CallableStatement and PreparedStatements are precompiled. Are they done with respect to a connection? I mean, lets assume there are some 100 connection objects residing in a connection pool of an app server. There's a class that uses Callable and PreparedStatements. Lets say the method that is used for that is :
public void invokePreparedAndCallableStatements(){
//Fetches connection from pool
Connection con = getConnectionFromPool();
CallableStatement cs = con.prepareCall(.....);
cs.register...(...);
cs.execute();
...
...
PreparedStatement st = con.prepareStatement(...);
st.setXXX(..);
st.executeUpdate();
...
}
Now when the method is called for the first time, a connection is fetched from pool and the request is processed. The Callable and Prepared Statements are compiled. When the method is called another 99 times, each time a different connection is fetched from the pool, then - will the statements be complied for each connection ?
What will be the most optimal way to use statements in this context ? I can't make them (con.prepareCall() or con.prepareStatement()) static because connection isn't static.
The code is actually compiled and stored in the shared pool of the database. Any number of connections using that same code will benefit from the cache. The compiled code is kept as long as the memory limits allow.
The statements will be precompiled. Pooling will be based on your specified parameters.
Note: If you are using JDBC 3.0, you can also pool your PreparedStatements. Reference: What's new in JDBC 3.0
Related
In EAR application running on Websphere application server 8.5.5 we have to execute CallableStatement (call stored procedure in Oracle DB) which runs more than five minutes or more depending on input data. The operation is automatically rolled back because of transaction timeout (code WTRN0006W) which is set to 120 seconds by default in Websphere AS. We can't change this value due to customers requirements.
We can split input data to smaller chunks and execute CallableStatement several times to achieve shorter run time (30 seconds or so). Processing whole data chunks still takes more than 120 seconds (as expected). But the transaction timeout still occurs although for every statement execution with small chunk (in loop) we are getting connection from datasource configured in WAS, set autocommit to false, after statement execution doing commit and closing connection. Then again with next chunk in next loop cycle.
The whole process of statement executions is done in Stateless EJB which is called from Singleton EJB scheduled to run twice a day. We are not using JTA neither JPA, just JDBC.
Is it possible to avoid transaction timeout if we execute statement several times?
How we obtain datasource during application start:
javax.naming.Context ctx = new InitialContext();
javax.sql.Datasource ds = (javax.sql.Datasource) ctx.lookup("jndi/datasource1");
How we obtain Connection:
java.sql.Connection conn = m24sb.getConnection();
conn.setAutoCommit(false)
How we execute statement:
try (CallableStatement sta = conn.prepareCall("{ call SOME_STORED_PROC }"))) {
// ... setting statement params
sta.execute();
// ... resolving returned values
}
and then commit and closing connection.
Thanks in advance for answers!
Try marking your stateless session bean method as transaction NOT_SUPPORTED or NEVER, which will cause it to run outside of a global transaction. (Note that you would need to do this anyway for your connection.commit() call to be valid -- it likely just isn't getting that far due to the timeout).
#javax.ejb.TransactionAttribute(javax.ejb.TransactionAttributeType.NEVER)
public void yourStatelessEJBMethod() {
... code that invokes stored procedure and commits transaction
}
Hikari: 2.4.7
PostgreSQL JDBC driver: 9.4-1201-jdbc41
I'm trying to understand what must be done to a java.sql.Connection object for it to be available again in the
connection pool?
I've just introduced connection pooling to a multi threaded application that was
previously standing up / tearing down connections with each SQL statement.
What I have noticed, after introducing Hikari, is that as soon as I hit maximumPoolSize every attempt
thereafter to HikariDataSource.getConnection will fail due to connectionTimeout. So it seems like I'm not "releasing" this connection somehow.
The typical use of the Connection object is:
# omits Exception handling, parameter substitution, result evaluation.
PreparedStatement preparedStatement = hikariDataSource.getConnection().prepareStatement(sql);
preparedStatement.executeQuery();
preparedStatement.close();
Is there anything else that is expected to be done on this connection to get it eligible for reuse in the connection pool?
Autocommit is on. Connection.close(), unless doing something special when provided by Hikari, seemed like the exact thing I wanted to avoid.
I don't know Hikari specifically, but for every connection you take out of a connection pool, you have to return that connection when you are done with it.
