hash.c

PostgreSQL7.4.6 for Linux

/*-------------------------------------------------------------------------
 *
 * hash.c
 *	  Implementation of Margo Seltzer's Hashing package for postgres.
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/access/hash/hash.c,v 1.68 2003/09/04 22:06:27 tgl Exp $
 *
 * NOTES
 *	  This file contains only the public interface routines.
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/genam.h"
#include "access/hash.h"
#include "access/heapam.h"
#include "access/xlogutils.h"
#include "catalog/index.h"
#include "executor/executor.h"
#include "miscadmin.h"


/* Working state for hashbuild and its callback */
typedef struct
{
	double		indtuples;
} HashBuildState;

static void hashbuildCallback(Relation index,
				  HeapTuple htup,
				  Datum *attdata,
				  char *nulls,
				  bool tupleIsAlive,
				  void *state);


/*
 *	hashbuild() -- build a new hash index.
 *
 *		We use a global variable to record the fact that we're creating
 *		a new index.  This is used to avoid high-concurrency locking,
 *		since the index won't be visible until this transaction commits
 *		and since building is guaranteed to be single-threaded.
 */
Datum
hashbuild(PG_FUNCTION_ARGS)
{
	Relation	heap = (Relation) PG_GETARG_POINTER(0);
	Relation	index = (Relation) PG_GETARG_POINTER(1);
	IndexInfo  *indexInfo = (IndexInfo *) PG_GETARG_POINTER(2);
	double		reltuples;
	HashBuildState buildstate;

	/*
	 * We expect to be called exactly once for any index relation. If
	 * that's not the case, big trouble's what we have.
	 */
	if (RelationGetNumberOfBlocks(index) != 0)
		elog(ERROR, "index \"%s\" already contains data",
			 RelationGetRelationName(index));

	/* initialize the hash index metadata page */
	_hash_metapinit(index);

	/* build the index */
	buildstate.indtuples = 0;

	/* do the heap scan */
	reltuples = IndexBuildHeapScan(heap, index, indexInfo,
								hashbuildCallback, (void *) &buildstate);

	/*
	 * Since we just counted the tuples in the heap, we update its stats
	 * in pg_class to guarantee that the planner takes advantage of the
	 * index we just created.  But, only update statistics during normal
	 * index definitions, not for indices on system catalogs created
	 * during bootstrap processing.  We must close the relations before
	 * updating statistics to guarantee that the relcache entries are
	 * flushed when we increment the command counter in UpdateStats(). But
	 * we do not release any locks on the relations; those will be held
	 * until end of transaction.
	 */
	if (IsNormalProcessingMode())
	{
		Oid			hrelid = RelationGetRelid(heap);
		Oid			irelid = RelationGetRelid(index);

		heap_close(heap, NoLock);
		index_close(index);
		UpdateStats(hrelid, reltuples);
		UpdateStats(irelid, buildstate.indtuples);
	}

	PG_RETURN_VOID();
}

/*
 * Per-tuple callback from IndexBuildHeapScan
 */
static void
hashbuildCallback(Relation index,
				  HeapTuple htup,
				  Datum *attdata,
				  char *nulls,
				  bool tupleIsAlive,
				  void *state)
{
	HashBuildState *buildstate = (HashBuildState *) state;
	IndexTuple	itup;
	HashItem	hitem;
	InsertIndexResult res;

	/* form an index tuple and point it at the heap tuple */
	itup = index_formtuple(RelationGetDescr(index), attdata, nulls);
	itup->t_tid = htup->t_self;

	/* Hash indexes don't index nulls, see notes in hashinsert */
	if (IndexTupleHasNulls(itup))
	{
		pfree(itup);
		return;
	}

	hitem = _hash_formitem(itup);

	res = _hash_doinsert(index, hitem);

	if (res)
		pfree(res);

	buildstate->indtuples += 1;

	pfree(hitem);
	pfree(itup);
}

/*
 *	hashinsert() -- insert an index tuple into a hash table.
 *
 *	Hash on the index tuple's key, find the appropriate location
 *	for the new tuple, put it there, and return an InsertIndexResult
 *	to the caller.
 */
Datum
hashinsert(PG_FUNCTION_ARGS)
{
	Relation	rel = (Relation) PG_GETARG_POINTER(0);
	Datum	   *datum = (Datum *) PG_GETARG_POINTER(1);
	char	   *nulls = (char *) PG_GETARG_POINTER(2);
	ItemPointer ht_ctid = (ItemPointer) PG_GETARG_POINTER(3);

#ifdef NOT_USED
	Relation	heapRel = (Relation) PG_GETARG_POINTER(4);
	bool		checkUnique = PG_GETARG_BOOL(5);
#endif
	InsertIndexResult res;
	HashItem	hitem;
	IndexTuple	itup;

	/* generate an index tuple */
	itup = index_formtuple(RelationGetDescr(rel), datum, nulls);
	itup->t_tid = *ht_ctid;

