Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * ts_selfuncs.c
4 : * Selectivity estimation functions for text search operators.
5 : *
6 : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
7 : *
8 : *
9 : * IDENTIFICATION
10 : * src/backend/tsearch/ts_selfuncs.c
11 : *
12 : *-------------------------------------------------------------------------
13 : */
14 : #include "postgres.h"
15 :
16 : #include "access/htup_details.h"
17 : #include "catalog/pg_statistic.h"
18 : #include "catalog/pg_type.h"
19 : #include "miscadmin.h"
20 : #include "nodes/nodes.h"
21 : #include "tsearch/ts_type.h"
22 : #include "utils/fmgrprotos.h"
23 : #include "utils/lsyscache.h"
24 : #include "utils/selfuncs.h"
25 :
26 :
27 : /*
28 : * The default text search selectivity is chosen to be small enough to
29 : * encourage indexscans for typical table densities. See selfuncs.h and
30 : * DEFAULT_EQ_SEL for details.
31 : */
32 : #define DEFAULT_TS_MATCH_SEL 0.005
33 :
34 : /* lookup table type for binary searching through MCELEMs */
35 : typedef struct
36 : {
37 : text *element;
38 : float4 frequency;
39 : } TextFreq;
40 :
41 : /* type of keys for bsearch'ing through an array of TextFreqs */
42 : typedef struct
43 : {
44 : char *lexeme;
45 : int length;
46 : } LexemeKey;
47 :
48 : static Selectivity tsquerysel(VariableStatData *vardata, Datum constval);
49 : static Selectivity mcelem_tsquery_selec(TSQuery query,
50 : const Datum *mcelem, int nmcelem,
51 : const float4 *numbers, int nnumbers);
52 : static Selectivity tsquery_opr_selec(QueryItem *item, char *operand,
53 : TextFreq *lookup, int length, float4 minfreq);
54 : static int compare_lexeme_textfreq(const void *e1, const void *e2);
55 :
56 : #define tsquery_opr_selec_no_stats(query) \
57 : tsquery_opr_selec(GETQUERY(query), GETOPERAND(query), NULL, 0, 0)
58 :
59 :
60 : /*
61 : * tsmatchsel -- Selectivity of "@@"
62 : *
63 : * restriction selectivity function for tsvector @@ tsquery and
64 : * tsquery @@ tsvector
65 : */
66 : Datum
67 513 : tsmatchsel(PG_FUNCTION_ARGS)
68 : {
69 513 : PlannerInfo *root = (PlannerInfo *) PG_GETARG_POINTER(0);
70 :
71 : #ifdef NOT_USED
72 : Oid operator = PG_GETARG_OID(1);
73 : #endif
74 513 : List *args = (List *) PG_GETARG_POINTER(2);
75 513 : int varRelid = PG_GETARG_INT32(3);
76 : VariableStatData vardata;
77 : Node *other;
78 : bool varonleft;
79 : Selectivity selec;
80 :
81 : /*
82 : * If expression is not variable = something or something = variable, then
83 : * punt and return a default estimate.
84 : */
85 513 : if (!get_restriction_variable(root, args, varRelid,
86 : &vardata, &other, &varonleft))
87 0 : PG_RETURN_FLOAT8(DEFAULT_TS_MATCH_SEL);
88 :
89 : /*
90 : * Can't do anything useful if the something is not a constant, either.
91 : */
92 513 : if (!IsA(other, Const))
93 : {
94 0 : ReleaseVariableStats(vardata);
95 0 : PG_RETURN_FLOAT8(DEFAULT_TS_MATCH_SEL);
96 : }
97 :
98 : /*
99 : * The "@@" operator is strict, so we can cope with NULL right away
100 : */
101 513 : if (((Const *) other)->constisnull)
102 : {
103 0 : ReleaseVariableStats(vardata);
104 0 : PG_RETURN_FLOAT8(0.0);
105 : }
106 :
107 : /*
108 : * OK, there's a Var and a Const we're dealing with here. We need the
109 : * Const to be a TSQuery, else we can't do anything useful. We have to
110 : * check this because the Var might be the TSQuery not the TSVector.
111 : *
112 : * Also check that the Var really is a TSVector, in case this estimator is
113 : * mistakenly attached to some other operator.
