Bug#17599258:- ERROR 1160 (08S01): GOT AN ERROR WRITING

Arun Kuruvila · Arun Kuruvila · commit a9b61b002971 · 2014-11-10T16:21:59.000+05:30
COMMUNICATION PACKETS; FEDERATED TABLE

Description:- Execution of FLUSH TABLES on a federated
table which has been idle for wait_timeout (on the remote
server) + tcp_keepalive_time, fails with an error,
"ERROR 1160 (08S01): Got an error writing communication
packets."

Analysis:- During FLUSH TABLE execution the federated
table is closed which will inturn close the federated
connection. While closing the connection, federated server
tries to communincate with the remote server. Since the
connection was idle for wait_timeout(on the remote server)+
tcp_keepalive_time, the socket gets closed. So this
communication fails because of broken pipe and the error is
thrown. But federated connections are expected to reconnect
silently. And also it cannot reconnect because the 
"auto_reconnect" variable is set to 0 in "mysql_close()".

Fix:- Before closing the federated connection, in
"ha_federated_close()", a check is added which will verify
wheather the connection is alive or not. If the connection
is not alive, then "mysql-&gt;net.error" is set to 2 which
will indicate that the connetion is broken. Also the
setting of "auto_reconnect" variable to 0 is delayed and is
done after "COM_QUIT" command.
      
NOTE:- For reproducing this issue, "tcp_keepalive_time" has
to be set to a smaller value. This value is set in the
"/proc/sys/net/ipv4/tcp_keepalive_time" file in Unix
systems. So we need root permission for changing it, which
can't be done through mtr test. So submitting the patch
without mtr test.
diff --git a/sql-common/client.c b/sql-common/client.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2003, 2014, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -3808,8 +3808,8 @@ void STDCALL mysql_close(MYSQL *mysql)
     {
       free_old_query(mysql);
       mysql->status=MYSQL_STATUS_READY; /* Force command */
-      mysql->reconnect=0;
       simple_command(mysql,COM_QUIT,(uchar*) 0,0,1);
+      mysql->reconnect=0;
       end_server(mysql);			/* Sets mysql->net.vio= 0 */
     }
     mysql_close_free_options(mysql);
diff --git a/storage/federated/ha_federated.cc b/storage/federated/ha_federated.cc
@@ -1,4 +1,4 @@
-/* Copyright (c) 2004, 2013, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2004, 2014, Oracle and/or its affiliates. All rights reserved.
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -1678,9 +1678,17 @@ int ha_federated::close(void)
   DBUG_ENTER("ha_federated::close");
 
   free_result();
-  
+
   delete_dynamic(&results);
-  
+
+  /*
+    Check to verify wheather the connection is still alive or not.
+    FLUSH TABLES will quit the connection and if connection is broken,
+    it will reconnect again and quit silently.
+  */
+  if (mysql && !vio_is_connected(mysql->net.vio))
+     mysql->net.error= 2;
+
   /* Disconnect from mysql */
   mysql_close(mysql);
   mysql= NULL;

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		`-/* Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.`
	`1`	`+/* Copyright (c) 2003, 2014, Oracle and/or its affiliates. All rights reserved.`
`2`	`2`
`3`	`3`	`This program is free software; you can redistribute it and/or modify`
`4`	`4`	`it under the terms of the GNU General Public License as published by`
`@@ -3808,8 +3808,8 @@ void STDCALL mysql_close(MYSQL *mysql)`
`3808`	`3808`	`{`
`3809`	`3809`	`free_old_query(mysql);`
`3810`	`3810`	`mysql->status=MYSQL_STATUS_READY; /* Force command */`
`3811`		`- mysql->reconnect=0;`
`3812`	`3811`	`simple_command(mysql,COM_QUIT,(uchar*) 0,0,1);`
	`3812`	`+ mysql->reconnect=0;`
`3813`	`3813`	`end_server(mysql); /* Sets mysql->net.vio= 0 */`
`3814`	`3814`	`}`
`3815`	`3815`	`mysql_close_free_options(mysql);`