Ilia Denisov
c66bf1eceb
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The "WAL archiving stalled" alert fired on prod during a quiet period. An idle Postgres archives nothing — it never force-switches an empty WAL segment on archive_timeout — so pg_stat_archiver_last_archive_age grows past 30 min even though archiving is perfectly healthy (failed_count 0, no .ready segments, pg_wal flat, backups current). A false positive: no data and no disk at risk (nothing was written, so the frozen recovery point equals the live state). Gate the age condition on pg_wal actually growing: (pg_stat_archiver_last_archive_age > 1800) and on() (delta(pg_wal_size_bytes[35m]) > 16MB) so it fires only when WAL is being produced but not archived (the real "pg_wal fills the disk" danger; genuine archive_command failures are already caught by pg_archive_failing). `and on()` bridges the two metrics' differing label sets (last_archive_age carries a server label, the pg_wal gauge does not); delta() (not increase) suits the gauge. pg_stat_wal is not exported by this postgres_exporter, so pg_wal size growth is the available signal. Validated on prod with promtool: the expression is empty while idle. Also fix the runbook command in both archive alerts' annotations: `pgbackrest check` needs `--pg1-user=scrabble`, or it connects as role "root" (which does not exist) and aborts with "no database found".