hash.c

关系型数据库 Postgresql 6.5.2

/*-------------------------------------------------------------------------
 *
 * hash.c
 *	  Implementation of Margo Seltzer's Hashing package for postgres.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /usr/local/cvsroot/pgsql/src/backend/access/hash/hash.c,v 1.26.2.1 1999/08/02 05:24:33 scrappy 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 "catalog/index.h"
#include "executor/executor.h"
#include "miscadmin.h"


bool		BuildingHash = false;

/*
 *	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.
 */
void
hashbuild(Relation heap,
		  Relation index,
		  int natts,
		  AttrNumber *attnum,
		  IndexStrategy istrat,
		  uint16 pcount,
		  Datum *params,
		  FuncIndexInfo *finfo,
		  PredInfo *predInfo)
{
	HeapScanDesc hscan;
	HeapTuple	htup;
	IndexTuple	itup;
	TupleDesc	htupdesc,
				itupdesc;
	Datum	   *attdata;
	bool	   *nulls;
	InsertIndexResult res;
	int			nhtups,
				nitups;
	int			i;
	HashItem	hitem;
	Buffer		buffer = InvalidBuffer;

#ifndef OMIT_PARTIAL_INDEX
	ExprContext *econtext;
	TupleTable	tupleTable;
	TupleTableSlot *slot;

#endif
	Oid			hrelid,
				irelid;
	Node	   *pred,
			   *oldPred;

	/* note that this is a new btree */
	BuildingHash = true;

	pred = predInfo->pred;
	oldPred = predInfo->oldPred;

	/* initialize the hash index metadata page (if this is a new index) */
	if (oldPred == NULL)
		_hash_metapinit(index);

	/* get tuple descriptors for heap and index relations */
	htupdesc = RelationGetDescr(heap);
	itupdesc = RelationGetDescr(index);

	/* get space for data items that'll appear in the index tuple */
	attdata = (Datum *) palloc(natts * sizeof(Datum));
	nulls = (bool *) palloc(natts * sizeof(bool));

	/*
	 * If this is a predicate (partial) index, we will need to evaluate
	 * the predicate using ExecQual, which requires the current tuple to
	 * be in a slot of a TupleTable.  In addition, ExecQual must have an
	 * ExprContext referring to that slot.	Here, we initialize dummy
	 * TupleTable and ExprContext objects for this purpose. --Nels, Feb
	 * '92
	 */
#ifndef OMIT_PARTIAL_INDEX
	if (pred != NULL || oldPred != NULL)
	{
		tupleTable = ExecCreateTupleTable(1);
		slot = ExecAllocTableSlot(tupleTable);
		econtext = makeNode(ExprContext);
		FillDummyExprContext(econtext, slot, htupdesc, buffer);
	}
	else
/* quiet the compiler */
	{
		econtext = NULL;
		tupleTable = 0;
		slot = 0;
	}
#endif	 /* OMIT_PARTIAL_INDEX */

	/* build the index */
	nhtups = nitups = 0;

	/* start a heap scan */
	hscan = heap_beginscan(heap, 0, SnapshotNow, 0, (ScanKey) NULL);

	while (HeapTupleIsValid(htup = heap_getnext(hscan, 0)))
	{

		nhtups++;

		/*
		 * If oldPred != NULL, this is an EXTEND INDEX command, so skip
		 * this tuple if it was already in the existing partial index
		 */
		if (oldPred != NULL)
		{
			/* SetSlotContents(slot, htup); */
#ifndef OMIT_PARTIAL_INDEX
			slot->val = htup;
			if (ExecQual((List *) oldPred, econtext) == true)
			{
				nitups++;
				continue;
			}
#endif	 /* OMIT_PARTIAL_INDEX */
		}

		/*
		 * Skip this tuple if it doesn't satisfy the partial-index
		 * predicate
		 */
		if (pred != NULL)
		{
#ifndef OMIT_PARTIAL_INDEX
			/* SetSlotContents(slot, htup); */
			slot->val = htup;
			if (ExecQual((List *) pred, econtext) == false)
				continue;
#endif	 /* OMIT_PARTIAL_INDEX */
		}

		nitups++;

		/*
		 * For the current heap tuple, extract all the attributes we use
		 * in this index, and note which are null.
		 */
		for (i = 1; i <= natts; i++)
		{
			int			attoff;
			bool		attnull;

