BUG #17602: Query backend process killed because it uses up all memory.

The following bug has been logged on the website:

Bug reference:      17602
Logged by:          alun
Email address:      higherone@gmail.com
PostgreSQL version: 12.8
Operating system:   centos
Description:

Hi,

I'm writing to seek for generic help on trouble shooting bugs related to
query backend process killed because of memory exhaust on this single query
process.

The query is a simple update or insert query like this, and sequence_id has
a btree index. The query process will use up all the memory very quickly
(about 10 minutes) and cause the server to restart.
update folders set sequence_id=40 where id=501;

I suspect the index is corrupt, but after drop the btree index, this issue
still can be reproduced. And when I use pg_amcheck tool to check the btree
index, it's showing no error.
And more strange, if I drop another gist index that's on another field of
the same table, this issue can not be reproduced anymore. But I don't think
the gist index is related to that bad update/insert sql. It's a pity that I
don't have a tool that can detect if gist index is corrupt.

I can not reproduce this issue on a clean db instance. However in my
snapshot db with prod data, I can reproduce this issue stably. It's a pity I
can not share the snapshot db for trouble shooting, so here I'm writing to
the group, hoping to get some suggestions on how to trouble shoot further.

Thanks a lot!