fix(remote): earn a statistics re-dump at a fifth, not a half

[veksen]

Goal

Queries should be costed against statistics that match the database they run on. The analyzer keeps a project's stored statistics current by re-dumping when the source has moved; this changes how far it has to move before that happens.

What

Before: a table had to grow by half, or shrink to half, before the analyzer re-dumped the source's statistics. Between re-dumps a table could sit at 1.5x its recorded size, and every query against it was costed a third light.

After: a fifth of movement is enough. A table at 1.25x its recorded size now earns a re-dump instead of being called current.

The re-dump itself is unchanged, as is the 24-hour floor that fires when nothing has drifted.

How

src/remote/stats-drift.ts is the whole change: DEFAULT_SIZE_DRIFT_RATIO goes from 0.5 to 0.2.

The number is bounded on both sides. Underneath, the check reads pg_class.reltuples, which Postgres only rewrites when autovacuum analyzes the table, by default once it has changed by autovacuum_analyze_scale_factor, 10%. A threshold below that reads sampling noise rather than data. Above, the threshold is how wrong a cost may be before it is worth acting on, and 0.5 tolerated a cost a third light.

0.2 also makes the growth and shrink sides close to even. The comparison is |now - before| / before, so 0.5 fired on 1.5x growth but needed a 2x shrink; at 0.2 the two are 1.25x and 1.2x.

Tests

src/remote/stats-drift.test.ts: a 1.25x move drifts, a 1.1x move does not. The near-miss case that names the closest table sits at 15% and 5%, either side of the new threshold.

Full suite passes (443 tests, 43 files), npm run typecheck clean.

[github-actions]

Query Doctor — 6 successful checks

 Cost regression — No query went up more than 5%
 Untested data access — No changed data-access file without a test
 New query — No new queries
 New query with index recommendation — No new query ships an index recommendation
 Schema drift — No schema changes
 High-value nudge — No index or rewrite past the threshold

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_{More details via MCP → get_ci_run({ runId: "019ffd57-3a69-7252-aba4-ab993ff5800c" }) · view run · docs
3 queries read against main on assumed statistics of 10,000,000 rows per table. Sync production stats for costs measured against your real data.}