bufmgr.h

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/*-------------------------------------------------------------------------
 *
 * bufmgr.h
 *    POSTGRES buffer manager definitions.
 *
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/bufmgr.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef BUFMGR_H
#define BUFMGR_H
 
#include "port/pg_iovec.h"
#include "storage/aio_types.h"
#include "storage/block.h"
#include "storage/buf.h"
#include "storage/bufpage.h"
#include "storage/relfilelocator.h"
#include "utils/relcache.h"
#include "utils/snapmgr.h"
 
typedef void *Block;
 
/*
 * Possible arguments for GetAccessStrategy().
 *
 * If adding a new BufferAccessStrategyType, also add a new IOContext so
 * IO statistics using this strategy are tracked.
 */
typedef enum BufferAccessStrategyType
{
    BAS_NORMAL,                 /* Normal random access */
    BAS_BULKREAD,               /* Large read-only scan (hint bit updates are
                                 * ok) */
    BAS_BULKWRITE,              /* Large multi-block write (e.g. COPY IN) */
    BAS_VACUUM,                 /* VACUUM */
} BufferAccessStrategyType;
 
/* Possible modes for ReadBufferExtended() */
typedef enum
{
    RBM_NORMAL,                 /* Normal read */
    RBM_ZERO_AND_LOCK,          /* Don't read from disk, caller will
                                 * initialize. Also locks the page. */
    RBM_ZERO_AND_CLEANUP_LOCK,  /* Like RBM_ZERO_AND_LOCK, but locks the page
                                 * in "cleanup" mode */
    RBM_ZERO_ON_ERROR,          /* Read, but return an all-zeros page on error */
    RBM_NORMAL_NO_LOG,          /* Don't log page as invalid during WAL
                                 * replay; otherwise same as RBM_NORMAL */
} ReadBufferMode;
 
/*
 * Type returned by PrefetchBuffer().
 */
typedef struct PrefetchBufferResult
{
    Buffer      recent_buffer;  /* If valid, a hit (recheck needed!) */
    bool        initiated_io;   /* If true, a miss resulting in async I/O */
} PrefetchBufferResult;
 
/*
 * Flags influencing the behaviour of ExtendBufferedRel*
 */
typedef enum ExtendBufferedFlags
{
    /*
     * Don't acquire extension lock. This is safe only if the relation isn't
     * shared, an access exclusive lock is held or if this is the startup
     * process.
     */
    EB_SKIP_EXTENSION_LOCK = (1 << 0),
 
    /* Is this extension part of recovery? */
    EB_PERFORMING_RECOVERY = (1 << 1),
 
    /*
     * Should the fork be created if it does not currently exist? This likely
     * only ever makes sense for relation forks.
     */
    EB_CREATE_FORK_IF_NEEDED = (1 << 2),
 
    /* Should the first (possibly only) return buffer be returned locked? */
    EB_LOCK_FIRST = (1 << 3),
 
    /* Should the smgr size cache be cleared? */
    EB_CLEAR_SIZE_CACHE = (1 << 4),
 
    /* internal flags follow */
    EB_LOCK_TARGET = (1 << 5),
}           ExtendBufferedFlags;
 
/* forward declared, to avoid including smgr.h here */
typedef struct SMgrRelationData *SMgrRelation;
 
/*
 * Some functions identify relations either by relation or smgr +
 * relpersistence, initialized via the BMR_REL()/BMR_SMGR() macros below.
 * This allows us to use the same function for both recovery and normal
 * operation.  When BMR_REL is used, it's not valid to cache its rd_smgr here,
 * because our pointer would be obsolete in case of relcache invalidation.
 * For simplicity, use BMR_GET_SMGR to read the smgr.
 */
typedef struct BufferManagerRelation
{
    Relation    rel;
    SMgrRelation smgr;
    char        relpersistence;
} BufferManagerRelation;
 
#define BMR_REL(p_rel) \
    ((BufferManagerRelation){.rel = p_rel})
#define BMR_SMGR(p_smgr, p_relpersistence) \
    ((BufferManagerRelation){.smgr = p_smgr, .relpersistence = p_relpersistence})
#define BMR_GET_SMGR(bmr) \
    (RelationIsValid((bmr).rel) ? RelationGetSmgr((bmr).rel) : (bmr).smgr)
 
/* Zero out page if reading fails. */
#define READ_BUFFERS_ZERO_ON_ERROR (1 << 0)
/* Call smgrprefetch() if I/O necessary. */
#define READ_BUFFERS_ISSUE_ADVICE (1 << 1)
/* Don't treat page as invalid due to checksum failures. */
#define READ_BUFFERS_IGNORE_CHECKSUM_FAILURES (1 << 2)
/* IO will immediately be waited for */
#define READ_BUFFERS_SYNCHRONOUSLY (1 << 3)
 
 
struct ReadBuffersOperation
{
    /* The following members should be set by the caller. */
    Relation    rel;            /* optional */
    SMgrRelation smgr;
    char        persistence;
    ForkNumber  forknum;
    BufferAccessStrategy strategy;
 
