- fixes a limitation iteration 2 shipped: compaction was supposed to
bound chain length, but wo_wal_should_compact triggers on a whole-log
byte ratio and cannot see one hot row's chain
- tier 1, flatten on update: the update path ALREADY folds the row for
index maintenance and the fold already walks hop by hop, so it reports
depth for free. Past a fixed K it writes a full row instead of a
delta. Read <= K+1 reads, replay O(K^2) per row. No format change, no
per-row RAM, no new trigger
- tier 2: our compaction policy has a proportional term and a
SUPPRESSOR misleadingly called a floor; postgres's floor TRIGGERS on
small absolute garbage. Add that term and a ceiling
- design read from .dev/reference/postgresql, not recalled:
heap_page_prune_opt gates on an O(1) on-page hint then page fullness
against Max(fillfactor, BLCKSZ/10); autovacuum uses base + scale *
reltuples clamped by a max (50, 0.2, 1e8). Neither thresholds on
new-bytes-versus-old-bytes
- K deliberately does NOT scale with table size: postgres scales a
table-level aggregate with proportional harm, ours is per-row with
additive cost, so scaling up would make big databases boot worst
- the story says plainly it should NOT be next: task 7 has still never
measured whether resident: keys beats the kernel's own paging
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
(cherry picked from commit f667cad2cfbe187b5973440ab1af015b2df288f8)
shoney.arickathil
cfd660a5e6