---
id: "bug-1147"
status: "fixed"
status_updated: "2026-09-24"
status_note: ""
component: "controller"
severity: "unknown"
timestamp: "2026-06-26T03:46:38.904419+00:00"
last_seen: "2026-09-19T09:00:00Z"
occurrences: 1
files: ["src/controller/persist.c:1374 (trim_wal_segments)"]
tags: ["durability", "permanent-gap", "stale-report", "trim", "bug-828", "raft-drive-async", "latent", "catch-up", "wal", "snapshot", "bug-795"]
related: ["bug-795", "bug-828", "bug-1060"]
legacy: true
---

# bug-1147: WAL trim_wal_segments deletes any closed segment regardless of standby catch-up cursor →…

## Description
WAL trim_wal_segments deletes any closed segment regardless of standby catch-up cursor → lagging/empty-rejoin standby loses its needed log range with no snapshot backfill (permanent committed-prefix gap)

## Environment
_Not recorded (migrated from buglog.json)._

## Reproduction
_Not recorded (migrated from buglog.json)._

## Root cause
trim_wal_segments bounds deletion ONLY by active_seg_lsn (the currently-open segment): `if (seg_start_lsn < active_seg_lsn) unlink()`. It consults no standby acked_lsn, no committed_lsn, no in-flight snapshot boundary. Strategy-A (cursor-bounded retention) discipline is absent. Strategy-B (entity-bearing snapshot install) is also not live — write_snapshot (persist.c:1247) writes only a 16-byte P0 sentinel, not materialized state. So a standby that lags by more than ~one open segment (down across segment rolls, slow link, >64MB lag, or empty rejoin from cursor=0) hits a log range that exists nowhere and cannot catch up.

## Fix
FIXED (verified 2026-07-02): src/controller/persist.c trim_wal_segments() computes `floor = repl_trim_lsn(&p->repl, active_seg_lsn, p->config.snap_interval_s)` (min of active segment, all standby acked_lsn, disconnected-slot guards) and only unlinks segments below that floor — comment inline explicitly cites 'bug-1147 guard'. Landed under raft-drive-async task 3.2 (all leaf tasks complete).

## Verification
_Not recorded (migrated from buglog.json)._

## References
- Related: bug-795, bug-828, bug-1060