From b8c798ebc528f6b6300174929e66b8128ac5cef8 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 31 Jul 2010 03:27:40 +0000
Subject: [PATCH] Tweak tsmatchsel() so that it examines the structure of the
tsquery whenever possible (ie, whenever the tsquery is a constant), even when
no statistics are available for the tsvector. For example, foo @@ 'a &
b'::tsquery can be expected to be more selective than foo @@ 'a'::tsquery,
whether or not we know anything about foo. We use DEFAULT_TS_MATCH_SEL as
the assumed selectivity of individual query terms when no stats are
available, then combine the terms according to the query's AND/OR structure
as usual.
Per experimentation with Artur Dabrowski's example. (The fact that there
are no stats available in that example is a problem in itself, but
nonetheless tsmatchsel should be smarter about the case.)
Back-patch to 8.4 to keep all versions of tsmatchsel() in sync.
---
src/backend/tsearch/ts_selfuncs.c | 41 +++++++++++++++++++------------
1 file changed, 25 insertions(+), 16 deletions(-)
diff --git a/src/backend/tsearch/ts_selfuncs.c b/src/backend/tsearch/ts_selfuncs.c
index a22dba55e5e..68d67c7a4e6 100644
--- a/src/backend/tsearch/ts_selfuncs.c
+++ b/src/backend/tsearch/ts_selfuncs.c
@@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/tsearch/ts_selfuncs.c,v 1.7 2010/01/04 02:44:39 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/tsearch/ts_selfuncs.c,v 1.8 2010/07/31 03:27:40 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -52,6 +52,9 @@ static Selectivity tsquery_opr_selec(QueryItem *item, char *operand,
TextFreq *lookup, int length, float4 minfreq);
static int compare_lexeme_textfreq(const void *e1, const void *e2);
+#define tsquery_opr_selec_no_stats(query) \
+ tsquery_opr_selec(GETQUERY(query), GETOPERAND(query), NULL, 0, 0)
+
/*
* tsmatchsel -- Selectivity of "@@"
@@ -101,21 +104,20 @@ tsmatchsel(PG_FUNCTION_ARGS)
}
/*
- * OK, there's a Var and a Const we're dealing with here. We need the Var
- * to be a TSVector (or else we don't have any useful statistic for it).
- * We have to check this because the Var might be the TSQuery not the
- * TSVector.
+ * OK, there's a Var and a Const we're dealing with here. We need the
+ * Const to be a TSQuery, else we can't do anything useful. We have to
+ * check this because the Var might be the TSQuery not the TSVector.
*/
- if (vardata.vartype == TSVECTOROID)
+ if (((Const *) other)->consttype == TSQUERYOID)
{
/* tsvector @@ tsquery or the other way around */
- Assert(((Const *) other)->consttype == TSQUERYOID);
+ Assert(vardata.vartype == TSVECTOROID);
selec = tsquerysel(&vardata, ((Const *) other)->constvalue);
}
else
{
- /* The Var is something we don't have useful statistics for */
+ /* If we can't see the query structure, must punt */
selec = DEFAULT_TS_MATCH_SEL;
}
@@ -184,14 +186,14 @@ tsquerysel(VariableStatData *vardata, Datum constval)
}
else
{
- /* No most-common-elements info, so we must punt */
- selec = (Selectivity) DEFAULT_TS_MATCH_SEL;
+ /* No most-common-elements info, so do without */
+ selec = tsquery_opr_selec_no_stats(query);
}
}
else
{
- /* No stats at all, so we must punt */
- selec = (Selectivity) DEFAULT_TS_MATCH_SEL;
+ /* No stats at all, so do without */
+ selec = tsquery_opr_selec_no_stats(query);
}
return selec;
@@ -214,7 +216,7 @@ mcelem_tsquery_selec(TSQuery query, Datum *mcelem, int nmcelem,
* cells are taken for minimal and maximal frequency. Punt if not.
*/
if (nnumbers != nmcelem + 2)
- return DEFAULT_TS_MATCH_SEL;
+ return tsquery_opr_selec_no_stats(query);
/*
* Transpose the data into a single array so we can use bsearch().
@@ -258,9 +260,12 @@ mcelem_tsquery_selec(TSQuery query, Datum *mcelem, int nmcelem,
* freq[val] in VAL nodes, if the value is in MCELEM
* min(freq[MCELEM]) / 2 in VAL nodes, if it is not
*
- *
* The MCELEM array is already sorted (see ts_typanalyze.c), so we can use
* binary search for determining freq[MCELEM].
+ *
+ * If we don't have stats for the tsvector, we still use this logic,
+ * except we always use DEFAULT_TS_MATCH_SEL for VAL nodes. This case
+ * is signaled by lookup == NULL.
*/
static Selectivity
tsquery_opr_selec(QueryItem *item, char *operand,
@@ -279,6 +284,10 @@ tsquery_opr_selec(QueryItem *item, char *operand,
{
QueryOperand *oper = (QueryOperand *) item;
+ /* If no stats for the variable, use DEFAULT_TS_MATCH_SEL */
+ if (lookup == NULL)
+ return (Selectivity) DEFAULT_TS_MATCH_SEL;
+
/*
* Prepare the key for bsearch().
*/
@@ -292,7 +301,7 @@ tsquery_opr_selec(QueryItem *item, char *operand,
if (searchres)
{
/*
- * The element is in MCELEM. Return precise selectivity (or at
+ * The element is in MCELEM. Return precise selectivity (or at
* least as precise as ANALYZE could find out).
*/
return (Selectivity) searchres->frequency;
@@ -300,7 +309,7 @@ tsquery_opr_selec(QueryItem *item, char *operand,
else
{
/*
- * The element is not in MCELEM. Punt, but assert that the
+ * The element is not in MCELEM. Punt, but assume that the
* selectivity cannot be more than minfreq / 2.
*/
return (Selectivity) Min(DEFAULT_TS_MATCH_SEL, minfreq / 2);
--
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