Typically this is done using Connection.close() - the pool hands out a wrapper function where close() doesn't physically close the connection, only returns it.
So your code should look like this:
Connection con = hikariDataSource.getConnection();
PreparedStatement preparedStatement = con.prepareStatement(sql);
preparedStatement.executeQuery();
preparedStatement.close();
con.close(); // this returns the connection to the pool
Of course the two close() methods should be called in a finally block.
I have a controller action that does the following things:
Gets a domain object from the database
Uses info on that object to find a data file (on disk) and writes contents of that file to the response output stream.
My problem is that the database connection is reserved for the duration of the action, including the (long) time required to stream the data. This results in a lot of unnecessary database connections when there are several users streaming data at the same time.
def stream() {
StreamDetails sd = StreamDetails.get(params.id)
// Extract info needed to read the stream
String filename = sd.filename
// The database connection is no longer needed, how to properly release it?
// Start writing the data stream to response output
// This may take a long time and does not use a db connection
streamService.writeToOutput(filename,response.getOutputStream())
}
I have tried:
Injecting the sessionFactory bean to the controller and calling sessionFactory.currentSession.close() before calling the service. However this causes a SessionException on the line calling the service, ie. before entering the writeToOutput() method (and nothing in that method needs a database connection). AND I don't think the session should be really closed, just released to the pool.
Copy-pasting the code from streamService.writeToOutput(...) to the controller to avoid the service call. In this case all the code gets executed but a SessionException is still thrown after the action is complete.
How to properly release the connection early?
Have you tried to inject the dataSource? You could use the DataSourceUtils to create a new connection that you can then use to get the filename. You can then manually close() this connection.
I don't know if you can use this connection in combination with gorm, so you might have to create a custom sql query as well.
I am pretty sure that somebody else already asked this question, but I still couldn't find a satisfactory answer to it.
So, here is my scenario: I want to use the Oracle's JDBC driver implicit statement caching (documented here: http://docs.oracle.com/cd/B28359_01/java.111/b31224/stmtcach.htm#i1072607)
I need to use the connections from a 3rd party JDBC pool provider (to be more specific, Tomcat JDBC) and I have no choice there.
The problem is that the way to enable the implicit caching is a two-step process (accordingly to the documentation):
1.
Call setImplicitCachingEnabled(true) on the connection
or
Call OracleDataSource.getConnection with the ImplicitCachingEnabled
property set to true. You set ImplicitCachingEnabled by calling
OracleDataSource.setImplicitCachingEnabled(true)
2.
In addition to calling one of these methods, you also need to call
OracleConnection.setStatementCacheSize on the physical connection. The
argument you supply is the maximum number of statements in the cache.
An argument of 0 specifies no caching.
I can live with 1 (somehow I can configure my pool to use the OracleDataSource as a primary connection factory and on that I can set the OracleDataSource.setImplicitCachingEnabled(true)).
But at the second step, I already need the connection to be present in order to call the setStatementCacheSize.
My question is if there is any possibility to specify at the data source level a default value for the statementCacheSize so that I can get from the OracleDataSource connections that are already enabled for implicit caching.
PS: some related questions I found here:
Oracle jdbc driver: implicit statement cache or setPoolable(true)?
Update (possible solution):
Eventually I did this:
Created a native connection pool using oracle.jdbc.pool.OracleDataSource.
Created a tomcat JDBC connection pool using org.apache.tomcat.jdbc.pool.DataSource that uses the native one (see the property dataSource).
Enabled via AOP a poincut so that after the execution of 'execution(public java.sql.Connection oracle.jdbc.pool.OracleDataSource.getConnection())' I pickup the object and perform the setting I wanted.
The solution works great; I am just unhappy that I had to write some boilerplate to do it (I was expecting a straight-forward property).
The white paper Oracle JDBC Memory Management says that
The 11.2 drivers also add a new property to enable the Implicit Statement Cache.
oracle.jdbc.implicitStatementCacheSize
The value of the property is an
integer string, e.g. “100”. It is the initial size of the statement
cache. Setting the property to a positive value enables the Implicit
Statement Cache. The default is “0”. The property can be set as a
System property via -D or as a connection property via getConnection.
You can only change statement cache size through OracleConnection.setStatementCacheSize method.
