Prometheus size-based retention counts the WAL toward its budget. With
retention.size=1GB and a stuck/corrupt WAL that had grown to 2.1GB, the
total was permanently over budget, so Prometheus deleted every
freshly-compacted block the moment it was written. Net effect: only the
in-memory ~2h head block was ever queryable — metrics appeared to "start
this morning" no matter when you looked, and last night's Caddy 502
spike (planner /api/overpass upstream stall, 18:33-18:34 UTC) was
unobservable in Prometheus (logs survived in Loki).
The corrupt WAL was cleared out-of-band on the flagship. This raises the
size backstop to 6GB so compacted blocks survive to the intended 15d
time-based retention. Disk is 38G (43% used), so 6GB is safe headroom.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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