On Wed, Nov 19, 2025 at 09:42:38AM +0100, Jozsef Kadlecsik via Postfix-users
wrote:
> We use mysql-driven lookups for almost everything and sometimes there are
> warnings in the logs saying:
>
> Nov 19 00:50:12 smtp2 postfix/trivial-rewrite[52211]: warning:
> proxy:mysql:/etc/postfix/mysql/user_transport.cf lookup error for "address"
> Nov 19 00:50:12 smtp2 postfix/trivial-rewrite[52211]: warning: transport_maps
> lookup failure
>
> The database is on the machine itself, connected over unix socket. It seems
> it is a temporary issue because next minute "it works". However it is a
> visible error for smtp clients which then must retry.
>
> What should be checked? How could mysql lookups be debugged?
Make sure that the database server doesn't preëmptively shut down idle
connections, and its connection count limit is high enough to
accommodate the expected concurrency from all other processes:
- 2 from each smtpd(8) and its associated backend cleanup(8)
- 1 for qmgr
- 1 for trivial-rewrite
- 2 for pickup(8) and backend cleanup(8)
- 1 for each local(8) process resolving addresses rewritten
by aliases(5).
Typically, twice the maximum count of smtpd(8) processes plus a few
more, but if local delivery is for some unexpected reason running at a
high concurrency, that can add more.
--
Viktor. 🇺🇦 Слава Україні!
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