Re: [Patch] ALTER SYSTEM READ ONLY

Amul Sul <sulamul@gmail.com>

From: Amul Sul <sulamul@gmail.com>

To: Dilip Kumar <dilipbalaut@gmail.com>

Cc: Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Ibrar Ahmed <ibrar.ahmad@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Prabhat Sahu <prabhat.sahu@enterprisedb.com>

Date: 2021-05-13T09:24:04Z

Lists: pgsql-hackers

Attachments

v28-0001-Refactor-separate-WAL-writing-code-from-StartupX.patch (application/x-patch) patch v28-0001
v28-0004-Documentation.patch (application/x-patch) patch v28-0004
v28-0003-Error-or-Assert-before-START_CRIT_SECTION-for-WA.patch (application/x-patch) patch v28-0003
v28-0002-Implement-wal-prohibit-state-using-global-barrie.patch (application/x-patch) patch v28-0002

On Thu, May 13, 2021 at 12:36 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> On Wed, May 12, 2021 at 5:55 PM Amul Sul <sulamul@gmail.com> wrote:
> >
>
> Thanks for the updated patch, while going through I noticed this comment.
>
> + /*
> + * WAL prohibit state changes not allowed during recovery except the crash
> + * recovery case.
> + */
> + PreventCommandDuringRecovery("pg_prohibit_wal()");
>
> Why do we need to allow state change during recovery?  Do you still
> need it after the latest changes you discussed here, I mean now
> XLogAcceptWrites() being called before sending barrier to backends.
> So now we are not afraid that the backend will write WAL before we
> call XLogAcceptWrites().  So now IMHO, we don't need to keep the
> system in recovery until pg_prohibit_wal(false) is called, right?
>

Your understanding is correct, and the previous patch also does the same, but
the code comment is wrong.  Fixed in the attached version, also rebased for the
latest master head. Sorry for the confusion.

Regards,
Amul

Commits

Initialize variable to placate compiler.
- a030a0c5ccb1 15.0 landed
StartupXLOG: Don't repeatedly disable/enable local xlog insertion.
- 18e0913a4203 15.0 landed
StartupXLOG: Call CleanupAfterArchiveRecovery after XLogReportParameters.
- a75dbf7f9ee6 15.0 landed
Postpone some end-of-recovery operations related to allowing WAL.
- 811051c2e7af 15.0 landed
Refactor some end-of-recovery code out of StartupXLOG().
- 6df1543abfed 15.0 landed
Re-enable contrib/bloom's TAP tests.
- 7d1aa6bf1c27 15.0 cited
Remove unnecessary call to ReadCheckpointRecord().
- 1d919de5eb3f 15.0 cited
Allow for error or refusal while absorbing a ProcSignalBarrier.
- a3ed4d1efe9f 14.0 landed
Add comment to explain an unused function parameter
- 101f903e51f5 14.0 cited
Extend the ProcSignal mechanism to support barriers.
- 16a4e4aecd47 13.0 cited
At promotion, don't leave behind a partial segment on the old timeline.
- 7cbee7c0a1db 9.5.0 cited