Re: Refactor pg_rewind code and make it work against a standby

From: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
To: Soumyadeep Chakraborty <soumyadeep2007(at)gmail(dot)com>
Cc: Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Refactor pg_rewind code and make it work against a standby
Date: 2020-11-12 12:58:02
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On 04/11/2020 11:23, Heikki Linnakangas wrote:
> I read through the patches one more time, fixed a bunch of typos and
> such, and pushed patches 1-4. I'm going to spend some more time on
> testing the last patch. It allows using a standby server as the source,
> and we don't have any tests for that yet. Thanks for the review!

Did some more testing, fixed one bug, and pushed.

To test this, I set up a cluster with one primary, a standby, and a
cascaded standby. I launched a test workload against the primary that
creates tables, inserts rows, and drops tables continuously. In another
shell, I promoted the cascaded standby, run some updates on the promoted
server, and finally, run pg_rewind pointed at the standby, and start it
again as a cascaded standby. Repeat.

Attached are the scripts I used. I edited them between test runs to test
slightly different scenarios. I don't expect them to be very useful to
anyone else, but the Internet is my backup.

I did find one bug in the patch with that, so the time was well spent:
the code in process_queued_fetch_requests() got confused and errored
out, if a file was removed in the source system while pg_rewind was
running. There was code to deal with that, but it was broken. Fixed that.

- Heikki

Attachment Content-Type Size
rewind-cascading-test.tar.gz application/gzip 2.0 KB

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