
 */
void
SlruPagePrecedesUnitTests(SlruCtl ctl, int per_page)
{
    /* Test first, middle and last entries of a page. */
    SlruPagePrecedesTestOffset(ctl, per_page, 0);
    SlruPagePrecedesTestOffset(ctl, per_page, per_page / 2);
    SlruPagePrecedesTestOffset(ctl, per_page, per_page - 1);
}
#endif
 
/*
 * SlruScanDirectory callback
 *      This callback reports true if there's any segment wholly prior to the
 *      one containing the page passed as "data".
 */
bool
SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int64 segpage,
                            void *data)
{
    int64       cutoffPage = *(int64 *) data;
 
    if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
        return true;            /* found one; don't iterate any more */
 
    return false;               /* keep going */
}
 
/*
 * SlruScanDirectory callback.
 *      This callback deletes segments prior to the one passed in as "data".
 */
static bool
SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int64 segpage,
                          void *data)
{
    int64       cutoffPage = *(int64 *) data;
 
    if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
        SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
 
    return false;               /* keep going */
}
 
/*
 * SlruScanDirectory callback.
 *      This callback deletes all segments.
 */
bool
SlruScanDirCbDeleteAll(SlruCtl ctl, char *filename, int64 segpage, void *data)
{
    SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
 
    return false;               /* keep going */
}
 
/*
 * An internal function used by SlruScanDirectory().
 *
 * Returns true if a file with a name of a given length may be a correct
 * SLRU segment.
 */
static inline bool
SlruCorrectSegmentFilenameLength(SlruCtl ctl, size_t len)
{
    if (ctl->long_segment_names)
        return (len == 15);     /* see SlruFileName() */
    else
 
        /*
         * Commit 638cf09e76d allowed 5-character lengths. Later commit
         * 73c986adde5 allowed 6-character length.
         *
         * Note: There is an ongoing plan to migrate all SLRUs to 64-bit page
         * numbers, and the corresponding 15-character file names, which may
         * eventually deprecate the support for 4, 5, and 6-character names.
         */
        return (len == 4 || len == 5 || len == 6);
}
 
/*
 * Scan the SimpleLru directory and apply a callback to each file found in it.
 *
 * If the callback returns true, the scan is stopped.  The last return value
 * from the callback is returned.
 *
 * The callback receives the following arguments: 1. the SlruCtl struct for the
 * slru being truncated; 2. the filename being considered; 3. the page number
 * for the first page of that file; 4. a pointer to the opaque data given to us
 * by the caller.
 *
 * Note that the ordering in which the directory is scanned is not guaranteed.
 *
 * Note that no locking is applied.
 */
bool
SlruScanDirectory(SlruCtl ctl, SlruScanCallback callback, void *data)
{
    bool        retval = false;
    DIR        *cldir;
    struct dirent *clde;
    int64       segno;
    int64       segpage;
 
    cldir = AllocateDir(ctl->Dir);
    while ((clde = ReadDir(cldir, ctl->Dir)) != NULL)
    {
        size_t      len;
 
        len = strlen(clde->d_name);
 
        if (SlruCorrectSegmentFilenameLength(ctl, len) &&
            strspn(clde->d_name, "0123456789ABCDEF") == len)
        {
            segno = strtoi64(clde->d_name, NULL, 16);
            segpage = segno * SLRU_PAGES_PER_SEGMENT;
 
            elog(DEBUG2, "SlruScanDirectory invoking callback on %s/%s",
                 ctl->Dir, clde->d_name);
            retval = callback(ctl, clde->d_name, segpage, data);
            if (retval)
                break;
        }
    }
    FreeDir(cldir);
 
    return retval;
}
 
/*
 * Individual SLRUs (clog, ...) have to provide a sync.c handler function so
 * that they can provide the correct "SlruCtl" (otherwise we don't know how to
 * build the path), but they just forward to this common implementation that
 * performs the fsync.
 */
int
SlruSyncFileTag(SlruCtl ctl, const FileTag *ftag, char *path)
{
    int         fd;
    int         save_errno;
    int         result;
 
    SlruFileName(ctl, path, ftag->segno);
 
    fd = OpenTransientFile(path, O_RDWR | PG_BINARY);
    if (fd < 0)
        return -1;
 
    pgstat_report_wait_start(WAIT_EVENT_SLRU_FLUSH_SYNC);
    result = pg_fsync(fd);
    pgstat_report_wait_end();
    save_errno = errno;
 
    CloseTransientFile(fd);
 
    errno = save_errno;
    return result;
}

MAX_WRITEALL_BUFFERS

#define MAX_WRITEALL_BUFFERS   16

Definition at line 123 of file slru.c.

SlotGetBankNumber

#define SlotGetBankNumber

(

slotno

)

((slotno) >> SLRU_BANK_BITSHIFT)

Definition at line 148 of file slru.c.

SLRU_BANK_BITSHIFT

#define SLRU_BANK_BITSHIFT   4

Definition at line 142 of file slru.c.

SLRU_BANK_SIZE

#define SLRU_BANK_SIZE   (1 << SLRU_BANK_BITSHIFT)

Definition at line 143 of file slru.c.

Typedef Documentation

SlruWriteAll

typedef struct SlruWriteAllData* SlruWriteAll

Definition at line 132 of file slru.c.

SlruWriteAllData

typedef struct SlruWriteAllData SlruWriteAllData

Enumeration Type Documentation

SlruErrorCause

enum SlruErrorCause

Enumerator
SLRU_OPEN_FAILED
SLRU_SEEK_FAILED
SLRU_READ_FAILED
SLRU_WRITE_FAILED
SLRU_FSYNC_FAILED
SLRU_CLOSE_FAILED

Definition at line 164 of file slru.c.

{
    SLRU_OPEN_FAILED,
    SLRU_SEEK_FAILED,
    SLRU_READ_FAILED,
    SLRU_WRITE_FAILED,
    SLRU_FSYNC_FAILED,
    SLRU_CLOSE_FAILED,
} SlruErrorCause;

Function Documentation

check_slru_buffers()

bool check_slru_buffers	(	const char *	name,
		int *	newval
	)

Definition at line 355 of file slru.c.

{
    /* Valid values are multiples of SLRU_BANK_SIZE */
    if (*newval % SLRU_BANK_SIZE == 0)
        return true;
 
    GUC_check_errdetail("\"%s\" must be a multiple of %d.", name,
                        SLRU_BANK_SIZE);
    return false;
}

References GUC_check_errdetail, name, newval, and SLRU_BANK_SIZE.

Referenced by check_commit_ts_buffers(), check_multixact_member_buffers(), check_multixact_offset_buffers(), check_notify_buffers(), check_serial_buffers(), check_subtrans_buffers(), and check_transaction_buffers().

SimpleLruAutotuneBuffers()

int SimpleLruAutotuneBuffers	(	int	divisor,
		int	max
	)

Definition at line 231 of file slru.c.

{
    return Min(max - (max % SLRU_BANK_SIZE),
               Max(SLRU_BANK_SIZE,
                   NBuffers / divisor - (NBuffers / divisor) % SLRU_BANK_SIZE));
}

References fb(), Max, Min, NBuffers, and SLRU_BANK_SIZE.

Referenced by CLOGShmemBuffers(), CommitTsShmemBuffers(), and SUBTRANSShmemBuffers().

SimpleLruDoesPhysicalPageExist()

bool SimpleLruDoesPhysicalPageExist	(	SlruCtl	ctl,
		int64	pageno
	)

Definition at line 771 of file slru.c.

{
    int64       segno = pageno / SLRU_PAGES_PER_SEGMENT;
    int         rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
    int         offset = rpageno * BLCKSZ;
    char        path[MAXPGPATH];
    int         fd;
    bool        result;
    off_t       endpos;
 
    /* update the stats counter of checked pages */
    pgstat_count_slru_blocks_exists(ctl->shared->slru_stats_idx);
 
    SlruFileName(ctl, path, segno);
 
    fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
    if (fd < 0)
    {
        /* expected: file doesn't exist */
        if (errno == ENOENT)
            return false;
 
        /* report error normally */
        slru_errcause = SLRU_OPEN_FAILED;
        slru_errno = errno;
        SlruReportIOError(ctl, pageno, 0);
    }
 
    if ((endpos = lseek(fd, 0, SEEK_END)) < 0)
    {
        slru_errcause = SLRU_SEEK_FAILED;
        slru_errno = errno;
        SlruReportIOError(ctl, pageno, 0);
    }
 
    result = endpos >= (off_t) (offset + BLCKSZ);
 
    if (CloseTransientFile(fd) != 0)
    {
        slru_errcause = SLRU_CLOSE_FAILED;
        slru_errno = errno;
        return false;
    }
 
    return result;
}

References CloseTransientFile(), ctl, endpos, fb(), fd(), MAXPGPATH, OpenTransientFile(), PG_BINARY, pgstat_count_slru_blocks_exists(), SlruWriteAllData::segno, SLRU_CLOSE_FAILED, slru_errcause, slru_errno, SLRU_OPEN_FAILED, SLRU_PAGES_PER_SEGMENT, SLRU_SEEK_FAILED, SlruFileName(), and SlruReportIOError().

