hashpage.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

/*-------------------------------------------------------------------------
 *
 * hashpage.c
 *	  Hash table page management code for the Postgres hash access method
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/access/hash/hashpage.c,v 1.52.2.1 2005/11/22 18:23:03 momjian Exp $
 *
 * NOTES
 *	  Postgres hash pages look like ordinary relation pages.  The opaque
 *	  data at high addresses includes information about the page including
 *	  whether a page is an overflow page or a true bucket, the bucket
 *	  number, and the block numbers of the preceding and following pages
 *	  in the same bucket.
 *
 *	  The first page in a hash relation, page zero, is special -- it stores
 *	  information describing the hash table; it is referred to as the
 *	  "meta page." Pages one and higher store the actual data.
 *
 *	  There are also bitmap pages, which are not manipulated here;
 *	  see hashovfl.c.
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/hash.h"
#include "miscadmin.h"
#include "storage/lmgr.h"
#include "utils/lsyscache.h"


static void _hash_splitbucket(Relation rel, Buffer metabuf,
				  Bucket obucket, Bucket nbucket,
				  BlockNumber start_oblkno,
				  BlockNumber start_nblkno,
				  uint32 maxbucket,
				  uint32 highmask, uint32 lowmask);


/*
 * We use high-concurrency locking on hash indexes (see README for an overview
 * of the locking rules).  However, we can skip taking lmgr locks when the
 * index is local to the current backend (ie, either temp or new in the
 * current transaction).  No one else can see it, so there's no reason to
 * take locks.	We still take buffer-level locks, but not lmgr locks.
 */
#define USELOCKING(rel)		(!RELATION_IS_LOCAL(rel))


/*
 * _hash_getlock() -- Acquire an lmgr lock.
 *
 * 'whichlock' should be zero to acquire the split-control lock, or the
 * block number of a bucket's primary bucket page to acquire the per-bucket
 * lock.  (See README for details of the use of these locks.)
 *
 * 'access' must be HASH_SHARE or HASH_EXCLUSIVE.
 */
void
_hash_getlock(Relation rel, BlockNumber whichlock, int access)
{
	if (USELOCKING(rel))
		LockPage(rel, whichlock, access);
}

/*
 * _hash_try_getlock() -- Acquire an lmgr lock, but only if it's free.
 *
 * Same as above except we return FALSE without blocking if lock isn't free.
 */
bool
_hash_try_getlock(Relation rel, BlockNumber whichlock, int access)
{
	if (USELOCKING(rel))
		return ConditionalLockPage(rel, whichlock, access);
	else
		return true;
}

/*
 * _hash_droplock() -- Release an lmgr lock.
 */
void
_hash_droplock(Relation rel, BlockNumber whichlock, int access)
{
	if (USELOCKING(rel))
		UnlockPage(rel, whichlock, access);
}

/*
 *	_hash_getbuf() -- Get a buffer by block number for read or write.
 *
 *		'access' must be HASH_READ, HASH_WRITE, or HASH_NOLOCK.
 *
 *		When this routine returns, the appropriate lock is set on the
 *		requested buffer and its reference count has been incremented
 *		(ie, the buffer is "locked and pinned").
 *
 *		XXX P_NEW is not used because, unlike the tree structures, we
 *		need the bucket blocks to be at certain block numbers.	we must
 *		depend on the caller to call _hash_pageinit on the block if it
 *		knows that this is a new block.
 */
Buffer
_hash_getbuf(Relation rel, BlockNumber blkno, int access)
{
	Buffer		buf;

	if (blkno == P_NEW)
		elog(ERROR, "hash AM does not use P_NEW");

	buf = ReadBuffer(rel, blkno);

	if (access != HASH_NOLOCK)
		LockBuffer(buf, access);

	/* ref count and lock type are correct */
	return buf;
}

/*
 *	_hash_relbuf() -- release a locked buffer.
 *
 * Lock and pin (refcount) are both dropped.  Note that either read or
 * write lock can be dropped this way, but if we modified the buffer,
 * this is NOT the right way to release a write lock.
 */
void
_hash_relbuf(Relation rel, Buffer buf)
{
	LockBuffer(buf, BUFFER_LOCK_UNLOCK);
	ReleaseBuffer(buf);
}

