src/include/storage/bufmgr.h

/*-------------------------------------------------------------------------
 *
 * bufmgr.h
 *	  POSTGRES buffer manager definitions.
 *
 *
 * Portions Copyright (c) 1996-2021, 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 "storage/block.h"
#include "storage/buf.h"
#include "storage/bufpage.h"
#include "storage/relfilenode.h"
#include "storage/smgr.h"
#include "utils/relcache.h"
#include "utils/snapmgr.h"

typedef void *Block;

/* Possible arguments for GetAccessStrategy() */
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;

/* forward declared, to avoid having to expose buf_internals.h here */
struct WritebackContext;

/* forward declared, to avoid including smgr.h here */
struct SMgrRelationData;

/* in globals.c ... this duplicates miscadmin.h */
extern PGDLLIMPORT int NBuffers;

/* in bufmgr.c */
extern bool zero_damaged_pages;
extern int	bgwriter_lru_maxpages;
extern double bgwriter_lru_multiplier;
extern bool track_io_timing;
extern int	effective_io_concurrency;
extern int	maintenance_io_concurrency;

extern int	checkpoint_flush_after;
extern int	backend_flush_after;
extern int	bgwriter_flush_after;

/* 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())
 */
#define BUFFER_LOCK_UNLOCK		0
#define BUFFER_LOCK_SHARE		1
#define BUFFER_LOCK_EXCLUSIVE	2

/*
 * These routines are beaten on quite heavily, hence the macroization.
 */

/*
 * 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.
 */
#define BufferIsValid(bufnum) \
( \
	AssertMacro((bufnum) <= NBuffers && (bufnum) >= -NLocBuffer), \
	(bufnum) != InvalidBuffer  \
)

/*
 * BufferGetBlock
 *		Returns a reference to a disk page image associated with a buffer.
 *
 * Note:
 *		Assumes buffer is valid.
 */
#define BufferGetBlock(buffer) \
( \
	AssertMacro(BufferIsValid(buffer)), \
	BufferIsLocal(buffer) ? \
		LocalBufferBlockPointers[-(buffer) - 1] \
	: \
		(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 */
#define BufferGetPageSize(buffer) \
( \
	AssertMacro(BufferIsValid(buffer)), \
	(Size)BLCKSZ \
)

/*
 * BufferGetPage
 *		Returns the page associated with a buffer.
 *
 * When this is called as part of a scan, there may be a need for a nearby
 * call to TestForOldSnapshot().  See the definition of that for details.
 */
#define BufferGetPage(buffer) ((Page)BufferGetBlock(buffer))

typedef Buffer (*ReadBuffer_hook_type)(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
                                          BlockNumber blockNum, ReadBufferMode mode,
                                          BufferAccessStrategy strategy, bool *hit);
extern PGDLLIMPORT ReadBuffer_hook_type ReadBuffer_hook;

/*
 * prototypes for functions in bufmgr.c
 */
extern PrefetchBufferResult PrefetchSharedBuffer(struct SMgrRelationData *smgr_reln,
												 ForkNumber forkNum,
												 BlockNumber blockNum);
extern PrefetchBufferResult PrefetchBuffer(Relation reln, ForkNumber forkNum,
										   BlockNumber blockNum);
extern bool ReadRecentBuffer(RelFileNode rnode, 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(RelFileNode rnode,
										ForkNumber forkNum, BlockNumber blockNum,
										ReadBufferMode mode, BufferAccessStrategy strategy);
extern void ReleaseBuffer(Buffer buffer);
extern void UnlockReleaseBuffer(Buffer buffer);
extern void MarkBufferDirty(Buffer buffer);
extern void IncrBufferRefCount(Buffer buffer);
extern Buffer ReleaseAndReadBuffer(Buffer buffer, Relation relation,
								   BlockNumber blockNum);

extern void InitBufferPool(void);
extern void InitBufferPoolAccess(void);
extern void InitBufferPoolBackend(void);
extern void AtEOXact_Buffers(bool isCommit);
extern void PrintBufferLeakWarning(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(struct SMgrRelationData **smgrs, int nrels);
extern void FlushDatabaseBuffers(Oid dbid);
extern void DropRelFileNodeBuffers(struct SMgrRelationData *smgr_reln, ForkNumber *forkNum,
								   int nforks, BlockNumber *firstDelBlock);
extern void DropRelFileNodesAllBuffers(struct SMgrRelationData **smgr_reln, int nnodes);
extern void DropDatabaseBuffers(Oid dbid);

/*
 * GPDB: it is possible to need to calculate the number of blocks from the table
 * size. An example use case is when we are the dispatcher and we need to
 * acquire the number of blocks from all segments.
 *
 * Use the same calculation that RelationGetNumberOfBlocksInFork is using.
 */
static inline BlockNumber
RelationGuessNumberOfBlocksFromSize(uint64 szbytes)
{
	return (szbytes + (BLCKSZ - 1)) / BLCKSZ;
}

#define RelationGetNumberOfBlocks(reln) \
	RelationGetNumberOfBlocksInFork(reln, MAIN_FORKNUM)

extern BlockNumber AcquireNumberOfBlocks(Relation onerel);
extern BlockNumber AcquireNumberOfAllVisibleBlocks(Relation onerel);

extern bool BufferIsPermanent(Buffer buffer);
extern XLogRecPtr BufferGetLSNAtomic(Buffer buffer);

#ifdef NOT_USED
extern void PrintPinnedBufs(void);
#endif
extern Size BufferShmemSize(void);
extern void BufferGetTag(Buffer buffer, RelFileNode *rnode,
						 ForkNumber *forknum, BlockNumber *blknum);

extern void MarkBufferDirtyHint(Buffer buffer, bool buffer_std);

extern void UnlockBuffers(void);
extern void LockBuffer(Buffer buffer, int 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 void AbortBufferIO(void);

extern void BufmgrCommit(void);
extern bool BgBufferSync(struct WritebackContext *wb_context);

extern void AtProcExit_LocalBuffers(void);

extern void TestForOldSnapshot_impl(Snapshot snapshot, Relation relation);

/* in freelist.c */
extern BufferAccessStrategy GetAccessStrategy(BufferAccessStrategyType btype);
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

/*
 * Check whether the given snapshot is too old to have safely read the given
 * page from the given table.  If so, throw a "snapshot too old" error.
 *
 * This test generally needs to be performed after every BufferGetPage() call
 * that is executed as part of a scan.  It is not needed for calls made for
 * modifying the page (for example, to position to the right place to insert a
 * new index tuple or for vacuuming).  It may also be omitted where calls to
 * lower-level functions will have already performed the test.
 *
 * Note that a NULL snapshot argument is allowed and causes a fast return
 * without error; this is to support call sites which can be called from
 * either scans or index modification areas.
 *
 * For best performance, keep the tests that are fastest and/or most likely to
 * exclude a page from old snapshot testing near the front.
 */
static inline void
TestForOldSnapshot(Snapshot snapshot, Relation relation, Page page)
{
	Assert(relation != NULL);

	if (old_snapshot_threshold >= 0
		&& (snapshot) != NULL
		&& ((snapshot)->snapshot_type == SNAPSHOT_MVCC
			|| (snapshot)->snapshot_type == SNAPSHOT_TOAST)
		&& !XLogRecPtrIsInvalid((snapshot)->lsn)
		&& PageGetLSN(page) > (snapshot)->lsn)
		TestForOldSnapshot_impl(snapshot, relation);
}

#endif							/* FRONTEND */

#endif							/* BUFMGR_H */