Referenced by ActivateCommitTs(), find_multixact_start(), and test_slru_page_exists().

SimpleLruInit()

void SimpleLruInit	(	SlruCtl	ctl,
		const char *	name,
		int	nslots,
		int	nlsns,
		const char *	subdir,
		int	buffer_tranche_id,
		int	bank_tranche_id,
		SyncRequestHandler	sync_handler,
		bool	long_segment_names
	)

Definition at line 252 of file slru.c.

{
    SlruShared  shared;
    bool        found;
    int         nbanks = nslots / SLRU_BANK_SIZE;
 
    Assert(nslots <= SLRU_MAX_ALLOWED_BUFFERS);
 
    shared = (SlruShared) ShmemInitStruct(name,
                                          SimpleLruShmemSize(nslots, nlsns),
                                          &found);
 
    if (!IsUnderPostmaster)
    {
        /* Initialize locks and shared memory area */
        char       *ptr;
        Size        offset;
 
        Assert(!found);
 
        memset(shared, 0, sizeof(SlruSharedData));
 
        shared->num_slots = nslots;
        shared->lsn_groups_per_page = nlsns;
 
        pg_atomic_init_u64(&shared->latest_page_number, 0);
 
        shared->slru_stats_idx = pgstat_get_slru_index(name);
 
        ptr = (char *) shared;
        offset = MAXALIGN(sizeof(SlruSharedData));
        shared->page_buffer = (char **) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(char *));
        shared->page_status = (SlruPageStatus *) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(SlruPageStatus));
        shared->page_dirty = (bool *) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(bool));
        shared->page_number = (int64 *) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(int64));
        shared->page_lru_count = (int *) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(int));
 
        /* Initialize LWLocks */
        shared->buffer_locks = (LWLockPadded *) (ptr + offset);
        offset += MAXALIGN(nslots * sizeof(LWLockPadded));
        shared->bank_locks = (LWLockPadded *) (ptr + offset);
        offset += MAXALIGN(nbanks * sizeof(LWLockPadded));
        shared->bank_cur_lru_count = (int *) (ptr + offset);
        offset += MAXALIGN(nbanks * sizeof(int));
 
        if (nlsns > 0)
        {
            shared->group_lsn = (XLogRecPtr *) (ptr + offset);
            offset += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr));
        }
 
        ptr += BUFFERALIGN(offset);
        for (int slotno = 0; slotno < nslots; slotno++)
        {
            LWLockInitialize(&shared->buffer_locks[slotno].lock,
                             buffer_tranche_id);
 
            shared->page_buffer[slotno] = ptr;
            shared->page_status[slotno] = SLRU_PAGE_EMPTY;
            shared->page_dirty[slotno] = false;
            shared->page_lru_count[slotno] = 0;
            ptr += BLCKSZ;
        }
 
        /* Initialize the slot banks. */
        for (int bankno = 0; bankno < nbanks; bankno++)
        {
            LWLockInitialize(&shared->bank_locks[bankno].lock, bank_tranche_id);
            shared->bank_cur_lru_count[bankno] = 0;
        }
 
        /* Should fit to estimated shmem size */
        Assert(ptr - (char *) shared <= SimpleLruShmemSize(nslots, nlsns));
    }
    else
    {
        Assert(found);
        Assert(shared->num_slots == nslots);
    }
 
    /*
     * Initialize the unshared control struct, including directory path. We
     * assume caller set PagePrecedes.
     */
    ctl->shared = shared;
    ctl->sync_handler = sync_handler;
    ctl->long_segment_names = long_segment_names;
    ctl->nbanks = nbanks;
    strlcpy(ctl->Dir, subdir, sizeof(ctl->Dir));
}

References Assert, SlruSharedData::bank_cur_lru_count, SlruSharedData::bank_locks, SlruSharedData::buffer_locks, BUFFERALIGN, ctl, fb(), SlruSharedData::group_lsn, IsUnderPostmaster, SlruSharedData::latest_page_number, LWLockPadded::lock, SlruSharedData::lsn_groups_per_page, LWLockInitialize(), MAXALIGN, name, SlruSharedData::num_slots, SlruSharedData::page_buffer, SlruSharedData::page_dirty, SlruSharedData::page_lru_count, SlruSharedData::page_number, SlruSharedData::page_status, pg_atomic_init_u64(), pgstat_get_slru_index(), ShmemInitStruct(), SimpleLruShmemSize(), SLRU_BANK_SIZE, SLRU_MAX_ALLOWED_BUFFERS, SLRU_PAGE_EMPTY, SlruSharedData::slru_stats_idx, and strlcpy().

Referenced by AsyncShmemInit(), CLOGShmemInit(), CommitTsShmemInit(), MultiXactShmemInit(), SerialInit(), SUBTRANSShmemInit(), and test_slru_shmem_startup().

SimpleLruReadPage()

int SimpleLruReadPage	(	SlruCtl	ctl,
		int64	pageno,
		bool	write_ok,
		TransactionId	xid
	)

Definition at line 527 of file slru.c.

{
    SlruShared  shared = ctl->shared;
    LWLock     *banklock = SimpleLruGetBankLock(ctl, pageno);
 
    Assert(LWLockHeldByMeInMode(banklock, LW_EXCLUSIVE));
 
    /* Outer loop handles restart if we must wait for someone else's I/O */
    for (;;)
    {
        int         slotno;
        bool        ok;
 
        /* See if page already is in memory; if not, pick victim slot */
        slotno = SlruSelectLRUPage(ctl, pageno);
 
        /* Did we find the page in memory? */
        if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
            shared->page_number[slotno] == pageno)
        {
            /*
             * If page is still being read in, we must wait for I/O.  Likewise
             * if the page is being written and the caller said that's not OK.
             */
            if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS ||
                (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS &&
                 !write_ok))
            {
                SimpleLruWaitIO(ctl, slotno);
                /* Now we must recheck state from the top */
                continue;
            }
            /* Otherwise, it's ready to use */
            SlruRecentlyUsed(shared, slotno);
 
            /* update the stats counter of pages found in the SLRU */
            pgstat_count_slru_blocks_hit(shared->slru_stats_idx);
 
            return slotno;
        }
 
        /* We found no match; assert we selected a freeable slot */
        Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
               (shared->page_status[slotno] == SLRU_PAGE_VALID &&
                !shared->page_dirty[slotno]));
 
        /* Mark the slot read-busy */
        shared->page_number[slotno] = pageno;
        shared->page_status[slotno] = SLRU_PAGE_READ_IN_PROGRESS;
        shared->page_dirty[slotno] = false;
 
        /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
        LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
 
        /* Release bank lock while doing I/O */
        LWLockRelease(banklock);
 
        /* Do the read */
        ok = SlruPhysicalReadPage(ctl, pageno, slotno);
 
        /* Set the LSNs for this newly read-in page to zero */
        SimpleLruZeroLSNs(ctl, slotno);
 
        /* Re-acquire bank control lock and update page state */
        LWLockAcquire(banklock, LW_EXCLUSIVE);
 
        Assert(shared->page_number[slotno] == pageno &&
               shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS &&
               !shared->page_dirty[slotno]);
 
        shared->page_status[slotno] = ok ? SLRU_PAGE_VALID : SLRU_PAGE_EMPTY;
 
        LWLockRelease(&shared->buffer_locks[slotno].lock);
 
        /* Now it's okay to ereport if we failed */
        if (!ok)
            SlruReportIOError(ctl, pageno, xid);
 
        SlruRecentlyUsed(shared, slotno);
 
        /* update the stats counter of pages not found in SLRU */
        pgstat_count_slru_blocks_read(shared->slru_stats_idx);
 
        return slotno;
    }
}

References Assert, SlruSharedData::buffer_locks, ctl, fb(), LWLockPadded::lock, LW_EXCLUSIVE, LWLockAcquire(), LWLockHeldByMeInMode(), LWLockRelease(), SlruSharedData::page_dirty, SlruSharedData::page_number, SlruSharedData::page_status, pgstat_count_slru_blocks_hit(), pgstat_count_slru_blocks_read(), SimpleLruGetBankLock(), SimpleLruWaitIO(), SimpleLruZeroLSNs(), SLRU_PAGE_EMPTY, SLRU_PAGE_READ_IN_PROGRESS, SLRU_PAGE_VALID, SLRU_PAGE_WRITE_IN_PROGRESS, SlruSharedData::slru_stats_idx, SlruPhysicalReadPage(), SlruRecentlyUsed(), SlruReportIOError(), and SlruSelectLRUPage().

