Re: Issues with ON CONFLICT UPDATE and REINDEX CONCURRENTLY

Hello, Michael.

> Isn't the issue that we may select as arbiter indexes stuff that's !indisvalid?

As far as I can see (1) !indisvalid indexes are filtered out.

But... It looks like this choice is not locked in any way (2), so index_concurrently_swap or index_concurrently_set_dead can change this index after the decision is made, even despite WaitForLockersMultiple (3). In some cases, it may cause a data loss...

But I was unable to reproduce that using some random usleep(), however - maybe it is a wrong assumption.

[1]: https://github.com/postgres/postgres/blob/915de706d28c433283e9dc63701e8f978488a2b9/src/backend/optimizer/util/plancat.c#L804 

[2]: https://github.com/postgres/postgres/blob/915de706d28c433283e9dc63701e8f978488a2b9/src/backend/optimizer/util/plancat.c#L924-L928

[3]: https://github.com/postgres/postgres/blob/8aee330af55d8a759b2b73f5a771d9d34a7b887f/src/backend/commands/indexcmds.c#L4153