[Tarantool-patches] [PATCH] applier: follow vclock to the last tx row

[Serge Petrenko <sergepetrenko@tarantool.org>]

Since the introduction of transaction boundaries in replication
protocol, appliers follow replicaset.applier.vclock to the lsn of the
first row in an arrived batch. This is enough and doesn't lead to errors
when replicating from other instances, respecting transaction boundaries
(instances with version 2.1.2 and up). However, if there's a 1.10
instance in 2.1.2+ cluster, it sends every single tx row as a separate
transaction, breaking the comparison with replicaset.applier.vclock and
making the applier apply part of the changes, it has already applied
when processing a full transaction coming from another 2.x instance.
Such behaviour leads to ER_TUPLE_FOUND errors in the scenario described
above.
In order to guard from such cases, follow replicaset.applier.vclock to
the lsn of the last row in tx.

Closes #4924
---
https://github.com/tarantool/tarantool/issues/4924
https://github.com/tarantool/tarantool/tree/sp/gh-4924-applier-duplicate-key

 src/box/applier.cc | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/box/applier.cc b/src/box/applier.cc
index 68de3c08c..eb0297f73 100644
--- a/src/box/applier.cc
+++ b/src/box/applier.cc
@@ -736,6 +736,7 @@ applier_apply_tx(struct stailq *rows)
 {
 	struct xrow_header *first_row = &stailq_first_entry(rows,
 					struct applier_tx_row, next)->row;
+	struct xrow_header *last_row;
 	struct replica *replica = replica_by_id(first_row->replica_id);
 	/*
 	 * In a full mesh topology, the same set of changes
@@ -827,8 +828,9 @@ applier_apply_tx(struct stailq *rows)
 		goto fail;
 
 	/* Transaction was sent to journal so promote vclock. */
-	vclock_follow(&replicaset.applier.vclock,
-		      first_row->replica_id, first_row->lsn);
+	last_row = &stailq_last_entry(rows, struct applier_tx_row, next)->row;
+	vclock_follow(&replicaset.applier.vclock, last_row->replica_id,
+		      last_row->lsn);
 	latch_unlock(latch);
 	return 0;
 rollback:
-- 
2.21.1 (Apple Git-122.3)