localbuf.c

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/*-------------------------------------------------------------------------
 *
 * localbuf.c
 *    local buffer manager. Fast buffer manager for temporary tables,
 *    which never need to be WAL-logged or checkpointed, etc.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994-5, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/storage/buffer/localbuf.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/parallel.h"
#include "catalog/catalog.h"
#include "executor/instrument.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/resowner_private.h"


/*#define LBDEBUG*/

/* entry for buffer lookup hashtable */
typedef struct
{
    BufferTag   key;            /* Tag of a disk page */
    int         id;             /* Associated local buffer's index */
} LocalBufferLookupEnt;

/* Note: this macro only works on local buffers, not shared ones! */
#define LocalBufHdrGetBlock(bufHdr) \
    LocalBufferBlockPointers[-((bufHdr)->buf_id + 2)]

int         NLocBuffer = 0;     /* until buffers are initialized */

BufferDesc *LocalBufferDescriptors = NULL;
Block      *LocalBufferBlockPointers = NULL;
int32      *LocalRefCount = NULL;

static int  nextFreeLocalBuf = 0;

static HTAB *LocalBufHash = NULL;


static void InitLocalBuffers(void);
static Block GetLocalBufferStorage(void);


/*
 * PrefetchLocalBuffer -
 *    initiate asynchronous read of a block of a relation
 *
 * Do PrefetchBuffer's work for temporary relations.
 * No-op if prefetching isn't compiled in.
 */
PrefetchBufferResult
PrefetchLocalBuffer(SMgrRelation smgr, ForkNumber forkNum,
                    BlockNumber blockNum)
{
    PrefetchBufferResult result = {InvalidBuffer, false};
    BufferTag   newTag;         /* identity of requested block */
    LocalBufferLookupEnt *hresult;

    INIT_BUFFERTAG(newTag, smgr->smgr_rnode.node, forkNum, blockNum);

    /* Initialize local buffers if first request in this session */
    if (LocalBufHash == NULL)
        InitLocalBuffers();

    /* See if the desired buffer already exists */
    hresult = (LocalBufferLookupEnt *)
        hash_search(LocalBufHash, (void *) &newTag, HASH_FIND, NULL);

    if (hresult)
    {
        /* Yes, so nothing to do */
        result.recent_buffer = -hresult->id - 1;
    }
    else
    {
#ifdef USE_PREFETCH
        /* Not in buffers, so initiate prefetch */
        smgrprefetch(smgr, forkNum, blockNum);
        result.initiated_io = true;
#endif                          /* USE_PREFETCH */
    }

    return result;
}


/*
 * LocalBufferAlloc -
 *    Find or create a local buffer for the given page of the given relation.
 *
 * API is similar to bufmgr.c's BufferAlloc, except that we do not need
 * to do any locking since this is all local.   Also, IO_IN_PROGRESS
 * does not get set.  Lastly, we support only default access strategy
 * (hence, usage_count is always advanced).
 */
BufferDesc *
LocalBufferAlloc(SMgrRelation smgr, ForkNumber forkNum, BlockNumber blockNum,
                 bool *foundPtr)
{
    BufferTag   newTag;         /* identity of requested block */
    LocalBufferLookupEnt *hresult;
    BufferDesc *bufHdr;
    int         b;
    int         trycounter;
    bool        found;
    uint32      buf_state;

    INIT_BUFFERTAG(newTag, smgr->smgr_rnode.node, forkNum, blockNum);

    /* Initialize local buffers if first request in this session */
    if (LocalBufHash == NULL)
        InitLocalBuffers();

    /* See if the desired buffer already exists */
    hresult = (LocalBufferLookupEnt *)
        hash_search(LocalBufHash, (void *) &newTag, HASH_FIND, NULL);

    if (hresult)
    {
        b = hresult->id;
        bufHdr = GetLocalBufferDescriptor(b);
        Assert(BUFFERTAGS_EQUAL(bufHdr->tag, newTag));
#ifdef LBDEBUG
        fprintf(stderr, "LB ALLOC (%u,%d,%d) %d\n",
                smgr->smgr_rnode.node.relNode, forkNum, blockNum, -b - 1);
#endif
        buf_state = pg_atomic_read_u32(&bufHdr->state);

        /* this part is equivalent to PinBuffer for a shared buffer */
        if (LocalRefCount[b] == 0)
        {
            if (BUF_STATE_GET_USAGECOUNT(buf_state) < BM_MAX_USAGE_COUNT)
            {
                buf_state += BUF_USAGECOUNT_ONE;
                pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
            }
        }
        LocalRefCount[b]++;
        ResourceOwnerRememberBuffer(CurrentResourceOwner,
                                    BufferDescriptorGetBuffer(bufHdr));
        if (buf_state & BM_VALID)
            *foundPtr = true;
        else
        {
            /* Previous read attempt must have failed; try again */
            *foundPtr = false;
        }
        return bufHdr;
    }

