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fix(memory): write meta before JSONL rewrite for crash safety

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In SetHistory and Compact, the JSONL file was rewritten before updating
the meta file. If the process crashed between the two writes, the meta
still had a large Skip value pointing past the now-shorter JSONL file,
causing GetHistory to return empty — effectively data loss.

Reverse the order: write meta (with Skip=0) first, then rewrite JSONL.
On crash between the two writes, the old uncompacted file is still
intact and GetHistory reads from line 1, returning stale-but-complete
data. The next operation self-corrects.
This commit is contained in:
xiaoen 2026-02-26 16:13:57 +08:00
parent 3f7fc90125
commit 8784dae5fb
1 changed files with 21 additions and 12 deletions
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33
pkg/memory/jsonl.go
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@ -361,11 +361,6 @@ func (s *JSONLStore) SetHistory(
l.Lock()
defer l.Unlock()
err := s.rewriteJSONL(sessionKey, history)
if err != nil {
return err
}
meta, err := s.readMeta(sessionKey)
if err != nil {
return err
@ -378,7 +373,16 @@ func (s *JSONLStore) SetHistory(
meta.Count = len(history)
meta.UpdatedAt = now
return s.writeMeta(sessionKey, meta)
// Write meta BEFORE rewriting the JSONL file. If we crash between
// the two writes, meta has Skip=0 and the old file is still intact,
// so GetHistory reads from line 1 — returning "too many" messages
// rather than losing data. The next SetHistory call corrects this.
err = s.writeMeta(sessionKey, meta)
if err != nil {
return err
}
return s.rewriteJSONL(sessionKey, history)
}
// Compact physically rewrites the JSONL file, dropping all logically
@ -409,16 +413,21 @@ func (s *JSONLStore) Compact(
return err
}
err = s.rewriteJSONL(sessionKey, active)
if err != nil {
return err
}
// Write meta BEFORE rewriting the JSONL file. If the process
// crashes between the two writes, meta has Skip=0 and the old
// (uncompacted) file is still intact, so GetHistory reads from
// line 1 — returning previously-truncated messages rather than
// losing data. The next Compact or TruncateHistory corrects this.
meta.Skip = 0
meta.Count = len(active)
meta.UpdatedAt = time.Now()
return s.writeMeta(sessionKey, meta)
err = s.writeMeta(sessionKey, meta)
if err != nil {
return err
}
return s.rewriteJSONL(sessionKey, active)
}
// rewriteJSONL atomically replaces the JSONL file with the given messages.