Fix bug in parallel tidbitmap iteration.

robertmhaas · robertmhaas · commit 6a468c343b31 · 2017-03-09T12:13:48.000-05:00
Avoid computing idxpages[istate->spageptr] until after checking that istate->spageptr is a legal index. Dilip Kumar, per a report from David Rowley Discussion: http://postgr.es/m/CAKJS1f8OtrHE+-P+=E=4ycnL29e9idZKuaTQ6o2MbhvGN9D8ig@mail.gmail.com
diff --git a/src/backend/nodes/tidbitmap.c b/src/backend/nodes/tidbitmap.c
@@ -1103,13 +1103,12 @@ tbm_shared_iterate(TBMSharedIterator *iterator)
 	if (istate->schunkptr < istate->nchunks)
 	{
 		PagetableEntry *chunk = &ptbase[idxchunks[istate->schunkptr]];
-		PagetableEntry *page = &ptbase[idxpages[istate->spageptr]];
 		BlockNumber chunk_blockno;
 
 		chunk_blockno = chunk->blockno + istate->schunkbit;
 
 		if (istate->spageptr >= istate->npages ||
-			chunk_blockno < page->blockno)
+			chunk_blockno < ptbase[idxpages[istate->spageptr]].blockno)
 		{
 			/* Return a lossy page indicator from the chunk */
 			output->blockno = chunk_blockno;

Original file line number	Diff line number	Diff line change
`@@ -1103,13 +1103,12 @@ tbm_shared_iterate(TBMSharedIterator *iterator)`
`1103`	`1103`	`if (istate->schunkptr < istate->nchunks)`
`1104`	`1104`	`{`
`1105`	`1105`	`PagetableEntry *chunk = &ptbase[idxchunks[istate->schunkptr]];`
`1106`		`- PagetableEntry *page = &ptbase[idxpages[istate->spageptr]];`
`1107`	`1106`	`BlockNumber chunk_blockno;`
`1108`	`1107`
`1109`	`1108`	`chunk_blockno = chunk->blockno + istate->schunkbit;`
`1110`	`1109`
`1111`	`1110`	`if (istate->spageptr >= istate->npages \|\|`
`1112`		`- chunk_blockno < page->blockno)`
	`1111`	`+ chunk_blockno < ptbase[idxpages[istate->spageptr]].blockno)`
`1113`	`1112`	`{`
`1114`	`1113`	`/* Return a lossy page indicator from the chunk */`
`1115`	`1114`	`output->blockno = chunk_blockno;`