DB-506 add a session variable to enable/disable bulk fetch default enabled

storage/tokudb/ha_tokudb.cc

@@ -4370,7 +4370,7 @@ static bool tokudb_do_bulk_fetch(THD *thd) {
     case SQLCOM_CREATE_TABLE:
     case SQLCOM_INSERT_SELECT:
     case SQLCOM_REPLACE_SELECT:
-        return true;
+        return THDVAR(thd, bulk_fetch) != 0;
     default:
         return false;
     }

storage/tokudb/hatoku_hton.cc

@@ -1428,6 +1428,7 @@ static struct st_mysql_sys_var *tokudb_system_variables[] = {
 #if TOKUDB_CHECK_JEMALLOC
     MYSQL_SYSVAR(check_jemalloc),
 #endif
+    MYSQL_SYSVAR(bulk_fetch),
     NULL
 };
 

storage/tokudb/hatoku_hton.h

@@ -515,6 +515,8 @@ static uint tokudb_check_jemalloc;
 static MYSQL_SYSVAR_UINT(check_jemalloc, tokudb_check_jemalloc, 0, "Check if jemalloc is linked", NULL, NULL, 1, 0, 1, 0);
 #endif
 
+static MYSQL_THDVAR_BOOL(bulk_fetch, PLUGIN_VAR_THDLOCAL, "enable bulk fetch", NULL /*check*/, NULL /*update*/, true /*default*/);
+
 extern HASH tokudb_open_tables;
 extern pthread_mutex_t tokudb_mutex;
 extern uint32_t tokudb_write_status_frequency;