114 : */
115 513 : if (((Const *) other)->consttype == TSQUERYOID &&
116 513 : vardata.vartype == TSVECTOROID)
117 : {
118 : /* tsvector @@ tsquery or the other way around */
119 513 : selec = tsquerysel(&vardata, ((Const *) other)->constvalue);
120 : }
121 : else
122 : {
123 : /* If we can't see the query structure, must punt */
124 0 : selec = DEFAULT_TS_MATCH_SEL;
125 : }
126 :
127 513 : ReleaseVariableStats(vardata);
128 :
129 513 : CLAMP_PROBABILITY(selec);
130 :
131 513 : PG_RETURN_FLOAT8((float8) selec);
132 : }
133 :
134 :
135 : /*
136 : * tsmatchjoinsel -- join selectivity of "@@"
137 : *
138 : * join selectivity function for tsvector @@ tsquery and tsquery @@ tsvector
139 : */
140 : Datum
141 0 : tsmatchjoinsel(PG_FUNCTION_ARGS)
142 : {
143 : /* for the moment we just punt */
144 0 : PG_RETURN_FLOAT8(DEFAULT_TS_MATCH_SEL);
145 : }
146 :
147 :
148 : /*
149 : * @@ selectivity for tsvector var vs tsquery constant
150 : */
151 : static Selectivity
152 513 : tsquerysel(VariableStatData *vardata, Datum constval)
153 : {
154 : Selectivity selec;
155 : TSQuery query;
156 :
157 : /* The caller made sure the const is a TSQuery, so get it now */
158 513 : query = DatumGetTSQuery(constval);
159 :
160 : /* Empty query matches nothing */
161 513 : if (query->size == 0)
162 0 : return (Selectivity) 0.0;
163 :
164 513 : if (HeapTupleIsValid(vardata->statsTuple))
165 : {
166 : Form_pg_statistic stats;
167 : AttStatsSlot sslot;
168 :
169 495 : stats = (Form_pg_statistic) GETSTRUCT(vardata->statsTuple);
170 :
171 : /* MCELEM will be an array of TEXT elements for a tsvector column */
172 495 : if (get_attstatsslot(&sslot, vardata->statsTuple,
173 : STATISTIC_KIND_MCELEM, InvalidOid,
174 : ATTSTATSSLOT_VALUES | ATTSTATSSLOT_NUMBERS))
175 : {
176 : /*
177 : * There is a most-common-elements slot for the tsvector Var, so
178 : * use that.
179 : */
180 495 : selec = mcelem_tsquery_selec(query, sslot.values, sslot.nvalues,
181 495 : sslot.numbers, sslot.nnumbers);
182 495 : free_attstatsslot(&sslot);
183 : }
184 : else
185 : {
186 : /* No most-common-elements info, so do without */
187 0 : selec = tsquery_opr_selec_no_stats(query);
188 : }
189 :
190 : /*
191 : * MCE stats count only non-null rows, so adjust for null rows.
192 : */
193 495 : selec *= (1.0 - stats->stanullfrac);
194 : }
195 : else
196 : {
197 : /* No stats at all, so do without */
198 18 : selec = tsquery_opr_selec_no_stats(query);
199 : /* we assume no nulls here, so no stanullfrac correction */
200 : }
201 :
202 513 : return selec;
203 : }
204 :
205 : /*
206 : * Extract data from the pg_statistic arrays into useful format.
207 : */
208 : static Selectivity
209 495 : mcelem_tsquery_selec(TSQuery query, const Datum *mcelem, int nmcelem,
210 : const float4 *numbers, int nnumbers)
211 : {
212 : float4 minfreq;
213 : TextFreq *lookup;
214 : Selectivity selec;
215 : int i;
216 :
217 : /*
218 : * There should be two more Numbers than Values, because the last two
219 : * cells are taken for minimal and maximal frequency. Punt if not.
220 : *
221 : * (Note: the MCELEM statistics slot definition allows for a third extra
222 : * number containing the frequency of nulls, but we're not expecting that
223 : * to appear for a tsvector column.)
224 : */
225 495 : if (nnumbers != nmcelem + 2)
226 0 : return tsquery_opr_selec_no_stats(query);
227 :
228 : /*
229 : * Transpose the data into a single array so we can use bsearch().
230 : */
231 495 : lookup = palloc_array(TextFreq, nmcelem);
232 495495 : for (i = 0; i < nmcelem; i++)
233 : {
234 : /*
235 : * The text Datums came from an array, so it cannot be compressed or
236 : * stored out-of-line -- it's safe to use VARSIZE_ANY*.
