Norbert van Nobelen Norbert van Nobelen - 1 month ago 4
Java Question

Why does my Tomcat only open 8 JDBC connections

When setting up the database connections in Tomcat 8, for some reason Tomcat is not following what I configured in the context.xml, with as result that I run out of connections, leading to resource contentions at the application server side (BLOCKED/WAITING threads). I always have 8 connections (show processlist in mariadb/mysql) after the pool initializes. My configuration states a minimum of 10 connections and a maximum of 100 connections.

I tested different configurations, but this does not make any difference at all, which is strange at least. The context.xml is used else it would not be able to connect to the database at all.

What is happening here? Why only 8 connections?

Software versions:
- MySQL JDBC driver: Latest (5.1.35)
- Java 1.8.0_05

I also observed with with my previous setup: Tomcat 7, Java 1.7, older MySQL JDBC drivers, MySQL instead of MariaDB. So the problem does not seem directly version related.

Show processlist output (Showing the 8 processes):

| Id | User | Host | db | Command | Time | State | Info | Progress |
+-------+---------------+---------------+-------------------+---------+------+-----------+-----------------+----------+
| 71153 | root | localhost | vnitdatacollector | Query | 0 | init | show processlist| 0.000 |
| 73473 | vnit_datacoll | virt005:58585 | vnitdatacollector | Sleep | 0 | | NULL | 0.000 |
| 73474 | vnit_datacoll | virt005:58586 | vnitdatacollector | Sleep | 0 | | NULL | 0.000 |
| 73482 | vnit_datacoll | virt005:58606 | vnitdatacollector | Query | 0 | update | INSERT INTO ... | 0.000 |
| 73483 | vnit_datacoll | virt005:58607 | vnitdatacollector | Sleep | 0 | | NULL | 0.000 |
| 73485 | vnit_datacoll | virt005:58618 | vnitdatacollector | Query | 0 | query end | INSERT INTO ... | 0.000 |
| 73487 | vnit_datacoll | virt005:58624 | vnitdatacollector | Sleep | 0 | | NULL | 0.000 |
| 73488 | vnit_datacoll | virt005:58634 | vnitdatacollector | Sleep | 0 | | NULL | 0.000 |
| 73489 | vnit_datacoll | virt005:58637 | vnitdatacollector | Query | 7 | update | INSERT INTO ... | 0.000 |
+-------+---------------+---------------+-------------------+---------+------+-----------+-----------------+----------+


I have the following context.xml configuration:

<?xml version="1.0" encoding="UTF-8"?>
<Context>
<Resource
name="jdbc/dbaccess"
auth="Container"
type="javax.sql.DataSource"
maxActive="100"
maxIdle="100"
minIdle="10"
maxWait="1000"
initialSize="10"
minEvictableIdleTimeMillis="5000"
testOnBorrow="true"
validationQuery="SELECT 1"
timeBetweenEvictionRunsMillis="5000"
testWhileIdle="true"
removeAbandoned="true"
removeAbandonedTimeout="60"
logAbandoned="true"
username="some_user"
password="{the password}"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://dbserver:3306/dbaccess?useFastDateParsing=false&amp;jdbcCompliantTruncation=false"
/>
<Resource
name="mail/emailconnection"
auth="Container"
type="javax.mail.Session"
mail.smtp.host="some.stmp.server"
/>
</Context>


The following thread issue then shows up after a (short) period:

"Thread-495" #517 daemon prio=5 os_prio=0 tid=0x00007f678c040800 nid=0x1642 waiting on condition [0x00007f67848f4000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000000f21933f0> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
at org.apache.tomcat.dbcp.pool2.impl.LinkedBlockingDeque.takeFirst(LinkedBlockingDeque.java:582)
at org.apache.tomcat.dbcp.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:439)
at org.apache.tomcat.dbcp.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:360)
at org.apache.tomcat.dbcp.dbcp2.PoolingDataSource.getConnection(PoolingDataSource.java:118)
at org.apache.tomcat.dbcp.dbcp2.BasicDataSource.getConnection(BasicDataSource.java:1412)
at com.hipersonik.util.ServiceLocator.getConnection(ServiceLocator.java:32)

Answer

Quote from "Tomcat Expert: Configuring jdbc-pool for high-concurrency":

When Tomcat reads the type="javax.sql.DataSource" it will automatically configure its repackaged DBCP, unless you specify a different factory. The factory object is what creates and configures the connection pool itself.

It turns out that DBCP package just ignores a series of settings. Adding the following line to the context.xml resource configuration, gets better response in the database:

<Resource 
 ....
factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
 ....
/>

Show processlist in mysql then immediately shows the desired behaviour.