MXS-1203: Better handling of batch queries

When batched queries are done through readwritesplit, it will now handle
them one by one. This allows batched queries to be used with
readwritesplit but it does impose a performance penalty when compared to
direct execution on the backend.

server/modules/routing/readwritesplit/readwritesplit.h

@@ -234,6 +234,39 @@ typedef struct sescmd_cursor_st
 #endif
 } sescmd_cursor_t;
 
+/** Enum for tracking client reply state */
+typedef enum
+{
+    REPLY_STATE_START,       /**< Query sent to backend */
+    REPLY_STATE_DONE,        /**< Complete reply received */
+    REPLY_STATE_RSET_COLDEF, /**< Resultset response, waiting for column definitions */
+    REPLY_STATE_RSET_ROWS    /**< Resultset response, waiting for rows */
+} reply_state_t;
+
+/**
+ * Helper function to convert reply_state_t to string
+ */
+static inline const char* rstostr(reply_state_t state)
+{
+    switch (state)
+    {
+    case REPLY_STATE_START:
+        return "REPLY_STATE_START";
+
+    case REPLY_STATE_DONE:
+        return "REPLY_STATE_DONE";
+
+    case REPLY_STATE_RSET_COLDEF:
+        return "REPLY_STATE_RSET_COLDEF";
+
+    case REPLY_STATE_RSET_ROWS:
+        return "REPLY_STATE_RSET_ROWS";
+    }
+
+    ss_dassert(false);
+    return "UNKNOWN";
+}
+
 /**
  * Reference to BACKEND.
  *
@@ -249,9 +282,9 @@ typedef struct backend_ref_st
     bref_state_t    bref_state;
     int             bref_num_result_wait;
     sescmd_cursor_t bref_sescmd_cur;
-    GWBUF*          bref_pending_cmd; /**< For stmt which can't be routed due active sescmd execution */
     unsigned char   reply_cmd;  /**< The reply the backend server sent to a session command.
                                  * Used to detect slaves that fail to execute session command. */
+    reply_state_t   reply_state; /**< Reply state of the current query */
 #if defined(SS_DEBUG)
     skygw_chk_t     bref_chk_tail;
 #endif
@@ -322,6 +355,8 @@ struct router_client_session
     DCB*             client_dcb;
     int              pos_generator;
     backend_ref_t    *forced_node; /*< Current server where all queries should be sent */
+    int              expected_responses; /**< Number of expected responses to the current query */
+    GWBUF*           query_queue; /**< Queued commands waiting to be executed */
 #if defined(PREP_STMT_CACHING)
     HASHTABLE*       rses_prep_stmt[2];
 #endif
@@ -359,6 +394,22 @@ typedef struct router_instance
 #define BACKEND_TYPE(b) (SERVER_IS_MASTER((b)->backend_server) ? BE_MASTER :    \
         (SERVER_IS_SLAVE((b)->backend_server) ? BE_SLAVE :  BE_UNDEFINED));
 
+/**
+ * @brief Route a stored query
+ *
+ * When multiple queries are executed in a pipeline fashion, the readwritesplit
+ * stores the extra queries in a queue. This queue is emptied after reading a
+ * reply from the backend server.
+ *
+ * @param rses Router client session
+ * @return True if a stored query was routed successfully
+ */
+bool route_stored_query(ROUTER_CLIENT_SES *rses);
+
+/** Reply state change debug logging */
+#define LOG_RS(a, b) MXS_DEBUG("[%s]:%d %s -> %s", (a)->ref->server->name, \
+    (a)->ref->server->port, rstostr((a)->reply_state), rstostr(b));
+
 MXS_END_DECLS
 
 #endif /*< _RWSPLITROUTER_H */