Referenced by AsyncNotifyFreezeXids(), asyncQueueAddEntries(), GetMultiXactIdMembers(), RecordNewMultiXact(), SerialAdd(), SetXidCommitTsInPage(), SimpleLruReadPage_ReadOnly(), SubTransSetParent(), test_slru_page_read(), TransactionIdSetPageStatusInternal(), TrimCLOG(), and TrimMultiXact().

SimpleLruReadPage_ReadOnly()

int SimpleLruReadPage_ReadOnly	(	SlruCtl	ctl,
		int64	pageno,
		TransactionId	xid
	)

Definition at line 630 of file slru.c.

{
    SlruShared  shared = ctl->shared;
    LWLock     *banklock = SimpleLruGetBankLock(ctl, pageno);
    int         bankno = pageno % ctl->nbanks;
    int         bankstart = bankno * SLRU_BANK_SIZE;
    int         bankend = bankstart + SLRU_BANK_SIZE;
 
    /* Try to find the page while holding only shared lock */
    LWLockAcquire(banklock, LW_SHARED);
 
    /* See if page is already in a buffer */
    for (int slotno = bankstart; slotno < bankend; slotno++)
    {
        if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
            shared->page_number[slotno] == pageno &&
            shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS)
        {
            /* See comments for SlruRecentlyUsed() */
            SlruRecentlyUsed(shared, slotno);
 
            /* update the stats counter of pages found in the SLRU */
            pgstat_count_slru_blocks_hit(shared->slru_stats_idx);
 
            return slotno;
        }
    }
 
    /* No luck, so switch to normal exclusive lock and do regular read */
    LWLockRelease(banklock);
    LWLockAcquire(banklock, LW_EXCLUSIVE);
 
    return SimpleLruReadPage(ctl, pageno, true, xid);
}

References ctl, fb(), LW_EXCLUSIVE, LW_SHARED, LWLockAcquire(), LWLockRelease(), SlruSharedData::page_number, SlruSharedData::page_status, pgstat_count_slru_blocks_hit(), SimpleLruGetBankLock(), SimpleLruReadPage(), SLRU_BANK_SIZE, SLRU_PAGE_EMPTY, SLRU_PAGE_READ_IN_PROGRESS, SlruSharedData::slru_stats_idx, and SlruRecentlyUsed().

Referenced by asyncQueueProcessPageEntries(), find_multixact_start(), SerialGetMinConflictCommitSeqNo(), SubTransGetParent(), test_slru_page_readonly(), TransactionIdGetCommitTsData(), and TransactionIdGetStatus().

SimpleLruShmemSize()

Size SimpleLruShmemSize	(	int	nslots,
		int	nlsns
	)

Definition at line 198 of file slru.c.

{
    int         nbanks = nslots / SLRU_BANK_SIZE;
    Size        sz;
 
    Assert(nslots <= SLRU_MAX_ALLOWED_BUFFERS);
    Assert(nslots % SLRU_BANK_SIZE == 0);
 
    /* we assume nslots isn't so large as to risk overflow */
    sz = MAXALIGN(sizeof(SlruSharedData));
    sz += MAXALIGN(nslots * sizeof(char *));    /* page_buffer[] */
    sz += MAXALIGN(nslots * sizeof(SlruPageStatus));    /* page_status[] */
    sz += MAXALIGN(nslots * sizeof(bool));  /* page_dirty[] */
    sz += MAXALIGN(nslots * sizeof(int64)); /* page_number[] */
    sz += MAXALIGN(nslots * sizeof(int));   /* page_lru_count[] */
    sz += MAXALIGN(nslots * sizeof(LWLockPadded));  /* buffer_locks[] */
    sz += MAXALIGN(nbanks * sizeof(LWLockPadded));  /* bank_locks[] */
    sz += MAXALIGN(nbanks * sizeof(int));   /* bank_cur_lru_count[] */
 
    if (nlsns > 0)
        sz += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr));    /* group_lsn[] */
 
    return BUFFERALIGN(sz) + BLCKSZ * nslots;
}

References Assert, BUFFERALIGN, fb(), MAXALIGN, SLRU_BANK_SIZE, and SLRU_MAX_ALLOWED_BUFFERS.

Referenced by AsyncShmemSize(), CLOGShmemSize(), CommitTsShmemSize(), MultiXactShmemSize(), PredicateLockShmemSize(), SimpleLruInit(), SUBTRANSShmemSize(), and test_slru_shmem_request().

SimpleLruTruncate()

void SimpleLruTruncate	(	SlruCtl	ctl,
		int64	cutoffPage
	)

Definition at line 1433 of file slru.c.

{
    SlruShared  shared = ctl->shared;
    int         prevbank;
 
    /* update the stats counter of truncates */
    pgstat_count_slru_truncate(shared->slru_stats_idx);
 
    /*
     * Scan shared memory and remove any pages preceding the cutoff page, to
     * ensure we won't rewrite them later.  (Since this is normally called in
     * or just after a checkpoint, any dirty pages should have been flushed
     * already ... we're just being extra careful here.)
     */
restart:
 
    /*
     * An important safety check: the current endpoint page must not be
     * eligible for removal.  This check is just a backstop against wraparound
     * bugs elsewhere in SLRU handling, so we don't care if we read a slightly
     * outdated value; therefore we don't add a memory barrier.
     */
    if (ctl->PagePrecedes(pg_atomic_read_u64(&shared->latest_page_number),
                          cutoffPage))
    {
        ereport(LOG,
                (errmsg("could not truncate directory \"%s\": apparent wraparound",
                        ctl->Dir)));
        return;
    }
 
    prevbank = SlotGetBankNumber(0);
    LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
    for (int slotno = 0; slotno < shared->num_slots; slotno++)
    {
        int         curbank = SlotGetBankNumber(slotno);
 
        /*
         * If the current bank lock is not same as the previous bank lock then
         * release the previous lock and acquire the new lock.
         */
        if (curbank != prevbank)
        {
            LWLockRelease(&shared->bank_locks[prevbank].lock);
            LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
            prevbank = curbank;
        }
 
        if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
            continue;
        if (!ctl->PagePrecedes(shared->page_number[slotno], cutoffPage))
            continue;
 
        /*
         * If page is clean, just change state to EMPTY (expected case).
         */
        if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
            !shared->page_dirty[slotno])
        {
            shared->page_status[slotno] = SLRU_PAGE_EMPTY;
            continue;
        }
 
        /*
         * Hmm, we have (or may have) I/O operations acting on the page, so
         * we've got to wait for them to finish and then start again. This is
         * the same logic as in SlruSelectLRUPage.  (XXX if page is dirty,
         * wouldn't it be OK to just discard it without writing it?
         * SlruMayDeleteSegment() uses a stricter qualification, so we might
         * not delete this page in the end; even if we don't delete it, we
         * won't have cause to read its data again.  For now, keep the logic
         * the same as it was.)
         */
        if (shared->page_status[slotno] == SLRU_PAGE_VALID)
            SlruInternalWritePage(ctl, slotno, NULL);
        else
            SimpleLruWaitIO(ctl, slotno);
 
        LWLockRelease(&shared->bank_locks[prevbank].lock);
        goto restart;
    }
 
    LWLockRelease(&shared->bank_locks[prevbank].lock);
 
    /* Now we can remove the old segment(s) */
    (void) SlruScanDirectory(ctl, SlruScanDirCbDeleteCutoff, &cutoffPage);
}

References SlruSharedData::bank_locks, ctl, ereport, errmsg(), fb(), SlruSharedData::latest_page_number, LWLockPadded::lock, LOG, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), SlruSharedData::num_slots, SlruSharedData::page_dirty, SlruSharedData::page_number, SlruSharedData::page_status, pg_atomic_read_u64(), pgstat_count_slru_truncate(), SimpleLruWaitIO(), SlotGetBankNumber, SLRU_PAGE_EMPTY, SLRU_PAGE_VALID, SlruSharedData::slru_stats_idx, SlruInternalWritePage(), SlruScanDirCbDeleteCutoff(), and SlruScanDirectory().

Referenced by asyncQueueAdvanceTail(), CheckPointPredicate(), clog_redo(), commit_ts_redo(), PerformMembersTruncation(), PerformOffsetsTruncation(), test_slru_page_truncate(), TruncateCLOG(), TruncateCommitTs(), and TruncateSUBTRANS().

SimpleLruWaitIO()

static void SimpleLruWaitIO ( SlruCtl  ctl, int  slotno  )

static

Definition at line 470 of file slru.c.

