Horton

Re: [Patch] ALTER SYSTEM READ ONLY

Amul Sul <sulamul@gmail.com>

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From: Amul Sul <sulamul@gmail.com>
To: Prabhat Sahu <prabhat.sahu@enterprisedb.com>
Cc: Ibrar Ahmed <ibrar.ahmad@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-04-05T05:31:16Z
Lists: pgsql-hackers

Attachments

Attached is the rebase version for the latest master head(commit # 9f6f1f9b8e6).

Regards,
Amul


On Mon, Mar 22, 2021 at 12:13 PM Amul Sul <sulamul@gmail.com> wrote:
>
> On Fri, Mar 19, 2021 at 7:17 PM Prabhat Sahu
> <prabhat.sahu@enterprisedb.com> wrote:
> >
> > Hi all,
> > While testing this feature with v20-patch, the server is crashing with below steps.
> >
> > Steps to reproduce:
> > 1. Configure master-slave replication setup.
> > 2. Connect to Slave.
> > 3. Execute below statements, it will crash the server:
> > SELECT pg_prohibit_wal(true);
> > SELECT pg_prohibit_wal(false);
> >
> > -- Slave:
> > postgres=# select pg_is_in_recovery();
> >  pg_is_in_recovery
> > -------------------
> >  t
> > (1 row)
> >
> > postgres=# SELECT pg_prohibit_wal(true);
> >  pg_prohibit_wal
> > -----------------
> >
> > (1 row)
> >
> > postgres=# SELECT pg_prohibit_wal(false);
> > WARNING:  terminating connection because of crash of another server process
> > DETAIL:  The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.
> > HINT:  In a moment you should be able to reconnect to the database and repeat your command.
> > server closed the connection unexpectedly
> > This probably means the server terminated abnormally
> > before or while processing the request.
> > The connection to the server was lost. Attempting reset: Failed.
> > !?>
>
> Thanks Prabhat.
>
> The assertion failure is due to wrong assumptions for the flag that were used
> for the XLogAcceptWrites() call. In the case of standby, the startup process
> never reached the place where it could call XLogAcceptWrites() and update the
> respective flag. Due to this flag value, pg_prohibit_wal() function does
> alter system state in recovery state which is incorrect.
>
> In the attached function I took enum value for that flag so that
> pg_prohibit_wal() is only allowed in the recovery mode, iff that flag indicates
> that XLogAcceptWrites() has been skipped previously.
>
> Regards,
> Amul

Commits

  1. Initialize variable to placate compiler.

  2. StartupXLOG: Don't repeatedly disable/enable local xlog insertion.

  3. StartupXLOG: Call CleanupAfterArchiveRecovery after XLogReportParameters.

  4. Postpone some end-of-recovery operations related to allowing WAL.

  5. Refactor some end-of-recovery code out of StartupXLOG().

  6. Re-enable contrib/bloom's TAP tests.

  7. Remove unnecessary call to ReadCheckpointRecord().

  8. Allow for error or refusal while absorbing a ProcSignalBarrier.

  9. Add comment to explain an unused function parameter

  10. Extend the ProcSignal mechanism to support barriers.

  11. At promotion, don't leave behind a partial segment on the old timeline.