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Companion to BENCH_XMIN_HORIZON.md covering the second main dead-tuple failure mode for SKIP LOCKED queues: steady-state churn under burst fan-out patterns where autovacuum is not blocked but cannot keep pace with periodic bursts. Defines four scenarios (F1–F4), two workloads, metrics, PG config, and file layout. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Rename category label "SKIP LOCKED queues" to "UPDATE/DELETE queues" throughout (the locking primitive is not what causes dead-tuple pain). Rewrite motivation paragraphs to keep dead tuples (pre-VACUUM, immediate harm) distinct from bloat (post-VACUUM, cumulative heap growth), and replace the "tuning reduces bloat" framing with the correct structural fix: avoiding UPDATE/DELETE on the hot path entirely. Add autovacuum_vacuum_insert_scale_factor = 0.005 to the PG config block so insert-heavy bursts trigger vacuum on the enqueue side too. Update PG17 → PG18 in the hardware section. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Under blocked xmin, VACUUM cannot remove dead tuples at all, so "only changes the rate" was wrong for that case — tuning does nothing. Split the single sentence into three that make the conditional explicit. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
blueprints/BENCH_FANOUT_CHURN.md, a companion benchmark spec toBENCH_XMIN_HORIZON.mdTest plan