/*
 *	_hash_dropbuf() -- release an unlocked buffer.
 *
 * This is used to unpin a buffer on which we hold no lock.  It is assumed
 * that the buffer is not dirty.
 */
void
_hash_dropbuf(Relation rel, Buffer buf)
{
	ReleaseBuffer(buf);
}

/*
 *	_hash_wrtbuf() -- write a hash page to disk.
 *
 *		This routine releases the lock held on the buffer and our refcount
 *		for it.  It is an error to call _hash_wrtbuf() without a write lock
 *		and a pin on the buffer.
 *
 * NOTE: actually, the buffer manager just marks the shared buffer page
 * dirty here; the real I/O happens later.	This is okay since we are not
 * relying on write ordering anyway.  The WAL mechanism is responsible for
 * guaranteeing correctness after a crash.
 */
void
_hash_wrtbuf(Relation rel, Buffer buf)
{
	LockBuffer(buf, BUFFER_LOCK_UNLOCK);
	WriteBuffer(buf);
}

/*
 *	_hash_wrtnorelbuf() -- write a hash page to disk, but do not release
 *						 our reference or lock.
 *
 *		It is an error to call _hash_wrtnorelbuf() without a write lock
 *		and a pin on the buffer.
 *
 * See above NOTE.
 */
void
_hash_wrtnorelbuf(Relation rel, Buffer buf)
{
	WriteNoReleaseBuffer(buf);
}

/*
 * _hash_chgbufaccess() -- Change the lock type on a buffer, without
 *			dropping our pin on it.
 *
 * from_access and to_access may be HASH_READ, HASH_WRITE, or HASH_NOLOCK,
 * the last indicating that no buffer-level lock is held or wanted.
 *
 * When from_access == HASH_WRITE, we assume the buffer is dirty and tell
 * bufmgr it must be written out.  If the caller wants to release a write
 * lock on a page that's not been modified, it's okay to pass from_access
 * as HASH_READ (a bit ugly, but handy in some places).
 */
void
_hash_chgbufaccess(Relation rel,
				   Buffer buf,
				   int from_access,
				   int to_access)
{
	if (from_access != HASH_NOLOCK)
		LockBuffer(buf, BUFFER_LOCK_UNLOCK);
	if (from_access == HASH_WRITE)
		WriteNoReleaseBuffer(buf);

	if (to_access != HASH_NOLOCK)
		LockBuffer(buf, to_access);
}


/*
 *	_hash_metapinit() -- Initialize the metadata page of a hash index,
 *				the two buckets that we begin with and the initial
 *				bitmap page.
 *
 * We are fairly cavalier about locking here, since we know that no one else
 * could be accessing this index.  In particular the rule about not holding
 * multiple buffer locks is ignored.
 */
void
_hash_metapinit(Relation rel)
{
	HashMetaPage metap;
	HashPageOpaque pageopaque;
	Buffer		metabuf;
	Buffer		buf;
	Page		pg;
	int32		data_width;
	int32		item_width;
	int32		ffactor;
	uint16		i;

	/* safety check */
	if (RelationGetNumberOfBlocks(rel) != 0)
		elog(ERROR, "cannot initialize non-empty hash index \"%s\"",
			 RelationGetRelationName(rel));

