when ever I keep my application idle for 10 or 15 hours, I will get Connection time out error. But when I frequently use my application then I couldn't able to see this error any time. Could any one please guide me whether I am making some thing wrong in the below code. This application is used by only two users and that too be not frequently.
<Context path="/****" reloadable="true">
<Resource
name="XXXX"
type="javax.sql.DataSource"
username="XXXX"
password="XXXX"
driverClassName="com.microsoft.sqlserver.jdbc.SQLServerDriver"
maxIdle="4"
maxWait="30000"
initialSize="2"
url="jdbc:sqlserver://localhost;database=XXXX"
maxActive="20"/>
</Context>
Unfortunately there is not so much information given in your example. Assumed that is a small piece of a Spring (Spring Framework) context configuration, i would prefer to configure a connection pooling for the database. This pool can hold an amount of idle connections for each request an can open new ones if no connection is available in the pool for the current request. I found this piece of XML in the MySql documentation.
<bean id="dataSource" destroy-method="close"
class="org.apache.commons.dbcp.BasicDataSource">
<property name="driverClassName" value="${db.driver}"/>
<property name="url" value="${db.jdbcurl}"/>
<property name="username" value="${db.username}"/>
<property name="password" value="${db.password}"/>
<property name="initialSize" value="3"/>
</bean>
Please be aware that the datasource is of type org.apache.commons.dbcp.BasicDataSource. For further information please refer to the Documentation of MySql, Spring Framework and DBCP
Based on information provided on question, i can see:
Most probably, application is not properly handling connection i.e. it is creating connection, but then somehow failed to close connection properly in application code.
As per question, if only 2 users are using this app then probably you might not able to catch connection exhausted error which usually thrown when connection pool reaches max limit.
But if you increase app users you will see your connection reached max limit very quickly.
Check number of connections that got created after application starts and observe behavior. Check if inactive connections are getting closed or not.
Also, I don't see inactive connection timeout property in configuration. Can you check if you have this property.
This is an issue with databases, it gets shutdown/locked up after a long idle period. In MySQL it is 8 hours by default. You have to use a connection pooling library like C3P0 which has configuration to talk to database and turn on the connection if it is closed.
It is possible to increase the timeout amount in databases, but not recommended. Therefor go for a system like I mentioned above which can turn on the connection for you.
Related
The following exceptions when happened, this means there is something wrong on the environment especially if those exceptions happened only on production environment with big number of users without any problem in testing environment with normal number of users.
1. Could not open connection: org.hibernate.exception.GenericJDBCException: Could not open connection.
2. java.sql.SQLRecoverableException: Closed Connection.
3. java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.
My environment information:
windows server 2012, oracle DB, jboss 7.1 application server and java application use hibernate 4 with c3p0 connection pools
I searched a lot about the related topics and I found many useful topics but the most useful topics was those two topics. topic_1 topic_2
I simulate this case when I decrease the configuration maxStatements inside c3p0 configuration file but as the definition for this parameter which defined here , it is the size of c3p0's global PreparedStatement cache.
I have the following questions:
Why I got error cannot open connection when I decrease maxStatements attributes which should effect only on the performance since this is cache attribute and this error disappears when I decrease it?
Why I got also cannot open connection when I increase maxStatements value with big number? How can I know the limitation from the database?
Is there any limitation from the database can limit this attributes and how can I check it?
I checked the connection pool maximum attributes with the database session parameter and I found that, the database session parameter is greater than the maximum pool size for my application which is right. I checked also the active and idle connections on the database and no problem in those numbers. Is there any other DB attributes should be checked instead of session parameter for database to be sure the database can give me the configured number of connection pools?