    /*
     * The following private members are private state for communication
     * between StartReadBuffers() and WaitReadBuffers(), initialized only if
     * an actual read is required, and should not be modified.
     */
    Buffer     *buffers;
    BlockNumber blocknum;
    int         flags;
    int16       nblocks;
    int16       nblocks_done;
    PgAioWaitRef io_wref;
    PgAioReturn io_return;
};
 
typedef struct ReadBuffersOperation ReadBuffersOperation;
 
/* to avoid having to expose buf_internals.h here */
typedef struct WritebackContext WritebackContext;
 
/* in globals.c ... this duplicates miscadmin.h */
extern PGDLLIMPORT int NBuffers;
 
/* in bufmgr.c */
extern PGDLLIMPORT bool zero_damaged_pages;
extern PGDLLIMPORT int bgwriter_lru_maxpages;
extern PGDLLIMPORT double bgwriter_lru_multiplier;
extern PGDLLIMPORT bool track_io_timing;
 
#define DEFAULT_EFFECTIVE_IO_CONCURRENCY 16
#define DEFAULT_MAINTENANCE_IO_CONCURRENCY 16
extern PGDLLIMPORT int effective_io_concurrency;
extern PGDLLIMPORT int maintenance_io_concurrency;
 
#define MAX_IO_COMBINE_LIMIT PG_IOV_MAX
#define DEFAULT_IO_COMBINE_LIMIT Min(MAX_IO_COMBINE_LIMIT, (128 * 1024) / BLCKSZ)
extern PGDLLIMPORT int io_combine_limit;    /* min of the two GUCs below */
extern PGDLLIMPORT int io_combine_limit_guc;
extern PGDLLIMPORT int io_max_combine_limit;
 
extern PGDLLIMPORT int checkpoint_flush_after;
extern PGDLLIMPORT int backend_flush_after;
extern PGDLLIMPORT int bgwriter_flush_after;
 
extern PGDLLIMPORT const PgAioHandleCallbacks aio_shared_buffer_readv_cb;
extern PGDLLIMPORT const PgAioHandleCallbacks aio_local_buffer_readv_cb;
 
/* in buf_init.c */
extern PGDLLIMPORT char *BufferBlocks;
 
/* in localbuf.c */
extern PGDLLIMPORT int NLocBuffer;
extern PGDLLIMPORT Block *LocalBufferBlockPointers;
extern PGDLLIMPORT int32 *LocalRefCount;
 
/* upper limit for effective_io_concurrency */
#define MAX_IO_CONCURRENCY 1000
 
/* special block number for ReadBuffer() */
#define P_NEW   InvalidBlockNumber  /* grow the file to get a new page */
 
/*
 * Buffer content lock modes (mode argument for LockBuffer())
 */
typedef enum BufferLockMode
{
    BUFFER_LOCK_UNLOCK,
 
    /*
     * A share lock conflicts with exclusive locks.
     */
    BUFFER_LOCK_SHARE,
 
    /*
     * A share-exclusive lock conflicts with itself and exclusive locks.
     */
    BUFFER_LOCK_SHARE_EXCLUSIVE,
 
    /*
     * An exclusive lock conflicts with every other lock type.
     */
    BUFFER_LOCK_EXCLUSIVE,
} BufferLockMode;
 
 
/*
 * prototypes for functions in bufmgr.c
 */
extern PrefetchBufferResult PrefetchSharedBuffer(SMgrRelation smgr_reln,
                                                 ForkNumber forkNum,
                                                 BlockNumber blockNum);
extern PrefetchBufferResult PrefetchBuffer(Relation reln, ForkNumber forkNum,
                                           BlockNumber blockNum);
extern bool ReadRecentBuffer(RelFileLocator rlocator, ForkNumber forkNum,
                             BlockNumber blockNum, Buffer recent_buffer);
extern Buffer ReadBuffer(Relation reln, BlockNumber blockNum);
extern Buffer ReadBufferExtended(Relation reln, ForkNumber forkNum,
                                 BlockNumber blockNum, ReadBufferMode mode,
                                 BufferAccessStrategy strategy);
extern Buffer ReadBufferWithoutRelcache(RelFileLocator rlocator,
                                        ForkNumber forkNum, BlockNumber blockNum,
                                        ReadBufferMode mode, BufferAccessStrategy strategy,
                                        bool permanent);
 
