MDEV-5744 OQGRAPH backing table changes not reflected in OQGRAPH table

Disable query cache for OQGRAPH

storage/oqgraph/ha_oqgraph.h

@@ -115,6 +115,20 @@ public:
   virtual const char *table_type() const { return hton_name(ht)->str; }
 #endif
 
+  my_bool register_query_cache_table(THD *thd, char *table_key,
+                                     uint key_length,
+                                     qc_engine_callback
+                                     *engine_callback,
+                                     ulonglong *engine_data)
+  {
+    /* 
+      Do not put data from OQGRAPH tables into query cache (because there 
+      is no way to tell whether the data in the backing table has changed or 
+      not)
+    */
+    return FALSE;
+  }
+
 private:
   int oqgraph_check_table_structure (TABLE *table_arg);
 

storage/oqgraph/mysql-test/oqgraph/regression_mdev5744.opt

+--query_cache_type=ON

storage/oqgraph/mysql-test/oqgraph/regression_mdev5744.result

+DROP TABLE IF EXISTS graph_base;
+DROP TABLE IF EXISTS graph;
+CREATE TABLE graph_base (
+from_id INT UNSIGNED NOT NULL,
+to_id INT UNSIGNED NOT NULL,
+PRIMARY KEY (from_id,to_id),
+INDEX (to_id)
+) ENGINE=MyISAM;
+CREATE TABLE graph (
+latch   VARCHAR(32) NULL,
+origid  BIGINT    UNSIGNED NULL,
+destid  BIGINT    UNSIGNED NULL,
+weight  DOUBLE    NULL,
+seq     BIGINT    UNSIGNED NULL,
+linkid  BIGINT    UNSIGNED NULL,
+KEY (latch, origid, destid) USING HASH,
+KEY (latch, destid, origid) USING HASH
+) ENGINE=OQGRAPH DATA_TABLE='graph_base' ORIGID='from_id', DESTID='to_id';
+INSERT INTO graph_base(from_id, to_id) VALUES (1,2), (2,1);
+SET @query_cache_size.saved = @@query_cache_size;
+SET GLOBAL query_cache_size = 1024*1024;
+SELECT * FROM graph;
+latch	origid	destid	weight	seq	linkid
+NULL	1	2	1	NULL	NULL
+NULL	2	1	1	NULL	NULL
+UPDATE graph_base SET to_id = 20 WHERE from_id = 1;
+SELECT * FROM graph;
+latch	origid	destid	weight	seq	linkid
+NULL	1	20	1	NULL	NULL
+NULL	2	1	1	NULL	NULL
+SELECT SQL_NO_CACHE * FROM graph;
+latch	origid	destid	weight	seq	linkid
+NULL	1	20	1	NULL	NULL
+NULL	2	1	1	NULL	NULL
+SET GLOBAL query_cache_size = 0;
+SELECT SQL_NO_CACHE * FROM graph;
+latch	origid	destid	weight	seq	linkid
+NULL	1	20	1	NULL	NULL
+NULL	2	1	1	NULL	NULL
+DROP TABLE graph_base, graph;
+SET GLOBAL query_cache_size = @query_cache_size.saved;

storage/oqgraph/mysql-test/oqgraph/regression_mdev5744.test

+# Regression test for https://mariadb.atlassian.net/browse/MDEV-5744
+#--reproduce bug where changes to backing table data are not reflected 
+# in a graph table due to query caching
+
+--disable_warnings
+DROP TABLE IF EXISTS graph_base;
+DROP TABLE IF EXISTS graph;
+--enable_warnings
+
+# Create the backing store
+CREATE TABLE graph_base (
+    from_id INT UNSIGNED NOT NULL,
+    to_id INT UNSIGNED NOT NULL,
+    PRIMARY KEY (from_id,to_id),
+    INDEX (to_id)
+  ) ENGINE=MyISAM;
+
+
+CREATE TABLE graph (
+    latch   VARCHAR(32) NULL,
+    origid  BIGINT    UNSIGNED NULL,
+    destid  BIGINT    UNSIGNED NULL,
+    weight  DOUBLE    NULL,
+    seq     BIGINT    UNSIGNED NULL,
+    linkid  BIGINT    UNSIGNED NULL,
+    KEY (latch, origid, destid) USING HASH,
+    KEY (latch, destid, origid) USING HASH
+  ) ENGINE=OQGRAPH DATA_TABLE='graph_base' ORIGID='from_id', DESTID='to_id';
+
+
+INSERT INTO graph_base(from_id, to_id) VALUES (1,2), (2,1);
+
+SET @query_cache_size.saved = @@query_cache_size;
+SET GLOBAL query_cache_size = 1024*1024;
+
+SELECT * FROM graph;
+UPDATE graph_base SET to_id = 20 WHERE from_id = 1;
+
+SELECT * FROM graph;
+SELECT SQL_NO_CACHE * FROM graph;
+
+SET GLOBAL query_cache_size = 0;
+
+SELECT SQL_NO_CACHE * FROM graph;
+
+DROP TABLE graph_base, graph;
+SET GLOBAL query_cache_size = @query_cache_size.saved;
+