[Mondrian] [Olap4j-devel] connection issues with mondrianOlap4j

Marc Batchelor mbatchelor at pentaho.com
Fri Jun 10 13:48:20 EDT 2011

If you can configure your connection using DBCP in Tomcat, the resource definition does in fact allow you to identify abandoned connections:

Look at the logAbandoned, removeAbandoned, and removeAbandonedTimeout settings:

<Resource name="jdbc/SampleData" auth="Container" type="javax.sql.DataSource" maxActive="100" maxIdle="5" maxWait="10000"
        username="pentaho_user" password="xxxxxx"
        driverClassName="com.mysql.jdbc.Driver" url="jdbc:mysql://localhost:3306/sampledata"
        validationQuery="/* ping */" 

What's nice is that when a connection is deemed abandoned, either by the reaping thread setup in the removeAbandonedTimeout, or when a finalizer kicks in on the connection instance, it will send to the log a stack dump of the code that grabbed the connection in the first place.


-----Original Message-----
From: mondrian-bounces at pentaho.org [mailto:mondrian-bounces at pentaho.org] On Behalf Of Paul Stoellberger
Sent: Friday, June 10, 2011 1:25 PM
To: Julian Hyde
Cc: olap4j-devel at lists.sourceforge.net; 'Mondrian developer mailing list'
Subject: Re: [Mondrian] [Olap4j-devel] connection issues with mondrianOlap4j


I was trying all afternoon to come up with a Testcase or even figure out how I could get more debug info from DBCP / Mondrian.
Unfortunately I was not successful at all.

There is no logging in DBCP or mondrian regarding the pool.
I think this issue is related to the internal Pool (RolapConnectionPool) since its happening to JDBC connection as well as JNDI.

Any input on how I could debug / test it would be appreciated.
Otherwise I need to file a bug without any more detailed info.


On Jun 8, 2011, at 20:57 , Julian Hyde wrote:

> Sounds like JDBC connections are being taken from the connection pool 
> but not returned. The pool is finite: there can be no more than N open 
> connections at a time. When they ask for connection N+1 it will block 
> and eventually time out.
> The connection leak is likely to be in Mondrian's code, and not your fault.
> Likely there is an error and Mondrian is not returning the connection 
> to the pool.
> Keeping olap4j connections open shouldn't be the problem. Mondrian 
> does not keep JDBC connections open for the duration of an olap4j 
> connection -- it opens & closes them (more precisely borrows & returns 
> them) for each access to the database.
> Please log a bug with a testcase. Or maybe there's tracing in dbcp you 
> can enable to show the callstack for each of the still-open connections.
> Julian
>> -----Original Message-----
>> From: mondrian-bounces at pentaho.org
>> [mailto:mondrian-bounces at pentaho.org] On Behalf Of Paul Stoellberger
>> Sent: Wednesday, June 08, 2011 10:12 AM
>> To: olap4j-devel at lists.sourceforge.net; Mondrian developer mailing 
>> list
>> Subject: [Mondrian] connection issues with mondrianOlap4j
>> Hi,
>> since quite a while we are experiencing very strange behaviour on our 
>> demo.
>> At some point olap4j / mondrian cant execute any queries anymore.
>> We were initially using normal jdbc based connections for mondrian / 
>> olap4j. Which resulted in "freeze" behaviour without any info in any 
>> log file what went wrong whenever mondrian tried to execute something 
>> on the database
>> Now with JNDI i get the following exception:
>>        at
>> mondrian.rolap.RolapConnection.execute(RolapConnection.java:582)
>>        ... 79 more
>> Caused by: org.apache.commons.dbcp.SQLNestedException: Cannot get a 
>> connection, pool error Timeout waiting for idle object
>>        at
>> org.apache.commons.dbcp.PoolingDataSource.getConnection(Poolin
>> gDataSource.java:104)
>>        at
>> org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDat
>> aSource.java:880)
>>        at mondrian.rolap.SqlStatement.execute(SqlStatement.java:123)
>>        ... 90 more
>> Caused by: java.util.NoSuchElementException: Timeout waiting for idle 
>> object
>>        at
>> org.apache.commons.pool.impl.GenericObjectPool.borrowObject(Ge
>> nericObjectPool.java:958)
>>        at
>> org.apache.commons.dbcp.PoolingDataSource.getConnection(Poolin
>> gDataSource.java:96)
>>        ... 92 more
>> In our workflow we create one olap4j connection on server startup and 
>> use that to create new Query objects.
>> We never close any connections, nor remove query objects that are 
>> abandoned by users, we keep them indefinitely at the moment.
>> I was looking at the log files and saw that the error occurred 
>> suddenly, not after a timeout or something. There was something 
>> successfully executed 5 mins before on the database.
>> Mysql doesn't report anything on "SHOW PROCESSLIST", so i'm assuming 
>> the connection pool is not exhausted from the DB point of view, but 
>> rather because of mondrian.
>> Is there anything in our workflow that could  cause mondrian to 
>> behave like that?
>> Does it not close its jdbc connections?
>> This error occurs with both, mysql and hsqldb.
>> I'm running out of ideas what i could do to fix or even debug this 
>> issues.
>> If anyone has any idea on what I could try, please step forward ;-)
>> -Paul
>> _______________________________________________
>> Mondrian mailing list
>> Mondrian at pentaho.org
>> http://lists.pentaho.org/mailman/listinfo/mondrian
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