text: /*-------------------------------------------------------------------------
   *
   * bufmgr.h
   *	  POSTGRES buffer manager definitions.
   *
   *
   * Portions Copyright (c) 1996-2019, 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 "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;
  
  /* forward declared, to avoid having to expose buf_internals.h here */
  struct WritebackContext;
  
  /* 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	target_prefetch_pages;
  
  extern int	checkpoint_flush_after;
  extern int	backend_flush_after;
  extern int	bgwriter_flush_after;
  
  /* in buf_init.c */
  extern PGDLLIMPORT char *BufferBlocks;
  
  /* in guc.c */
  extern int	effective_io_concurrency;
  
  /* 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))
  
  /*
   * prototypes for functions in bufmgr.c
   */
  extern bool ComputeIoConcurrency(int io_concurrency, double *target);
  extern void PrefetchBuffer(Relation reln, ForkNumber forkNum,
  						   BlockNumber blockNum);
  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 FlushDatabaseBuffers(Oid dbid);
  extern void DropRelFileNodeBuffers(RelFileNodeBackend rnode,
  								   ForkNumber forkNum, BlockNumber firstDelBlock);
  extern void DropRelFileNodesAllBuffers(RelFileNodeBackend *rnodes, int nnodes);
  extern void DropDatabaseBuffers(Oid dbid);
  
  extern BlockNumber RelationGuessNumberOfBlocksFromSize(uint64 szbytes);
  
  #define RelationGetNumberOfBlocks(reln) \
  	RelationGetNumberOfBlocksInFork(reln, MAIN_FORKNUM)
  
  extern BlockNumber AcquireNumberOfBlocks(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 */
  