Fix bug in parallel tidbitmap iteration.

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
index 44cc9daa03f25d1d2de8e06013e8165d5d832acb..8e915646d93a1a6a06875835033c121572de2424 100644 (file)
--- 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;