Track session state only when required

The protocol should not track the session state as the parsing is quite
expensive with the current code. This change is a workaround that enables
the parsing only when required. A proper way to handle this would be to do
all the response processing in one place thus avoiding the duplication of
work.

include/maxscale/buffer.h

@@ -56,6 +56,7 @@ typedef enum
     GWBUF_TYPE_RESULT         = (1 << 3),
     GWBUF_TYPE_REPLY_OK       = (1 << 4),
     GWBUF_TYPE_REPLAYED       = (1 << 5),
+    GWBUF_TYPE_TRACK_STATE    = (1 << 6),
 } gwbuf_type_t;
 
 #define GWBUF_IS_TYPE_UNDEFINED(b)     ((b)->gwbuf_type == 0)
@@ -65,7 +66,10 @@ typedef enum
 #define GWBUF_IS_REPLY_OK(b)           ((b)->gwbuf_type & GWBUF_TYPE_REPLY_OK)
 
 // True if the query is not initiated by the client but an internal replaying mechanism
-#define GWBUF_IS_REPLAYED(b)           ((b)->gwbuf_type & GWBUF_TYPE_REPLAYED)
+#define GWBUF_IS_REPLAYED(b) ((b)->gwbuf_type & GWBUF_TYPE_REPLAYED)
+
+// Track session state change response
+#define GWBUF_SHOULD_TRACK_STATE(b) ((b)->gwbuf_type & GWBUF_TYPE_TRACK_STATE)
 
 typedef enum
 {

include/maxscale/protocol/mysql.h

@@ -338,6 +338,7 @@ typedef struct
     GWBUF*                 stored_query;                /*< Temporarily stored queries */
     bool                   collect_result;              /*< Collect the next result set as one buffer */
     bool                   changing_user;
+    bool                   track_state;     /*< Track session state */
     uint32_t               num_eof_packets; /*< Encountered eof packet number, used for check
                                              * packet type */
     bool large_query;                       /*< Whether to ignore the command byte of the next

server/modules/protocol/MySQL/mariadbbackend/mysql_backend.cc

@@ -447,6 +447,8 @@ static inline void prepare_for_write(DCB* dcb, GWBUF* buffer)
     {
         proto->collect_result = true;
     }
+
+    proto->track_state = GWBUF_SHOULD_TRACK_STATE(buffer);
 }
 
 /*******************************************************************************
@@ -836,7 +838,8 @@ static int gw_read_and_write(DCB* dcb)
          * The OK packets sent in response to COM_STMT_PREPARE are of a different
          * format so we need to detect and skip them. */
         if (rcap_type_required(capabilities, RCAP_TYPE_SESSION_STATE_TRACKING)
-            && !expecting_ps_response(proto))
+            && !expecting_ps_response(proto)
+            && proto->track_state)
         {
             mxs_mysql_get_session_track_info(tmp, proto);
         }

server/modules/protocol/MySQL/mysql_common.cc

@@ -63,6 +63,7 @@ MySQLProtocol* mysql_protocol_init(DCB* dcb, int fd)
     p->changing_user = false;
     p->num_eof_packets = 0;
     p->large_query = false;
+    p->track_state = false;
     /*< Assign fd with protocol */
     p->fd = fd;
     p->owner_dcb = dcb;

server/modules/routing/readwritesplit/rwsplit_route_stmt.cc

@@ -280,6 +280,11 @@ bool RWSplitSession::route_single_stmt(GWBUF* querybuf)
         }
         else if (TARGET_IS_MASTER(route_target))
         {
+            if (m_config.causal_reads)
+            {
+                gwbuf_set_type(querybuf, GWBUF_TYPE_TRACK_STATE);
+            }
+
             succp = handle_master_is_target(&target);
 
             if (!succp && should_migrate_trx(target))