			/*
			 * Offsets are from the start of the tuple, and are
			 * zero-based; indices are one-based.  The next call returns i
			 * - 1.  That's data hiding for you.
			 */

			/* attoff = i - 1 */
			attoff = AttrNumberGetAttrOffset(i);

			/*
			 * below, attdata[attoff] set to equal some datum & attnull is
			 * changed to indicate whether or not the attribute is null
			 * for this tuple
			 */
			attdata[attoff] = GetIndexValue(htup,
											htupdesc,
											attoff,
											attnum,
											finfo,
											&attnull);
			nulls[attoff] = (attnull ? 'n' : ' ');
		}

		/* form an index tuple and point it at the heap tuple */
		itup = index_formtuple(itupdesc, attdata, nulls);

		/*
		 * 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 (itup->t_info & INDEX_NULL_MASK)
		{
			pfree(itup);
			continue;
		}

		itup->t_tid = htup->t_self;
		hitem = _hash_formitem(itup);
		res = _hash_doinsert(index, hitem);
		pfree(hitem);
		pfree(itup);
		pfree(res);
	}

	/* okay, all heap tuples are indexed */
	heap_endscan(hscan);

	if (pred != NULL || oldPred != NULL)
	{
#ifndef OMIT_PARTIAL_INDEX
		ExecDestroyTupleTable(tupleTable, true);
		pfree(econtext);
#endif	 /* OMIT_PARTIAL_INDEX */
	}

	/*
	 * 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. Finally, only update statistics during
	 * normal index definitions, not for indices on system catalogs
	 * created during bootstrap processing.  We must close the relations
	 * before updatings statistics to guarantee that the relcache entries
	 * are flushed when we increment the command counter in UpdateStats().
	 */
	if (IsNormalProcessingMode())
	{
		hrelid = RelationGetRelid(heap);
		irelid = RelationGetRelid(index);
		heap_close(heap);
		index_close(index);
		UpdateStats(hrelid, nhtups, true);
		UpdateStats(irelid, nitups, false);
		if (oldPred != NULL)
		{
			if (nitups == nhtups)
				pred = NULL;
			UpdateIndexPredicate(irelid, oldPred, pred);
		}
	}

	/* be tidy */
	pfree(nulls);
	pfree(attdata);

	/* all done */
	BuildingHash = false;
}

/*
 *	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.
 */
InsertIndexResult
hashinsert(Relation rel, Datum *datum, char *nulls, ItemPointer ht_ctid, Relation heapRel)
{
	HashItem	hitem;
	IndexTuple	itup;
	InsertIndexResult res;


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

	if (itup->t_info & INDEX_NULL_MASK)
		return (InsertIndexResult) NULL;

	hitem = _hash_formitem(itup);

	res = _hash_doinsert(rel, hitem);

	pfree(hitem);
	pfree(itup);

	return res;
}


/*
 *	hashgettuple() -- Get the next tuple in the scan.
 */
char *
hashgettuple(IndexScanDesc scan, ScanDirection dir)
{
	RetrieveIndexResult res;

	/*
	 * 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)))
		res = _hash_next(scan, dir);
	else
		res = _hash_first(scan, dir);

	return (char *) res;
}


/*
 *	hashbeginscan() -- start a scan on a hash index
 */
char *
hashbeginscan(Relation rel,
			  bool fromEnd,
			  uint16 keysz,
			  ScanKey scankey)
{
	IndexScanDesc scan;
	HashScanOpaque so;

	scan = RelationGetIndexScan(rel, fromEnd, keysz, scankey);
	so = (HashScanOpaque) palloc(sizeof(HashScanOpaqueData));
	so->hashso_curbuf = so->hashso_mrkbuf = InvalidBuffer;
	scan->opaque = so;
	scan->flags = 0x0;

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

	return (char *) scan;
}

/*
 *	hashrescan() -- rescan an index relation
 */
void
hashrescan(IndexScanDesc scan, bool fromEnd, ScanKey scankey)
{
	ItemPointer iptr;
	HashScanOpaque so;

	so = (HashScanOpaque) scan->opaque;