{
    SlruShared  shared = ctl->shared;
    int         bankno = SlotGetBankNumber(slotno);
 
    Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
 
    /* See notes at top of file */
    LWLockRelease(&shared->bank_locks[bankno].lock);
    LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED);
    LWLockRelease(&shared->buffer_locks[slotno].lock);
    LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
 
    /*
     * If the slot is still in an io-in-progress state, then either someone
     * already started a new I/O on the slot, or a previous I/O failed and
     * neglected to reset the page state.  That shouldn't happen, really, but
     * it seems worth a few extra cycles to check and recover from it. We can
     * cheaply test for failure by seeing if the buffer lock is still held (we
     * assume that transaction abort would release the lock).
     */
    if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS ||
        shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS)
    {
        if (LWLockConditionalAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED))
        {
            /* indeed, the I/O must have failed */
            if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS)
                shared->page_status[slotno] = SLRU_PAGE_EMPTY;
            else                /* write_in_progress */
            {
                shared->page_status[slotno] = SLRU_PAGE_VALID;
                shared->page_dirty[slotno] = true;
            }
            LWLockRelease(&shared->buffer_locks[slotno].lock);
        }
    }
}

References Assert, SlruSharedData::bank_locks, SlruSharedData::buffer_locks, ctl, fb(), LWLockPadded::lock, LW_EXCLUSIVE, LW_SHARED, LWLockAcquire(), LWLockConditionalAcquire(), LWLockRelease(), SlruSharedData::page_dirty, SlruSharedData::page_status, SlotGetBankNumber, SLRU_PAGE_EMPTY, SLRU_PAGE_READ_IN_PROGRESS, SLRU_PAGE_VALID, and SLRU_PAGE_WRITE_IN_PROGRESS.

Referenced by SimpleLruReadPage(), SimpleLruTruncate(), SlruDeleteSegment(), SlruInternalWritePage(), and SlruSelectLRUPage().

SimpleLruWriteAll()

void SimpleLruWriteAll	(	SlruCtl	ctl,
		bool	allow_redirtied
	)

Definition at line 1347 of file slru.c.

{
    SlruShared  shared = ctl->shared;
    SlruWriteAllData fdata;
    int64       pageno = 0;
    int         prevbank = SlotGetBankNumber(0);
    bool        ok;
 
    /* update the stats counter of flushes */
    pgstat_count_slru_flush(shared->slru_stats_idx);
 
    /*
     * Find and write dirty pages
     */
    fdata.num_files = 0;
 
    LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
 
    for (int slotno = 0; slotno < shared->num_slots; slotno++)
    {
        int         curbank = SlotGetBankNumber(slotno);
 
        /*
         * If the current bank lock is not same as the previous bank lock then
         * release the previous lock and acquire the new lock.
         */
        if (curbank != prevbank)
        {
            LWLockRelease(&shared->bank_locks[prevbank].lock);
            LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
            prevbank = curbank;
        }
 
        /* Do nothing if slot is unused */
        if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
            continue;
 
        SlruInternalWritePage(ctl, slotno, &fdata);
 
        /*
         * In some places (e.g. checkpoints), we cannot assert that the slot
         * is clean now, since another process might have re-dirtied it
         * already.  That's okay.
         */
        Assert(allow_redirtied ||
               shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
               (shared->page_status[slotno] == SLRU_PAGE_VALID &&
                !shared->page_dirty[slotno]));
    }
 
    LWLockRelease(&shared->bank_locks[prevbank].lock);
 
    /*
     * Now close any files that were open
     */
    ok = true;
    for (int i = 0; i < fdata.num_files; i++)
    {
        if (CloseTransientFile(fdata.fd[i]) != 0)
        {
            slru_errcause = SLRU_CLOSE_FAILED;
            slru_errno = errno;
            pageno = fdata.segno[i] * SLRU_PAGES_PER_SEGMENT;
            ok = false;
        }
    }
    if (!ok)
        SlruReportIOError(ctl, pageno, InvalidTransactionId);
 
    /* Ensure that directory entries for new files are on disk. */
    if (ctl->sync_handler != SYNC_HANDLER_NONE)
        fsync_fname(ctl->Dir, true);
}

References Assert, SlruSharedData::bank_locks, CloseTransientFile(), ctl, fb(), fsync_fname(), i, InvalidTransactionId, LWLockPadded::lock, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), SlruSharedData::num_slots, SlruSharedData::page_dirty, SlruSharedData::page_status, pgstat_count_slru_flush(), SlotGetBankNumber, SLRU_CLOSE_FAILED, slru_errcause, slru_errno, SLRU_PAGE_EMPTY, SLRU_PAGE_VALID, SLRU_PAGES_PER_SEGMENT, SlruSharedData::slru_stats_idx, SlruInternalWritePage(), SlruReportIOError(), and SYNC_HANDLER_NONE.

Referenced by CheckPointCLOG(), CheckPointCommitTs(), CheckPointMultiXact(), CheckPointPredicate(), CheckPointSUBTRANS(), find_multixact_start(), and test_slru_page_writeall().

SimpleLruWritePage()

void SimpleLruWritePage	(	SlruCtl	ctl,
		int	slotno
	)

Definition at line 757 of file slru.c.

{
    Assert(ctl->shared->page_status[slotno] != SLRU_PAGE_EMPTY);
 
    SlruInternalWritePage(ctl, slotno, NULL);
}

References Assert, ctl, fb(), SLRU_PAGE_EMPTY, and SlruInternalWritePage().

Referenced by SimpleLruZeroAndWritePage(), and test_slru_page_write().

SimpleLruZeroAndWritePage()

void SimpleLruZeroAndWritePage	(	SlruCtl	ctl,
		int64	pageno
	)

Definition at line 444 of file slru.c.

{
    int         slotno;
    LWLock     *lock;
 
    lock = SimpleLruGetBankLock(ctl, pageno);
    LWLockAcquire(lock, LW_EXCLUSIVE);
 
    /* Create and zero the page */
    slotno = SimpleLruZeroPage(ctl, pageno);
 
    /* Make sure it's written out */
    SimpleLruWritePage(ctl, slotno);
    Assert(!ctl->shared->page_dirty[slotno]);
 
    LWLockRelease(lock);
}

References Assert, ctl, fb(), LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), SimpleLruGetBankLock(), SimpleLruWritePage(), and SimpleLruZeroPage().

Referenced by ActivateCommitTs(), BootStrapCLOG(), BootStrapMultiXact(), BootStrapSUBTRANS(), clog_redo(), commit_ts_redo(), and multixact_redo().

SimpleLruZeroLSNs()

static void SimpleLruZeroLSNs ( SlruCtl  ctl, int  slotno  )

static

Definition at line 428 of file slru.c.

{
    SlruShared  shared = ctl->shared;
 
    if (shared->lsn_groups_per_page > 0)
        MemSet(&shared->group_lsn[slotno * shared->lsn_groups_per_page], 0,
               shared->lsn_groups_per_page * sizeof(XLogRecPtr));
}

References ctl, fb(), SlruSharedData::group_lsn, SlruSharedData::lsn_groups_per_page, and MemSet.

Referenced by SimpleLruReadPage(), and SimpleLruZeroPage().

SimpleLruZeroPage()

int SimpleLruZeroPage	(	SlruCtl	ctl,
		int64	pageno
	)

Definition at line 375 of file slru.c.

{
    SlruShared  shared = ctl->shared;
    int         slotno;
 
    Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
 
    /* Find a suitable buffer slot for the page */
    slotno = SlruSelectLRUPage(ctl, pageno);
    Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
           (shared->page_status[slotno] == SLRU_PAGE_VALID &&
            !shared->page_dirty[slotno]) ||
           shared->page_number[slotno] == pageno);
 
    /* Mark the slot as containing this page */
    shared->page_number[slotno] = pageno;
    shared->page_status[slotno] = SLRU_PAGE_VALID;
    shared->page_dirty[slotno] = true;
    SlruRecentlyUsed(shared, slotno);
 
    /* Set the buffer to zeroes */
    MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
 
    /* Set the LSNs for this new page to zero */
    SimpleLruZeroLSNs(ctl, slotno);
 
    /*
     * Assume this page is now the latest active page.
     *
     * Note that because both this routine and SlruSelectLRUPage run with a
     * SLRU bank lock held, it is not possible for this to be zeroing a page
     * that SlruSelectLRUPage is going to evict simultaneously.  Therefore,
     * there's no memory barrier here.
     */
    pg_atomic_write_u64(&shared->latest_page_number, pageno);
 
    /* update the stats counter of zeroed pages */
    pgstat_count_slru_blocks_zeroed(shared->slru_stats_idx);
 
    return slotno;
}

References Assert, ctl, fb(), SlruSharedData::latest_page_number, LW_EXCLUSIVE, LWLockHeldByMeInMode(), MemSet, SlruSharedData::page_buffer, SlruSharedData::page_dirty, SlruSharedData::page_number, SlruSharedData::page_status, pg_atomic_write_u64(), pgstat_count_slru_blocks_zeroed(), SimpleLruGetBankLock(), SimpleLruZeroLSNs(), SLRU_PAGE_EMPTY, SLRU_PAGE_VALID, SlruSharedData::slru_stats_idx, SlruRecentlyUsed(), and SlruSelectLRUPage().

