Re: Issues with ON CONFLICT UPDATE and REINDEX CONCURRENTLY

Hello, Michael!

> This is a non-fresh Friday-afternoon idea, but it would make sure that
> we don't have any transactions using the indexes switched to _ccold
> with indisvalid that are waiting for a drop in phase 5. Your tests
> seem to pass with that, and that keeps the operation intact
> concurrent-wise (I'm really wishing for isolation tests with injection
> points just now, because I could use them here).

Yes, I also have tried that approach, but it doesn't work, unfortunately.
You may fail test increasing number of connections:

'--no-vacuum --client=10 -j 2 --transactions=1000',

The source of the issue is not the swap of the indexes (and not related to
REINDEX CONCURRENTLY only), but the fact that indexes are fetched once
during planning (to find the arbiter), but then later reread with a new
catalog snapshot for the the actual execution.

So, other possible fixes I see:
* fallback to replanning in case we see something changed during the
execution
* select arbiter indexes during actual execution

> That's a HEAD-only thing IMO,
> though.
Do you mean that it needs to be moved to a separate patch?

Best regards,
Mikhail.