nbtutils.c

PostgreSQL7.4.6 for Linux

/*-------------------------------------------------------------------------
 *
 * btutils.c
 *	  Utility code for Postgres btree implementation.
 *
 * 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/nbtree/nbtutils.c,v 1.54 2003/08/04 02:39:57 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/genam.h"
#include "access/istrat.h"
#include "access/nbtree.h"
#include "catalog/catalog.h"
#include "executor/execdebug.h"


static int	_bt_getstrategynumber(RegProcedure sk_procedure, StrategyMap map);


/*
 * _bt_mkscankey
 *		Build a scan key that contains comparison data from itup
 *		as well as comparator routines appropriate to the key datatypes.
 *
 *		The result is intended for use with _bt_compare().
 */
ScanKey
_bt_mkscankey(Relation rel, IndexTuple itup)
{
	ScanKey		skey;
	TupleDesc	itupdesc;
	int			natts;
	int			i;
	FmgrInfo   *procinfo;
	Datum		arg;
	bool		null;
	bits16		flag;

	itupdesc = RelationGetDescr(rel);
	natts = RelationGetNumberOfAttributes(rel);

	skey = (ScanKey) palloc(natts * sizeof(ScanKeyData));

	for (i = 0; i < natts; i++)
	{
		procinfo = index_getprocinfo(rel, i + 1, BTORDER_PROC);
		arg = index_getattr(itup, i + 1, itupdesc, &null);
		flag = null ? SK_ISNULL : 0x0;
		ScanKeyEntryInitializeWithInfo(&skey[i],
									   flag,
									   (AttrNumber) (i + 1),
									   procinfo,
									   CurrentMemoryContext,
									   arg);
	}

	return skey;
}

/*
 * _bt_mkscankey_nodata
 *		Build a scan key that contains comparator routines appropriate to
 *		the key datatypes, but no comparison data.
 *
 *		The result cannot be used with _bt_compare().  Currently this
 *		routine is only called by utils/sort/tuplesort.c, which has its
 *		own comparison routine.
 */
ScanKey
_bt_mkscankey_nodata(Relation rel)
{
	ScanKey		skey;
	int			natts;
	int			i;
	FmgrInfo   *procinfo;

	natts = RelationGetNumberOfAttributes(rel);

	skey = (ScanKey) palloc(natts * sizeof(ScanKeyData));

	for (i = 0; i < natts; i++)
	{
		procinfo = index_getprocinfo(rel, i + 1, BTORDER_PROC);
		ScanKeyEntryInitializeWithInfo(&skey[i],
									   SK_ISNULL,
									   (AttrNumber) (i + 1),
									   procinfo,
									   CurrentMemoryContext,
									   (Datum) 0);
	}

	return skey;
}

/*
 * free a scan key made by either _bt_mkscankey or _bt_mkscankey_nodata.
 */
void
_bt_freeskey(ScanKey skey)
{
	pfree(skey);
}

/*
 * free a retracement stack made by _bt_search.
 */
void
_bt_freestack(BTStack stack)
{
	BTStack		ostack;

	while (stack != (BTStack) NULL)
	{
		ostack = stack;
		stack = stack->bts_parent;
		pfree(ostack);
	}
}

/*
 * Construct a BTItem from a plain IndexTuple.
 *
 * This is now useless code, since a BTItem *is* an index tuple with
 * no extra stuff.	We hang onto it for the moment to preserve the
 * notational distinction, in case we want to add some extra stuff
 * again someday.
 */
BTItem
_bt_formitem(IndexTuple itup)
{
	int			nbytes_btitem;
	BTItem		btitem;
	Size		tuplen;

	/* make a copy of the index tuple with room for extra stuff */
	tuplen = IndexTupleSize(itup);
	nbytes_btitem = tuplen + (sizeof(BTItemData) - sizeof(IndexTupleData));

	btitem = (BTItem) palloc(nbytes_btitem);
	memcpy((char *) &(btitem->bti_itup), (char *) itup, tuplen);

