---
id: "bug-543"
status: "fixed"
status_updated: "2026-09-24"
status_note: ""
component: "controller"
severity: "unknown"
timestamp: "2026-06-14T09:36:36.967406Z"
last_seen: "2026-09-19T09:00:00Z"
occurrences: 1
files: ["src/controller/config_repl.c"]
tags: ["ha", "replication", "wal", "cold-start", "lsn-0", "catch-up", "correctness", "off-by-one"]
related: []
legacy: true
---

# bug-543: WAL HOLE on cold-start catch-up: a fresh EMPTY standby (standby_lsn=0) catching up to a primary…

## Description
WAL HOLE on cold-start catch-up: a fresh EMPTY standby (standby_lsn=0) catching up to a primary holding [0,1] receives ONLY lsn 1, missing lsn 0

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

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

## Root cause
ha_stream_wal_to_standby filter `if (hdr.lsn > standby_lsn)` excludes lsn 0 when standby_lsn==0 (0>0 is false). standby_lsn=0 is ambiguous: it means BOTH 'empty standby (applied nothing)' AND 'standby has applied lsn 0'. The streamer cannot distinguish, computes start_lsn=standby_lsn+1=1, and drops the genuine lsn-0 entry. Only non-cosmetic because lsn-0 entries can be REAL data (first-ever WAL entry of a fresh cluster is lsn 0 from a real write OR the promotion NOOP).

## Fix
FIXED via reserve-lsn-0: persist_init() now sets current_lsn=1 on a fresh store (persist.c), so lsn 0 is reserved as the none/empty sentinel and the first-ever WAL entry (promotion NOOP) is lsn 1. The streamer filter hdr.lsn>standby_lsn now yields 1>0=true for an empty standby (standby_lsn=0), streaming the first entry — no hole. No streamer change needed; the reserved base makes the existing filter correct. Also fixes the uncommittable cold-start NOOP (now lsn 1, committable 0->1) and the own-term writable_lsn gate (now 1, effective). Test: test_coldstart_lsn0.c H1-H4 all green incl H4 no-hole. Base-shift fallout fixed in test_commit_engine, test_commit_barrier_rollout, test_commit_barrier_reply, test_p2_integration, test_egress_filter (removed now-redundant priming appends / wired engine).

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

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