Referenced by asyncQueueAddEntries(), ExtendCLOG(), ExtendCommitTs(), ExtendMultiXactMember(), ExtendMultiXactOffset(), ExtendSUBTRANS(), SerialAdd(), SimpleLruZeroAndWritePage(), StartupSUBTRANS(), test_slru_page_write(), and TrimMultiXact().

SlruCorrectSegmentFilenameLength()

static bool SlruCorrectSegmentFilenameLength ( SlruCtl  ctl, size_t  len  )

inlinestatic

Definition at line 1783 of file slru.c.

{
    if (ctl->long_segment_names)
        return (len == 15);     /* see SlruFileName() */
    else
 
        /*
         * Commit 638cf09e76d allowed 5-character lengths. Later commit
         * 73c986adde5 allowed 6-character length.
         *
         * Note: There is an ongoing plan to migrate all SLRUs to 64-bit page
         * numbers, and the corresponding 15-character file names, which may
         * eventually deprecate the support for 4, 5, and 6-character names.
         */
        return (len == 4 || len == 5 || len == 6);
}

References ctl, and len.

Referenced by SlruScanDirectory().

SlruDeleteSegment()

void SlruDeleteSegment	(	SlruCtl	ctl,
		int64	segno
	)

Definition at line 1551 of file slru.c.

{
    SlruShared  shared = ctl->shared;
    int         prevbank = SlotGetBankNumber(0);
    bool        did_write;
 
    /* Clean out any possibly existing references to the segment. */
    LWLockAcquire(&shared->bank_locks[prevbank].lock, LW_EXCLUSIVE);
restart:
    did_write = false;
    for (int slotno = 0; slotno < shared->num_slots; slotno++)
    {
        int64       pagesegno;
        int         curbank = SlotGetBankNumber(slotno);
 
        /*
         * If the current bank lock is not same as the previous bank lock then
         * release the previous lock and acquire the new lock.
         */
        if (curbank != prevbank)
        {
            LWLockRelease(&shared->bank_locks[prevbank].lock);
            LWLockAcquire(&shared->bank_locks[curbank].lock, LW_EXCLUSIVE);
            prevbank = curbank;
        }
 
        if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
            continue;
 
        pagesegno = shared->page_number[slotno] / SLRU_PAGES_PER_SEGMENT;
        /* not the segment we're looking for */
        if (pagesegno != segno)
            continue;
 
        /* If page is clean, just change state to EMPTY (expected case). */
        if (shared->page_status[slotno] == SLRU_PAGE_VALID &&
            !shared->page_dirty[slotno])
        {
            shared->page_status[slotno] = SLRU_PAGE_EMPTY;
            continue;
        }
 
        /* Same logic as SimpleLruTruncate() */
        if (shared->page_status[slotno] == SLRU_PAGE_VALID)
            SlruInternalWritePage(ctl, slotno, NULL);
        else
            SimpleLruWaitIO(ctl, slotno);
 
        did_write = true;
    }
 
    /*
     * Be extra careful and re-check. The IO functions release the control
     * lock, so new pages could have been read in.
     */
    if (did_write)
        goto restart;
 
    SlruInternalDeleteSegment(ctl, segno);
 
    LWLockRelease(&shared->bank_locks[prevbank].lock);
}

References SlruSharedData::bank_locks, ctl, fb(), LWLockPadded::lock, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), SlruSharedData::num_slots, SlruSharedData::page_dirty, SlruSharedData::page_number, SlruSharedData::page_status, SlruWriteAllData::segno, SimpleLruWaitIO(), SlotGetBankNumber, SLRU_PAGE_EMPTY, SLRU_PAGE_VALID, SLRU_PAGES_PER_SEGMENT, SlruInternalDeleteSegment(), and SlruInternalWritePage().

Referenced by test_slru_page_delete().

SlruFileName()

static int SlruFileName ( SlruCtl  ctl, char *  path, int64  segno  )

inlinestatic

Definition at line 91 of file slru.c.

{
    if (ctl->long_segment_names)
    {
        /*
         * We could use 16 characters here but the disadvantage would be that
         * the SLRU segments will be hard to distinguish from WAL segments.
         *
         * For this reason we use 15 characters. It is enough but also means
         * that in the future we can't decrease SLRU_PAGES_PER_SEGMENT easily.
         */
        Assert(segno >= 0 && segno <= INT64CONST(0xFFFFFFFFFFFFFFF));
        return snprintf(path, MAXPGPATH, "%s/%015" PRIX64, ctl->Dir, segno);
    }
    else
    {
        /*
         * Despite the fact that %04X format string is used up to 24 bit
         * integers are allowed. See SlruCorrectSegmentFilenameLength()
         */
        Assert(segno >= 0 && segno <= INT64CONST(0xFFFFFF));
        return snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir,
                        (unsigned int) segno);
    }
}

References Assert, ctl, fb(), INT64CONST, MAXPGPATH, and snprintf.

Referenced by SimpleLruDoesPhysicalPageExist(), SlruInternalDeleteSegment(), SlruPhysicalReadPage(), SlruPhysicalWritePage(), SlruReportIOError(), and SlruSyncFileTag().

SlruInternalDeleteSegment()

static void SlruInternalDeleteSegment ( SlruCtl  ctl, int64  segno  )

static

Definition at line 1528 of file slru.c.

{
    char        path[MAXPGPATH];
 
    /* Forget any fsync requests queued for this segment. */
    if (ctl->sync_handler != SYNC_HANDLER_NONE)
    {
        FileTag     tag;
 
        INIT_SLRUFILETAG(tag, ctl->sync_handler, segno);
        RegisterSyncRequest(&tag, SYNC_FORGET_REQUEST, true);
    }
 
    /* Unlink the file. */
    SlruFileName(ctl, path, segno);
    ereport(DEBUG2, (errmsg_internal("removing file \"%s\"", path)));
    unlink(path);
}

References ctl, DEBUG2, ereport, errmsg_internal(), fb(), INIT_SLRUFILETAG, MAXPGPATH, RegisterSyncRequest(), SlruWriteAllData::segno, SlruFileName(), SYNC_FORGET_REQUEST, and SYNC_HANDLER_NONE.

Referenced by SlruDeleteSegment(), SlruScanDirCbDeleteAll(), and SlruScanDirCbDeleteCutoff().

SlruInternalWritePage()

static void SlruInternalWritePage ( SlruCtl  ctl, int  slotno, SlruWriteAll  fdata  )

static

Definition at line 677 of file slru.c.

{
    SlruShared  shared = ctl->shared;
    int64       pageno = shared->page_number[slotno];
    int         bankno = SlotGetBankNumber(slotno);
    bool        ok;
 
    Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
    Assert(LWLockHeldByMeInMode(SimpleLruGetBankLock(ctl, pageno), LW_EXCLUSIVE));
 
    /* If a write is in progress, wait for it to finish */
    while (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS &&
           shared->page_number[slotno] == pageno)
    {
        SimpleLruWaitIO(ctl, slotno);
    }
 
    /*
     * Do nothing if page is not dirty, or if buffer no longer contains the
     * same page we were called for.
     */
    if (!shared->page_dirty[slotno] ||
        shared->page_status[slotno] != SLRU_PAGE_VALID ||
        shared->page_number[slotno] != pageno)
        return;
 
    /*
     * Mark the slot write-busy, and clear the dirtybit.  After this point, a
     * transaction status update on this page will mark it dirty again.
     */
    shared->page_status[slotno] = SLRU_PAGE_WRITE_IN_PROGRESS;
    shared->page_dirty[slotno] = false;
 
    /* Acquire per-buffer lock (cannot deadlock, see notes at top) */
    LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE);
 
    /* Release bank lock while doing I/O */
    LWLockRelease(&shared->bank_locks[bankno].lock);
 
    /* Do the write */
    ok = SlruPhysicalWritePage(ctl, pageno, slotno, fdata);
 
    /* If we failed, and we're in a flush, better close the files */
    if (!ok && fdata)
    {
        for (int i = 0; i < fdata->num_files; i++)
            CloseTransientFile(fdata->fd[i]);
    }
 
    /* Re-acquire bank lock and update page state */
    LWLockAcquire(&shared->bank_locks[bankno].lock, LW_EXCLUSIVE);
 
    Assert(shared->page_number[slotno] == pageno &&
           shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS);
 