#ifdef LBDEBUG
    fprintf(stderr, "LB ALLOC (%u,%d,%d) %d\n",
            smgr->smgr_rnode.node.relNode, forkNum, blockNum,
            -nextFreeLocalBuf - 1);
#endif

    /*
     * Need to get a new buffer.  We use a clock sweep algorithm (essentially
     * the same as what freelist.c does now...)
     */
    trycounter = NLocBuffer;
    for (;;)
    {
        b = nextFreeLocalBuf;

        if (++nextFreeLocalBuf >= NLocBuffer)
            nextFreeLocalBuf = 0;

        bufHdr = GetLocalBufferDescriptor(b);

        if (LocalRefCount[b] == 0)
        {
            buf_state = pg_atomic_read_u32(&bufHdr->state);

            if (BUF_STATE_GET_USAGECOUNT(buf_state) > 0)
            {
                buf_state -= BUF_USAGECOUNT_ONE;
                pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
                trycounter = NLocBuffer;
            }
            else
            {
                /* Found a usable buffer */
                LocalRefCount[b]++;
                ResourceOwnerRememberBuffer(CurrentResourceOwner,
                                            BufferDescriptorGetBuffer(bufHdr));
                break;
            }
        }
        else if (--trycounter == 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INSUFFICIENT_RESOURCES),
                     errmsg("no empty local buffer available")));
    }

    /*
     * this buffer is not referenced but it might still be dirty. if that's
     * the case, write it out before reusing it!
     */
    if (buf_state & BM_DIRTY)
    {
        SMgrRelation oreln;
        Page        localpage = (char *) LocalBufHdrGetBlock(bufHdr);

        /* Find smgr relation for buffer */
        oreln = smgropen(bufHdr->tag.rnode, MyBackendId);

        PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);

        /* And write... */
        smgrwrite(oreln,
                  bufHdr->tag.forkNum,
                  bufHdr->tag.blockNum,
                  localpage,
                  false);

        /* Mark not-dirty now in case we error out below */
        buf_state &= ~BM_DIRTY;
        pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);

        pgBufferUsage.local_blks_written++;
    }

    /*
     * lazy memory allocation: allocate space on first use of a buffer.
     */
    if (LocalBufHdrGetBlock(bufHdr) == NULL)
    {
        /* Set pointer for use by BufferGetBlock() macro */
        LocalBufHdrGetBlock(bufHdr) = GetLocalBufferStorage();
    }

    /*
     * Update the hash table: remove old entry, if any, and make new one.
     */
    if (buf_state & BM_TAG_VALID)
    {
        hresult = (LocalBufferLookupEnt *)
            hash_search(LocalBufHash, (void *) &bufHdr->tag,
                        HASH_REMOVE, NULL);
        if (!hresult)           /* shouldn't happen */
            elog(ERROR, "local buffer hash table corrupted");
        /* mark buffer invalid just in case hash insert fails */
        CLEAR_BUFFERTAG(bufHdr->tag);
        buf_state &= ~(BM_VALID | BM_TAG_VALID);
        pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
    }

    hresult = (LocalBufferLookupEnt *)
        hash_search(LocalBufHash, (void *) &newTag, HASH_ENTER, &found);
    if (found)                  /* shouldn't happen */
        elog(ERROR, "local buffer hash table corrupted");
    hresult->id = b;

    /*
     * it's all ours now.
     */
    bufHdr->tag = newTag;
    buf_state &= ~(BM_VALID | BM_DIRTY | BM_JUST_DIRTIED | BM_IO_ERROR);
    buf_state |= BM_TAG_VALID;
    buf_state &= ~BUF_USAGECOUNT_MASK;
    buf_state += BUF_USAGECOUNT_ONE;
    pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);

    *foundPtr = false;
    return bufHdr;
}

/*
 * MarkLocalBufferDirty -
 *    mark a local buffer dirty
 */
void
MarkLocalBufferDirty(Buffer buffer)
{
    int         bufid;
    BufferDesc *bufHdr;
    uint32      buf_state;

    Assert(BufferIsLocal(buffer));

#ifdef LBDEBUG
    fprintf(stderr, "LB DIRTY %d\n", buffer);
#endif

    bufid = -(buffer + 1);

