Re: Performance Issue after upgrade from 9 to 11

On 1/29/20 1:58 PM, Perumal Raj wrote:
> Hi Tom /Adrian,
>
> Issue is not specific to a table or particular Query. Also there is no
> change in DB parameter after upgrade.

You obviously are seeing some difference, so pick a query and do an
EXPLAIN ANALYZE on it. Without some actual performance data this issue
is not going to be solved.

>
> That the only way i can make it most of the the query to run as like
> before upgrade.
>
> Note:
> Some web reference says , Engine will take some time to adjust until it
> runs autovacuum .

The above assumes you have not done a manual ANALYZE on the database, as
ANALYZE is done as part of autovacuum.

>
>
>
>
> On Wed, Jan 29, 2020 at 10:22 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us
> <mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us>> wrote:
>
> Perumal Raj <perucinci(at)gmail(dot)com <mailto:perucinci(at)gmail(dot)com>> writes:
> > We have recently upgraded postgres from 9.2 to 11.6 and started
> seeing
> > performance issue immediately and  able to fix the performance
> issue after
> > disabling parameter: enable_seqscan.
> > Question :
> > Should i keep the above parameter always disabled ? If not why
> the behavior
> > changed in Higher version ?
>
> This is unanswerable with the amount of information you've given.
> Yes, turning off enable_seqscan is a bad idea in general, but why
> you got a worse plan without that requires details.
>
> https://wiki.postgresql.org/wiki/Slow_Query_Questions
>
>                         regards, tom lane
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com