237 : */
238 : Assert(!VARATT_IS_COMPRESSED(DatumGetPointer(mcelem[i])) && !VARATT_IS_EXTERNAL(DatumGetPointer(mcelem[i])));
239 495000 : lookup[i].element = (text *) DatumGetPointer(mcelem[i]);
240 495000 : lookup[i].frequency = numbers[i];
241 : }
242 :
243 : /*
244 : * Grab the lowest MCE frequency. compute_tsvector_stats() stored it for
245 : * us in the one before the last cell of the Numbers array.
246 : */
247 495 : minfreq = numbers[nnumbers - 2];
248 :
249 495 : selec = tsquery_opr_selec(GETQUERY(query), GETOPERAND(query), lookup,
250 : nmcelem, minfreq);
251 :
252 495 : pfree(lookup);
253 :
254 495 : return selec;
255 : }
256 :
257 : /*
258 : * Traverse the tsquery in preorder, calculating selectivity as:
259 : *
260 : * selec(left_oper) * selec(right_oper) in AND & PHRASE nodes,
261 : *
262 : * selec(left_oper) + selec(right_oper) -
263 : * selec(left_oper) * selec(right_oper) in OR nodes,
264 : *
265 : * 1 - select(oper) in NOT nodes
266 : *
267 : * histogram-based estimation in prefix VAL nodes
268 : *
269 : * freq[val] in exact VAL nodes, if the value is in MCELEM
270 : * min(freq[MCELEM]) / 2 in VAL nodes, if it is not
271 : *
272 : * The MCELEM array is already sorted (see ts_typanalyze.c), so we can use
273 : * binary search for determining freq[MCELEM].
274 : *
275 : * If we don't have stats for the tsvector, we still use this logic,
276 : * except we use default estimates for VAL nodes. This case is signaled
277 : * by lookup == NULL.
278 : */
279 : static Selectivity
280 1539 : tsquery_opr_selec(QueryItem *item, char *operand,
281 : TextFreq *lookup, int length, float4 minfreq)
282 : {
283 : Selectivity selec;
284 :
285 : /* since this function recurses, it could be driven to stack overflow */
286 1539 : check_stack_depth();
287 :
288 1539 : if (item->type == QI_VAL)
289 : {
290 921 : QueryOperand *oper = (QueryOperand *) item;
291 : LexemeKey key;
292 :
293 : /*
294 : * Prepare the key for bsearch().
295 : */
296 921 : key.lexeme = operand + oper->distance;
297 921 : key.length = oper->length;
298 :
299 921 : if (oper->prefix)
300 : {
301 : /* Prefix match, ie the query item is lexeme:* */
302 : Selectivity matched,
303 : allmces;
304 : int i,
305 : n_matched;
306 :
307 : /*
308 : * Our strategy is to scan through the MCELEM list and combine the
309 : * frequencies of the ones that match the prefix. We then
310 : * extrapolate the fraction of matching MCELEMs to the remaining
311 : * rows, assuming that the MCELEMs are representative of the whole
312 : * lexeme population in this respect. (Compare
313 : * histogram_selectivity().) Note that these are most common
314 : * elements not most common values, so they're not mutually
315 : * exclusive. We treat occurrences as independent events.
316 : *
317 : * This is only a good plan if we have a pretty fair number of
318 : * MCELEMs available; we set the threshold at 100. If no stats or
319 : * insufficient stats, arbitrarily use DEFAULT_TS_MATCH_SEL*4.
320 : */
321 51 : if (lookup == NULL || length < 100)
322 21 : return (Selectivity) (DEFAULT_TS_MATCH_SEL * 4);
323 :
324 36 : matched = allmces = 0;
325 36 : n_matched = 0;
326 36036 : for (i = 0; i < length; i++)
327 : {
328 36000 : TextFreq *t = lookup + i;
329 36000 : int tlen = VARSIZE_ANY_EXHDR(t->element);
330 :
331 36000 : if (tlen >= key.length &&
332 36000 : strncmp(key.lexeme, VARDATA_ANY(t->element),
333 36000 : key.length) == 0)
334 : {
335 1296 : matched += t->frequency - matched * t->frequency;
336 1296 : n_matched++;
337 : }
338 36000 : allmces += t->frequency - allmces * t->frequency;
339 : }
340 :
341 : /* Clamp to ensure sanity in the face of roundoff error */
342 36 : CLAMP_PROBABILITY(matched);
343 36 : CLAMP_PROBABILITY(allmces);
344 :
345 36 : selec = matched + (1.0 - allmces) * ((double) n_matched / length);
346 :
347 : /*
348 : * In any case, never believe that a prefix match has selectivity
349 : * less than we would assign for a non-MCELEM lexeme. This
350 : * preserves the property that "word:*" should be estimated to
351 : * match at least as many rows as "word" would be.
