multi.c

关系型数据库 Postgresql 6.5.2

/*-------------------------------------------------------------------------
 *
 * multi.c
 *	  multi level lock table manager
 *
 *	  Standard multi-level lock manager as per the Gray paper
 *	  (at least, that is what it is supposed to be).  We implement
 *	  three levels -- RELN, PAGE, TUPLE.  Tuple is actually TID
 *	  a physical record pointer.  It isn't an object id.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /usr/local/cvsroot/pgsql/src/backend/storage/lmgr/multi.c,v 1.29 1999/05/25 16:11:22 momjian Exp $
 *
 * NOTES:
 *	 (1) The lock.c module assumes that the caller here is doing
 *		 two phase locking.
 *
 *-------------------------------------------------------------------------
 */
#include <stdio.h>
#include <string.h>
#include "postgres.h"
#include "storage/lmgr.h"
#include "storage/multilev.h"

#include "utils/rel.h"
#include "miscadmin.h"			/* MyDatabaseId */

static bool MultiAcquire(LOCKMETHOD lockmethod, LOCKTAG *tag,
			 LOCKMODE lockmode, PG_LOCK_LEVEL level);
static bool MultiRelease(LOCKMETHOD lockmethod, LOCKTAG *tag,
			 LOCKMODE lockmode, PG_LOCK_LEVEL level);

/*
 * INTENT indicates to higher level that a lower level lock has been
 * set.  For example, a write lock on a tuple conflicts with a write
 * lock on a relation.	This conflict is detected as a WRITE_INTENT/
 * WRITE conflict between the tuple's intent lock and the relation's
 * write lock.
 */
static MASK MultiConflicts[] = {
	(int) NULL,
	/* All reads and writes at any level conflict with a write lock */
	(1 << WRITE_LOCK) | (1 << WRITE_INTENT) | (1 << READ_LOCK) | (1 << READ_INTENT),
	/* read locks conflict with write locks at curr and lower levels */
	(1 << WRITE_LOCK) | (1 << WRITE_INTENT),
	/* write intent locks */
	(1 << READ_LOCK) | (1 << WRITE_LOCK),
	/* read intent locks */
	(1 << WRITE_LOCK),

	/*
	 * extend locks for archive storage manager conflict only w/extend
	 * locks
	 */
	(1 << EXTEND_LOCK)
};

/*
 * write locks have higher priority than read locks and extend locks.  May
 * want to treat INTENT locks differently.
 */
static int	MultiPrios[] = {
	(int) NULL,
	2,
	1,
	2,
	1,
	1
};

/*
 * Lock table identifier for this lock table.  The multi-level
 * lock table is ONE lock table, not three.
 */
LOCKMETHOD	MultiTableId = (LOCKMETHOD) NULL;
LOCKMETHOD	LongTermTableId = (LOCKMETHOD) NULL;

#ifdef NOT_USED
LOCKMETHOD	ShortTermTableId = (LOCKMETHOD) NULL;

#endif

/*
 * Create the lock table described by MultiConflicts and Multiprio.
 */
LOCKMETHOD
InitMultiLevelLocks()
{
	int			lockmethod;

	lockmethod = LockMethodTableInit("MultiLevelLockTable",
						  MultiConflicts, MultiPrios, MAX_LOCKMODES - 1);
	MultiTableId = lockmethod;
	if (!(MultiTableId))
		elog(ERROR, "InitMultiLocks: couldnt initialize lock table");
	/* -----------------------
	 * No short term lock table for now.  -Jeff 15 July 1991
	 *
	 * ShortTermTableId = LockMethodTableRename(lockmethod);
	 * if (! (ShortTermTableId)) {
	 *	 elog(ERROR,"InitMultiLocks: couldnt rename lock table");
	 * }
	 * -----------------------
	 */

#ifdef USER_LOCKS

	/*
	 * Allocate another tableId for long-term locks
	 */
	LongTermTableId = LockMethodTableRename(MultiTableId);
	if (!(LongTermTableId))
	{
		elog(ERROR,
			 "InitMultiLevelLocks: couldn't rename long-term lock table");
	}
#endif

	return MultiTableId;
}

/*
 * MultiLockReln -- lock a relation
 *
 * Returns: TRUE if the lock can be set, FALSE otherwise.
 */
bool
MultiLockReln(LockInfo lockinfo, LOCKMODE lockmode)
{
	LOCKTAG		tag;

	/*
	 * LOCKTAG has two bytes of padding, unfortunately.  The hash function
	 * will return miss if the padding bytes aren't zero'd.
	 */
	MemSet(&tag, 0, sizeof(tag));
	tag.relId = lockinfo->lockRelId.relId;
	tag.dbId = lockinfo->lockRelId.dbId;
	return MultiAcquire(MultiTableId, &tag, lockmode, RELN_LEVEL);
}

