| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Soumyadeep Chakraborty <soumyadeep2007(at)gmail(dot)com> |
| Cc: | Amul Sul <sulamul(at)gmail(dot)com>, Prabhat Sahu <prabhat(dot)sahu(at)enterprisedb(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, tushar <tushar(dot)ahuja(at)enterprisedb(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [Patch] ALTER SYSTEM READ ONLY |
| Date: | 2020-07-24 14:33:55 |
| Message-ID: | CA+Tgmoa-a=LB65mbzeKnLm+u2LCexddQT-fECKQNkzV6wO8oCQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Jul 23, 2020 at 12:11 PM Soumyadeep Chakraborty
<soumyadeep2007(at)gmail(dot)com> wrote:
> In the read-only level I was suggesting, I wasn't suggesting that we
> stop WAL flushes, in fact we should flush the WAL before we mark the
> system as read-only. Once the system declares itself as read-only, it
> will not perform any more on-disk changes; It may perform all the
> flushes it needs as a part of the read-only request handling.
I think that's already how the patch works, or at least how it should
work. You stop new writes, flush any existing WAL, and then declare
the system read-only. That can all be done quickly.
> What I am saying is it doesn't have to be just the queries. I think we
> can cater to all the other use cases simply by forcing a checkpoint
> before marking the system as read-only.
But that part can't, which means that if we did that, it would break
the feature for the originally intended use case. I'm not on board
with that.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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