Re: Do not check unlogged indexes on standby

On Mon, Aug 12, 2019 at 2:58 AM Andrey Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
> Currently, if we check indexes on standby we often get
>
> man-psbpshn0skhsxynd/xiva_xtable_testing_01 R # select bt_index_check('xiva_loadtest.pk_uid');
> ERROR: 58P01: could not open file "base/16453/125407": No such file or directory
>
> I think that we should print warning and that's it. Amcheck should not give false positives.

I agree -- amcheck should just skip over unlogged tables during
recovery, since there is simply nothing to check.

I pushed your patch to all branches that have amcheck just now, so now
we skip over unlogged relations when in recovery, though I made some
revisions.

Your patch didn't handle temp tables/indexes that were created in the
first session correctly -- we must be careful about the distinction
between unlogged tables, and tables that don't require WAL logging
(the later includes temp tables). Also, I thought that it was a good
idea to actively test for the presence of a main fork when we don't
skip (i.e. when the system isn't in recovery and the B-Tree indexes
isn't unlogged) -- we now give a clean report of corruption when that
happens, rather than letting an ambiguous "can't happen" error get
raised by low-level code. This might be possible with system catalog
corruption, for example. Finally, I thought that the WARNING was a bit
strong -- a NOTICE is more appropriate.

Thanks!

--
Peter Geoghegan