#ifdef NOT_USED
/*
 * MultiLockTuple -- Lock the TID associated with a tuple
 *
 * Returns: TRUE if lock is set, FALSE otherwise.
 *
 * Side Effects: causes intention level locks to be set
 *		at the page and relation level.
 */
bool
MultiLockTuple(LockInfo lockinfo, ItemPointer tidPtr, LOCKMODE lockmode)
{
	LOCKTAG		tag;

	/*
	 * LOCKTAG has two bytes of padding, unfortunately.  The hash function
	 * will return miss if the padding bytes aren't zero'd.
	 */
	MemSet(&tag, 0, sizeof(tag));

	tag.relId = lockinfo->lockRelId.relId;
	tag.dbId = lockinfo->lockRelId.dbId;

	/* not locking any valid Tuple, just the page */
	tag.tupleId = *tidPtr;
	return MultiAcquire(MultiTableId, &tag, lockmode, TUPLE_LEVEL);
}

#endif

/*
 * same as above at page level
 */
bool
MultiLockPage(LockInfo lockinfo, ItemPointer tidPtr, LOCKMODE lockmode)
{
	LOCKTAG		tag;

	/*
	 * LOCKTAG has two bytes of padding, unfortunately.  The hash function
	 * will return miss if the padding bytes aren't zero'd.
	 */
	MemSet(&tag, 0, sizeof(tag));


	/* ----------------------------
	 * Now we want to set the page offset to be invalid
	 * and lock the block.	There is some confusion here as to what
	 * a page is.  In Postgres a page is an 8k block, however this
	 * block may be partitioned into many subpages which are sometimes
	 * also called pages.  The term is overloaded, so don't be fooled
	 * when we say lock the page we mean the 8k block. -Jeff 16 July 1991
	 * ----------------------------
	 */
	tag.relId = lockinfo->lockRelId.relId;
	tag.dbId = lockinfo->lockRelId.dbId;
	BlockIdCopy(&(tag.tupleId.ip_blkid), &(tidPtr->ip_blkid));
	return MultiAcquire(MultiTableId, &tag, lockmode, PAGE_LEVEL);
}

/*
 * MultiAcquire -- acquire multi level lock at requested level
 *
 * Returns: TRUE if lock is set, FALSE if not
 * Side Effects:
 */
static bool
MultiAcquire(LOCKMETHOD lockmethod,
			 LOCKTAG *tag,
			 LOCKMODE lockmode,
			 PG_LOCK_LEVEL level)
{
	LOCKMODE	locks[N_LEVELS];
	int			i,
				status;
	LOCKTAG		xxTag,
			   *tmpTag = &xxTag;
	int			retStatus = TRUE;

	/*
	 * Three levels implemented.  If we set a low level (e.g. Tuple) lock,
	 * we must set INTENT locks on the higher levels.  The intent lock
	 * detects conflicts between the low level lock and an existing high
	 * level lock.	For example, setting a write lock on a tuple in a
	 * relation is disallowed if there is an existing read lock on the
	 * entire relation.  The write lock would set a WRITE + INTENT lock on
	 * the relation and that lock would conflict with the read.
	 */
	switch (level)
	{
		case RELN_LEVEL:
			locks[0] = lockmode;
			locks[1] = NO_LOCK;
			locks[2] = NO_LOCK;
			break;
		case PAGE_LEVEL:
			locks[0] = lockmode + INTENT;
			locks[1] = lockmode;
			locks[2] = NO_LOCK;
			break;
		case TUPLE_LEVEL:
			locks[0] = lockmode + INTENT;
			locks[1] = lockmode + INTENT;
			locks[2] = lockmode;
			break;
		default:
			elog(ERROR, "MultiAcquire: bad lock level");
			return FALSE;
	}

	/*
	 * construct a new tag as we go. Always loop through all levels, but
	 * if we arent' seting a low level lock, locks[i] is set to NO_LOCK
	 * for the lower levels.  Always start from the highest level and go
	 * to the lowest level.
	 */
	MemSet(tmpTag, 0, sizeof(*tmpTag));
	tmpTag->relId = tag->relId;
	tmpTag->dbId = tag->dbId;

	for (i = 0; i < N_LEVELS; i++)
	{
		if (locks[i] != NO_LOCK)
		{
			switch (i)
			{
				case RELN_LEVEL:
					/* -------------
					 * Set the block # and offset to invalid
					 * -------------
					 */
					BlockIdSet(&(tmpTag->tupleId.ip_blkid), InvalidBlockNumber);
					tmpTag->tupleId.ip_posid = InvalidOffsetNumber;
					break;
				case PAGE_LEVEL:
					/* -------------
					 * Copy the block #, set the offset to invalid
					 * -------------
					 */
					BlockIdCopy(&(tmpTag->tupleId.ip_blkid),
								&(tag->tupleId.ip_blkid));
					tmpTag->tupleId.ip_posid = InvalidOffsetNumber;
					break;
				case TUPLE_LEVEL:
					/* --------------
					 * Copy the entire tuple id.
					 * --------------
					 */
					ItemPointerCopy(&tmpTag->tupleId, &tag->tupleId);
					break;
			}

			status = LockAcquire(lockmethod, tmpTag, locks[i]);
			if (!status)
			{

				/*
				 * failed for some reason. Before returning we have to
				 * release all of the locks we just acquired.
				 * MultiRelease(xx,xx,xx, i) means release starting from
				 * the last level lock we successfully acquired
				 */
				retStatus = FALSE;
				MultiRelease(lockmethod, tag, lockmode, i);
				/* now leave the loop.	Don't try for any more locks */
				break;
			}
		}
	}
	return retStatus;
}

