ha_innodb.cc:

  Add comments about why the InnoDB latching order is obeyed also for the MySQL query cache mutex; add an error printf if that is not the case
sync0sync.h:
  Assign sync0sync.h ranks also for the MySQL query cache mutex and the MySQL binlog mutex; the latching order must be obeyed also for these
row0ins.c:
  Add a comment why the query cache invalidate operation cannot deadlock in a cascaded FOREIGN KEY operation


innobase/row/row0ins.c:
  Add a comment why the query cache invalidate operation cannot deadlock in a cascaded FOREIGN KEY operation
innobase/include/sync0sync.h:
  Assign sync0sync.h ranks also for the MySQL query cache mutex and the MySQL binlog mutex; the latching order must be obeyed also for these
sql/ha_innodb.cc:
  Add comments about why the InnoDB latching order is obeyed also for the MySQL query cache mutex; add an error printf if that is not the case

1 files changed, 19 insertions, 1 deletions

diff --git a/sql/ha_innodb.cc b/sql/ha_innodb.cc
index 0bca8c21715..3df61333b75 100644
--- a/sql/ha_innodb.cc
+++ b/sql/ha_innodb.cc
@@ -765,7 +765,14 @@ returns TRUE for all tables in the query.
 
 If thd is not in the autocommit state, this function also starts a new
 transaction for thd if there is no active trx yet, and assigns a consistent
-read view to it if there is no read view yet. */
+read view to it if there is no read view yet.
+
+Why a deadlock of threads is not possible: the query cache calls this function
+at the start of a SELECT processing. Then the calling thread cannot be
+holding any InnoDB semaphores. The calling thread is holding the
+query cache mutex, and this function will reserver the InnoDB kernel mutex.
+Thus, the 'rank' in sync0sync.h of the MySQL query cache mutex is above
+the InnoDB kernel mutex. */
 
 my_bool
 innobase_query_caching_of_table_permitted(
@@ -802,6 +809,13 @@ innobase_query_caching_of_table_permitted(
 		trx = check_trx_exists(thd);
 	}
 
+	if (trx->has_search_latch) {
+		ut_print_timestamp(stderr);
+		fprintf(stderr,
+"  InnoDB: Error: the calling thread is holding the adaptive search\n"
+"InnoDB: latch though calling innobase_query_caching_of_table_permitted\n");
+	}
+
 	innobase_release_stat_resources(trx);
 
 	if (!(thd->options & (OPTION_NOT_AUTOCOMMIT | OPTION_BEGIN))) {
@@ -877,6 +891,10 @@ innobase_invalidate_query_cache(
 	ulint	full_name_len)	/* in: full name length where also the null
 				chars count */
 {
+	/* Note that the sync0sync.h rank of the query cache mutex is just
+	above the InnoDB kernel mutex. The caller of this function must not
+	have latches of a lower rank. */
+
 	/* Argument TRUE below means we are using transactions */
 #ifdef HAVE_QUERY_CACHE
 	query_cache.invalidate((THD*)(trx->mysql_thd),