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feat(raft-apply-decoupling): resolve pending continuations on demotion/truncation (task 1.4)

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commit_resolve_pending_above(ce, lsn_floor, rc) fails every registered
continuation for lsn > lsn_floor, reusing commit_resolve()'s existing
exactly-once/idempotent guarantee (no parallel bookkeeping path).

Truncation: a new on_truncate/truncate_cb_ctx callback on persist_t
(same inversion-of-control shape as the existing on_durable_advance
hook) fires from persist_truncate_wal_above after releasing p->lock,
only when entries were actually removed. This one wrapper covers all
three real truncation call sites: raft_cb_become_leader's
post-election truncate, the library's on_truncate_from
conflict-reconcile, and ha_demotion_convergence_fn's post-demotion
truncate.

Demotion: raft_cb_become_follower calls
commit_resolve_pending_above(&c->commit, 0, -XCE_ERR_STANDBY) --
lsn_floor=0 fails everything, since a demoted node can never
authoritatively confirm anything still pending (CP posture).

Without this, a demoted or truncated node would leave any pending
async command permanently unresolved -- the requester would simply
never get a reply, worse than today's bounded-timeout behavior.

Also closes bug-1407 (pre-existing test_config_repl flake, unrelated
to this feature) -- confirmed fixed as a side effect of prior tasks
in this series, 70/70 passing across 3 independent runs.
This commit is contained in:
Rongsong Shen 2026-07-03 11:58:10 +00:00
parent 530a02bda3
commit 9b4b805a27
9 changed files with 748 additions and 301 deletions
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26
src/controller/include/commit.h
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@ -179,6 +179,32 @@ int commit_submit_async(commit_engine_t* ce, uint64_t lsn,
void commit_resolve(commit_engine_t* ce, uint64_t lsn, commit_outcome_t outcome,
int rc);
/* raft-apply-decoupling task 1.4: resolve every currently pending registered
* continuation whose lsn > lsn_floor as FAILED with rc, in one bounded pass --
* the FAILED-outcome sibling of commit_resolve's internal majority-ack scan.
* Two intended callers:
* - log-tail truncation: lsn_floor = the new tail (cutoff_lsn) AFTER a
* truncation actually removed entries above it. Those entries no longer
* exist in the log and can never commit. A continuation registered AT OR
* BELOW the new tail is UNAFFECTED and stays pending -- its entry is
* still in the log and may still reach majority.
* - demotion (loss of leadership): lsn_floor = 0. A demoted node can never
* advance committed_lsn again for anything it had pending, so every
* currently registered continuation fails, regardless of its lsn. lsn ==
* 0 is never a real registration (the free-slot sentinel -- see
* commit_continuation_t), so lsn_floor = 0 correctly means "all".
* Snapshot-then-resolve, mirroring commit_resolve_pending's own pattern:
* takes a bounded snapshot of matching lsns under ce->lock, then resolves
* each from an unlocked context via the self-locking commit_resolve()
* (dispatch-after-unlock ordering rule, design §Commit Engine Resolve).
* Idempotent: a continuation already resolved by a concurrent caller (e.g.
* the timeout-sweep thread winning a race) is a silent no-op via
* commit_resolve's own exactly-once guarantee -- no continuation is ever
* double-resolved. Safe to call from any thread that does NOT already hold
* ce->lock. */
void commit_resolve_pending_above(commit_engine_t* ce, uint64_t lsn_floor,
int rc);
/* iomgr path: record standby ACK, evaluate majority, advance committed_lsn
* contiguously, wake satisfied waiters. Never blocks. */
void commit_on_ack(commit_engine_t* ce, int standby_idx, uint64_t acked_lsn);