postgresql/src/include/storage/buf_internals.h

/*-------------------------------------------------------------------------
 *
 * buf_internals.h
 *	  Internal definitions for buffer manager and the buffer replacement
 *    strategy.
 *
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/include/storage/buf_internals.h,v 1.70 2004/04/21 18:06:29 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef BUFMGR_INTERNALS_H
#define BUFMGR_INTERNALS_H

#include "storage/backendid.h"
#include "storage/buf.h"
#include "storage/lmgr.h"
#include "storage/lwlock.h"


/*
 * Flags for buffer descriptors
 */
#define BM_DIRTY				(1 << 0) /* data needs writing */
#define BM_VALID				(1 << 1) /* data is valid */
#define BM_IO_IN_PROGRESS		(1 << 2) /* read or write in progress */
#define BM_IO_ERROR				(1 << 3) /* previous I/O failed */
#define BM_JUST_DIRTIED			(1 << 4) /* dirtied since write started */
#define BM_PIN_COUNT_WAITER		(1 << 5) /* have waiter for sole pin */

typedef bits16 BufFlags;

/*
 * Buffer tag identifies which disk block the buffer contains.
 *
 * Note: the BufferTag data must be sufficient to determine where to write the
 * block, even during a "blind write" with no relcache entry.  It's possible
 * that the backend flushing the buffer doesn't even believe the relation is
 * visible yet (its xact may have started before the xact that created the
 * rel).  The storage manager must be able to cope anyway.
 *
 * Note: if there's any pad bytes in the struct, INIT_BUFFERTAG will have
 * to be fixed to zero them, since this struct is used as a hash key.
 */
typedef struct buftag
{
	RelFileNode rnode;			/* physical relation identifier */
	BlockNumber blockNum;		/* blknum relative to begin of reln */
} BufferTag;

#define CLEAR_BUFFERTAG(a) \
( \
	(a).rnode.tblNode = InvalidOid, \
	(a).rnode.relNode = InvalidOid, \
	(a).blockNum = InvalidBlockNumber \
)

#define INIT_BUFFERTAG(a,xx_reln,xx_blockNum) \
( \
	(a).rnode = (xx_reln)->rd_node, \
	(a).blockNum = (xx_blockNum) \
)

#define BUFFERTAGS_EQUAL(a,b) \
( \
	RelFileNodeEquals((a).rnode, (b).rnode) && \
	(a).blockNum == (b).blockNum \
)

/*
 *	BufferDesc -- shared buffer cache metadata for a single
 *				  shared buffer descriptor.
 */
typedef struct sbufdesc
{
	Buffer		bufNext;		/* link in freelist chain */
	SHMEM_OFFSET data;			/* pointer to data in buf pool */

	/* tag and id must be together for table lookup (still true?) */
	BufferTag	tag;			/* file/block identifier */
	int			buf_id;			/* buffer's index number (from 0) */

	BufFlags	flags;			/* see bit definitions above */
	unsigned	refcount;		/* # of backends holding pins on buffer */

	LWLockId	io_in_progress_lock;	/* to wait for I/O to complete */
	LWLockId	cntx_lock;		/* to lock access to page context */

	bool		cntxDirty;		/* new way to mark block as dirty */

	/*
	 * We can't physically remove items from a disk page if another
	 * backend has the buffer pinned.  Hence, a backend may need to wait
	 * for all other pins to go away.  This is signaled by storing its own
	 * backend ID into wait_backend_id and setting flag bit
	 * BM_PIN_COUNT_WAITER. At present, there can be only one such waiter
	 * per buffer.
	 */
	BackendId	wait_backend_id;	/* backend ID of pin-count waiter */
} BufferDesc;

#define BufferDescriptorGetBuffer(bdesc) ((bdesc)->buf_id + 1)