	/* we hold a read lock on the current page in the scan */
	if (ItemPointerIsValid(iptr = &(scan->currentItemData)))
	{
		_hash_relbuf(scan->relation, so->hashso_curbuf, HASH_READ);
		so->hashso_curbuf = InvalidBuffer;
		ItemPointerSetInvalid(iptr);
	}
	if (ItemPointerIsValid(iptr = &(scan->currentMarkData)))
	{
		_hash_relbuf(scan->relation, so->hashso_mrkbuf, HASH_READ);
		so->hashso_mrkbuf = InvalidBuffer;
		ItemPointerSetInvalid(iptr);
	}

	/* reset the scan key */
	if (scan->numberOfKeys > 0)
	{
		memmove(scan->keyData,
				scankey,
				scan->numberOfKeys * sizeof(ScanKeyData));
	}
}

/*
 *	hashendscan() -- close down a scan
 */
void
hashendscan(IndexScanDesc scan)
{

	ItemPointer iptr;
	HashScanOpaque so;

	so = (HashScanOpaque) scan->opaque;

	/* release any locks we still hold */
	if (ItemPointerIsValid(iptr = &(scan->currentItemData)))
	{
		_hash_relbuf(scan->relation, so->hashso_curbuf, HASH_READ);
		so->hashso_curbuf = InvalidBuffer;
		ItemPointerSetInvalid(iptr);
	}

	if (ItemPointerIsValid(iptr = &(scan->currentMarkData)))
	{
		if (BufferIsValid(so->hashso_mrkbuf))
			_hash_relbuf(scan->relation, so->hashso_mrkbuf, HASH_READ);
		so->hashso_mrkbuf = InvalidBuffer;
		ItemPointerSetInvalid(iptr);
	}

	/* don't need scan registered anymore */
	_hash_dropscan(scan);

	/* be tidy */
	pfree(scan->opaque);
}

/*
 *	hashmarkpos() -- save current scan position
 *
 */
void
hashmarkpos(IndexScanDesc scan)
{
	ItemPointer iptr;
	HashScanOpaque so;

	/*
	 * see if we ever call this code. if we do, then so_mrkbuf a useful
	 * element in the scan->opaque structure. if this procedure is never
	 * called, so_mrkbuf should be removed from the scan->opaque
	 * structure.
	 */
	elog(NOTICE, "Hashmarkpos() called.");

	so = (HashScanOpaque) scan->opaque;

	/* release lock on old marked data, if any */
	if (ItemPointerIsValid(iptr = &(scan->currentMarkData)))
	{
		_hash_relbuf(scan->relation, so->hashso_mrkbuf, HASH_READ);
		so->hashso_mrkbuf = InvalidBuffer;
		ItemPointerSetInvalid(iptr);
	}

	/* bump lock on currentItemData and copy to currentMarkData */
	if (ItemPointerIsValid(&(scan->currentItemData)))
	{
		so->hashso_mrkbuf = _hash_getbuf(scan->relation,
								 BufferGetBlockNumber(so->hashso_curbuf),
										 HASH_READ);
		scan->currentMarkData = scan->currentItemData;
	}
}

/*
 *	hashrestrpos() -- restore scan to last saved position
 */
void
hashrestrpos(IndexScanDesc scan)
{
	ItemPointer iptr;
	HashScanOpaque so;

	/*
	 * see if we ever call this code. if we do, then so_mrkbuf a useful
	 * element in the scan->opaque structure. if this procedure is never
	 * called, so_mrkbuf should be removed from the scan->opaque
	 * structure.
	 */
	elog(NOTICE, "Hashrestrpos() called.");

	so = (HashScanOpaque) scan->opaque;

	/* release lock on current data, if any */
	if (ItemPointerIsValid(iptr = &(scan->currentItemData)))
	{
		_hash_relbuf(scan->relation, so->hashso_curbuf, HASH_READ);
		so->hashso_curbuf = InvalidBuffer;
		ItemPointerSetInvalid(iptr);
	}

	/* bump lock on currentMarkData and copy to currentItemData */
	if (ItemPointerIsValid(&(scan->currentMarkData)))
	{
		so->hashso_curbuf = _hash_getbuf(scan->relation,
								 BufferGetBlockNumber(so->hashso_mrkbuf),
										 HASH_READ);

		scan->currentItemData = scan->currentMarkData;
	}
}

/* stubs */
void
hashdelete(Relation rel, ItemPointer tid)
{
	/* adjust any active scans that will be affected by this deletion */
	_hash_adjscans(rel, tid);

	/* delete the data from the page */
	_hash_pagedel(rel, tid);
}