Re: Switching XLog source from archive to streaming when primary available

Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>

From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>

To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>

Cc: nathandbossart@gmail.com, cary.huang@highgo.ca, pgsql-hackers@lists.postgresql.org, satyanarlapuram@gmail.com

Date: 2022-09-09T06:44:25Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Add basic TAP tests for the low-level backup method, take two
- 071e3ad59d6f 17.0 cited
Add a failover option to subscriptions.
- 776621a5e479 17.0 cited
Make all Perl warnings fatal
- c5385929593d 17.0 cited
Add PostgreSQL::Test::Cluster::advance_wal
- c161ab74f76a 17.0 cited
Rename wal_keep_segments to wal_keep_size.
- c3fe108c025e 14.0 cited

On Fri, Sep 9, 2022 at 10:57 AM Kyotaro Horiguchi
<horikyota.ntt@gmail.com> wrote:
>
> At Thu, 8 Sep 2022 10:53:56 -0700, Nathan Bossart <nathandbossart@gmail.com> wrote in
> > On Thu, Sep 08, 2022 at 05:16:53PM +0530, Bharath Rupireddy wrote:
> > > I'm attaching the v3 patch with the review comments addressed, please
> > > review it further.
> >
> > My general point is that we should probably offer some basic preventative
> > measure against flipping back and forth between streaming and archive
> > recovery while making zero progress.  As I noted, maybe that's as simple as
> > having WaitForWALToBecomeAvailable() attempt to restore a file from archive
> > at least once before the new parameter forces us to switch to streaming
> > replication.  There might be other ways to handle this.
>
> +1.

Hm. In that case, I think we can get rid of timeout based switching
mechanism and have this behaviour - the standby can attempt to switch
to streaming mode from archive, say, after fetching 1, 2 or a
configurable number of WAL files. In fact, this is the original idea
proposed by Satya in this thread.

If okay, I can code on that. Thoughts?

-- 
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com