/*
 * Each backend has its own BufferLocks[] array holding flag bits
 * showing what locks it has set on each buffer.
 *
 * We have to free these locks during ereport(ERROR)...
 */
#define BL_IO_IN_PROGRESS	(1 << 0)	/* unimplemented */
#define BL_PIN_COUNT_LOCK	(1 << 1)

/* entry for buffer lookup hashtable */
typedef struct
{
	BufferTag	key;			/* Tag of a disk page */
	int			id;				/* CDB id of associated CDB */
} BufferLookupEnt;

/*
 * Definitions for the buffer replacement strategy
 */
#define STRAT_LIST_UNUSED	(-1)
#define STRAT_LIST_B1		0
#define STRAT_LIST_T1		1
#define STRAT_LIST_T2		2
#define STRAT_LIST_B2		3
#define STRAT_NUM_LISTS		4

/*
 * The Cache Directory Block (CDB) of the Adaptive Replacement Cache (ARC)
 */
typedef struct
{
	int				prev;		/* list links */
	int				next;
	short			list;		/* ID of list it is currently in */
	bool			t1_vacuum;	/* t => present only because of VACUUM */
	TransactionId	t1_xid;		/* the xid this entry went onto T1 */
	BufferTag		buf_tag;	/* page identifier */
	int				buf_id;		/* currently assigned data buffer, or -1 */
} BufferStrategyCDB;

/*
 * The shared ARC control information.
 */
typedef struct
{
	int		target_T1_size;				/* What T1 size are we aiming for */
	int		listUnusedCDB;				/* All unused StrategyCDB */
	int		listHead[STRAT_NUM_LISTS];	/* ARC lists B1, T1, T2 and B2 */
	int		listTail[STRAT_NUM_LISTS];
	int		listSize[STRAT_NUM_LISTS];
	Buffer	listFreeBuffers;			/* List of unused buffers */

	long	num_lookup;					/* Some hit statistics */
	long	num_hit[STRAT_NUM_LISTS];
	time_t	stat_report;

	/* Array of CDB's starts here */
	BufferStrategyCDB	cdb[1];			/* VARIABLE SIZE ARRAY */
} BufferStrategyControl;

 
/* counters in buf_init.c */
extern long int ReadBufferCount;
extern long int ReadLocalBufferCount;
extern long int BufferHitCount;
extern long int LocalBufferHitCount;
extern long int BufferFlushCount;
extern long int LocalBufferFlushCount;


/*
 * Bufmgr Interface:
 */

/* Internal routines: only called by bufmgr */

/* freelist.c */
extern BufferDesc *StrategyBufferLookup(BufferTag *tagPtr, bool recheck,
										int *cdb_found_index);
extern BufferDesc *StrategyGetBuffer(int *cdb_replace_index);
extern void StrategyReplaceBuffer(BufferDesc *buf, BufferTag *newTag,
								  int cdb_found_index, int cdb_replace_index);
extern void StrategyInvalidateBuffer(BufferDesc *buf);
extern void StrategyHintVacuum(bool vacuum_active);
extern int StrategyDirtyBufferList(BufferDesc **buffers, BufferTag *buftags,
								   int max_buffers);
extern void StrategyInitialize(bool init);

/* buf_table.c */
extern void InitBufTable(int size);
extern int BufTableLookup(BufferTag *tagPtr);
extern void BufTableInsert(BufferTag *tagPtr, int cdb_id);
extern void BufTableDelete(BufferTag *tagPtr);

/* bufmgr.c */
extern BufferDesc *BufferDescriptors;
extern bits8 *BufferLocks;

/* localbuf.c */
extern BufferDesc *LocalBufferDescriptors;

extern BufferDesc *LocalBufferAlloc(Relation reln, BlockNumber blockNum,
				 bool *foundPtr);
extern void WriteLocalBuffer(Buffer buffer, bool release);
extern void AtEOXact_LocalBuffers(bool isCommit);

#endif   /* BUFMGR_INTERNALS_H */