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From Phil Steitz <>
Subject Re: DBCP problem with idle object
Date Wed, 03 Dec 2008 02:07:22 GMT
Martin Dyulgerov wrote:
> Hello again group!
> Phil: I followed your advice and remove some of the configuration 
> lines for my pool, here is the configuration i use at the moment:
> GenericObjectPool.Config config=new GenericObjectPool.Config();
> config.maxActive=15;
> config.maxWait=1000;
> config.testOnBorrow=true;
> and still i get the following error:
> "Exception: Cannot get a connection, pool error Timeout waiting for 
> idle object SQL Exception Connection is closed. SQLException 
> Connection is closed."
> MySQL shows that there are active 19 connections (19 rows in set (0.00 
> sec)) as a result of "mysql> SHOW FULL PROCESSLIST\G; "... When i 
> begin to work on my application (about 3 hours earlier today), there 
> were only 6 connections, and then, at some point they increment to 
> that number (i am more than sure that no one is using the application 
> besides me, and all the connections use the same database as my 
> application - so they have to belong to it, to the pool) My 
> application is running for about 7 hours to this moment after i made 
> the changes and restarted it. Can you please help me with some 
> suggestions onconfiguring the pool wright... I am getting pretty 
> desperate by now :( Thanks in advance!
Looks like you may not be closing your connections on all control 
paths.  Are you sure there are not exception conditions that could cause 
your close() activations to be missed? 
> Martin
> Phil Steitz wrote:
>> Martin Dyulgerov wrote:
>>> Hello group!
>>> This is the first time i actuali write something in here. First of 
>>> all - please excuse my bad english, it is not my native language. 
>>> Now to get to the point... I have problems implementing DBCP on my 
>>> Tomcat 6.0.18 in my web applications. I don't want to use JNDI, that 
>>> is why i have ServletContextListener, in witch i do as follows in 
>>> order:
>>> 1.Define GenericObject Pool
>>> 2. Define ConnectionFactory as implementation of 
>>> DriverManagerConnectionFactory
>>> 3.Define PoolableConnectionFactory with the previously created 
>>> GenericObjectPool and ConnectionFactory
>>> 4.Define PoolingDataSource with the GenericObjectPool object from 
>>> step 1
>>> Then i "stick" my PoolingDataSource to the servlet context, retreive 
>>> it in my JSPs and servlets and aquire a connection via 
>>> "getConnection()" (which returns Connection object). I make sure to 
>>> close() all my connections at the edn of the pages...I am sure that 
>>> the connections that are opened dont exceed the number 100 (which is 
>>> the maximum number of connections on my database - a MySQL database 
>>> system), so i think there must be something wrong with my pooling 
>>> code. The exact error i get is:
>>> "Exception: Cannot get a connection, pool error Timeout waiting for 
>>> idle object SQL Exception Connection is closed. SQLException 
>>> Connection is closed." At some point i began to ask myself if it the 
>>> problem is caused by the restarts(reloads) i do for that exact 
>>> application, because the other work fine (byt i dont play with them 
>>> that much)... My configurations for the GenericObjectPool and 
>>> DriverManagerConnectionFactory are as follows:
>>> GenericObjectPool.Config config=new GenericObjectPool.Config();
>>>            config.maxActive=15;
>>>            config.maxIdle=10;
>>>            config.minIdle=5;
>>>            config.maxWait=3000;
>>>            config.testOnBorrow=true;
>>>            config.testOnReturn=true;
>>>            config.testWhileIdle=true;
>>>            config.timeBetweenEvictionRunsMillis=1000;
>>>            config.minEvictableIdleTimeMillis=1000;
>>> Properties p=new Properties();
>>>            p.setProperty("user", user);
>>>            p.setProperty("password", password);
>>>            p.setProperty("useUnicode", "true");
>>>            p.setProperty("characterEncoding", "CP1251");
>>>            p.setProperty("autoReconnect", "true");
>>> Can You help me please? Any help will be appriciated. Thanks in 
>>> advance, and accept my apologies if i have breaked some rules of the 
>>> group or something like that.
>> These settings make it hard for the pool to manage connections:
>>           config.maxIdle=10;
>>           config.minIdle=5;
>>           config.timeBetweenEvictionRunsMillis=1000;
>>           config.minEvictableIdleTimeMillis=1000;
>> The first two force the pool to try to keep the number of idle 
>> connections between 5 and 10, which is going to force it to close / 
>> open frequently to stay within that relatively narrow range.   Unless 
>> you really need both of these, I would recommend eliminating one or 
>> both of them.
>> The second two are probably the source of your problem.  These 
>> parameters are specified in milliseconds (thousandths of a second).  
>> The first one tells the pool to kick off an evictor run every second 
>> and the second tells it to destroy any connections that sit idle for 
>> more than a second.  This will create lots of connection churn and 
>> also pool access contention as the idle object evictor runs every 
>> second and closes connections that have been idle and then tries to 
>> create new ones to reach minIdle.  You should either increase both of 
>> these by at least an order of magnitude or drop  them.   Unless you 
>> really want to close connections that have been idle in the pool for 
>> longer than a specified idle timeout, I would drop these.
>> Phil
>>> All best,
>>> Martin
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