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List:       jakarta-commons-dev
Subject:    [dbcp] Connections closed and opened again when using fixed size
From:       M4N - Arjan Tijms <arjan.tijms () m4n ! nl>
Date:       2008-10-31 12:45:47
Message-ID: 490AFDFB.4010007 () m4n ! nl
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Hi,

I'm trying to use DBCP 1.2.1 and 1.2.2 (as supplied with Tomcat 6.0.14 
resp 6.0.16). I've set the pool's configuration to be a fixed size. My 
(test) config is this:

 <Resource
name="jdbc/test_ds"
factory="org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory"
type="javax.sql.DataSource"
scope="Shareable"
auth="Container"

driverClassName="org.postgresql.Driver"
username="*****" password="******"
url="*****"

poolPreparedStatements="true"
accessToUnderlyingConnectionAllowed="false"
defaultAutoCommit="true"
defaultReadOnly="false"
defaultTransactionIsolation="READ_COMMITTED"

validationQuery="select 1"
testOnBorrow="true"
testOnReturn="false"
testWhileIdle="false"

initialSize="5"
minIdle="5"
maxIdle="5"
maxActive="5"
maxWait="10"

removeAbandoned="true"
removeAbandonedTimeout="10"
logAbandoned="true"

timeBetweenEvictionRunsMillis="2000"
minEvictableIdleTimeMillis="10000"
numTestsPerEvictionRun="5"
/>

This seems to be a fixed size pool to me. However, in my postgresql log 
I see that every ~10 seconds all 5 connections are closed and 
immediately opened again:

2008-10-31 13:26:09 CET LOG: connection received: host=localhost port=38231
2008-10-31 13:26:09 CET LOG: connection received: host=localhost port=38232
2008-10-31 13:26:09 CET LOG: connection received: host=localhost port=38233
2008-10-31 13:26:09 CET LOG: connection received: host=localhost port=38234
2008-10-31 13:26:09 CET LOG: connection received: host=localhost port=38235
2008-10-31 13:26:09 CET LOG: connection received: host=localhost port=38236
2008-10-31 13:26:20 CET LOG: disconnection: session time: 0:00:10.690 
user=test database=test_db host=localhost port=38232
2008-10-31 13:26:20 CET LOG: disconnection: session time: 0:00:10.686 
user=test database=test_db host=localhost port=38233
2008-10-31 13:26:20 CET LOG: disconnection: session time: 0:00:10.668 
user=test database=test_db host=localhost port=38236
2008-10-31 13:26:20 CET LOG: disconnection: session time: 0:00:10.675 
user=test database=test_db host=localhost port=38235
2008-10-31 13:26:20 CET LOG: connection received: host=localhost port=38237
2008-10-31 13:26:20 CET LOG: disconnection: session time: 0:00:10.683 
user=test database=test_db host=localhost port=38234
2008-10-31 13:26:20 CET LOG: connection received: host=localhost port=38238
2008-10-31 13:26:20 CET LOG: connection received: host=localhost port=38239
2008-10-31 13:26:20 CET LOG: connection received: host=localhost port=38240
2008-10-31 13:26:20 CET LOG: connection received: host=localhost port=38241
2008-10-31 13:26:31 CET LOG: disconnection: session time: 0:00:10.999 
user=test database=test_db host=localhost port=38237
2008-10-31 13:26:31 CET LOG: disconnection: session time: 0:00:10.993 
user=test database=test_db host=localhost port=38238
2008-10-31 13:26:31 CET LOG: disconnection: session time: 0:00:10.990 
user=test database=test_db host=localhost port=38239
2008-10-31 13:26:31 CET LOG: disconnection: session time: 0:00:10.988 
user=test database=test_db host=localhost port=38240
2008-10-31 13:26:31 CET LOG: disconnection: session time: 0:00:10.985 
user=test database=test_db host=localhost port=38241

Of course, these timings are consistent with the time set for 
"minEvictableIdleTimeMillis". Nevertheless, I don't really understand 
why the pool closes all 5 and then immediately re-opens them. Since 
minIdle is set to 5, even though connections have been idle for more 
than 10 seconds, there seems to be no point in closing them. In general, 
there seems to be no point in closing idle connections such that the 
total number of them falls below minIdle.

Maybe I'm missing something though. Basically I only want to have an 
evictor thread running for checking abandoned connections. Since I have 
a fixed size pool, I don't care about any idle connections being closed.

Maybe related to this, on the documentation page 
(http://commons.apache.org/dbcp/configuration.html), the term "idle" 
seems to be used for both the condition that a connection sits in the 
pool, waiting for being requested, and the condition that client code 
has requested a connection and failed to return it to the pool within 
some time frame. This slightly adds to the confusion I have with 
understanding these settings.

Kind regards,
Arjan Tijms

-- 
It's a cult. If you've coded for any length of time, you've run across someone from \
this warped brotherhood. Their creed: if you can write complicated code, you must be \
good.


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