[PATCH 3/4] vinyl: do not panic if secondary index is inconsistent with primary

[Vladimir Davydov <vdavydov.dev@gmail.com>]

Although the bug in vy_task_dump_complete() due to which a tuple could
be lost during dump was fixed, there still may be affected deployments
as the bug was persisted on disk. To avoid occasional crashes on such
deployments, let's make vinyl_iterator_secondary_next() skip tuples that
are present in a secondary index but missing in the primary.

Closes #3393
---
 src/box/vinyl.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/box/vinyl.c b/src/box/vinyl.c
index ff4c2831..05aab30b 100644
--- a/src/box/vinyl.c
+++ b/src/box/vinyl.c
@@ -3844,6 +3844,7 @@ vinyl_iterator_secondary_next(struct iterator *base, struct tuple **ret)
 	assert(it->lsm->index_id > 0);
 	struct tuple *tuple;
 
+next:
 	if (it->tx == NULL) {
 		diag_set(ClientError, ER_CURSOR_NO_TRANSACTION);
 		goto fail;
@@ -3853,7 +3854,6 @@ vinyl_iterator_secondary_next(struct iterator *base, struct tuple **ret)
 		goto fail;
 	}
 
-
 	if (vy_read_iterator_next(&it->iterator, &tuple) != 0)
 		goto fail;
 
@@ -3876,11 +3876,26 @@ vinyl_iterator_secondary_next(struct iterator *base, struct tuple **ret)
 	 * Note, there's no need in vy_tx_track() as the
 	 * tuple is already tracked in the secondary index.
 	 */
+	struct tuple *full_tuple;
 	if (vy_point_lookup(it->lsm->pk, it->tx, vy_tx_read_view(it->tx),
-			    tuple, &tuple) != 0)
+			    tuple, &full_tuple) != 0)
 		goto fail;
-	*ret = tuple_bless(tuple);
-	tuple_unref(tuple);
+	if (full_tuple == NULL) {
+		/*
+		 * All indexes of a space must be consistent, i.e.
+		 * if a tuple is present in one index, it must be
+		 * present in all other indexes as well, so we can
+		 * get here only if there's a bug somewhere in vinyl.
+		 * Don't abort as core dump won't really help us in
+		 * this case. Just warn the user and proceed to the
+		 * next tuple.
+		 */
+		say_warn("%s: key %s missing in primary index",
+			 vy_lsm_name(it->lsm), vy_stmt_str(tuple));
+		goto next;
+	}
+	*ret = tuple_bless(full_tuple);
+	tuple_unref(full_tuple);
 	if (*ret != NULL)
 		return 0;
 fail:
-- 
2.11.0