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Commit410bed2

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Improve GiST index search performance for trigram regex queries.
The initial coding just descended the index if any of the target trigramswere possibly present at the next level down. But actually we can applytrigramsMatchGraph() so as to take advantage of AND requirements when thereare some. The input data might contain false positive matches, but thatcan only result in a false positive result, not false negative, so it'ssafe to do it this way.Alexander Korotkov
1 parente08fdf1 commit410bed2

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+13
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1 file changed

+13
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‎contrib/pg_trgm/trgm_gist.c

Lines changed: 13 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -401,18 +401,24 @@ gtrgm_consistent(PG_FUNCTION_ARGS)
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len=ARRNELEM(qtrg);
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trgm*ptr=GETARR(qtrg);
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BITVECPsign=GETSIGN(key);
404+
bool*check;
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405-
/* descend only if at least one trigram is present */
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res= false;
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/*
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* GETBIT() tests may give false positives, due to limited
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* size of the sign array.But since trigramsMatchGraph()
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* implements a monotone boolean function, false positives
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* in the check array can't lead to false negative answer.
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* So we can apply trigramsMatchGraph despite uncertainty,
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* and that usefully improves the quality of the search.
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*/
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check= (bool*)palloc(len*sizeof(bool));
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for (k=0;k<len;k++)
408416
{
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CPTRGM(((char*)&tmp),ptr+k);
410-
if (GETBIT(sign,HASHVAL(tmp)))
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{
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res= true;
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break;
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}
418+
check[k]=GETBIT(sign,HASHVAL(tmp));
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}
420+
res=trigramsMatchGraph(cache->graph,check);
421+
pfree(check);
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}
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}
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else

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