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From "Phil Steitz" <>
Subject Re: maxActive/maxWait
Date Mon, 03 Mar 2008 14:23:15 GMT
On Mon, Mar 3, 2008 at 6:36 AM, Purnima Venkatram
<> wrote:
> Hi all.
>  I am using commons dbcp through Tomcat.
>  Configuration:
>  1) Spring 2.5.1
>  2) Tomcat 5.5.25
>  3) mysql 5.0.21.
>  Have put the commons-dbcp-1.2.2.jar / commonds-pool-1.4.jar /
>  commonds-logging-1.0.4.jar into tomcat's common/lib.
>  The dataSource is accessed through a JNDI lookup. I want to check connection
>  pooling.
>  For the same I tried the following for the dataSource definition.
>  In context.xml I have:
>   <Resource
>        name="jdbc/XYZ"
>        auth="Container" type="javax.sql.DataSource"
>        maxActive="1"
>        maxWait="0"
>        maxIdle="0"
>        validationQuery="SELECT 1"
>        username="test"
>        password="test123"
>        driverClassName="com.mysql.jdbc.Driver"
>        factory="org.apache.commons.dbcp.BasicDataSourceFactory"
>        logAbandoned="true"
>        url="jdbc:mysql://"/>
>  Setting maxActive to 1 means that only 1 connection will be allocated at the
>  same time. Which means that If i establish two concurrent requests to the
>  application, then the second one should fail.

Not necessarily, depending on configuration, the second request may
wait for a connection to be returned to the pool.  Unfortunately, 0 is
interpreted similarly to the default, -1, as a configuration parameter
for maxWait, so maxWait = 0 means wait indefinitely. (This behavior
was introduced in early versions of commons pool and has not been
changed to preserve backward compatability).  There is no way to get
BasicDataSource to fail *immediately* when the pool is exhausted.  To
get that behavior, you would need to set up the pool yourself and
create a PoolingDataSource from it, setting the whenExhaustedAction to
WHEN_EXHAUSTED_FAIL. Setting maxWait to a very small positive number,
e.g. 1, with BasicDataSource should effectively accomplish the same
thing, though.

I don't see this happen. I
>  initially thought that I had very few rows in the db and hence the mysql
>  operation was finishing quickly due to which the second request was also
>  getting processed. But putting a loop and executing the mysql statement also
>  results in both the requests getting served.
>  I tried this with Jmeter too. I tried a Forever loop with Jmeter. And during
>  that time maxActive=1 and then from the browser again tried a request to the
>  jsp and this time I got a 'JDBC exception : Communications link failure' -
>  Address already in use. If i stop Jmeter tests, an redo the browser test, it
>  only succeeds after a while. ie the first few runs still fail with the same
>  exceptions and then it seems like the connections are released and then this
>  call succeeds. But in this time interval , in mysql 'show processlist' I
>  dont see the connections.
>  I have tried this for a lot of time and any suggestions/comments would be
>  appreciated.
>  I have checked the source of BasicDataSource and saw that it uses the
>  ObjectPool and PoolableConnectionFactory. Hence am assuming there isnt
>  anything else that I need to do to get pooling to work.
>  I also tried deleting the naming-dbcp jar from tomcat's common lib since
>  that seemed to have the same classes as commons-dbcp.
>  Is anything else required ?
>  In spring this is accessed using getBean and then the corresponding dao
>  method is called.
>  Also, as soon as it finishes the operation, the connection is removed from
>  the 'show processlist' of mysql. Does that mean , Tomcat drops and creates
>  connections for every call ? Isn't that against connection pooling ? Most of
>  the time I see the status as 'null' / 'sleep' / 'query' with validatation
>  query and very less time for the actual select query.
I am not a MySql expert, but IIRC, show processlist reports on
*running* threads, so it does not show idle connections.  The one
active connection will be idle between requests or when the engine has
finished responding.


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