    /* If we failed to write, mark the page dirty again */
    if (!ok)
        shared->page_dirty[slotno] = true;
 
    shared->page_status[slotno] = SLRU_PAGE_VALID;
 
    LWLockRelease(&shared->buffer_locks[slotno].lock);
 
    /* Now it's okay to ereport if we failed */
    if (!ok)
        SlruReportIOError(ctl, pageno, InvalidTransactionId);
 
    /* If part of a checkpoint, count this as a SLRU buffer written. */
    if (fdata)
    {
        CheckpointStats.ckpt_slru_written++;
        PendingCheckpointerStats.slru_written++;
    }
}

References Assert, SlruSharedData::bank_locks, SlruSharedData::buffer_locks, CheckpointStats, CheckpointStatsData::ckpt_slru_written, CloseTransientFile(), ctl, fb(), i, InvalidTransactionId, LWLockPadded::lock, LW_EXCLUSIVE, LWLockAcquire(), LWLockHeldByMeInMode(), LWLockRelease(), SlruSharedData::page_dirty, SlruSharedData::page_number, SlruSharedData::page_status, PendingCheckpointerStats, SimpleLruGetBankLock(), SimpleLruWaitIO(), SlotGetBankNumber, SLRU_PAGE_EMPTY, SLRU_PAGE_VALID, SLRU_PAGE_WRITE_IN_PROGRESS, PgStat_CheckpointerStats::slru_written, SlruPhysicalWritePage(), and SlruReportIOError().

Referenced by SimpleLruTruncate(), SimpleLruWriteAll(), SimpleLruWritePage(), SlruDeleteSegment(), and SlruSelectLRUPage().

SlruMayDeleteSegment()

static bool SlruMayDeleteSegment ( SlruCtl  ctl, int64  segpage, int64  cutoffPage  )

static

Definition at line 1628 of file slru.c.

{
    int64       seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1;
 
    Assert(segpage % SLRU_PAGES_PER_SEGMENT == 0);
 
    return (ctl->PagePrecedes(segpage, cutoffPage) &&
            ctl->PagePrecedes(seg_last_page, cutoffPage));
}

References Assert, ctl, fb(), and SLRU_PAGES_PER_SEGMENT.

Referenced by SlruScanDirCbDeleteCutoff(), and SlruScanDirCbReportPresence().

SlruPhysicalReadPage()

static bool SlruPhysicalReadPage ( SlruCtl  ctl, int64  pageno, int  slotno  )

static

Definition at line 829 of file slru.c.

{
    SlruShared  shared = ctl->shared;
    int64       segno = pageno / SLRU_PAGES_PER_SEGMENT;
    int         rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
    off_t       offset = rpageno * BLCKSZ;
    char        path[MAXPGPATH];
    int         fd;
 
    SlruFileName(ctl, path, segno);
 
    /*
     * In a crash-and-restart situation, it's possible for us to receive
     * commands to set the commit status of transactions whose bits are in
     * already-truncated segments of the commit log (see notes in
     * SlruPhysicalWritePage).  Hence, if we are InRecovery, allow the case
     * where the file doesn't exist, and return zeroes instead.
     */
    fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
    if (fd < 0)
    {
        if (errno != ENOENT || !InRecovery)
        {
            slru_errcause = SLRU_OPEN_FAILED;
            slru_errno = errno;
            return false;
        }
 
        ereport(LOG,
                (errmsg("file \"%s\" doesn't exist, reading as zeroes",
                        path)));
        MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
        return true;
    }
 
    errno = 0;
    pgstat_report_wait_start(WAIT_EVENT_SLRU_READ);
    if (pg_pread(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ)
    {
        pgstat_report_wait_end();
        slru_errcause = SLRU_READ_FAILED;
        slru_errno = errno;
        CloseTransientFile(fd);
        return false;
    }
    pgstat_report_wait_end();
 
    if (CloseTransientFile(fd) != 0)
    {
        slru_errcause = SLRU_CLOSE_FAILED;
        slru_errno = errno;
        return false;
    }
 
    return true;
}

References CloseTransientFile(), ctl, ereport, errmsg(), fb(), fd(), InRecovery, LOG, MAXPGPATH, MemSet, OpenTransientFile(), SlruSharedData::page_buffer, PG_BINARY, pg_pread, pgstat_report_wait_end(), pgstat_report_wait_start(), SlruWriteAllData::segno, SLRU_CLOSE_FAILED, slru_errcause, slru_errno, SLRU_OPEN_FAILED, SLRU_PAGES_PER_SEGMENT, SLRU_READ_FAILED, and SlruFileName().

Referenced by SimpleLruReadPage().

SlruPhysicalWritePage()

static bool SlruPhysicalWritePage ( SlruCtl  ctl, int64  pageno, int  slotno, SlruWriteAll  fdata  )

static

Definition at line 901 of file slru.c.

{
    SlruShared  shared = ctl->shared;
    int64       segno = pageno / SLRU_PAGES_PER_SEGMENT;
    int         rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
    off_t       offset = rpageno * BLCKSZ;
    char        path[MAXPGPATH];
    int         fd = -1;
 
    /* update the stats counter of written pages */
    pgstat_count_slru_blocks_written(shared->slru_stats_idx);
 
    /*
     * Honor the write-WAL-before-data rule, if appropriate, so that we do not
     * write out data before associated WAL records.  This is the same action
     * performed during FlushBuffer() in the main buffer manager.
     */
    if (shared->group_lsn != NULL)
    {
        /*
         * We must determine the largest async-commit LSN for the page. This
         * is a bit tedious, but since this entire function is a slow path
         * anyway, it seems better to do this here than to maintain a per-page
         * LSN variable (which'd need an extra comparison in the
         * transaction-commit path).
         */
        XLogRecPtr  max_lsn;
        int         lsnindex;
 
        lsnindex = slotno * shared->lsn_groups_per_page;
        max_lsn = shared->group_lsn[lsnindex++];
        for (int lsnoff = 1; lsnoff < shared->lsn_groups_per_page; lsnoff++)
        {
            XLogRecPtr  this_lsn = shared->group_lsn[lsnindex++];
 
            if (max_lsn < this_lsn)
                max_lsn = this_lsn;
        }
 
        if (XLogRecPtrIsValid(max_lsn))
        {
            /*
             * As noted above, elog(ERROR) is not acceptable here, so if
             * XLogFlush were to fail, we must PANIC.  This isn't much of a
             * restriction because XLogFlush is just about all critical
             * section anyway, but let's make sure.
             */
            START_CRIT_SECTION();
            XLogFlush(max_lsn);
            END_CRIT_SECTION();
        }
    }
 
    /*
     * During a SimpleLruWriteAll, we may already have the desired file open.
     */
    if (fdata)
    {
        for (int i = 0; i < fdata->num_files; i++)
        {
            if (fdata->segno[i] == segno)
            {
                fd = fdata->fd[i];
                break;
            }
        }
    }
 
    if (fd < 0)
    {
        /*
         * If the file doesn't already exist, we should create it.  It is
         * possible for this to need to happen when writing a page that's not
         * first in its segment; we assume the OS can cope with that. (Note:
         * it might seem that it'd be okay to create files only when
         * SimpleLruZeroPage is called for the first page of a segment.
         * However, if after a crash and restart the REDO logic elects to
         * replay the log from a checkpoint before the latest one, then it's
         * possible that we will get commands to set transaction status of
         * transactions that have already been truncated from the commit log.
         * Easiest way to deal with that is to accept references to
         * nonexistent files here and in SlruPhysicalReadPage.)
         *
         * Note: it is possible for more than one backend to be executing this
         * code simultaneously for different pages of the same file. Hence,
         * don't use O_EXCL or O_TRUNC or anything like that.
         */
        SlruFileName(ctl, path, segno);
        fd = OpenTransientFile(path, O_RDWR | O_CREAT | PG_BINARY);
        if (fd < 0)
        {
            slru_errcause = SLRU_OPEN_FAILED;
            slru_errno = errno;
            return false;
        }
 
        if (fdata)
        {
            if (fdata->num_files < MAX_WRITEALL_BUFFERS)
            {
                fdata->fd[fdata->num_files] = fd;
                fdata->segno[fdata->num_files] = segno;
                fdata->num_files++;
            }
            else
            {
                /*
                 * In the unlikely event that we exceed MAX_WRITEALL_BUFFERS,
                 * fall back to treating it as a standalone write.
                 */
                fdata = NULL;
            }
        }
    }
 
    errno = 0;
    pgstat_report_wait_start(WAIT_EVENT_SLRU_WRITE);
    if (pg_pwrite(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ)
    {
        pgstat_report_wait_end();
        /* if write didn't set errno, assume problem is no disk space */
        if (errno == 0)
            errno = ENOSPC;
        slru_errcause = SLRU_WRITE_FAILED;
        slru_errno = errno;
        if (!fdata)
            CloseTransientFile(fd);
        return false;
    }
    pgstat_report_wait_end();
 