    Assert(LocalRefCount[bufid] > 0);

    bufHdr = GetLocalBufferDescriptor(bufid);

    buf_state = pg_atomic_read_u32(&bufHdr->state);

    if (!(buf_state & BM_DIRTY))
        pgBufferUsage.local_blks_dirtied++;

    buf_state |= BM_DIRTY;

    pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
}

/*
 * DropRelFileNodeLocalBuffers
 *      This function removes from the buffer pool all the pages of the
 *      specified relation that have block numbers >= firstDelBlock.
 *      (In particular, with firstDelBlock = 0, all pages are removed.)
 *      Dirty pages are simply dropped, without bothering to write them
 *      out first.  Therefore, this is NOT rollback-able, and so should be
 *      used only with extreme caution!
 *
 *      See DropRelFileNodeBuffers in bufmgr.c for more notes.
 */
void
DropRelFileNodeLocalBuffers(RelFileNode rnode, ForkNumber forkNum,
                            BlockNumber firstDelBlock)
{
    int         i;

    for (i = 0; i < NLocBuffer; i++)
    {
        BufferDesc *bufHdr = GetLocalBufferDescriptor(i);
        LocalBufferLookupEnt *hresult;
        uint32      buf_state;

        buf_state = pg_atomic_read_u32(&bufHdr->state);

        if ((buf_state & BM_TAG_VALID) &&
            RelFileNodeEquals(bufHdr->tag.rnode, rnode) &&
            bufHdr->tag.forkNum == forkNum &&
            bufHdr->tag.blockNum >= firstDelBlock)
        {
            if (LocalRefCount[i] != 0)
                elog(ERROR, "block %u of %s is still referenced (local %u)",
                     bufHdr->tag.blockNum,
                     relpathbackend(bufHdr->tag.rnode, MyBackendId,
                                    bufHdr->tag.forkNum),
                     LocalRefCount[i]);
            /* Remove entry from hashtable */
            hresult = (LocalBufferLookupEnt *)
                hash_search(LocalBufHash, (void *) &bufHdr->tag,
                            HASH_REMOVE, NULL);
            if (!hresult)       /* shouldn't happen */
                elog(ERROR, "local buffer hash table corrupted");
            /* Mark buffer invalid */
            CLEAR_BUFFERTAG(bufHdr->tag);
            buf_state &= ~BUF_FLAG_MASK;
            buf_state &= ~BUF_USAGECOUNT_MASK;
            pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
        }
    }
}

/*
 * DropRelFileNodeAllLocalBuffers
 *      This function removes from the buffer pool all pages of all forks
 *      of the specified relation.
 *
 *      See DropRelFileNodesAllBuffers in bufmgr.c for more notes.
 */
void
DropRelFileNodeAllLocalBuffers(RelFileNode rnode)
{
    int         i;

    for (i = 0; i < NLocBuffer; i++)
    {
        BufferDesc *bufHdr = GetLocalBufferDescriptor(i);
        LocalBufferLookupEnt *hresult;
        uint32      buf_state;

        buf_state = pg_atomic_read_u32(&bufHdr->state);

        if ((buf_state & BM_TAG_VALID) &&
            RelFileNodeEquals(bufHdr->tag.rnode, rnode))
        {
            if (LocalRefCount[i] != 0)
                elog(ERROR, "block %u of %s is still referenced (local %u)",
                     bufHdr->tag.blockNum,
                     relpathbackend(bufHdr->tag.rnode, MyBackendId,
                                    bufHdr->tag.forkNum),
                     LocalRefCount[i]);
            /* Remove entry from hashtable */
            hresult = (LocalBufferLookupEnt *)
                hash_search(LocalBufHash, (void *) &bufHdr->tag,
                            HASH_REMOVE, NULL);
            if (!hresult)       /* shouldn't happen */
                elog(ERROR, "local buffer hash table corrupted");
            /* Mark buffer invalid */
            CLEAR_BUFFERTAG(bufHdr->tag);
            buf_state &= ~BUF_FLAG_MASK;
            buf_state &= ~BUF_USAGECOUNT_MASK;
            pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
        }
    }
}

/*
 * InitLocalBuffers -
 *    init the local buffer cache. Since most queries (esp. multi-user ones)
 *    don't involve local buffers, we delay allocating actual memory for the
 *    buffers until we need them; just make the buffer headers here.
 */
static void
InitLocalBuffers(void)
{
    int         nbufs = num_temp_buffers;
    HASHCTL     info;
    int         i;

    /*
     * Parallel workers can't access data in temporary tables, because they
     * have no visibility into the local buffers of their leader.  This is a
     * convenient, low-cost place to provide a backstop check for that.  Note
     * that we don't wish to prevent a parallel worker from accessing catalog
     * metadata about a temp table, so checks at higher levels would be
     * inappropriate.
     */
    if (IsParallelWorker())
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TRANSACTION_STATE),
                 errmsg("cannot access temporary tables during a parallel operation")));

    /* Allocate and zero buffer headers and auxiliary arrays */
    LocalBufferDescriptors = (BufferDesc *) calloc(nbufs, sizeof(BufferDesc));
    LocalBufferBlockPointers = (Block *) calloc(nbufs, sizeof(Block));
    LocalRefCount = (int32 *) calloc(nbufs, sizeof(int32));
    if (!LocalBufferDescriptors || !LocalBufferBlockPointers || !LocalRefCount)
        ereport(FATAL,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory")));

    nextFreeLocalBuf = 0;

