BUG #15489: Segfault on DELETE

The following bug has been logged on the website:

Bug reference:      15489
Logged by:          Kanwei Li
Email address:      kanwei@gmail.com
PostgreSQL version: 11.0
Operating system:   Debian 9
Description:

We started seeing a segfault crash on our postgresql 11 server instance
today when attempting to delete certain rows in the database:

2018-11-06 21:02:07.553 UTC [60606] LOG:  server process (PID 66881) was
terminated by signal 11: Segmentation fault
2018-11-06 21:02:07.553 UTC [60606] DETAIL:  Failed process was running:
        delete from integration_account
        where partner_id = 24

Attempting to delete certain rows were causing this segfault, and attempting
to delete other rows did not. There didn't seem to be a pattern, and because
this was on production we couldn't risk playing around too much.

Doing a SELECT on the rows that couldn't be deleted worked fine. There
didn't seem to be data corruption since all the data could be read. However,
attempting to DELETE certain rows would crash it. pg_dump also worked
fine.

What fixed it was performing a VACUUM ANALYZE on the database. After that,
the deletes worked again.

I'm sorry I can no longer list steps to reproduce this, since the VACUUM
fixed it, but I figured I should report it in case others have seen it, or
if anyone can maybe guess what the problem is.