    /* Queue up a sync request for the checkpointer. */
    if (ctl->sync_handler != SYNC_HANDLER_NONE)
    {
        FileTag     tag;
 
        INIT_SLRUFILETAG(tag, ctl->sync_handler, segno);
        if (!RegisterSyncRequest(&tag, SYNC_REQUEST, false))
        {
            /* No space to enqueue sync request.  Do it synchronously. */
            pgstat_report_wait_start(WAIT_EVENT_SLRU_SYNC);
            if (pg_fsync(fd) != 0)
            {
                pgstat_report_wait_end();
                slru_errcause = SLRU_FSYNC_FAILED;
                slru_errno = errno;
                CloseTransientFile(fd);
                return false;
            }
            pgstat_report_wait_end();
        }
    }
 
    /* Close file, unless part of flush request. */
    if (!fdata)
    {
        if (CloseTransientFile(fd) != 0)
        {
            slru_errcause = SLRU_CLOSE_FAILED;
            slru_errno = errno;
            return false;
        }
    }
 
    return true;
}

References CloseTransientFile(), ctl, END_CRIT_SECTION, fb(), fd(), SlruSharedData::group_lsn, i, INIT_SLRUFILETAG, SlruSharedData::lsn_groups_per_page, MAX_WRITEALL_BUFFERS, MAXPGPATH, OpenTransientFile(), SlruSharedData::page_buffer, PG_BINARY, pg_fsync(), pg_pwrite, pgstat_count_slru_blocks_written(), pgstat_report_wait_end(), pgstat_report_wait_start(), RegisterSyncRequest(), SlruWriteAllData::segno, SLRU_CLOSE_FAILED, slru_errcause, slru_errno, SLRU_FSYNC_FAILED, SLRU_OPEN_FAILED, SLRU_PAGES_PER_SEGMENT, SlruSharedData::slru_stats_idx, SLRU_WRITE_FAILED, SlruFileName(), START_CRIT_SECTION, SYNC_HANDLER_NONE, SYNC_REQUEST, XLogFlush(), and XLogRecPtrIsValid.

Referenced by SlruInternalWritePage().

SlruRecentlyUsed()

static void SlruRecentlyUsed ( SlruShared  shared, int  slotno  )

inlinestatic

Definition at line 1148 of file slru.c.

{
    int         bankno = SlotGetBankNumber(slotno);
    int         new_lru_count = shared->bank_cur_lru_count[bankno];
 
    Assert(shared->page_status[slotno] != SLRU_PAGE_EMPTY);
 
    /*
     * The reason for the if-test is that there are often many consecutive
     * accesses to the same page (particularly the latest page).  By
     * suppressing useless increments of bank_cur_lru_count, we reduce the
     * probability that old pages' counts will "wrap around" and make them
     * appear recently used.
     *
     * We allow this code to be executed concurrently by multiple processes
     * within SimpleLruReadPage_ReadOnly().  As long as int reads and writes
     * are atomic, this should not cause any completely-bogus values to enter
     * the computation.  However, it is possible for either bank_cur_lru_count
     * or individual page_lru_count entries to be "reset" to lower values than
     * they should have, in case a process is delayed while it executes this
     * function.  With care in SlruSelectLRUPage(), this does little harm, and
     * in any case the absolute worst possible consequence is a nonoptimal
     * choice of page to evict.  The gain from allowing concurrent reads of
     * SLRU pages seems worth it.
     */
    if (new_lru_count != shared->page_lru_count[slotno])
    {
        shared->bank_cur_lru_count[bankno] = ++new_lru_count;
        shared->page_lru_count[slotno] = new_lru_count;
    }
}

References Assert, SlruSharedData::bank_cur_lru_count, fb(), SlruSharedData::page_lru_count, SlruSharedData::page_status, SlotGetBankNumber, and SLRU_PAGE_EMPTY.

Referenced by SimpleLruReadPage(), SimpleLruReadPage_ReadOnly(), and SimpleLruZeroPage().

SlruReportIOError()

static void SlruReportIOError ( SlruCtl  ctl, int64  pageno, TransactionId  xid  )

static

Definition at line 1073 of file slru.c.

{
    int64       segno = pageno / SLRU_PAGES_PER_SEGMENT;
    int         rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
    int         offset = rpageno * BLCKSZ;
    char        path[MAXPGPATH];
 
    SlruFileName(ctl, path, segno);
    errno = slru_errno;
    switch (slru_errcause)
    {
        case SLRU_OPEN_FAILED:
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not access status of transaction %u", xid),
                     errdetail("Could not open file \"%s\": %m.", path)));
            break;
        case SLRU_SEEK_FAILED:
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not access status of transaction %u", xid),
                     errdetail("Could not seek in file \"%s\" to offset %d: %m.",
                               path, offset)));
            break;
        case SLRU_READ_FAILED:
            if (errno)
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not access status of transaction %u", xid),
                         errdetail("Could not read from file \"%s\" at offset %d: %m.",
                                   path, offset)));
            else
                ereport(ERROR,
                        (errmsg("could not access status of transaction %u", xid),
                         errdetail("Could not read from file \"%s\" at offset %d: read too few bytes.", path, offset)));
            break;
        case SLRU_WRITE_FAILED:
            if (errno)
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not access status of transaction %u", xid),
                         errdetail("Could not write to file \"%s\" at offset %d: %m.",
                                   path, offset)));
            else
                ereport(ERROR,
                        (errmsg("could not access status of transaction %u", xid),
                         errdetail("Could not write to file \"%s\" at offset %d: wrote too few bytes.",
                                   path, offset)));
            break;
        case SLRU_FSYNC_FAILED:
            ereport(data_sync_elevel(ERROR),
                    (errcode_for_file_access(),
                     errmsg("could not access status of transaction %u", xid),
                     errdetail("Could not fsync file \"%s\": %m.",
                               path)));
            break;
        case SLRU_CLOSE_FAILED:
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not access status of transaction %u", xid),
                     errdetail("Could not close file \"%s\": %m.",
                               path)));
            break;
        default:
            /* can't get here, we trust */
            elog(ERROR, "unrecognized SimpleLru error cause: %d",
                 (int) slru_errcause);
            break;
    }
}

References ctl, data_sync_elevel(), elog, ereport, errcode_for_file_access(), errdetail(), errmsg(), ERROR, fb(), MAXPGPATH, SlruWriteAllData::segno, SLRU_CLOSE_FAILED, slru_errcause, slru_errno, SLRU_FSYNC_FAILED, SLRU_OPEN_FAILED, SLRU_PAGES_PER_SEGMENT, SLRU_READ_FAILED, SLRU_SEEK_FAILED, SLRU_WRITE_FAILED, and SlruFileName().

Referenced by SimpleLruDoesPhysicalPageExist(), SimpleLruReadPage(), SimpleLruWriteAll(), and SlruInternalWritePage().

SlruScanDirCbDeleteAll()

bool SlruScanDirCbDeleteAll	(	SlruCtl	ctl,
		char *	filename,
		int64	segpage,
		void *	data
	)

Definition at line 1769 of file slru.c.

{
    SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
 
    return false;               /* keep going */
}

References ctl, fb(), SLRU_PAGES_PER_SEGMENT, and SlruInternalDeleteSegment().

Referenced by AsyncShmemInit(), DeactivateCommitTs(), and test_slru_scan_cb().

SlruScanDirCbDeleteCutoff()

static bool SlruScanDirCbDeleteCutoff ( SlruCtl  ctl, char *  filename, int64  segpage, void *  data  )

static

Definition at line 1753 of file slru.c.

{
    int64       cutoffPage = *(int64 *) data;
 
    if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
        SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT);
 
    return false;               /* keep going */
}

References ctl, data, fb(), SLRU_PAGES_PER_SEGMENT, SlruInternalDeleteSegment(), and SlruMayDeleteSegment().

Referenced by SimpleLruTruncate().

SlruScanDirCbReportPresence()

bool SlruScanDirCbReportPresence	(	SlruCtl	ctl,
		char *	filename,
		int64	segpage,
		void *	data
	)

Definition at line 1737 of file slru.c.

{
    int64       cutoffPage = *(int64 *) data;
 
    if (SlruMayDeleteSegment(ctl, segpage, cutoffPage))
        return true;            /* found one; don't iterate any more */
 
    return false;               /* keep going */
}

References ctl, data, fb(), and SlruMayDeleteSegment().

Referenced by TruncateCLOG(), and TruncateCommitTs().

SlruScanDirectory()

bool SlruScanDirectory	(	SlruCtl	ctl,
		SlruScanCallback	callback,
		void *	data
	)

Definition at line 1816 of file slru.c.

