Horton

Re: [Patch] ALTER SYSTEM READ ONLY

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, amul sul <sulamul@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2020-06-18T10:56:06Z
Lists: pgsql-hackers 
On Wed, Jun 17, 2020 at 9:37 PM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Wed, Jun 17, 2020 at 10:58 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> > Lastly, the arguments in favor seem pretty bogus.  HA switchover normally
> > involves just killing the primary server, not expecting that you can
> > leisurely issue some commands to it first.
>
> Yeah, that's exactly the problem I want to fix. If you kill the master
> server, then you have interrupted service, even for read-only queries.
>

Yeah, but if there is a synchronuos_standby (standby that provide sync
replication), user can always route the connections to it
(automatically if there is some middleware which can detect and route
the connection to standby)

> That sucks. Also, even if you don't care about interrupting service on
> the master, it's actually sorta hard to guarantee a clean switchover.
>

Fair enough.  However, it is not described in the initial email
(unless I have missed it; there is a mention that this patch is one
part of that bigger feature but no further explanation of that bigger
feature) how this feature will allow a clean switchover.  I think
before we put the system into READ ONLY state, there could be some WAL
which we haven't sent to standby, what we do we do for that.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com

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.