My c3p0-config is the following:
<default-config>
<property name="checkoutTimeout">300</property>
<property name="idleConnectionTestPeriod">70</property>
<property name="initialPoolSize">50</property>
<property name="maxIdleTime">270</property>
<property name="maxPoolSize">500</property>
<property name="minPoolSize">50</property>
<property name="maxStatements">400</property>
<property name="maxStatementsPerConnection">0</property>
<property name="testConnectionOnCheckout">true</property>
<property name="testConnectionOnCheckin">true</property>
<property name="preferredTestQuery">SELECT 1 from dual</property>
<property name="acquireRetryAttempts">0</property>
<property name="acquireRetryDelay">1000</property>
<property name="breakAfterAcquireFailure">false</property>
<property name="unreturnedConnectionTimeout">270</property>
<property name="debugUnreturnedConnectionStackTraces">true</property>
</default-config>
If I launch my application after it was idle for some time, I used to get below error. ( I am using Spring+Hibernate+MySQL as DB )
ERROR [org.hibernate.util.JDBCExceptionReporter]The last packet successfully received from the server was 74,188,684 milliseconds ago.
The last packet sent successfully to the server was 74,188,685 milliseconds ago. is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem.
org.hibernate.exception.JDBCConnectionException: could not execute query
I solved this issue by adding below to my servlet-context.xml.
<beans:property name="validationQuery" value="SELECT 1"/>
I had asked this question here which was more specific to solution.I need to know why I was getting that error.
I tried the 1st (Configure the connection string with autoReconnect=true ) and 3rd option (Configuring the connection pool to test the validity of the connection) provided in the above link and both worked. Still I dont get why in first place I was getting the error.
Here is my updated servlet-context.xml file and I am using ApacheDBCP for connection pooling.
<beans:bean id="MyID" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
<beans:property name="driverClassName" value="com.mysql.jdbc.Driver"/>
<beans:property name="url" value="jdbc:mysql://localhost:17761/myDB"/>
<beans:property name="username" value="myname"/>
<beans:property name="password" value="mypwd"/>
<beans:property name="maxIdle" value="5"/>
<beans:property name="maxActive" value="20"/>
<beans:property name="minIdle" value="5"/>
<beans:property name="validationQuery" value="SELECT 1"/>
</beans:bean>
Is it some connection expiry issue ? Please help me to understand.
Here is the flow of events to illustrate what's happening:
A connection is requested and used by the caller (application or connection pool)
The caller keeps a reference to it so that the connection can be re-used
The caller goes through a period of inactivity (for example, a dev system overnight or a QA system over the weekend).
Once that database connection is not in use, the database considers the connection to be idle. Because it is idle, after a certain amount of time (MySQL default is 8 hours) the database closes the connection.
The caller still has a handle to the connection, and when the caller tries to use the connection again unpleasantly discovers that connection has been closed.
The reason autoReconnect=true works, and that the pool testing the validity of the connection works, is that you are instructing the calling system to test the connection for this situation and to try again if this situation happens.
As for whether the validation query will affect performance: In theory it is using a connection to do something. In practice that something is so trivial that its effect is negligible in the context of your entire system.
[EDIT]
In this case Apache DBCP is the connection pool hanging on to the connection, but you do NOT want DBCP to close the connection after every call. The point of the connection pool is to keep a connection ready for the next call because creating connections is expensive. The connection objects maintained by the pool are backed by actual database connections, and the database is the one who closes that actual connection after the idle timeout period. Note that the timeout to close idle connections is configured on the database, not on the connection pool. Because of this, DBCP has no way of knowing whether the connection has been closed or not unless it actually tries to connect with it. That’s why you need a validation query.
For more information about configuring DBCP, see the configuration page and the API docs.
I have a web application that uses c3p0 as the connection pool. we use hibernate as the orm tool.
Recently, we have been getting connection timeout exceptions. To debug these exception, i enabled the logging fro C3p0 and got some information in logs. Can anybody help me in making complete sense out of it.
DEBUG 2012-08-05 14:43:52,590 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0] com.mchange.v2.c3p0.stmt.GooGooStatementCache: checkinAll(): com.mchange.v2.c3p0.stmt.GlobalMaxOnlyStatementCache stats -- total size: 2; checked out: 0; num connections: 1; num keys: 2
from the above, i can observe that the total size of the connection pool is 2. No. of checked out connections are 0. Is this right? And what are num_connections and num keys in the above?
Thanks..
