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feat(raft-drive-async): add drive-async config constants + liveness-reservation helper (task 1.1)

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drive_async_liveness_reserved = max(1, min(n_peers-1, n_vcpus-1)) — single
source of truth for VTASK_LIVENESS_RESERVED (deadlock-freedom floor applied
last). New DEFAULT_CONNECT_TIMEOUT_MS / DEFAULT_SLOWLANE_* constants. Resolved
reservation logged at init; under-provisioned (n_vcpus<n_peers) clamp WARNs
loudly, never self-terminates. 8 unit cases, mutation-verified.
This commit is contained in:
Rongsong Shen 2026-06-26 04:58:07 +00:00
parent 295769d8ae
commit 729055a37f
8 changed files with 329 additions and 0 deletions
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18
src/controller/ha.c
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@ -580,6 +580,24 @@ uint64_t ha_promotion_truncate_floor(uint64_t safe_lsn, uint64_t durable_tip)
return safe_lsn > durable_tip ? safe_lsn : durable_tip;
}
/* ── raft-drive-async task 1.1: peer-scaled liveness reservation ─────────────
*
* Pure: reserved = max(1, min(n_peers - 1, n_vcpus - 1)). The floor of 1 is
* applied LAST so deadlock-freedom (>=1 guaranteed-free liveness worker) holds
* even when the n_vcpus ceiling would otherwise drive the value to 0 (e.g.
* n_vcpus == 1). See ha.h for the full rationale; the caller WARNs on the
* under-provisioned (n_vcpus < n_peers) clamp — this helper never logs. */
int drive_async_liveness_reserved(int n_peers, int n_vcpus)
{
int desired = n_peers - 1; /* worst-case concurrent liveness work */
int ceiling = n_vcpus - 1; /* keep >=1 commit (REQ_BLOCK) slot */
int reserved = desired < ceiling ? desired : ceiling; /* min(desired, ceiling) */
if (reserved < 1) /* floor applied LAST — always wins */
reserved = 1;
return reserved;
}
/* ── ha-commit-durability task 4.3: pre-promotion eligibility gate ───────────
*
* ha_promotion_gate_decision: pure decision (Req 2.2, 2.5, 2.6). Build the Boot