Re: Issues with ON CONFLICT UPDATE and REINDEX CONCURRENTLY

Hello.

> But I was unable to reproduce that using some random usleep(), however -
maybe it is a wrong assumption.
It seems like the assumption is correct - we may use an invalid index as
arbiter due to race condition.

The attached patch adds a check for that case, and now the test fails like
this:

# pgbench: error: client 16 script 1 aborted in command 1 query 0:
ERROR: duplicate key value violates unique constraint "tbl_pkey_ccold"
# DETAIL: Key (i)=(42) already exists.
# pgbench: error: client 9 script 1 aborted in command 1 query 0:
ERROR: ON CONFLICT does not support invalid indexes as arbiters
# pgbench: error: client 0 script 2 aborted in command 1 query 0:
ERROR: duplicate key value violates unique constraint "tbl_pkey"
# DETAIL: Key (i)=(69) already exists.
# pgbench: error: client 7 script 0 aborted in command 1 query 0:
ERROR: ON CONFLICT does not support invalid indexes as arbiters
# pgbench: error: client 10 script 0 aborted in command 1 query 0:
ERROR: ON CONFLICT does not support invalid indexes as arbiters
# pgbench: error: client 11 script 0 aborted in command 1 query 0:
ERROR: ON CONFLICT does not support invalid indexes as arbiters

I think It is even possible to see !alive index in the same situation (it
is worse case), but I was unable to reproduce it so far.

Best regards,
Mikhail.