What you are seeing in the bit of log that you've quoted is a snapshot of the Statement cache, not the Connection pool. There were two cached PreparedStatements, which belonged to a single Connection, at the time that message was logged. Neither of the Statements was checked out/in use.
I hope this helps!
The exceptions might be due to incorrectly defining the C3P0 settings. Ensure that you link to the right jar file Your application must be linked to "hibernate-c3p0*.jar" and not to "c3p0*.jar". The hibernate.cfg file must have the hibernate.connection.provider_class property defined in order for the c3p0 settings to take effect. Below is a sample settings
<property name="hibernate.connection.provider_class"> org.hibernate.connection.C3P0ConnectionProvider </property>
<property name="hibernate.c3p0.min_size">5</property>
<property name="hibernate.c3p0.max_size">10</property>
<property name="hibernate.c3p0.timeout">300</property>
<property name="hibernate.c3p0.max_statements">50</property>
<property name="hibernate.c3p0.idle_test_period">3000</property>
The log entry specifies that there are 4 connections in the pool and all the 4 connections are available for the application to use. Running a query towards your database to list all the active connections will show the pool connections. For eg in Mysql you could run "show processlist;" to see these connections.
I have a project that uses EclipseLink 2.1.3 under Tomcat 7.
What's bugging me is that the connection to the server doesn't persist through all of the app's life.
For a ServerSession to start I have to access the application manually.
Is there a way to automatically start a ServerSession when the application deploys and keep it running at all times ? So that I can access the application after a long idle time without having to wait ?
Thank you!
EDIT:
I have the following lines in persistence.xml
<property name="eclipselink.jdbc.read-connections.min" value="5"/>
<property name="eclipselink.jdbc.read-connections.max" value="10"/>
<property name="eclipselink.jdbc.write-connections.min" value="6"/>
<property name="eclipselink.jdbc.write-connections.max" value="12"/>
Server applications usually use a JDBC connection pool to get connections and reuse them. Depending on the pool you use, you may configure it to keep a given number of connections open.
I have a machine running a java app talking to a mysql instance running on the same instance. the app
uses jdbc4 drivers from mysql. I keep getting com.mysql.jdbc.exceptions.jdbc4.CommunicationsException
at random times.
Here is the whole message.
Could not open JDBC Connection for transaction; nested exception is
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was25899 milliseconds ago.The last packet sent successfully to the server was 25899 milliseconds ago, which is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem.
For mysql, the value of global 'wait_timeout' and 'interactive_timeout' is set to 3600 seconds and 'connect_timeout' is set to 60 secs. the wait timeout value is much higher than the 26 secs(25899 msecs). mentioned in the exception trace.
I use dbcp for connection pooling and here is spring bean config for the datasource.
<bean id="dataSource" destroy-method="close" class="org.apache.commons.dbcp.BasicDataSource" >
<property name="driverClassName" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/db"/>
<property name="username" value="xxx"/>
<property name="password" value="xxx" />
<property name="poolPreparedStatements" value="false" />
<property name="maxActive" value="3" />
<property name="maxIdle" value="3" />
</bean>
Any idea why this could be happening? Will using c3p0 solve the problem ?
Try setting up the Apache Commons DBCP correctly.
You need to set:
validationQuery to SELECT 1+1
testOnBorrow to true
That should fix the problem.
Can you describe how your app is handling connection pooling? I doubt that autoReconnect=true in the JDBC driver would re-pool connections from your app. The app needs to reconnect when it loses a connection.
I'd follow the advice in the exception. You should consider either:
expiring and/or testing connection validity before use in your application,
increasing the server configured values for client timeouts, or
using the Connector/J connection property 'autoReconnect=true' to avoid this problem. Try adding that to your connection URL (consult the docs for the exact syntax) and see if it helps.
I doubt that C3P0 will be that much better than the DBCP that you're already using. The exception is giving you some specific advice. You've tried #3. What about the other two?
I know how to ask WebLogic to check connections before using them. You should find out how to do the same with Tomcat.
I have seen before that Windows machines which have been moved on the network have had trouble with connecting to themselves.
Is there any connectivity problems outside the JVM - i.e. mysql client connecting to the server, and timing out, etc?