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From Phil Steitz <>
Subject Re: [dbcp] Re: DBCP minIdle
Date Mon, 21 Jun 2010 12:06:08 GMT
mehul mehta wrote:
> So if we end up with 40 idle connections with a setting of 30 maxIdle

You will never have 40 idle connections if you set maxIdle at 30 -
the excess idle connections will be destroyed when they are returned
to the pool.
 and 50 maxActive connections, does it mean that maxActive overrides
maxIdle as far as idle connections are concerned
 (evictor is off)?

MaxActive bounds the number of connections that can be either idle
or active at any given time. If you have maxActive set at 50 and
maxIdle set at 30, then you will never have more than 50 connections
total opened by the pool and among these, no more than 30 will be
idle at any time.

> Is there a way to log connection creation other than overriding BasicDataSource.getConnection?

No, DBCP does not log connection creation.  Most database engines
provide a way to monitor this, though.

Also, not sure if there is a way to log how long the evictor runs?

 We are trying to see if application's poor performance is tied to
the connection pool in any way.

It would help if you posted the versions of dbcp and pool that you
are running and if you have not done so, upgrade to the latest versions.

> - Mehul
>> Date: Sun, 20 Jun 2010 08:24:44 -0400
>> From:
>> To:
>> Subject: Re: [dbcp] Re: DBCP minIdle
>> mehul mehta wrote:
>>> If we turn off the evictor, does it mean that the connections keep growing indefinitely
in the pool?
>> No.  The maxActive bound limits the total number of connections that
>> can be either idle in the pool or checked out to clients at any
>> given time.  (I would seriously consider reducing that value from
>> where you have it set.)  The maxIdle setting, which works with or
>> without the evictor, bounds the number of connections that can be
>> idle in the pool.
>> Phil
>>>> Date: Sat, 19 Jun 2010 21:28:00 -0400
>>>> From:
>>>> To:
>>>> Subject: Re: [dbcp] Re: DBCP minIdle
>>>> mehul mehta wrote:
>>>>> Here is our config:
>>>>>   maxActive="10000" maxWait="60000" minIdle="25" maxIdle="50" 
>>>>>         validationQuery="select current_date from sysibm/sysdummy1" 
>>>>>         testOnBorrow="true" 
>>>>>         testWhileIdle="false" 
>>>>>         testOnReturn="true" 
>>>>>         timeBetweenEvictionRunsMillis="5000" 
>>>>>         minEvictableIdleTimeMillis="60000" 
>>>>>         numTestsPerEvictionRun="5" 
>>>>>         removeAbandoned="true" 
>>>>>         removeAbandonedTimeout="300" 
>>>>>         logAbandoned="true"
>>>>> It appears that our minEvictableIdleTimeMillis is too short. Probably,
we should set it to the default which is 30 minutes.
>>>>> Also, is there any down side of setting timeBetweenEvictionRunsMillis
to -1 (no evictor)?
>>>>> Not sure if you observe any thing else in the config that can cause performance
>>>> Yes, running the evictor every 5 seconds is likely to cause
>>>> performance problems, especially during periods of heavy load or
>>>> when using pool 1.3.
>>>> If you turn off the evictor altogether, minIdle will not be
>>>> maintained, there will be no abandoned connection removal, and no
>>>> "eviction" of connections that have been idle in the pool for longer
>>>> than the minEvictableIdleTimeMillis.  If your application does not
>>>> need these things, you are better off turning off the evictor.
>>>> Having maxActive so much larger than maxIdle could cause connection
>>>> churn if load comes in spikes and you regularly go significantly
>>>> above 50 active connections.
>>>> Phil
>>>>> - Mehul
>>>>>> Date: Sat, 19 Jun 2010 12:45:31 -0400
>>>>>> From:
>>>>>> To:
>>>>>> Subject: [dbcp] Re: DBCP minIdle
>>>>>> mehul mehta wrote:
>>>>>>> Hello, We have dbcp configuration in production set as minIdle
= 25, maxIdle = 50, maxActive = 10000. We often experience slow down in queries to the database
that normally do not take that long. We are pretty sure that it is not the database.Let us
say the idle connections are 25. Now one of the idle connections is used up. Does dbcp create
a new connection right away to maintain 25 idle connections. Or does dbcp wait for 25 idle
connections to be used up and then create 25 new connections at one time? Regards,
>>>>>> The pool does not attempt to ensure minIdle after each
>>>>>> borrow/return. It does this each time the "evictor" maintenance
>>>>>> thread runs, which is once every timeBetweenEvictionRunsMillis
>>>>>> milliseconds.
>>>>>> maxIdle is enforced on each return to the pool - i.e., if there are
>>>>>> maxIdle connections idle in the pool when a connection is returned,
>>>>>> it is destroyed.
>>>>>> What versions of dbcp and pool are you running and what is your
>>>>>> timeBetweenEvictionRunsMillis setting?
>>>>>> Phil
>>>>>>> - Mehul 		 	   		  
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