Re: Parallel Seq Scan

On Wed, Sep 30, 2015 at 7:05 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Thu, Sep 24, 2015 at 2:31 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
wrote:
> > [ parallel_seqscan_partialseqscan_v18.patch ]
>
> I spent a bit of time reviewing the heapam.c changes in this patch
> this evening, and I think that your attempt to add support for
> synchronized scans has some problems.
>

Thanks for the review and I agree with all the suggestions provided
by you. Fixed all of them in attached patch
(parallel_seqscan_heapscan_v1.patch).

I have rebased partial seq scan patch (as attached with this mail) to
test synchronized scan and parallelheapscan patch. Also I have added
Log (parallel_seqscan_heapscan_test_v1.patch) to see the start positions
during synchronized parallel heap scans. I have done various tests
with parallel scans and found that it works fine for sync scans as well
as without sync scan.

Basic test to verify the patch:
CREATE TABLE t1(c1, c2) AS SELECT g, repeat('x', 5) FROM
generate_series(1, 10000000) g;

CREATE TABLE t2(c1, c2) AS SELECT g, repeat('x', 5) FROM
generate_series(1, 1000000) g;

set parallel_tuple_cost=0.001

set max_parallel_degree=2;

set parallel_setup_cost=0;

SELECT count(*) FROM t1 JOIN t2 ON t1.c1 = t2.c1 AND t1.c1 BETWEEN 100 AND
200;

Run the above Select query from multiple clients and notice start scan
positions and Results of the query. It returns the expected results
(Count as 101 rows).

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com