	/*
	 * If the single index key is null, we don't insert it into the index.
	 * Hash tables support scans on '='. Relational algebra says that A =
	 * B returns null if either A or B is null.  This means that no
	 * qualification used in an index scan could ever return true on a
	 * null attribute.	It also means that indices can't be used by ISNULL
	 * or NOTNULL scans, but that's an artifact of the strategy map
	 * architecture chosen in 1986, not of the way nulls are handled here.
	 */
	if (IndexTupleHasNulls(itup))
	{
		pfree(itup);
		PG_RETURN_POINTER((InsertIndexResult) NULL);
	}

	hitem = _hash_formitem(itup);

	res = _hash_doinsert(rel, hitem);

	pfree(hitem);
	pfree(itup);

	PG_RETURN_POINTER(res);
}


/*
 *	hashgettuple() -- Get the next tuple in the scan.
 */
Datum
hashgettuple(PG_FUNCTION_ARGS)
{
	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
	ScanDirection dir = (ScanDirection) PG_GETARG_INT32(1);
	HashScanOpaque so = (HashScanOpaque) scan->opaque;
	Relation	rel = scan->indexRelation;
	Page		page;
	OffsetNumber offnum;
	bool		res;

	/*
	 * We hold pin but not lock on current buffer while outside the hash AM.
	 * Reacquire the read lock here.
	 */
	if (BufferIsValid(so->hashso_curbuf))
		_hash_chgbufaccess(rel, so->hashso_curbuf, HASH_NOLOCK, HASH_READ);

	/*
	 * If we've already initialized this scan, we can just advance it in
	 * the appropriate direction.  If we haven't done so yet, we call a
	 * routine to get the first item in the scan.
	 */
	if (ItemPointerIsValid(&(scan->currentItemData)))
	{
		/*
		 * Check to see if we should kill the previously-fetched tuple.
		 */
		if (scan->kill_prior_tuple)
		{
			/*
			 * Yes, so mark it by setting the LP_DELETE bit in the item
			 * flags.
			 */
			offnum = ItemPointerGetOffsetNumber(&(scan->currentItemData));
			page = BufferGetPage(so->hashso_curbuf);
			PageGetItemId(page, offnum)->lp_flags |= LP_DELETE;

			/*
			 * Since this can be redone later if needed, it's treated the
			 * same as a commit-hint-bit status update for heap tuples: we
			 * mark the buffer dirty but don't make a WAL log entry.
			 */
			SetBufferCommitInfoNeedsSave(so->hashso_curbuf);
		}

		/*
		 * Now continue the scan.
		 */
		res = _hash_next(scan, dir);
	}
	else
		res = _hash_first(scan, dir);

	/*
	 * Skip killed tuples if asked to.
	 */
	if (scan->ignore_killed_tuples)
	{
		while (res)
		{
			offnum = ItemPointerGetOffsetNumber(&(scan->currentItemData));
			page = BufferGetPage(so->hashso_curbuf);
			if (!ItemIdDeleted(PageGetItemId(page, offnum)))
				break;
			res = _hash_next(scan, dir);
		}
	}

	/* Release read lock on current buffer, but keep it pinned */
	if (BufferIsValid(so->hashso_curbuf))
		_hash_chgbufaccess(rel, so->hashso_curbuf, HASH_READ, HASH_NOLOCK);

	PG_RETURN_BOOL(res);
}


/*
 *	hashbeginscan() -- start a scan on a hash index
 */
Datum
hashbeginscan(PG_FUNCTION_ARGS)
{
	Relation	rel = (Relation) PG_GETARG_POINTER(0);
	int			keysz = PG_GETARG_INT32(1);
	ScanKey		scankey = (ScanKey) PG_GETARG_POINTER(2);
	IndexScanDesc scan;
	HashScanOpaque so;

	scan = RelationGetIndexScan(rel, keysz, scankey);
	so = (HashScanOpaque) palloc(sizeof(HashScanOpaqueData));
	so->hashso_bucket_valid = false;
	so->hashso_bucket_blkno = 0;
	so->hashso_curbuf = so->hashso_mrkbuf = InvalidBuffer;
	scan->opaque = so;

	/* register scan in case we change pages it's using */
	_hash_regscan(scan);

	PG_RETURN_POINTER(scan);
}

/*
 *	hashrescan() -- rescan an index relation
 */
Datum
hashrescan(PG_FUNCTION_ARGS)
{
	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
	ScanKey		scankey = (ScanKey) PG_GETARG_POINTER(1);
	HashScanOpaque so = (HashScanOpaque) scan->opaque;
	Relation	rel = scan->indexRelation;

	/* if we are called from beginscan, so is still NULL */
	if (so)
	{
		/* release any pins we still hold */
		if (BufferIsValid(so->hashso_curbuf))
			_hash_dropbuf(rel, so->hashso_curbuf);
		so->hashso_curbuf = InvalidBuffer;

		if (BufferIsValid(so->hashso_mrkbuf))
			_hash_dropbuf(rel, so->hashso_mrkbuf);