	/*
	 * Determine the target fill factor (tuples per bucket) for this index.
	 * The idea is to make the fill factor correspond to pages about 3/4ths
	 * full.  We can compute it exactly if the index datatype is fixed-width,
	 * but for var-width there's some guessing involved.
	 */
	data_width = get_typavgwidth(RelationGetDescr(rel)->attrs[0]->atttypid,
								 RelationGetDescr(rel)->attrs[0]->atttypmod);
	item_width = MAXALIGN(sizeof(HashItemData)) + MAXALIGN(data_width) +
		sizeof(ItemIdData);		/* include the line pointer */
	ffactor = (BLCKSZ * 3 / 4) / item_width;
	/* keep to a sane range */
	if (ffactor < 10)
		ffactor = 10;

	metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_WRITE);
	pg = BufferGetPage(metabuf);
	_hash_pageinit(pg, BufferGetPageSize(metabuf));

	pageopaque = (HashPageOpaque) PageGetSpecialPointer(pg);
	pageopaque->hasho_prevblkno = InvalidBlockNumber;
	pageopaque->hasho_nextblkno = InvalidBlockNumber;
	pageopaque->hasho_bucket = -1;
	pageopaque->hasho_flag = LH_META_PAGE;
	pageopaque->hasho_filler = HASHO_FILL;

	metap = (HashMetaPage) pg;

	metap->hashm_magic = HASH_MAGIC;
	metap->hashm_version = HASH_VERSION;
	metap->hashm_ntuples = 0;
	metap->hashm_nmaps = 0;
	metap->hashm_ffactor = ffactor;
	metap->hashm_bsize = BufferGetPageSize(metabuf);
	/* find largest bitmap array size that will fit in page size */
	for (i = _hash_log2(metap->hashm_bsize); i > 0; --i)
	{
		if ((1 << i) <= (metap->hashm_bsize -
						 (MAXALIGN(sizeof(PageHeaderData)) +
						  MAXALIGN(sizeof(HashPageOpaqueData)))))
			break;
	}
	Assert(i > 0);
	metap->hashm_bmsize = 1 << i;
	metap->hashm_bmshift = i + BYTE_TO_BIT;
	Assert((1 << BMPG_SHIFT(metap)) == (BMPG_MASK(metap) + 1));

	metap->hashm_procid = index_getprocid(rel, 1, HASHPROC);

	/*
	 * We initialize the index with two buckets, 0 and 1, occupying physical
	 * blocks 1 and 2.	The first freespace bitmap page is in block 3.
	 */
	metap->hashm_maxbucket = metap->hashm_lowmask = 1;	/* nbuckets - 1 */
	metap->hashm_highmask = 3;	/* (nbuckets << 1) - 1 */

	MemSet(metap->hashm_spares, 0, sizeof(metap->hashm_spares));
	MemSet(metap->hashm_mapp, 0, sizeof(metap->hashm_mapp));

	metap->hashm_spares[1] = 1; /* the first bitmap page is only spare */
	metap->hashm_ovflpoint = 1;
	metap->hashm_firstfree = 0;

	/*
	 * Initialize the first two buckets
	 */
	for (i = 0; i <= 1; i++)
	{
		buf = _hash_getbuf(rel, BUCKET_TO_BLKNO(metap, i), HASH_WRITE);
		pg = BufferGetPage(buf);
		_hash_pageinit(pg, BufferGetPageSize(buf));
		pageopaque = (HashPageOpaque) PageGetSpecialPointer(pg);
		pageopaque->hasho_prevblkno = InvalidBlockNumber;
		pageopaque->hasho_nextblkno = InvalidBlockNumber;
		pageopaque->hasho_bucket = i;
		pageopaque->hasho_flag = LH_BUCKET_PAGE;
		pageopaque->hasho_filler = HASHO_FILL;
		_hash_wrtbuf(rel, buf);
	}

	/*
	 * Initialize first bitmap page.  Can't do this until we create the first
	 * two buckets, else smgr will complain.
	 */
	_hash_initbitmap(rel, metap, 3);

	/* all done */
	_hash_wrtbuf(rel, metabuf);
}

/*
 *	_hash_pageinit() -- Initialize a new hash index page.
 */
void
_hash_pageinit(Page page, Size size)
{
	Assert(PageIsNew(page));
	PageInit(page, size, sizeof(HashPageOpaqueData));
}

/*
 * Attempt to expand the hash table by creating one new bucket.
 *
 * This will silently do nothing if it cannot get the needed locks.
 *