	return btitem;
}

/*----------
 *	_bt_orderkeys() -- Put keys in a sensible order for conjunctive quals.
 *
 * After this routine runs, the scan keys are ordered by index attribute
 * (all quals for attr 1, then all for attr 2, etc) and within each attr
 * the keys are ordered by constraint type: ">", ">=", "=", "<=", "<".
 * Furthermore, redundant keys are eliminated: we keep only the tightest
 * >/>= bound and the tightest </<= bound, and if there's an = key then
 * that's the only one returned.  (So, we return either a single = key,
 * or one or two boundary-condition keys for each attr.)
 *
 * As a byproduct of this work, we can detect contradictory quals such
 * as "x = 1 AND x > 2".  If we see that, we return so->quals_ok = FALSE,
 * indicating the scan need not be run at all since no tuples can match.
 *
 * Another byproduct is to determine how many quals must be satisfied to
 * continue the scan.  _bt_checkkeys uses this.  For example, if the quals
 * are "x = 1 AND y < 4 AND z < 5", then _bt_checkkeys will reject a tuple
 * (1,2,7), but we must continue the scan in case there are tuples (1,3,z).
 * But once we reach tuples like (1,4,z) we can stop scanning because no
 * later tuples could match.  This is reflected by setting
 * so->numberOfRequiredKeys to the number of leading keys that must be
 * matched to continue the scan.  numberOfRequiredKeys is equal to the
 * number of leading "=" keys plus the key(s) for the first non "="
 * attribute, which can be seen to be correct by considering the above
 * example.
 *
 * Furthermore, we detect the case where the index is unique and we have
 * equality quals for all columns.	In this case there can be at most one
 * (visible) matching tuple.  index_getnext uses this to avoid uselessly
 * continuing the scan after finding one match.
 *
 * The initial ordering of the keys is expected to be by attribute already
 * (see group_clauses_by_indexkey() in indxpath.c).  The task here is to
 * standardize the appearance of multiple keys for the same attribute.
 *
 * XXX this routine is one of many places that fail to handle SK_COMMUTE
 * scankeys properly.  Currently, the planner is careful never to generate
 * any indexquals that would require SK_COMMUTE to be set.	Someday we ought
 * to try to fix this, though it's not real critical as long as indexable
 * operators all have commutators...
 *
 * Note: this routine invokes comparison operators via OidFunctionCallN,
 * ie, without caching function lookups.  No point in trying to be smarter,
 * since these comparisons are executed only when the user expresses a
 * hokey qualification, and happen only once per scan anyway.
 *----------
 */
void
_bt_orderkeys(IndexScanDesc scan)
{
	Relation	relation = scan->indexRelation;
	BTScanOpaque so = (BTScanOpaque) scan->opaque;
	ScanKeyData xform[BTMaxStrategyNumber];
	bool		init[BTMaxStrategyNumber];
	int			numberOfKeys = so->numberOfKeys;
	ScanKey		key;
	ScanKey		cur;
	StrategyMap map;
	Datum		test;
	int			i,
				j;
	AttrNumber	attno;
	int			new_numberOfKeys;
	bool		allEqualSoFar;

	so->qual_ok = true;
	so->numberOfRequiredKeys = 0;
	scan->keys_are_unique = false;

	if (numberOfKeys < 1)
		return;					/* done if qual-less scan */

	key = so->keyData;
	cur = &key[0];
	/* check input keys are correctly ordered */
	if (cur->sk_attno != 1)
		elog(ERROR, "key(s) for attribute 1 missed");

	/* We can short-circuit most of the work if there's just one key */
	if (numberOfKeys == 1)
	{
		/*
		 * We don't use indices for 'A is null' and 'A is not null'
		 * currently and 'A < = > <> NULL' will always fail - so qual is
		 * not Ok if comparison value is NULL.		- vadim 03/21/97
		 */
		if (cur->sk_flags & SK_ISNULL)
			so->qual_ok = false;
		else if (relation->rd_index->indisunique &&
				 relation->rd_rel->relnatts == 1)
		{
			/* it's a unique index, do we have an equality qual? */
			map = IndexStrategyGetStrategyMap(RelationGetIndexStrategy(relation),
											  BTMaxStrategyNumber,
											  1);
			j = _bt_getstrategynumber(cur->sk_procedure, map);
			if (j == (BTEqualStrategyNumber - 1))
				scan->keys_are_unique = true;
		}
		so->numberOfRequiredKeys = 1;
		return;
	}

	/*
	 * Otherwise, do the full set of pushups.
	 */
	new_numberOfKeys = 0;
	allEqualSoFar = true;

	/*
	 * Initialize for processing of keys for attr 1.
	 *
	 * xform[i] holds a copy of the current scan key of strategy type i+1, if
	 * any; init[i] is TRUE if we have found such a key for this attr.
	 */
	attno = 1;
	map = IndexStrategyGetStrategyMap(RelationGetIndexStrategy(relation),
									  BTMaxStrategyNumber,
									  attno);
	MemSet(xform, 0, sizeof(xform));	/* not really necessary */
	MemSet(init, 0, sizeof(init));

	/*
	 * Loop iterates from 0 to numberOfKeys inclusive; we use the last
	 * pass to handle after-last-key processing.  Actual exit from the
	 * loop is at the "break" statement below.
	 */
	for (i = 0;; cur++, i++)