/* ------------------
 * Release a page in the multi-level lock table
 * ------------------
 */
#ifdef NOT_USED
bool
MultiReleasePage(LockInfo lockinfo, ItemPointer tidPtr, LOCKMODE lockmode)
{
	LOCKTAG		tag;

	/* ------------------
	 * LOCKTAG has two bytes of padding, unfortunately.  The
	 * hash function will return miss if the padding bytes aren't
	 * zero'd.
	 * ------------------
	 */
	MemSet(&tag, 0, sizeof(LOCKTAG));

	tag.relId = lockinfo->lockRelId.relId;
	tag.dbId = lockinfo->lockRelId.dbId;
	BlockIdCopy(&(tag.tupleId.ip_blkid), &(tidPtr->ip_blkid));

	return MultiRelease(MultiTableId, &tag, lockmode, PAGE_LEVEL);
}

#endif

/* ------------------
 * Release a relation in the multi-level lock table
 * ------------------
 */
bool
MultiReleaseReln(LockInfo lockinfo, LOCKMODE lockmode)
{
	LOCKTAG		tag;

	/* ------------------
	 * LOCKTAG has two bytes of padding, unfortunately.  The
	 * hash function will return miss if the padding bytes aren't
	 * zero'd.
	 * ------------------
	 */
	MemSet(&tag, 0, sizeof(LOCKTAG));
	tag.relId = lockinfo->lockRelId.relId;
	tag.dbId = lockinfo->lockRelId.dbId;

	return MultiRelease(MultiTableId, &tag, lockmode, RELN_LEVEL);
}

/*
 * MultiRelease -- release a multi-level lock
 *
 * Returns: TRUE if successful, FALSE otherwise.
 */
static bool
MultiRelease(LOCKMETHOD lockmethod,
			 LOCKTAG *tag,
			 LOCKMODE lockmode,
			 PG_LOCK_LEVEL level)
{
	LOCKMODE	locks[N_LEVELS];
	int			i,
				status;
	LOCKTAG		xxTag,
			   *tmpTag = &xxTag;

	/*
	 * same level scheme as MultiAcquire().
	 */
	switch (level)
	{
		case RELN_LEVEL:
			locks[0] = lockmode;
			locks[1] = NO_LOCK;
			locks[2] = NO_LOCK;
			break;
		case PAGE_LEVEL:
			locks[0] = lockmode + INTENT;
			locks[1] = lockmode;
			locks[2] = NO_LOCK;
			break;
		case TUPLE_LEVEL:
			locks[0] = lockmode + INTENT;
			locks[1] = lockmode + INTENT;
			locks[2] = lockmode;
			break;
		default:
			elog(ERROR, "MultiRelease: bad lockmode");
	}

	/*
	 * again, construct the tag on the fly.  This time, however, we
	 * release the locks in the REVERSE order -- from lowest level to
	 * highest level.
	 *
	 * Must zero out the tag to set padding byes to zero and ensure hashing
	 * consistency.
	 */
	MemSet(tmpTag, 0, sizeof(*tmpTag));
	tmpTag->relId = tag->relId;
	tmpTag->dbId = tag->dbId;

	for (i = (N_LEVELS - 1); i >= 0; i--)
	{
		if (locks[i] != NO_LOCK)
		{
			switch (i)
			{
				case RELN_LEVEL:
					/* -------------
					 * Set the block # and offset to invalid
					 * -------------
					 */
					BlockIdSet(&(tmpTag->tupleId.ip_blkid), InvalidBlockNumber);
					tmpTag->tupleId.ip_posid = InvalidOffsetNumber;
					break;
				case PAGE_LEVEL:
					/* -------------
					 * Copy the block #, set the offset to invalid
					 * -------------
					 */
					BlockIdCopy(&(tmpTag->tupleId.ip_blkid),
								&(tag->tupleId.ip_blkid));
					tmpTag->tupleId.ip_posid = InvalidOffsetNumber;
					break;
				case TUPLE_LEVEL:
					ItemPointerCopy(&tmpTag->tupleId, &tag->tupleId);
					break;
			}
			status = LockRelease(lockmethod, tmpTag, locks[i]);
			if (!status)
				elog(ERROR, "MultiRelease: couldn't release after error");
		}
	}
	/* shouldn't reach here */
	return false;
}