refs codership/mysql-wsrep#201

- Fixes query cache so that it is aware of wsrep_sync_wait.
  Query cache would return (possibly stale) results to the
  client, regardless of the value of wsrep_sync_wait.
- Includes the test case that reproduced the issue.

mysql-test/suite/galera/r/mysql-wsrep#201.result

+CREATE TABLE t1 (id INT PRIMARY KEY AUTO_INCREMENT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (DEFAULT);
+SET GLOBAL query_cache_size=1355776;
+SET SESSION wsrep_sync_wait = 7;

mysql-test/suite/galera/t/mysql-wsrep#201-master.opt

+--query_cache_type=1

mysql-test/suite/galera/t/mysql-wsrep#201.test

+--source include/galera_cluster.inc
+--source include/have_innodb.inc
+--source include/have_query_cache.inc
+
+CREATE TABLE t1 (id INT PRIMARY KEY AUTO_INCREMENT) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (DEFAULT);
+
+--connection node_2
+--let $qcache_size_orig = `SELECT @@GLOBAL.query_cache_size`
+SET GLOBAL query_cache_size=1355776;
+SET SESSION wsrep_sync_wait = 7;
+
+--disable_query_log
+
+--let $count = 10000
+while ($count)
+{
+  --connection node_1
+  INSERT INTO t1 VALUES (DEFAULT);
+  --let $val1 = `SELECT LAST_INSERT_ID()`
+  --connection node_2
+  --let $val2 = `SELECT MAX(id) FROM t1`
+  --let $val3 = `SELECT $val1 != $val2`
+  if ($val3)
+  {
+    --echo $val1 $val2
+    --die wsrep_sync_wait failed
+  }
+  --dec $count
+}
+
+--eval SET GLOBAL query_cache_size = $qcache_size_orig
+DROP TABLE t1;

sql/sql_cache.cc

@@ -1804,6 +1804,7 @@ Query_cache::send_result_to_client(THD *thd, char *org_sql, uint query_length)
       goto err;
     }
   }
+
   /*
     Try to obtain an exclusive lock on the query cache. If the cache is
     disabled or if a full cache flush is in progress, the attempt to
@@ -1915,6 +1916,25 @@ def_week_frmt: %lu, in_trans: %d, autocommit: %d",
   }
   DBUG_PRINT("qcache", ("Query in query hash 0x%lx", (ulong)query_block));
 
+#ifdef WITH_WSREP
+  if (WSREP_CLIENT(thd) && wsrep_must_sync_wait(thd)) {
+    unlock();
+    if (wsrep_sync_wait(thd))
+      goto err;
+    if (try_lock(TRUE))
+      goto err;
+    query_block = (Query_cache_block *) my_hash_search(&queries,
+                                                       (uchar*) sql,
+                                                       tot_length);
+    if (query_block == 0 ||
+        query_block->query()->result() == 0 ||
+        query_block->query()->result()->type != Query_cache_block::RESULT)
+    {
+      goto err_unlock;
+    }
+  }
+#endif /* WITH_WSREP */
+
   /* Now lock and test that nothing changed while blocks was unlocked */
   BLOCK_LOCK_RD(query_block);
 

sql/sql_class.cc

@@ -1118,6 +1118,7 @@ THD::THD()
   wsrep_bf_thd            = NULL;
   wsrep_TOI_pre_query     = NULL;
   wsrep_TOI_pre_query_len = 0;
+  wsrep_sync_wait_gtid= WSREP_GTID_UNDEFINED;
 #endif
   /* Call to init() below requires fully initialized Open_tables_state. */
   reset_open_tables_state(this);
@@ -1487,6 +1488,7 @@ void THD::init(void)
   wsrep_bf_thd = NULL;
   wsrep_TOI_pre_query     = NULL;
   wsrep_TOI_pre_query_len = 0;
+  wsrep_sync_wait_gtid= WSREP_GTID_UNDEFINED;
 
   /*
     @@wsrep_causal_reads is now being handled via wsrep_sync_wait, update it
@@ -2137,6 +2139,10 @@ void THD::cleanup_after_query()
     rli_slave->cleanup_after_query();
 #endif
 
+#ifdef WITH_WSREP
+  wsrep_sync_wait_gtid= WSREP_GTID_UNDEFINED;
+#endif /* WITH_WSREP */
+
   DBUG_VOID_RETURN;
 }
 

sql/sql_class.h

@@ -2395,6 +2395,7 @@ public:
   size_t                    wsrep_TOI_pre_query_len;
   void*                     wsrep_apply_format;
   bool                      wsrep_apply_toi; /* applier processing in TOI */
+  wsrep_gtid_t              wsrep_sync_wait_gtid;
 #endif /* WITH_WSREP */
   /**
     Internal parser state.

sql/wsrep_mysqld.cc

@@ -866,19 +866,24 @@ bool wsrep_start_replication()
   return true;
 }
 
+bool wsrep_must_sync_wait (THD* thd, uint mask)
+{
+  return (thd->variables.wsrep_sync_wait & mask) &&
+    thd->variables.wsrep_on &&
+    !thd->in_active_multi_stmt_transaction() &&
+    thd->wsrep_conflict_state != REPLAYING &&
+    thd->wsrep_sync_wait_gtid.seqno == WSREP_SEQNO_UNDEFINED;
+}
+
 bool wsrep_sync_wait (THD* thd, uint mask)
 {
-  if ((thd->variables.wsrep_sync_wait & mask) &&
-      thd->variables.wsrep_on &&
-      !thd->in_active_multi_stmt_transaction() &&
-      thd->wsrep_conflict_state != REPLAYING)
+  if (wsrep_must_sync_wait(thd, mask))
   {
     WSREP_DEBUG("wsrep_sync_wait: thd->variables.wsrep_sync_wait = %u, mask = %u",
                 thd->variables.wsrep_sync_wait, mask);
     // This allows autocommit SELECTs and a first SELECT after SET AUTOCOMMIT=0
     // TODO: modify to check if thd has locked any rows.
-    wsrep_gtid_t  gtid;
-    wsrep_status_t ret= wsrep->causal_read (wsrep, &gtid);
+    wsrep_status_t ret= wsrep->causal_read (wsrep, &thd->wsrep_sync_wait_gtid);
 
     if (unlikely(WSREP_OK != ret))
     {

sql/wsrep_mysqld.h

@@ -183,6 +183,7 @@ extern void wsrep_kill_mysql(THD *thd);
 /* new defines */
 extern void wsrep_stop_replication(THD *thd);
 extern bool wsrep_start_replication();
+extern bool wsrep_must_sync_wait (THD* thd, uint mask = WSREP_SYNC_WAIT_BEFORE_READ);
 extern bool wsrep_sync_wait (THD* thd, uint mask = WSREP_SYNC_WAIT_BEFORE_READ);
 extern int  wsrep_check_opts (int argc, char* const* argv);
 extern void wsrep_prepend_PATH (const char* path);