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Commit80fb2c1

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Repair memory leakage while ANALYZE-ing complex index expressions.
The general design of memory management in Postgres is that intermediateresults computed by an expression are not freed until the end of the tuplecycle. For expression indexes, ANALYZE has to re-evaluate each expressionfor each of its sample rows, and it wasn't bothering to free intermediateresults until the end of processing of that index. This could lead to verysubstantial leakage if the intermediate results were large, as in a recentexample from Jakub Ouhrabka. Fix by doing ResetExprContext for each samplerow. This necessitates adding a datumCopy step to ensure that the finalexpression value isn't recycled too. Some quick testing suggests that thischange adds at worst about 10% to the time needed to analyze a table withan expression index; which is annoying, but seems a tolerable price to payto avoid unexpected out-of-memory problems.Back-patch to all supported branches.
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‎src/backend/commands/analyze.c

Lines changed: 20 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -695,6 +695,12 @@ compute_index_stats(Relation onerel, double totalrows,
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{
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HeapTupleheapTuple=rows[rowno];
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/*
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* Reset the per-tuple context each time, to reclaim any cruft
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* left behind by evaluating the predicate or index expressions.
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*/
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ResetExprContext(econtext);
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/* Set up for predicate or expression evaluation */
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ExecStoreTuple(heapTuple,slot,InvalidBuffer, false);
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@@ -719,15 +725,26 @@ compute_index_stats(Relation onerel, double totalrows,
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isnull);
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/*
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* Save just the columns we care about.
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* Save just the columns we care about. We copy the values
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* into ind_context from the estate's per-tuple context.
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*/
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for (i=0;i<attr_cnt;i++)
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{
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VacAttrStats*stats=thisdata->vacattrstats[i];
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intattnum=stats->attr->attnum;
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729-
exprvals[tcnt]=values[attnum-1];
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exprnulls[tcnt]=isnull[attnum-1];
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if (isnull[attnum-1])
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{
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exprvals[tcnt]= (Datum)0;
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exprnulls[tcnt]= true;
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}
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else
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{
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exprvals[tcnt]=datumCopy(values[attnum-1],
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stats->attrtype->typbyval,
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stats->attrtype->typlen);
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exprnulls[tcnt]= false;
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}
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tcnt++;
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}
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}

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