Re: [Patch] ALTER SYSTEM READ ONLY

On Thu, Jul 23, 2020 at 12:11 PM Soumyadeep Chakraborty
<soumyadeep2007@gmail.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
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