Re: pgsql: Check that oldestXID and oldestMulti are consistent at pg_upgrad

On 2026-09-18 Fr 5:32 PM, Heikki Linnakangas wrote:
> Check that oldestXID and oldestMulti are consistent at pg_upgrade
>
> Now that pg_upgrade will rewrite multixid members, starting from
> oldestMulti, it's important that oldestMulti is valid. Add a sanity
> check that oldestMulti is not newer than the oldest datminmxid value
> in pg_database.
>
> One case where this could happen is if the cluster was previously
> upgraded to version 9.3 with a buggy pg_upgrade version that didn't
> have commit a61daa14d5. This new pg_upgrade check is similar to the
> defence that was added in commit 78db307bb2 to VACUUM to avoid
> truncating away multixids if oldestMulti is too new. This pg_upgrade
> check differs in that we don't try to soldier on with the upgrade if
> the oldestMultiXID is inconsistent, but rather just abort the upgrade.
>
> Reported-by: Noah Misch <noah(at)leadboat(dot)com>
> Discussion: https://www.postgresql.org/message-id/20260827231757.78.noahmisch@microsoft.com
> Backpatch-through: 19
>
> Branch
> ------
> REL_19_STABLE
>
> Details
> -------
> https://git.postgresql.org/pg/commitdiff/5cd84ed6274ecd552f2991c54710608c0ef4cdc7
>
> Modified Files
> --------------
> src/backend/access/transam/multixact.c | 28 --------------
> src/bin/pg_upgrade/check.c | 71 ++++++++++++++++++++++++++++++++++
> src/include/access/multixact.h | 31 +++++++++++++--
> 3 files changed, 99 insertions(+), 31 deletions(-)

This has broken upgrade from release 9.2 still supposedly supported in
release 19 (but not 20, for which the minimum will be 10). The log
complains that datminmxid doesn't exist. Since we didn't have multixids
until 9.3 could we just skip this check if upgrading from 9.2?

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com