    /* initialize fields that need to start off nonzero */
    for (i = 0; i < nbufs; i++)
    {
        BufferDesc *buf = GetLocalBufferDescriptor(i);

        /*
         * negative to indicate local buffer. This is tricky: shared buffers
         * start with 0. We have to start with -2. (Note that the routine
         * BufferDescriptorGetBuffer adds 1 to buf_id so our first buffer id
         * is -1.)
         */
        buf->buf_id = -i - 2;

        /*
         * Intentionally do not initialize the buffer's atomic variable
         * (besides zeroing the underlying memory above). That way we get
         * errors on platforms without atomics, if somebody (re-)introduces
         * atomic operations for local buffers.
         */
    }

    /* Create the lookup hash table */
    info.keysize = sizeof(BufferTag);
    info.entrysize = sizeof(LocalBufferLookupEnt);

    LocalBufHash = hash_create("Local Buffer Lookup Table",
                               nbufs,
                               &info,
                               HASH_ELEM | HASH_BLOBS);

    if (!LocalBufHash)
        elog(ERROR, "could not initialize local buffer hash table");

    /* Initialization done, mark buffers allocated */
    NLocBuffer = nbufs;
}

/*
 * GetLocalBufferStorage - allocate memory for a local buffer
 *
 * The idea of this function is to aggregate our requests for storage
 * so that the memory manager doesn't see a whole lot of relatively small
 * requests.  Since we'll never give back a local buffer once it's created
 * within a particular process, no point in burdening memmgr with separately
 * managed chunks.
 */
static Block
GetLocalBufferStorage(void)
{
    static char *cur_block = NULL;
    static int  next_buf_in_block = 0;
    static int  num_bufs_in_block = 0;
    static int  total_bufs_allocated = 0;
    static MemoryContext LocalBufferContext = NULL;

    char       *this_buf;

    Assert(total_bufs_allocated < NLocBuffer);

    if (next_buf_in_block >= num_bufs_in_block)
    {
        /* Need to make a new request to memmgr */
        int         num_bufs;

        /*
         * We allocate local buffers in a context of their own, so that the
         * space eaten for them is easily recognizable in MemoryContextStats
         * output.  Create the context on first use.
         */
        if (LocalBufferContext == NULL)
            LocalBufferContext =
                AllocSetContextCreate(TopMemoryContext,
                                      "LocalBufferContext",
                                      ALLOCSET_DEFAULT_SIZES);

        /* Start with a 16-buffer request; subsequent ones double each time */
        num_bufs = Max(num_bufs_in_block * 2, 16);
        /* But not more than what we need for all remaining local bufs */
        num_bufs = Min(num_bufs, NLocBuffer - total_bufs_allocated);
        /* And don't overflow MaxAllocSize, either */
        num_bufs = Min(num_bufs, MaxAllocSize / BLCKSZ);

        cur_block = (char *) MemoryContextAlloc(LocalBufferContext,
                                                num_bufs * BLCKSZ);
        next_buf_in_block = 0;
        num_bufs_in_block = num_bufs;
    }

    /* Allocate next buffer in current memory block */
    this_buf = cur_block + next_buf_in_block * BLCKSZ;
    next_buf_in_block++;
    total_bufs_allocated++;

    return (Block) this_buf;
}

/*
 * CheckForLocalBufferLeaks - ensure this backend holds no local buffer pins
 *
 * This is just like CheckForBufferLeaks(), but for local buffers.
 */
static void
CheckForLocalBufferLeaks(void)
{
#ifdef USE_ASSERT_CHECKING
    if (LocalRefCount)
    {
        int         RefCountErrors = 0;
        int         i;

        for (i = 0; i < NLocBuffer; i++)
        {
            if (LocalRefCount[i] != 0)
            {
                Buffer      b = -i - 1;

                PrintBufferLeakWarning(b);
                RefCountErrors++;
            }
        }
        Assert(RefCountErrors == 0);
    }
#endif
}

/*
 * AtEOXact_LocalBuffers - clean up at end of transaction.
 *
 * This is just like AtEOXact_Buffers, but for local buffers.
 */
void
AtEOXact_LocalBuffers(bool isCommit)
{
    CheckForLocalBufferLeaks();
}

/*
 * AtProcExit_LocalBuffers - ensure we have dropped pins during backend exit.
 *
 * This is just like AtProcExit_Buffers, but for local buffers.
 */
void
AtProcExit_LocalBuffers(void)
{
    /*
     * We shouldn't be holding any remaining pins; if we are, and assertions
     * aren't enabled, we'll fail later in DropRelFileNodeBuffers while trying
     * to drop the temp rels.
     */
    CheckForLocalBufferLeaks();
}