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

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