338894 – [DB][Mysql] Exception when CDO is idle for a while

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Bug 338894 - [DB][Mysql] Exception when CDO is idle for a while

Summary: [DB][Mysql] Exception when CDO is idle for a while

Status:	CLOSED FIXED

Alias:	None

Product:	EMF
Classification:	Modeling
Component:	cdo.core (show other bugs)
Version:	4.0
Hardware:	All All

Importance:	P2 normal (vote)
Target Milestone:	---
Assignee:	Caspar D.
QA Contact:	Eike Stepper

URL:
Whiteboard:
Keywords:

Depends on:
Blocks:

Reported:	2011-03-04 03:07 EST by Egidijus Vaisnora
Modified:	2011-06-23 03:38 EDT (History)
CC List:	3 users (show)

See Also:

Flags:	stepper: review+

Attachments
Patch (13.02 KB, patch) 2011-03-24 01:49 EDT, Caspar D.	no flags	Details \| Diff
Patch v2 (13.02 KB, patch) 2011-03-24 02:23 EDT, Caspar D.	no flags	Details \| Diff
Patch v3 (13.93 KB, patch) 2011-03-24 04:21 EDT, Caspar D.	no flags	Details \| Diff
Patch v4 (22.15 KB, patch) 2011-04-04 01:41 EDT, Eike Stepper	no flags	Details \| Diff
Show Obsolete (4) View All Add an attachment (proposed patch, testcase, etc.)

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Description Egidijus Vaisnora

2011-03-04 03:07:19 EST

I left CDO server idle for a while and found stack trace in log:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Last packet sent to the server was 1 ms ago.
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
	at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)
	at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2985)
	at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2871)
	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3414)
	at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1936)
	at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060)
	at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2536)
	at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2465)
	at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1383)
	at org.eclipse.emf.cdo.server.internal.db.DBStoreAccessor$ConnectionKeepAliveTask.run(DBStoreAccessor.java:1285)
	at java.util.TimerThread.mainLoop(Timer.java:512)
	at java.util.TimerThread.run(Timer.java:462)
Caused by: java.net.SocketException: Connection reset
	at java.net.SocketInputStream.read(SocketInputStream.java:168)
	at com.mysql.jdbc.util.ReadAheadInputStream.fill(ReadAheadInputStream.java:113)
	at com.mysql.jdbc.util.ReadAheadInputStream.readFromUnderlyingStreamIfNecessary(ReadAheadInputStream.java:160)
	at com.mysql.jdbc.util.ReadAheadInputStream.read(ReadAheadInputStream.java:188)
	at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2428)
	at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2882)
	... 10 more

Comment 1 Stefan Winkler

2011-03-04 03:27:20 EST

Can you specify what "a while" is, roughly?

MySQL disvonnects a client after an idle time of 8 hours (default value, please check your MySQL server for your setting).

To prevent the disconnection, there is a timer facility in CDO which should prevent this by issuing a query every 4 hours (again, this is a default value that can be configured).

That said, there has been some work in the past year (I think Eike did it) to reduce the amount of single timers on the server. Maybe something got optimized away too much ;-)

Comment 2 Egidijus Vaisnora

2011-03-04 04:16:00 EST

I left it for a night... However I was able to use server after I discovered stack trace, hence I cannot say that it spoil server. On another hand, maybe server was responding by taking values from the cache, without connecting to DB, I cannot tell this exactly.

Comment 3 Caspar D.

2011-03-23 05:29:54 EDT

(In reply to comment #1)
> To prevent the disconnection, there is a timer facility in CDO which should
> prevent this by issuing a query every 4 hours

Er, yes. As can be seen from the stack trace, it is this keepalive
statement itself that fails.

Logical (but not the only possible) conclusion: the MySQL instance that
caused this 'incident', disconnected the client before the keepAlive
task got executed, and that means earlier than 4 hours.

> (again, this is a default value that can be configured).

How is that? At DBStoreAccessor.java:750, the task gets scheduled with
hardcoded values...

Comment 4 Caspar D.

2011-03-23 05:36:19 EDT

I propose we do two things:

1. Make the keepAlive period really configurable
2. If the keepAlive statement fails, try to open a new connection.

Comment 5 Caspar D.

2011-03-24 01:49:49 EDT

Created attachment 191804 [details]
Patch

Comment 6 Caspar D.

2011-03-24 02:09:08 EDT

MySQL's JDBC driver offers a property 'autoReconnect' which 
can be set to 'true' to make the driver itself attempt 
to reconnect when it discovers that the connection is no longer
alive. See:

http://dev.mysql.com/doc/refman/5.0/en/connector-j-reference-configuration-properties.html

Perhaps other drivers support something similar. Neverthless, the reconnect
code that I've added to ConnectionKeepAliveTask, is still useful for JDBC
drivers that do offer such support.

Comment 7 Caspar D.

2011-03-24 02:20:13 EDT

As further info: in the case of MySQL, the disconnects can be avoided
altogether by configuring the MySQL server's wait_timeout variable to some
large value. As Stefan said, the default is 28800, i.e. 8 hours.

Comment 8 Caspar D.

2011-03-24 02:23:02 EDT

Created attachment 191805 [details]
Patch v2

Comment 9 Caspar D.

2011-03-24 04:21:49 EDT

Created attachment 191810 [details]
Patch v3

Comment 10 Eike Stepper

2011-04-04 01:41:52 EDT

Created attachment 192435 [details]
Patch v4

Renamed xyzPropertyValues() to xyzPersistentProperties()

Comment 11 Eike Stepper

2011-04-04 01:42:32 EDT

Please also add a section below http://wiki.eclipse.org/CDO/Server_Configuration_Reference#Element_store

Comment 12 Caspar D.

2011-04-04 05:12:13 EDT

Committed revisions 7580, 7581, 7582, 7583, 7584.

Committed in chunks to work around inexplicable refusal of SVN client
to commit in one go. Will commit from command line from now on.

Comment 13 Caspar D.

2011-04-04 05:39:36 EDT

Wiki updated.

Comment 14 Eike Stepper

2011-06-23 03:38:36 EDT

Available in R20110608-1407