[Tarantool-patches] [PATCH v4 02/16] txn_limbo: fix promote term filtering

[Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

txn_limbo_process() used to filter out promote requests whose term was
equal to the greatest term seen. This wasn't correct for PROMOTE entries
with term 1.

Such entries appear after box.ctl.promote() is issued on an instance
with disabled elections. Every PROMOTE entry from such an instance has
term 1, but should still be applied. Fix this in the patch.

Also, when an outdated PROMOTE entry with term smaller than already
applied from some replica arrived, it wasn't filtered at all. Such a
situation shouldn't be possible, but fix it as well.

Part-of #6034
---
 src/box/txn_limbo.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/box/txn_limbo.c b/src/box/txn_limbo.c
index fdea287c7..6e5d6d04e 100644
--- a/src/box/txn_limbo.c
+++ b/src/box/txn_limbo.c
@@ -707,15 +707,18 @@ txn_limbo_process(struct txn_limbo *limbo, const struct synchro_request *req)
 	uint32_t origin = req->origin_id;
 	if (txn_limbo_replica_term(limbo, origin) < term) {
 		vclock_follow(&limbo->promote_term_map, origin, term);
-		if (term > limbo->promote_greatest_term) {
+		if (term > limbo->promote_greatest_term)
 			limbo->promote_greatest_term = term;
-		} else if (req->type == IPROTO_PROMOTE) {
-			/*
-			 * PROMOTE for outdated term. Ignore.
-			 */
-			return;
-		}
+	} else if (req->type == IPROTO_PROMOTE &&
+		   limbo->promote_greatest_term > 1) {
+		/* PROMOTE for outdated term. Ignore. */
+		say_info("RAFT: ignoring PROMOTE request from instance "
+			 "id %u for term %llu. Greatest term seen "
+			 "before (%llu) is bigger.", origin, (long long)term,
+			 (long long)limbo->promote_greatest_term);
+		return;
 	}
+
 	int64_t lsn = req->lsn;
 	if (req->replica_id == REPLICA_ID_NIL) {
 		/*
-- 
2.30.1 (Apple Git-130)