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Tweak tsmatchsel() so that it examines the structure of the tsquery whenever

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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.
This commit is contained in:
Tom Lane 2010-07-31 03:27:40 +00:00
parent 2ab57e089b
commit b8c798ebc5
1 changed files with 25 additions and 16 deletions
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39
src/backend/tsearch/ts_selfuncs.c
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@ -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().
*/
@ -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);