Re: logical replication worker accesses catalogs in error context callback

Hi,

On 2021-02-03 16:35:29 +0530, Bharath Rupireddy wrote:
> On Sat, Jan 30, 2021 at 8:23 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > On 2021-01-28 11:14:03 +0530, Amit Kapila wrote:
> > > On Wed, Jan 27, 2021 at 9:38 AM Bharath Rupireddy
> > > <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
> > > >
> > > > On Wed, Jan 27, 2021 at 7:48 AM Zhihong Yu <zyu(at)yugabyte(dot)com> wrote:
> > > >
> > > > Thanks for pointing to the changes in the commit message. I corrected
> > > > them. Attaching v4 patch set, consider it for further review.
> > > >
> > >
> > > About 0001, have we tried to reproduce the actual bug here which means
> > > when the error_callback is called we should face some problem? I feel
> > > with the correct testcase we should hit the Assert
> > > (Assert(IsTransactionState());) in SearchCatCacheInternal because
> > > there we expect the transaction to be in a valid state. I understand
> > > that the transaction is in a broken state at that time but having a
> > > testcase to hit the actual bug makes it easy to test the fix.
> >
> > I think it's easy to hit - add a trivial DEBUG message to XLogWrite(),
> > and run anything involving logical rep using a low enough log
> > level. There might even be enough messages with a low enough level
> > already somewhere in the relevant paths.
>
> I'm not sure how adding a DEBUG message to XLogWrite() would ensure
> the logical replication worker on the subscriber system enters
> slot_store_error_callback and hits the Assert(IsTransactionState());?
> Could you please elaborate? Or I may be missing something here to
> understand.

XLogWrite() is in a critical section, the DEBUG messages triggers error
context callbacks to be called, the callbacks allocate memory, which
triggers an assertion.

Greetings,

Andres Freund