{
    bool        retval = false;
    DIR        *cldir;
    struct dirent *clde;
    int64       segno;
    int64       segpage;
 
    cldir = AllocateDir(ctl->Dir);
    while ((clde = ReadDir(cldir, ctl->Dir)) != NULL)
    {
        size_t      len;
 
        len = strlen(clde->d_name);
 
        if (SlruCorrectSegmentFilenameLength(ctl, len) &&
            strspn(clde->d_name, "0123456789ABCDEF") == len)
        {
            segno = strtoi64(clde->d_name, NULL, 16);
            segpage = segno * SLRU_PAGES_PER_SEGMENT;
 
            elog(DEBUG2, "SlruScanDirectory invoking callback on %s/%s",
                 ctl->Dir, clde->d_name);
            retval = callback(ctl, clde->d_name, segpage, data);
            if (retval)
                break;
        }
    }
    FreeDir(cldir);
 
    return retval;
}

References AllocateDir(), callback(), ctl, data, DEBUG2, elog, fb(), FreeDir(), len, ReadDir(), SLRU_PAGES_PER_SEGMENT, and SlruCorrectSegmentFilenameLength().

Referenced by AsyncShmemInit(), DeactivateCommitTs(), SimpleLruTruncate(), test_slru_delete_all(), TruncateCLOG(), and TruncateCommitTs().

SlruSelectLRUPage()

static int SlruSelectLRUPage ( SlruCtl  ctl, int64  pageno  )

static

Definition at line 1194 of file slru.c.

{
    SlruShared  shared = ctl->shared;
 
    /* Outer loop handles restart after I/O */
    for (;;)
    {
        int         cur_count;
        int         bestvalidslot = 0;  /* keep compiler quiet */
        int         best_valid_delta = -1;
        int64       best_valid_page_number = 0; /* keep compiler quiet */
        int         bestinvalidslot = 0;    /* keep compiler quiet */
        int         best_invalid_delta = -1;
        int64       best_invalid_page_number = 0;   /* keep compiler quiet */
        int         bankno = pageno % ctl->nbanks;
        int         bankstart = bankno * SLRU_BANK_SIZE;
        int         bankend = bankstart + SLRU_BANK_SIZE;
 
        Assert(LWLockHeldByMe(SimpleLruGetBankLock(ctl, pageno)));
 
        /* See if page already has a buffer assigned */
        for (int slotno = bankstart; slotno < bankend; slotno++)
        {
            if (shared->page_status[slotno] != SLRU_PAGE_EMPTY &&
                shared->page_number[slotno] == pageno)
                return slotno;
        }
 
        /*
         * If we find any EMPTY slot, just select that one. Else choose a
         * victim page to replace.  We normally take the least recently used
         * valid page, but we will never take the slot containing
         * latest_page_number, even if it appears least recently used.  We
         * will select a slot that is already I/O busy only if there is no
         * other choice: a read-busy slot will not be least recently used once
         * the read finishes, and waiting for an I/O on a write-busy slot is
         * inferior to just picking some other slot.  Testing shows the slot
         * we pick instead will often be clean, allowing us to begin a read at
         * once.
         *
         * Normally the page_lru_count values will all be different and so
         * there will be a well-defined LRU page.  But since we allow
         * concurrent execution of SlruRecentlyUsed() within
         * SimpleLruReadPage_ReadOnly(), it is possible that multiple pages
         * acquire the same lru_count values.  In that case we break ties by
         * choosing the furthest-back page.
         *
         * Notice that this next line forcibly advances cur_lru_count to a
         * value that is certainly beyond any value that will be in the
         * page_lru_count array after the loop finishes.  This ensures that
         * the next execution of SlruRecentlyUsed will mark the page newly
         * used, even if it's for a page that has the current counter value.
         * That gets us back on the path to having good data when there are
         * multiple pages with the same lru_count.
         */
        cur_count = (shared->bank_cur_lru_count[bankno])++;
        for (int slotno = bankstart; slotno < bankend; slotno++)
        {
            int         this_delta;
            int64       this_page_number;
 
            if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
                return slotno;
 
            this_delta = cur_count - shared->page_lru_count[slotno];
            if (this_delta < 0)
            {
                /*
                 * Clean up in case shared updates have caused cur_count
                 * increments to get "lost".  We back off the page counts,
                 * rather than trying to increase cur_count, to avoid any
                 * question of infinite loops or failure in the presence of
                 * wrapped-around counts.
                 */
                shared->page_lru_count[slotno] = cur_count;
                this_delta = 0;
            }
 
            /*
             * If this page is the one most recently zeroed, don't consider it
             * an eviction candidate. See comments in SimpleLruZeroPage for an
             * explanation about the lack of a memory barrier here.
             */
            this_page_number = shared->page_number[slotno];
            if (this_page_number ==
                pg_atomic_read_u64(&shared->latest_page_number))
                continue;
 
            if (shared->page_status[slotno] == SLRU_PAGE_VALID)
            {
                if (this_delta > best_valid_delta ||
                    (this_delta == best_valid_delta &&
                     ctl->PagePrecedes(this_page_number,
                                       best_valid_page_number)))
                {
                    bestvalidslot = slotno;
                    best_valid_delta = this_delta;
                    best_valid_page_number = this_page_number;
                }
            }
            else
            {
                if (this_delta > best_invalid_delta ||
                    (this_delta == best_invalid_delta &&
                     ctl->PagePrecedes(this_page_number,
                                       best_invalid_page_number)))
                {
                    bestinvalidslot = slotno;
                    best_invalid_delta = this_delta;
                    best_invalid_page_number = this_page_number;
                }
            }
        }
 
        /*
         * If all pages (except possibly the latest one) are I/O busy, we'll
         * have to wait for an I/O to complete and then retry.  In that
         * unhappy case, we choose to wait for the I/O on the least recently
         * used slot, on the assumption that it was likely initiated first of
         * all the I/Os in progress and may therefore finish first.
         */
        if (best_valid_delta < 0)
        {
            SimpleLruWaitIO(ctl, bestinvalidslot);
            continue;
        }
 
        /*
         * If the selected page is clean, we're set.
         */
        if (!shared->page_dirty[bestvalidslot])
            return bestvalidslot;
 
        /*
         * Write the page.
         */
        SlruInternalWritePage(ctl, bestvalidslot, NULL);
 
        /*
         * Now loop back and try again.  This is the easiest way of dealing
         * with corner cases such as the victim page being re-dirtied while we
         * wrote it.
         */
    }
}

References Assert, SlruSharedData::bank_cur_lru_count, ctl, fb(), SlruSharedData::latest_page_number, LWLockHeldByMe(), SlruSharedData::page_dirty, SlruSharedData::page_lru_count, SlruSharedData::page_number, SlruSharedData::page_status, pg_atomic_read_u64(), SimpleLruGetBankLock(), SimpleLruWaitIO(), SLRU_BANK_SIZE, SLRU_PAGE_EMPTY, SLRU_PAGE_VALID, and SlruInternalWritePage().

Referenced by SimpleLruReadPage(), and SimpleLruZeroPage().

SlruSyncFileTag()

int SlruSyncFileTag	(	SlruCtl	ctl,
		const FileTag *	ftag,
		char *	path
	)

Definition at line 1856 of file slru.c.

{
    int         fd;
    int         save_errno;
    int         result;
 
    SlruFileName(ctl, path, ftag->segno);
 
    fd = OpenTransientFile(path, O_RDWR | PG_BINARY);
    if (fd < 0)
        return -1;
 
    pgstat_report_wait_start(WAIT_EVENT_SLRU_FLUSH_SYNC);
    result = pg_fsync(fd);
    pgstat_report_wait_end();
    save_errno = errno;
 
    CloseTransientFile(fd);
 
    errno = save_errno;
    return result;
}

References CloseTransientFile(), ctl, fb(), fd(), OpenTransientFile(), PG_BINARY, pg_fsync(), pgstat_report_wait_end(), pgstat_report_wait_start(), FileTag::segno, and SlruFileName().

Referenced by clogsyncfiletag(), committssyncfiletag(), multixactmemberssyncfiletag(), multixactoffsetssyncfiletag(), and test_slru_page_sync().

Variable Documentation

slru_errcause

SlruErrorCause slru_errcause

static

Definition at line 174 of file slru.c.

Referenced by SimpleLruDoesPhysicalPageExist(), SimpleLruWriteAll(), SlruPhysicalReadPage(), SlruPhysicalWritePage(), and SlruReportIOError().

slru_errno

int slru_errno

static

Definition at line 175 of file slru.c.

Referenced by SimpleLruDoesPhysicalPageExist(), SimpleLruWriteAll(), SlruPhysicalReadPage(), SlruPhysicalWritePage(), and SlruReportIOError().