[joker-777]

Two sync steps were quadratic in the number of local changes. This makes them linear. No behaviour change.

Changes

• markLocalChangesAsSynced looked up each pushed record with affectedRecords.find(). Affected records are now indexed by table and id in a Map
• Applying a pull checked every created and updated record with locallyDeletedIds.includes(). Locally deleted ids are now a Set, built once per table
• The rest of src/sync/ already uses Sets and Maps for its lookups. Not changed: addToRawSet (per record, bounded by the column count) and LokiJS adapter internals

Tests

Two new Jest tests count array element reads through a Proxy instead of timing, so they aren't flaky: 2000 pushed records, and 1000 pulled updates to locally deleted records. Master needs 2,001,000 and 501,500 reads; this branch stays under 4000 and 3000.

Verification

• On this branch: Jest passes on the host, 79 suites (the sqlite-node suite was left out because better-sqlite3 does not build on the host's Node; this change does not touch the adapters). flow check is clean, and ESLint is clean on the changed files
• The four sync PRs from us ([Sync] Apply batched pulls sequentially and notify observers once per pull #1984, [Sync] Validate the whole pulled changeset before applying any of it #1985, [Sync] Track changed columns on locally created records #1986, [Sync] Make sync bookkeeping linear-time #1987) touch applyRemote.js and its tests in separate places. They merge into master together without conflicts, and Jest passes on the result

🤖 Generated with Claude Code

[StasDoskalenko]

Hi @joker-777, thank you, and I really like the Proxy trick for testing this without relying on timing!

I maintain NitromelonDB, a maintained fork of WatermelonDB (New Architecture, Nitro Modules). We've done a fair bit of sync performance work there, but both of these are still quadratic: affectedRecords.find() in src/sync/impl/markAsSynced.ts and locallyDeletedIds.includes() in src/sync/impl/applyRemote.ts.

Our fork was rewritten in TypeScript (strict mode) to reduce the chance of bugs slipping through, so I think the community would really benefit if you opened your PRs against it too.

If you don't have the time or would rather not, no worries at all, I'm happy to port it myself. Just let me know. Thanks a lot!