[Tarantool-patches] [PATCH 3/3] txn: warn "too long WAL" on write, not on commit

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

"Too long WAL write" is supposed to warn a user that either the
disk write was too long, or the event loop is too slow, maybe due
to certain fibers not doing yields often enough.

It was printed by the code doing the transaction commit. As a
result, for synchronous transactions the check also included the
replication time, often overflowing a threshold and printing
"too long WAL write" even when it had nothing to do with a WAL
write or the event loop being too slow.

The patch makes so the warning is checked and printed after WAL
write right away, not after commit.

Closes #5139
---
 src/box/txn.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/box/txn.c b/src/box/txn.c
index fd77a934a..c26116f1d 100644
--- a/src/box/txn.c
+++ b/src/box/txn.c
@@ -543,14 +543,6 @@ txn_complete_fail(struct txn *txn)
 void
 txn_complete_success(struct txn *txn)
 {
-	double stop_tm = ev_monotonic_now(loop());
-	if (stop_tm - txn->start_tm > too_long_threshold) {
-		int n_rows = txn->n_new_rows + txn->n_applier_rows;
-		say_warn_ratelimited("too long WAL write: %d rows at LSN %lld: "
-				     "%.3f sec", n_rows,
-				     txn->signature - n_rows + 1,
-				     stop_tm - txn->start_tm);
-	}
 	assert(!txn_has_flag(txn, TXN_IS_DONE));
 	assert(!txn_has_flag(txn, TXN_WAIT_SYNC));
 	assert(txn->signature >= 0);
@@ -587,6 +579,14 @@ txn_on_journal_write(struct journal_entry *entry)
 		txn_complete_fail(txn);
 		goto finish;
 	}
+	double stop_tm = ev_monotonic_now(loop());
+	if (stop_tm - txn->start_tm > too_long_threshold) {
+		int n_rows = txn->n_new_rows + txn->n_applier_rows;
+		say_warn_ratelimited("too long WAL write: %d rows at "
+				     "LSN %lld: %.3f sec", n_rows,
+				     txn->signature - n_rows + 1,
+				     stop_tm - txn->start_tm);
+	}
 	if (txn_has_flag(txn, TXN_HAS_TRIGGERS))
 		txn_run_wal_write_triggers(txn);
 	if (!txn_has_flag(txn, TXN_WAIT_SYNC))
-- 
2.21.1 (Apple Git-122.3)