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author | Tom Lane <tgl@sss.pgh.pa.us> | 2008-09-19 19:03:41 +0000 |
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committer | Tom Lane <tgl@sss.pgh.pa.us> | 2008-09-19 19:03:41 +0000 |
commit | 4e57668da475f47242d8552df371a3dbef5205f8 (patch) | |
tree | e57955d9d4e771ce6a2412651e98a060044d9d37 /src/backend/tsearch/ts_selfuncs.c | |
parent | e2b7d0c65c611ae3044eb3a49ada71aa22cbca80 (diff) | |
download | postgresql-4e57668da475f47242d8552df371a3dbef5205f8.tar.gz |
Create a selectivity estimation function for the text search @@ operator.
Jan Urbanski
Diffstat (limited to 'src/backend/tsearch/ts_selfuncs.c')
-rw-r--r-- | src/backend/tsearch/ts_selfuncs.c | 363 |
1 files changed, 363 insertions, 0 deletions
diff --git a/src/backend/tsearch/ts_selfuncs.c b/src/backend/tsearch/ts_selfuncs.c new file mode 100644 index 0000000000..abd62dfa4e --- /dev/null +++ b/src/backend/tsearch/ts_selfuncs.c @@ -0,0 +1,363 @@ +/*------------------------------------------------------------------------- + * + * ts_selfuncs.c + * Selectivity estimation functions for text search operators. + * + * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group + * + * + * IDENTIFICATION + * $PostgreSQL: pgsql/src/backend/tsearch/ts_selfuncs.c,v 1.1 2008/09/19 19:03:40 tgl Exp $ + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include "catalog/pg_statistic.h" +#include "catalog/pg_type.h" +#include "miscadmin.h" +#include "nodes/nodes.h" +#include "tsearch/ts_type.h" +#include "utils/lsyscache.h" +#include "utils/selfuncs.h" +#include "utils/syscache.h" + + +/* + * The default text search selectivity is chosen to be small enough to + * encourage indexscans for typical table densities. See selfuncs.h and + * DEFAULT_EQ_SEL for details. + */ +#define DEFAULT_TS_MATCH_SEL 0.005 + +/* lookup table type for binary searching through MCELEMs */ +typedef struct +{ + text *element; + float4 frequency; +} TextFreq; + +/* type of keys for bsearch'ing through an array of TextFreqs */ +typedef struct +{ + char *lexeme; + int length; +} LexemeKey; + +static Selectivity tsquerysel(VariableStatData *vardata, Datum constval); +static Selectivity mcelem_tsquery_selec(TSQuery query, + Datum *mcelem, int nmcelem, + float4 *numbers, int nnumbers); +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); + + +/* + * tsmatchsel -- Selectivity of "@@" + * + * restriction selectivity function for tsvector @@ tsquery and + * tsquery @@ tsvector + */ +Datum +tsmatchsel(PG_FUNCTION_ARGS) +{ + PlannerInfo *root = (PlannerInfo *) PG_GETARG_POINTER(0); +#ifdef NOT_USED + Oid operator = PG_GETARG_OID(1); +#endif + List *args = (List *) PG_GETARG_POINTER(2); + int varRelid = PG_GETARG_INT32(3); + VariableStatData vardata; + Node *other; + bool varonleft; + Selectivity selec; + + /* + * If expression is not variable = something or something = variable, then + * punt and return a default estimate. + */ + if (!get_restriction_variable(root, args, varRelid, + &vardata, &other, &varonleft)) + PG_RETURN_FLOAT8(DEFAULT_TS_MATCH_SEL); + + /* + * Can't do anything useful if the something is not a constant, either. + */ + if (!IsA(other, Const)) + { + ReleaseVariableStats(vardata); + PG_RETURN_FLOAT8(DEFAULT_TS_MATCH_SEL); + } + + /* + * The "@@" operator is strict, so we can cope with NULL right away + */ + if (((Const *) other)->constisnull) + { + ReleaseVariableStats(vardata); + PG_RETURN_FLOAT8(0.0); + } + + /* + * 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. + */ + if (vardata.vartype == TSVECTOROID) + { + /* tsvector @@ tsquery or the other way around */ + Assert(((Const *) other)->consttype == TSQUERYOID); + + selec = tsquerysel(&vardata, ((Const *) other)->constvalue); + } + else + { + /* The Var is something we don't have useful statistics for */ + selec = DEFAULT_TS_MATCH_SEL; + } + + ReleaseVariableStats(vardata); + + CLAMP_PROBABILITY(selec); + + PG_RETURN_FLOAT8((float8) selec); +} + + +/* + * tsmatchjoinsel -- join selectivity of "@@" + * + * join selectivity function for tsvector @@ tsquery and tsquery @@ tsvector + */ +Datum +tsmatchjoinsel(PG_FUNCTION_ARGS) +{ + /* for the moment we just punt */ + PG_RETURN_FLOAT8(DEFAULT_TS_MATCH_SEL); +} + + +/* + * @@ selectivity for tsvector var vs tsquery constant + */ +static Selectivity +tsquerysel(VariableStatData *vardata, Datum constval) +{ + Selectivity selec; + + if (HeapTupleIsValid(vardata->statsTuple)) + { + TSQuery query; + Form_pg_statistic stats; + Datum *values; + int nvalues; + float4 *numbers; + int nnumbers; + + /* The caller made sure the const is a TSQuery, so get it now */ + query = DatumGetTSQuery(constval); + + stats = (Form_pg_statistic) GETSTRUCT(vardata->statsTuple); + + /* MCELEM will be an array of TEXT elements for a tsvector column */ + if (get_attstatsslot(vardata->statsTuple, + TEXTOID, -1, + STATISTIC_KIND_MCELEM, InvalidOid, + &values, &nvalues, + &numbers, &nnumbers)) + { + /* + * There is a most-common-elements slot for the tsvector Var, so + * use that. + */ + selec = mcelem_tsquery_selec(query, values, nvalues, + numbers, nnumbers); + free_attstatsslot(TEXTOID, values, nvalues, numbers, nnumbers); + } + else + { + /* No most-common-elements info, so we must punt */ + selec = (Selectivity) DEFAULT_TS_MATCH_SEL; + } + } + else + { + /* No stats at all, so we must punt */ + selec = (Selectivity) DEFAULT_TS_MATCH_SEL; + } + + return selec; +} + +/* + * Extract data from the pg_statistic arrays into useful format. + */ +static Selectivity +mcelem_tsquery_selec(TSQuery query, Datum *mcelem, int nmcelem, + float4 *numbers, int nnumbers) +{ + float4 minfreq; + TextFreq *lookup; + Selectivity selec; + int i; + + /* + * There should be two more Numbers than Values, because the last two + * cells are taken for minimal and maximal frequency. Punt if not. + */ + if (nnumbers != nmcelem + 2) + return DEFAULT_TS_MATCH_SEL; + + /* + * Transpose the data into a single array so we can use bsearch(). + */ + lookup = (TextFreq *) palloc(sizeof(TextFreq) * nmcelem); + for (i = 0; i < nmcelem; i++) + { + /* + * The text Datums came from an array, so it cannot be compressed + * or stored out-of-line -- it's safe to use VARSIZE_ANY*. + */ + Assert(!VARATT_IS_COMPRESSED(mcelem[i]) && !VARATT_IS_EXTERNAL(mcelem[i])); + lookup[i].element = (text *) DatumGetPointer(mcelem[i]); + lookup[i].frequency = numbers[i]; + } + + /* + * Grab the lowest frequency. compute_tsvector_stats() stored it for us in + * the one before the last cell of the Numbers array. See ts_typanalyze.c + */ + minfreq = numbers[nnumbers - 2]; + + selec = tsquery_opr_selec(GETQUERY(query), GETOPERAND(query), lookup, + nmcelem, minfreq); + + pfree(lookup); + + return selec; +} + +/* + * Traverse the tsquery in preorder, calculating selectivity as: + * + * selec(left_oper) * selec(right_oper) in AND nodes, + * + * selec(left_oper) + selec(right_oper) - + * selec(left_oper) * selec(right_oper) in OR nodes, + * + * 1 - select(oper) in NOT nodes + * + * 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]. + */ +static Selectivity +tsquery_opr_selec(QueryItem *item, char *operand, + TextFreq *lookup, int length, float4 minfreq) +{ + LexemeKey key; + TextFreq *searchres; + Selectivity selec, s1, s2; + + /* since this function recurses, it could be driven to stack overflow */ + check_stack_depth(); + + if (item->type == QI_VAL) + { + QueryOperand *oper = (QueryOperand *) item; + + /* + * Prepare the key for bsearch(). + */ + key.lexeme = operand + oper->distance; + key.length = oper->length; + + searchres = (TextFreq *) bsearch(&key, lookup, length, + sizeof(TextFreq), + compare_lexeme_textfreq); + + if (searchres) + { + /* + * The element is in MCELEM. Return precise selectivity (or at + * least as precise as ANALYZE could find out). + */ + return (Selectivity) searchres->frequency; + } + else + { + /* + * The element is not in MCELEM. Punt, but assert that the + * selectivity cannot be more than minfreq / 2. + */ + return (Selectivity) Min(DEFAULT_TS_MATCH_SEL, minfreq / 2); + } + } + + /* Current TSQuery node is an operator */ + switch (item->operator.oper) + { + case OP_NOT: + selec = 1.0 - tsquery_opr_selec(item + 1, operand, + lookup, length, minfreq); + break; + + case OP_AND: + s1 = tsquery_opr_selec(item + 1, operand, + lookup, length, minfreq); + s2 = tsquery_opr_selec(item + item->operator.left, operand, + lookup, length, minfreq); + selec = s1 * s2; + break; + + case OP_OR: + s1 = tsquery_opr_selec(item + 1, operand, + lookup, length, minfreq); + s2 = tsquery_opr_selec(item + item->operator.left, operand, + lookup, length, minfreq); + selec = s1 + s2 - s1 * s2; + break; + + default: + elog(ERROR, "unrecognized operator: %d", item->operator.oper); + selec = 0; /* keep compiler quiet */ + break; + } + + /* Clamp intermediate results to stay sane despite roundoff error */ + CLAMP_PROBABILITY(selec); + + return selec; +} + +/* + * bsearch() comparator for a lexeme (non-NULL terminated string with length) + * and a TextFreq. Use length, then byte-for-byte comparison, because that's + * how ANALYZE code sorted data before storing it in a statistic tuple. + * See ts_typanalyze.c for details. + */ +static int +compare_lexeme_textfreq(const void *e1, const void *e2) +{ + const LexemeKey *key = (const LexemeKey *) e1; + const TextFreq *t = (const TextFreq *) e2; + int len1, + len2; + + len1 = key->length; + len2 = VARSIZE_ANY_EXHDR(t->element); + + /* Compare lengths first, possibly avoiding a strncmp call */ + if (len1 > len2) + return 1; + else if (len1 < len2) + return -1; + + /* Fall back on byte-for-byte comparison */ + return strncmp(key->lexeme, VARDATA_ANY(t->element), len1); +} |