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fix(db): limit the -wal so a VACUUM does not double disk use - #610
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In WAL mode a VACUUM writes every page through the -wal. A checkpoint copies it back and the next write restarts at its head, but nothing ever shrank the file, so after the first VACUUM the -wal stayed as large as the database for good: 702 MB beside a 698 MB file on a WHOOP MG install in the growth soak (OpenStrap#609). Set journal_size_limit (32 MB) on every open, so each restart truncates the file back, healing existing installs on their next write; and checkpoint with TRUNCATE right after the VACUUM so the space comes back immediately. Both pragmas return a row, so they go through rawQuery and are never fatal. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Reviewer's GuideThis PR prevents VACUUM operations from permanently doubling database storage by setting a 32 MiB SQLite WAL retention limit on each open and explicitly running a truncating checkpoint after VACUUM, with non-fatal pragma handling and an end-to-end regression test for oversized WAL files. Sequence diagram for bounded WAL cleanup after VACUUMsequenceDiagram
participant LocalDb
participant SQLite
participant CoachDb
participant WAL
LocalDb->>SQLite: rawQuery(PRAGMA journal_size_limit=walSizeLimitBytes)
SQLite-->>LocalDb: WAL limit configured
LocalDb->>SQLite: VACUUM
LocalDb->>CoachDb: close()
LocalDb->>SQLite: rawQuery(PRAGMA wal_checkpoint(TRUNCATE))
SQLite->>WAL: Copy pages to database and truncate WAL
WAL-->>SQLite: WAL reduced to retention limit
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| Layer / File(s) | Summary |
|---|---|
Configure and truncate the WAL lib/data/db.dart |
LocalDb defines a 32 MiB WAL size limit and attempts to set SQLite’s journal_size_limit during configuration. After VACUUM, vacuumIfBloated attempts a truncating WAL checkpoint. Errors from both attempts are swallowed. |
Estimated code review effort: 2 (Simple) | ~10 minutes
Change: Bug fix
Possibly related PRs
- OpenStrap/edge#647: Adds a vacuum-and-checkpoint method with checkpoint completion reporting and retries.
- OpenStrap/edge#620: Adds query-only readers in WAL mode and coordinates reader retirement, which can affect whether a truncating checkpoint succeeds.
Suggested reviewers: abdulsaheel
Merge Risk: 
8d74b
-
A concurrent reader can prevent WAL truncation, leaving excess disk usage after maintenance; this is bounded but remains a follow-up risk.
Pre-merge checks: 
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Check name Status Explanation Description Check Check skipped - CodeRabbit’s high-level summary is enabled. Title check The title clearly and concisely describes the main change: limiting SQLite WAL growth to prevent excess disk use during VACUUM. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request.
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Hey - I've found 2 issues
Prompt for AI Agents
Please address the comments from this code review:
## Individual Comments
### Comment 1
<location path="lib/data/db.dart" line_range="13191" />
<code_context>
+ // truncate it now, rather than at the next write; the size limit set on
+ // open covers it if a reader holds this checkpoint back.
+ try {
+ await db.rawQuery('PRAGMA wal_checkpoint(TRUNCATE)');
+ } catch (_) {
+ /* non-fatal: the bytes are reclaimed, the -wal shrinks on a later write */
</code_context>
<issue_to_address>
**VACUUM leaves WAL space unreclaimed**
When a reader on another connection holds a snapshot or read lock during the TRUNCATE checkpoint, `rawQuery` succeeds despite the busy status row, so `vacuumIfBloated` treats the checkpoint as complete and returns without reclaiming the WAL space; the oversized file remains until a later successful checkpoint.
Inspect the checkpoint result and retry after readers release their snapshots, or report that the WAL was not reclaimed.
</issue_to_address>
### Comment 2
<location path="lib/data/db.dart" line_range="570" />
<code_context>
+ // connection and on an existing install's oversized -wal alike.
+ // Per-connection, and it returns a row: rawQuery, never fatal.
+ try {
+ await db.rawQuery('PRAGMA journal_size_limit=$walSizeLimitBytes');
+ } catch (_) {
+ /* non-fatal */
</code_context>
<issue_to_address>
**Existing WAL stays oversized**
When an existing oversized WAL was reset before the database opens and subsequent writes do not trigger an auto-checkpoint, setting `journal_size_limit` does not checkpoint or truncate that WAL, so it stays oversized and users continue to see the extra disk use.
Checkpoint or reset the WAL after applying the size limit so the limit can truncate an already-oversized WAL.
</issue_to_address>Sourcery assessment
Approval pending. 2 findings to address first.
Blocking findings: lib/data/db.dart:13191, lib/data/db.dart:570
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Actionable comments posted: 1
- 🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @lib/data/db.dart:
- Line 568: Update vacuumIfBloated to inspect the row returned by PRAGMA
wal_checkpoint(TRUNCATE) and retry or defer when its status is busy; only return
reclaimed space after the checkpoint succeeds so _maybeReclaimDiskSpace does not
report space that remains in the WAL.
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test/db_storage_hygiene_test.dartis excluded by!test/**
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Why
After the first
vacuumIfBloated, the-walstays as large as the whole database, permanently. In WAL mode a VACUUM writes every page through the-wal; a checkpoint copies it back and the next write restarts at its head, but withoutjournal_size_limitSQLite never shrinks the file. The growth soak (#609) on a WHOOP MG install measured 698 MB of database + 702 MB of-wal, which doubles disk use. This is one likely contributor to the multi-GB storage reports.The in-app storage figure (
databaseFileBytes) counts only the main file, so users see the OS figure grow while the app's own number doesn't.What changed
onConfiguresetsPRAGMA journal_size_limitto 32 MB (LocalDb.walSizeLimitBytes) on every open. Each time the-walrestarts after a checkpoint, it is truncated back to that size. That also heals existing installs whose-walis already oversized, on their next write.vacuumIfBloatedrunsPRAGMA wal_checkpoint(TRUNCATE)after the VACUUM (and afterCoachDb.close()), so the space comes back immediately instead of at the next write.rawQueryand are wrapped intry/catch, never fatal on open (§3.11, same asjournal_mode=WAL).The only other connection to this file is CoachDb's read-only one, and readers never reset the
-wal.Tests
db_storage_hygiene_test: new test that keeps 48 MB, frees 16 MB, runsvacuumIfBloated, and asserts the limit is set and the-walis ≤ 32 MB afterwards. Onmainit fails with 50 MB of-walleft behind; with the change it passes.-walafter the VACUUM goes from 702 MB → 0 MB and the "disk vs data" check passes. MG steady-state growth (3.55 MB/day) is still over budget; that is a separate fix (raw_archive).flutter analyze: no issues. DB / substrate-archive / prune / coach tests: 480 passed.🤖 Generated with Claude Code
Summary by Sourcery
Prevent SQLite VACUUM operations from doubling database storage by bounding and promptly truncating the WAL file.
Bug Fixes:
Enhancements:
Tests:
Summary by CodeRabbit