From 10df27873ecbdd90c922e9a53ccb64e9eb285926 Mon Sep 17 00:00:00 2001 From: zzstoatzz Date: Mon, 17 Aug 2026 02:10:14 -0500 Subject: [PATCH] docs: compaction cadence corrected (sequential loop, ~9.9h cycle) + age-tiering falsified Co-Authored-By: Claude Fable 5 --- docs/compaction-cost.md | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/docs/compaction-cost.md b/docs/compaction-cost.md index feb7f1f..1840ea6 100644 --- a/docs/compaction-cost.md +++ b/docs/compaction-cost.md @@ -129,11 +129,20 @@ compressed frame verbatim. Consequences: -- **Pass duration (~4.5h+) exceeds the 4h interval**, so the steady - compactor refires immediately on completion: compaction is effectively - continuous. Upstream's loop behaves identically at this archive size — - shared design cost, not a config error. The interval stays at - upstream's 4h default (decided 2026-08-16; do not re-litigate). +- **Pass duration (5h27m measured, first completed pass 2026-08-17 + 06:16Z: 6,358/6,666 rewritten, 3.56M rows dropped) exceeds the 4h + interval — but the loop is sequential and the timer resets AFTER a + pass completes**, so the real cadence is pass+interval ≈ 9.9h per + cycle (~55% duty), not continuous. Upstream's loop behaves identically + at this archive size — shared design cost, not a config error. The + interval stays at upstream's 4h default (decided 2026-08-16; do not + re-litigate). +- **Age-tiered skipping is falsified by the archive's demographics** + (first completed pass's rewritten-age histogram): only 84 rewritten + segments were younger than 7 days; 6,274 sat in the 7–30d bucket. + Steady state seals only ~6-7 segments/day, so the archive is + overwhelmingly the backfill-era mass and that is where tombstoned rows + live. Tiering by age would exempt almost nothing. - **More rewrite workers would not help this box**: the volume is saturated at 4. (`--compaction-rewrite-workers=4` vs upstream's default 8 is now a non-difference here.) -- 2.51.2