extern bool StartReadBuffer(ReadBuffersOperation *operation,
                            Buffer *buffer,
                            BlockNumber blocknum,
                            int flags);
extern bool StartReadBuffers(ReadBuffersOperation *operation,
                             Buffer *buffers,
                             BlockNumber blockNum,
                             int *nblocks,
                             int flags);
extern void WaitReadBuffers(ReadBuffersOperation *operation);
 
extern void ReleaseBuffer(Buffer buffer);
extern void UnlockReleaseBuffer(Buffer buffer);
extern bool BufferIsLockedByMe(Buffer buffer);
extern bool BufferIsLockedByMeInMode(Buffer buffer, BufferLockMode mode);
extern bool BufferIsDirty(Buffer buffer);
extern void MarkBufferDirty(Buffer buffer);
extern void IncrBufferRefCount(Buffer buffer);
extern void CheckBufferIsPinnedOnce(Buffer buffer);
extern Buffer ReleaseAndReadBuffer(Buffer buffer, Relation relation,
                                   BlockNumber blockNum);
 
extern Buffer ExtendBufferedRel(BufferManagerRelation bmr,
                                ForkNumber forkNum,
                                BufferAccessStrategy strategy,
                                uint32 flags);
extern BlockNumber ExtendBufferedRelBy(BufferManagerRelation bmr,
                                       ForkNumber fork,
                                       BufferAccessStrategy strategy,
                                       uint32 flags,
                                       uint32 extend_by,
                                       Buffer *buffers,
                                       uint32 *extended_by);
extern Buffer ExtendBufferedRelTo(BufferManagerRelation bmr,
                                  ForkNumber fork,
                                  BufferAccessStrategy strategy,
                                  uint32 flags,
                                  BlockNumber extend_to,
                                  ReadBufferMode mode);
 
extern void InitBufferManagerAccess(void);
extern void AtEOXact_Buffers(bool isCommit);
#ifdef USE_ASSERT_CHECKING
extern void AssertBufferLocksPermitCatalogRead(void);
#endif
extern char *DebugPrintBufferRefcount(Buffer buffer);
extern void CheckPointBuffers(int flags);
extern BlockNumber BufferGetBlockNumber(Buffer buffer);
extern BlockNumber RelationGetNumberOfBlocksInFork(Relation relation,
                                                   ForkNumber forkNum);
extern void FlushOneBuffer(Buffer buffer);
extern void FlushRelationBuffers(Relation rel);
extern void FlushRelationsAllBuffers(SMgrRelation *smgrs, int nrels);
extern void CreateAndCopyRelationData(RelFileLocator src_rlocator,
                                      RelFileLocator dst_rlocator,
                                      bool permanent);
extern void FlushDatabaseBuffers(Oid dbid);
extern void DropRelationBuffers(SMgrRelation smgr_reln,
                                ForkNumber *forkNum,
                                int nforks, BlockNumber *firstDelBlock);
extern void DropRelationsAllBuffers(SMgrRelation *smgr_reln,
                                    int nlocators);
extern void DropDatabaseBuffers(Oid dbid);
 
#define RelationGetNumberOfBlocks(reln) \
    RelationGetNumberOfBlocksInFork(reln, MAIN_FORKNUM)
 
extern bool BufferIsPermanent(Buffer buffer);
extern XLogRecPtr BufferGetLSNAtomic(Buffer buffer);
extern void BufferGetTag(Buffer buffer, RelFileLocator *rlocator,
                         ForkNumber *forknum, BlockNumber *blknum);
 
extern void MarkBufferDirtyHint(Buffer buffer, bool buffer_std);
 
extern void UnlockBuffers(void);
extern void UnlockBuffer(Buffer buffer);
extern void LockBufferInternal(Buffer buffer, BufferLockMode mode);
 
/*
 * Handling BUFFER_LOCK_UNLOCK in bufmgr.c leads to sufficiently worse branch
 * prediction to impact performance. Therefore handle that switch here, where
 * most of the time `mode` will be a constant and thus can be optimized out by
 * the compiler.
 */
static inline void
LockBuffer(Buffer buffer, BufferLockMode mode)
{
    if (mode == BUFFER_LOCK_UNLOCK)
        UnlockBuffer(buffer);
    else
        LockBufferInternal(buffer, mode);
}
 
extern bool ConditionalLockBuffer(Buffer buffer);
extern void LockBufferForCleanup(Buffer buffer);
extern bool ConditionalLockBufferForCleanup(Buffer buffer);
extern bool IsBufferCleanupOK(Buffer buffer);
extern bool HoldingBufferPinThatDelaysRecovery(void);
 