352 : */
353 36 : selec = Max(Min(DEFAULT_TS_MATCH_SEL, minfreq / 2), selec);
354 : }
355 : else
356 : {
357 : /* Regular exact lexeme match */
358 : TextFreq *searchres;
359 :
360 : /* If no stats for the variable, use DEFAULT_TS_MATCH_SEL */
361 870 : if (lookup == NULL)
362 6 : return (Selectivity) DEFAULT_TS_MATCH_SEL;
363 :
364 864 : searchres = (TextFreq *) bsearch(&key, lookup, length,
365 : sizeof(TextFreq),
366 : compare_lexeme_textfreq);
367 :
368 864 : if (searchres)
369 : {
370 : /*
371 : * The element is in MCELEM. Return precise selectivity (or
372 : * at least as precise as ANALYZE could find out).
373 : */
374 804 : selec = searchres->frequency;
375 : }
376 : else
377 : {
378 : /*
379 : * The element is not in MCELEM. Estimate its frequency as
380 : * half that of the least-frequent MCE. (We know it cannot be
381 : * more than minfreq, and it could be a great deal less. Half
382 : * seems like a good compromise.) For probably-historical
383 : * reasons, clamp to not more than DEFAULT_TS_MATCH_SEL.
384 : */
385 60 : selec = Min(DEFAULT_TS_MATCH_SEL, minfreq / 2);
386 : }
387 : }
388 : }
389 : else
390 : {
391 : /* Current TSQuery node is an operator */
392 : Selectivity s1,
393 : s2;
394 :
395 618 : switch (item->qoperator.oper)
396 : {
397 210 : case OP_NOT:
398 210 : selec = 1.0 - tsquery_opr_selec(item + 1, operand,
399 : lookup, length, minfreq);
400 210 : break;
401 :
402 285 : case OP_PHRASE:
403 : case OP_AND:
404 285 : s1 = tsquery_opr_selec(item + 1, operand,
405 : lookup, length, minfreq);
406 285 : s2 = tsquery_opr_selec(item + item->qoperator.left, operand,
407 : lookup, length, minfreq);
408 285 : selec = s1 * s2;
409 285 : break;
410 :
411 123 : case OP_OR:
412 123 : s1 = tsquery_opr_selec(item + 1, operand,
413 : lookup, length, minfreq);
414 123 : s2 = tsquery_opr_selec(item + item->qoperator.left, operand,
415 : lookup, length, minfreq);
416 123 : selec = s1 + s2 - s1 * s2;
417 123 : break;
418 :
419 0 : default:
420 0 : elog(ERROR, "unrecognized operator: %d", item->qoperator.oper);
421 : selec = 0; /* keep compiler quiet */
422 : break;
423 : }
424 : }
425 :
426 : /* Clamp intermediate results to stay sane despite roundoff error */
427 1518 : CLAMP_PROBABILITY(selec);
428 :
429 1518 : return selec;
430 : }
431 :
432 : /*
433 : * bsearch() comparator for a lexeme (non-NULL terminated string with length)
434 : * and a TextFreq. Use length, then byte-for-byte comparison, because that's
435 : * how ANALYZE code sorted data before storing it in a statistic tuple.
436 : * See ts_typanalyze.c for details.
437 : */
438 : static int
439 6672 : compare_lexeme_textfreq(const void *e1, const void *e2)
440 : {
441 6672 : const LexemeKey *key = (const LexemeKey *) e1;
442 6672 : const TextFreq *t = (const TextFreq *) e2;
443 : int len1,
444 : len2;
445 :
446 6672 : len1 = key->length;
447 6672 : len2 = VARSIZE_ANY_EXHDR(t->element);
448 :
449 : /* Compare lengths first, possibly avoiding a strncmp call */
450 6672 : if (len1 > len2)
451 540 : return 1;
452 6132 : else if (len1 < len2)
453 0 : return -1;
454 :
455 : /* Fall back on byte-for-byte comparison */
456 6132 : return strncmp(key->lexeme, VARDATA_ANY(t->element), len1);
457 : }
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