MXS-1066 Add query hint to route to last used server

Add new hint type and support for it in the readwritesplit router.

include/maxscale/hint.h

@@ -31,6 +31,7 @@ typedef enum
     HINT_ROUTE_TO_NAMED_SERVER,
     HINT_ROUTE_TO_UPTODATE_SERVER, /*< not supported by RWSplit and HintRouter */
     HINT_ROUTE_TO_ALL, /*< not supported by RWSplit, supported by HintRouter */
+    HINT_ROUTE_TO_LAST_USED,
     HINT_PARAMETER
 } HINT_TYPE;
 

include/maxscale/queryclassifier.hh

@@ -117,7 +117,8 @@ public:
         TARGET_SLAVE        = 0x02,
         TARGET_NAMED_SERVER = 0x04,
         TARGET_ALL          = 0x08,
-        TARGET_RLAG_MAX     = 0x10
+        TARGET_RLAG_MAX     = 0x10,
+        TARGET_LAST_USED    = 0x20
     };
 
     static bool target_is_master(uint32_t t)
@@ -145,6 +146,11 @@ public:
         return (t & TARGET_RLAG_MAX);
     }
 
+    static bool target_is_last_used(uint32_t t)
+    {
+        return (t & TARGET_LAST_USED);
+    }
+
     enum current_target_t
     {
         CURRENT_TARGET_UNDEFINED, /**< Current target has not been set. */

server/core/queryclassifier.cc

@@ -530,6 +530,11 @@ uint32_t QueryClassifier::get_route_target(uint8_t command, uint32_t qtype, HINT
                 ss_dassert(false);
                 break;
 
+            case HINT_ROUTE_TO_LAST_USED:
+                MXS_DEBUG("Hint: route to last used");
+                target = TARGET_LAST_USED;
+                break;
+
             case HINT_PARAMETER:
                 if (strncasecmp((char*)pHint->data, "max_slave_replication_lag",
                                 strlen("max_slave_replication_lag")) == 0)

server/modules/filter/hintfilter/hintparser.cc

@@ -49,6 +49,7 @@ static struct
     { "master", TOK_MASTER},
     { "slave", TOK_SLAVE},
     { "server", TOK_SERVER},
+    { "last" , TOK_LAST},
     { NULL, static_cast<TOKEN_VALUE>(0)}
 };
 
@@ -334,6 +335,12 @@ hint_parser(HINT_SESSION *session, GWBUF *request)
                 rval = hint_create_route(rval,
                                          HINT_ROUTE_TO_SLAVE, NULL);
                 break;
+
+            case TOK_LAST:
+                rval = hint_create_route(rval,
+                                         HINT_ROUTE_TO_LAST_USED, NULL);
+                break;
+
             case TOK_SERVER:
                 state = HS_ROUTE_SERVER;
                 break;

server/modules/filter/hintfilter/mysqlhint.h

@@ -40,6 +40,7 @@ typedef enum
     TOK_MASTER,
     TOK_SLAVE,
     TOK_SERVER,
+    TOK_LAST,
     TOK_LINEBRK,
     TOK_END
 } TOKEN_VALUE;

server/modules/routing/readwritesplit/rwsplit_route_stmt.cc

@@ -281,6 +281,13 @@ bool RWSplitSession::route_single_stmt(GWBUF *querybuf)
                 succp = true;
             }
         }
+        else if (TARGET_IS_LAST_USED(route_target))
+        {
+            if ((target = get_last_used_backend()))
+            {
+                succp = true;
+            }
+        }
         else if (TARGET_IS_SLAVE(route_target))
         {
             if ((target = handle_slave_is_target(command, stmt_id)))
@@ -644,6 +651,11 @@ SRWBackend RWSplitSession::get_master_backend()
     return rval;
 }
 
+SRWBackend RWSplitSession::get_last_used_backend()
+{
+    return m_prev_target ? m_prev_target : get_master_backend();
+}
+
 /**
  * Provide the router with a reference to a suitable backend
  *

server/modules/routing/readwritesplit/rwsplitsession.cc

@@ -993,6 +993,7 @@ bool RWSplitSession::supports_hint(HINT_TYPE hint_type) const
     case HINT_ROUTE_TO_MASTER:
     case HINT_ROUTE_TO_SLAVE:
     case HINT_ROUTE_TO_NAMED_SERVER:
+    case HINT_ROUTE_TO_LAST_USED:
     case HINT_PARAMETER:
         break;
 

server/modules/routing/readwritesplit/rwsplitsession.hh

@@ -27,6 +27,7 @@
 #define TARGET_IS_NAMED_SERVER(t)   maxscale::QueryClassifier::target_is_named_server(t)
 #define TARGET_IS_ALL(t)            maxscale::QueryClassifier::target_is_all(t)
 #define TARGET_IS_RLAG_MAX(t)       maxscale::QueryClassifier::target_is_rlag_max(t)
+#define TARGET_IS_LAST_USED(t)      maxscale::QueryClassifier::target_is_last_used(t)
 
 typedef std::map<uint32_t, uint32_t> ClientHandleMap;  /** External ID to internal ID */
 
@@ -57,6 +58,7 @@ public:
         TARGET_NAMED_SERVER = maxscale::QueryClassifier::TARGET_NAMED_SERVER,
         TARGET_ALL          = maxscale::QueryClassifier::TARGET_ALL,
         TARGET_RLAG_MAX     = maxscale::QueryClassifier::TARGET_RLAG_MAX,
+        TARGET_LAST_USED    = maxscale::QueryClassifier::TARGET_LAST_USED,
     };
 
     enum otrx_state
@@ -174,6 +176,7 @@ private:
     mxs::SRWBackend get_hinted_backend(char *name);
     mxs::SRWBackend get_slave_backend(int max_rlag);
     mxs::SRWBackend get_master_backend();
+    mxs::SRWBackend get_last_used_backend();
     mxs::SRWBackend get_target_backend(backend_type_t btype, char *name, int max_rlag);
 
     bool handle_target_is_all(route_target_t route_target, GWBUF *querybuf,