Re: Parallel Seq Scan

On Mon, Oct 5, 2015 at 11:20 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> For now, I have fixed this by not preserving the startblock incase of rescan
> for parallel scan. Note that, I have created a separate patch
> (parallel_seqscan_heaprescan_v1.patch) for support of rescan (for parallel
> scan).

while testing parallel seqscan, My colleague Jing Wang has found a problem in
parallel_seqscan_heapscan_v2.patch.

In function initscan, the allow_sync flag is set to false as the
number of pages in the
table are less than NBuffers/4.

if (!RelationUsesLocalBuffers(scan->rs_rd) &&
scan->rs_nblocks > NBuffers / 4)

As allow_sync flag is false, the function
heap_parallelscan_initialize_startblock is not
called in initscan function to initialize the
parallel_scan->phs_cblock parameter. Because
of this reason while getting the next page in
heap_parallelscan_nextpage, it returns
InvalidBlockNumber, thus it ends the scan without returning the results.

Regards,
Hari Babu
Fujitsu Australia