Re: [PATCH] postgres_fdw connection caching - cause remote sessions linger till the local session exit

On Fri, Jan 29, 2021 at 1:52 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> writes:
> > On Tue, Jan 26, 2021 at 1:55 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
> >> Thanks for the patch! I also created that patch, confirmed that the test
> >> successfully passed with -DENFORCE_REGRESSION_TEST_NAME_RESTRICTIONS,
> >> and pushed the patch.
>
> > Thanks a lot!
>
> Seems you're not out of the woods yet:
>
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=trilobite&dt=2021-01-26%2019%3A59%3A40
>
> This is a CLOBBER_CACHE_ALWAYS build, so I suspect what it's
> telling us is that the patch's behavior is unstable in the face
> of unexpected cache flushes.

Thanks a lot! It looks like the syscache invalidation messages are
generated too frequently with -DCLOBBER_CACHE_ALWAYS build due to
which pgfdw_inval_callback gets called many times in which the cached
entries are marked as invalid and closed if they are not used in the
txn. The new function postgres_fdw_get_connections outputs the
information of the cached connections such as name if the connection
is still open and their validity. Hence the output of the
postgres_fdw_get_connections became unstable in the buildfarm member.

I will further analyze making tests stable, meanwhile any suggestions
are welcome.

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com