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fix(ha): close permanent catch-up wedge from duplicated replication-target formula (bug-1478)

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Two independent call sites duplicated target = max(committed_lsn,
last_written): ha.c's heartbeat/stateReport dispatch (repl_ack_decode_and_
dispatch) and config_repl.c's catchup_derive_target (used by the ACK-driven
catch-up continuation path). Once config-upgrade-snapshot's marker-triggered
checkpoint advances last_written one LSN past an already-committed
committed_lsn (the checkpoint's own consumed, never-replicated LSN slot),
the unconditional max() permanently wedges every standby's catch-up target
at an unreachable value -- the primary re-streams an empty range every
heartbeat forever.

Extracted the shared, pure ha_compute_repl_target_lsn(committed_lsn,
last_written) (ha.h/ha.c), which only falls back to last_written on genuine
committed_lsn==0 bootstrap, and pointed both call sites at it so they can
never disagree again.

Fixing the second call site exposed three pre-existing tests in
test_convergence_verification.c that hardcoded the old buggy formula's
output as their expected target; updated their fixture values (committed_lsn
4->9, matching appended_lsn) to decouple them from the now-fixed edge case,
which already has dedicated pure-function coverage in test_ha_role.c.

GREEN: full controller_unit_test suite = 1040 tests, 0 failures, clean
across multiple runs. Live-verified via run-ha-soak.sh
--config-upgrade-wal-trim (18 jobs, zero job loss, ctrl-1 reconverged 3-of-3
using the preserved floor segment) -- unblocks config-upgrade-snapshot
task 8.9.
This commit is contained in:
Rongsong Shen 2026-07-28 09:53:20 +00:00
parent 71223ec712
commit 102e263cce
9 changed files with 850 additions and 20 deletions
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18
src/controller/ha.h
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@ -1127,6 +1127,24 @@ void ha_process_standby_state(ha_state_t *ha, int peer_idx,
uint64_t reported_tag, uint64_t reported_lsn,
uint64_t committed_tag, uint64_t committed_lsn);
/*
* ha_compute_repl_target_lsn: the replication/convergence target used by
* ha_dispatch_repl_action_for_standby's heartbeat-driven decision — normally
* committed_lsn itself, falling back to last_written (the raw locally-
* appended WAL tip) ONLY when committed_lsn is genuinely stuck at 0
* (cluster bootstrap, before any standby has ever acked anything).
*
* bug-1478: the fallback must NOT apply once committed_lsn is already > 0 —
* see ha.c's doc comment on this function for the full mechanism (a
* local-only WAL_CHECKPOINT trailing an already-advancing committed_lsn
* otherwise leaks an unstreamable/unreachable target into every subsequent
* heartbeat decision, permanently wedging catch-up).
*
* Pure, side-effect-free.
*/
uint64_t ha_compute_repl_target_lsn(uint64_t committed_lsn,
uint64_t last_written);
/* ── Task 3.5c: Standby snapshot receive handler ──────────────────────────── */
/*