Re: [Patch] ALTER SYSTEM READ ONLY

On Wed, Sep 15, 2021 at 6:49 AM Amul Sul <sulamul(at)gmail(dot)com> wrote:
> Initially, I thought to
> use SharedRecoveryState which is always set to RECOVERY_STATE_ARCHIVE,
> if the archive recovery requested. But there is another case where
> SharedRecoveryState could be RECOVERY_STATE_ARCHIVE irrespective of
> ArchiveRecoveryRequested value, that is the presence of a backup label
> file.

Right, there's a difference between whether archive recovery has been
*requested* and whether it is actually *happening*.

> If we want to use SharedRecoveryState, we need one more state
> which could differentiate between ArchiveRecoveryRequested and the
> backup label file presence case. To move ahead, I have copied
> ArchiveRecoveryRequested into shared memory and it will be cleared
> once archive cleanup is finished. With all these changes, we could get
> rid of xlogaction argument and DetermineRecoveryXlogAction() function.
> Could move its logic to PerformRecoveryXLogAction() directly.

Putting these changes into 0001 seems to make no sense. It seems like
they should be part of 0003, or maybe a new 0004 patch.

> And for ThisTimeLineID, I don't think we need to do anything since this
> value is available with all the backend as per the following comment:
> "
> /*
> * ThisTimeLineID will be same in all backends --- it identifies current
> * WAL timeline for the database system.
> */
> TimeLineID ThisTimeLineID = 0;

I'm not sure I find that argument totally convincing. The two
variables aren't assigned at exactly the same places in the code,
nonwithstanding the comment. I'm not saying you're wrong. I'm just
saying I don't believe it just because the comment says so.

--
Robert Haas
EDB: http://www.enterprisedb.com