Horton

Re: BUG #17994: Invalidating relcache corrupts tupDesc inside ExecEvalFieldStoreDeForm()

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Dunstan <andrew@dunslane.net>
Cc: Andres Freund <andres@anarazel.de>, exclusion@gmail.com, pgsql-bugs@lists.postgresql.org
Date: 2023-06-29T14:26:24Z
Lists: pgsql-bugs 
Andrew Dunstan <andrew@dunslane.net> writes:
> After (not) sleeping on this overnight, and discussing it with a 
> colleague this morning, here's a suggestion. We have a hash table, keyed 
> by (tdtypeid, attnum) where we store a datumCopy'd version of the value. 
> If it's present just return the value instead of getting it from the 
> tupdesc. The hash table is blown away at the end of the transaction. 
> Assuming that's workable I think it would not be a large patch.

That sounds possibly workable.  I'm a bit concerned about added
overhead, and about whether the hashtable needs invalidation support.
It might be better to key it off (relfilenode, attnum).

> My colleague did ask if we had live reproducible case.

I have not attempted to build one, but it'd probably be fairly
easy to do if you turn on debug_discard_caches.

			regards, tom lane

Commits

  1. Cache by-reference missing values in a long lived context

  2. Fix order of operations in ExecEvalFieldStoreDeForm().