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Commitfb0f5f0

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Fix memory leak when de-toasting compressed values in VACUUM FULL/CLUSTER
VACUUM FULL and CLUSTER can be used to enforce the use of the existingcompression method of a toastable column if a value currently stored iscompressed with a method that does not match the column's definedmethod. The code in charge of decompressing and recompressing toastvalues at rewrite left around the detoasted values, causing anaccumulation of memory allocated in TopTransactionContext.When processing large relations, this could cause the system to run outof memory. The detoasted values are not needed once their tuple isrewritten, and this commit ensures that the necessary cleanup happens.Issue introduced bybbe0a81. The comments of the area are reordered abit while on it.Reported-by: Andres FreundAnalyzed-by: Andres FreundAuthor: Michael PaquierReviewed-by: Dilip KumarDiscussion:https://postgr.es/m/20210521211929.pcehg6f23icwstdb@alap3.anarazel.de
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‎src/backend/access/heap/heapam_handler.c

Lines changed: 22 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -2463,24 +2463,27 @@ reform_and_rewrite_tuple(HeapTuple tuple,
24632463
TupleDescnewTupDesc=RelationGetDescr(NewHeap);
24642464
HeapTuplecopiedTuple;
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inti;
2466+
boolvalues_free[MaxTupleAttributeNumber];
2467+
2468+
memset(values_free,0,newTupDesc->natts*sizeof(bool));
24662469

24672470
heap_deform_tuple(tuple,oldTupDesc,values,isnull);
24682471

2469-
/* Be sure to null out any dropped columns */
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for (i=0;i<newTupDesc->natts;i++)
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{
2474+
/* Be sure to null out any dropped columns */
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if (TupleDescAttr(newTupDesc,i)->attisdropped)
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isnull[i]= true;
2474-
2475-
/*
2476-
* Use this opportunity to force recompression of any data that's
2477-
* compressed with some TOAST compression method other than the one
2478-
* configured for the column. We don't actually need to perform the
2479-
* compression here; we just need to decompress. That will trigger
2480-
* recompression later on.
2481-
*/
24822477
elseif (!isnull[i]&&TupleDescAttr(newTupDesc,i)->attlen==-1)
24832478
{
2479+
/*
2480+
* Use this opportunity to force recompression of any data that's
2481+
* compressed with some TOAST compression method other than the
2482+
* one configured for the column. We don't actually need to
2483+
* perform the compression here; we just need to decompress. That
2484+
* will trigger recompression later on.
2485+
*/
2486+
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structvarlena*new_value;
24852488
ToastCompressionIdcmid;
24862489
charcmethod;
@@ -2507,7 +2510,10 @@ reform_and_rewrite_tuple(HeapTuple tuple,
25072510

25082511
/* if compression method doesn't match then detoast the value */
25092512
if (TupleDescAttr(newTupDesc,i)->attcompression!=cmethod)
2513+
{
25102514
values[i]=PointerGetDatum(detoast_attr(new_value));
2515+
values_free[i]= true;
2516+
}
25112517
}
25122518
}
25132519

@@ -2516,6 +2522,13 @@ reform_and_rewrite_tuple(HeapTuple tuple,
25162522
/* The heap rewrite module does the rest */
25172523
rewrite_heap_tuple(rwstate,tuple,copiedTuple);
25182524

2525+
/* Free any value detoasted previously */
2526+
for (i=0;i<newTupDesc->natts;i++)
2527+
{
2528+
if (values_free[i])
2529+
pfree(DatumGetPointer(values[i]));
2530+
}
2531+
25192532
heap_freetuple(copiedTuple);
25202533
}
25212534

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