extern bool BgBufferSync(WritebackContext *wb_context);
 
extern uint32 GetPinLimit(void);
extern uint32 GetLocalPinLimit(void);
extern uint32 GetAdditionalPinLimit(void);
extern uint32 GetAdditionalLocalPinLimit(void);
extern void LimitAdditionalPins(uint32 *additional_pins);
extern void LimitAdditionalLocalPins(uint32 *additional_pins);
 
extern bool EvictUnpinnedBuffer(Buffer buf, bool *buffer_flushed);
extern void EvictAllUnpinnedBuffers(int32 *buffers_evicted,
                                    int32 *buffers_flushed,
                                    int32 *buffers_skipped);
extern void EvictRelUnpinnedBuffers(Relation rel,
                                    int32 *buffers_evicted,
                                    int32 *buffers_flushed,
                                    int32 *buffers_skipped);
extern bool MarkDirtyUnpinnedBuffer(Buffer buf, bool *buffer_already_dirty);
extern void MarkDirtyRelUnpinnedBuffers(Relation rel,
                                        int32 *buffers_dirtied,
                                        int32 *buffers_already_dirty,
                                        int32 *buffers_skipped);
extern void MarkDirtyAllUnpinnedBuffers(int32 *buffers_dirtied,
                                        int32 *buffers_already_dirty,
                                        int32 *buffers_skipped);
 
/* in buf_init.c */
extern void BufferManagerShmemInit(void);
extern Size BufferManagerShmemSize(void);
 
/* in localbuf.c */
extern void AtProcExit_LocalBuffers(void);
 
/* in freelist.c */
 
extern BufferAccessStrategy GetAccessStrategy(BufferAccessStrategyType btype);
extern BufferAccessStrategy GetAccessStrategyWithSize(BufferAccessStrategyType btype,
                                                      int ring_size_kb);
extern int  GetAccessStrategyBufferCount(BufferAccessStrategy strategy);
extern int  GetAccessStrategyPinLimit(BufferAccessStrategy strategy);
 
extern void FreeAccessStrategy(BufferAccessStrategy strategy);
 
 
/* inline functions */
 
/*
 * Although this header file is nominally backend-only, certain frontend
 * programs like pg_waldump include it.  For compilers that emit static
 * inline functions even when they're unused, that leads to unsatisfied
 * external references; hence hide these with #ifndef FRONTEND.
 */
 
#ifndef FRONTEND
 
/*
 * BufferIsValid
 *      True iff the given buffer number is valid (either as a shared
 *      or local buffer).
 *
 * Note: For a long time this was defined the same as BufferIsPinned,
 * that is it would say False if you didn't hold a pin on the buffer.
 * I believe this was bogus and served only to mask logic errors.
 * Code should always know whether it has a buffer reference,
 * independently of the pin state.
 *
 * Note: For a further long time this was not quite the inverse of the
 * BufferIsInvalid() macro, in that it also did sanity checks to verify
 * that the buffer number was in range.  Most likely, this macro was
 * originally intended only to be used in assertions, but its use has
 * since expanded quite a bit, and the overhead of making those checks
 * even in non-assert-enabled builds can be significant.  Thus, we've
 * now demoted the range checks to assertions within the macro itself.
 */
static inline bool
BufferIsValid(Buffer bufnum)
{
    Assert(bufnum <= NBuffers);
    Assert(bufnum >= -NLocBuffer);
 
    return bufnum != InvalidBuffer;
}
 
/*
 * BufferGetBlock
 *      Returns a reference to a disk page image associated with a buffer.
 *
 * Note:
 *      Assumes buffer is valid.
 */
static inline Block
BufferGetBlock(Buffer buffer)
{
    Assert(BufferIsValid(buffer));
 
    if (BufferIsLocal(buffer))
        return LocalBufferBlockPointers[-buffer - 1];
    else
        return (Block) (BufferBlocks + ((Size) (buffer - 1)) * BLCKSZ);
}
 
/*
 * BufferGetPageSize
 *      Returns the page size within a buffer.
 *
 * Notes:
 *      Assumes buffer is valid.
 *
 *      The buffer can be a raw disk block and need not contain a valid
 *      (formatted) disk page.
 */
/* XXX should dig out of buffer descriptor */
static inline Size
BufferGetPageSize(Buffer buffer)
{
    Assert(BufferIsValid(buffer));
    return (Size) BLCKSZ;
}
 
/*
 * BufferGetPage
 *      Returns the page associated with a buffer.
 */
static inline Page
BufferGetPage(Buffer buffer)
{
    return (Page) BufferGetBlock(buffer);
}
 
#endif                          /* FRONTEND */
 
#endif                          /* BUFMGR_H */