Instead of modifying your application to call OracleConnection.setStatementCacheSize on every connection, you can create a JDBC interceptor.
#Override
public void reset(ConnectionPool pool, PooledConnection connection) {
if (connection == null) {
return;
}
Connection original = connection.getConnection();
if (!(original instanceof OracleConnection)) {
return;
}
try {
if (!((OracleConnection) original).getImplicitCachingEnabled() && implicitCachingEnabled) {
((OracleConnection) original).setImplicitCachingEnabled(implicitCachingEnabled);
log.info("Activated statement cache");
((OracleConnection) original).setStatementCacheSize(statementCacheSize);
log.info("Statement cache size set to " + statementCacheSize);
}
} catch (SQLException e) {
log.error(e.getMessage(), e);
}
}
We have our JBoss and Oracle on separate servers. The connections seem to be dropped and is causing issues with JBoss. How can I have the JBoss reconnect to Oracle if the connection is bad while we figure out why the connections are being dropped in the first place?
Whilst you can use the old "select 1 from dual" trick, the downside with this is that it issues an extra query each and every time you borrow a connection from the pool. For high volumes, this is wasteful.
JBoss provides a special connection validator which should be used for Oracle:
<valid-connection-checker-class-name>
org.jboss.resource.adapter.jdbc.vendor.OracleValidConnectionChecker
</valid-connection-checker-class-name>
This makes use of the proprietary ping() method on the Oracle JDBC Connection class, and uses the driver's underlying networking code to determine if the connection is still alive.
However, it's still wasteful to run this each and every time a connection is borrowed, so you may want to use the facility where a background thread checks the connections in the pool, and silently discards the dead ones. This is much more efficient, but means that if the connections do go dead, any attempt to use them before the background thread runs its check will fail.
See the wiki docs for how to configure the background checking (look for background-validation-millis).
There is usually a configuration option on the pool to enable a validation query to be executed on borrow. If the validation query executes successfully, the pool will return that connection. If the query does not execute successfully, the pool will create a new connection.
The JBoss Wiki documents the various attributes of the pool.
<check-valid-connection-sql>select 1 from dual</check-valid-connection-sql>
Seems like it should do the trick.
Not enough rep for a comment, so it's in a form of an answer. The 'Select 1 from dual' and skaffman's org.jboss.resource.adapter.jdbc.vendor.OracleValidConnectionChecker method are equivalent , although the connection check does provide a level of abstraction. We had to decompile the oracle jdbc drivers for a troubleshooting exercise and Oracle's internal implementation of the ping is to perform a 'Select 'x' from dual'. Natch.
JBoss provides 2 ways to Validate connection:
- Ping based AND
- Query based
You can use as per requirement. This is scheduled by separate thread as per duration defined in datasource configuration file.
<background-validation>true</background-validation> <background-validation-minutes>1</background-validation-minutes>
Some time if you are not having right oracle driver at Jboss, you may get classcast or related error and for that connection may start dropout from connection pool. You can try creating your own ConnectionValidator class by implementing org.jboss.resource.adapter.jdbc.ValidConnectionChecker interface. This interface provides only single method 'isValidConnection()' and expecting 'NULL' in return for valid connection.
Ex:
public class OracleValidConnectionChecker implements ValidConnectionChecker, Serializable {
private Method ping;
// The timeout (apparently the timeout is ignored?)
private static Object[] params = new Object[] { new Integer(5000) };
public SQLException isValidConnection(Connection c) {
try {
Integer status = (Integer) ping.invoke(c, params);
if (status.intValue() < 0) {
return new SQLException("pingDatabase failed status=" + status);
}
}
catch (Exception e) {
log.warn("Unexpected error in pingDatabase", e);
}
// OK
return null;
}
}
A little update to #skaffman's answer. In JBoss 7 you have to use "class-name" attribute when setting valid connection checker and also package is different:
<valid-connection-checker class-name="org.jboss.jca.adapters.jdbc.extensions.oracle.OracleValidConnectionChecker" />
We've recently had some floating request handling failures caused by orphaned oracle DBMS_LOCK session locks that retained indefinitely in client-side connection pool.
So here is a solution that forces session expiry in 30 minutes but doesn't affect application's operation:
<check-valid-connection-sql>select case when 30/60/24 > sysdate-LOGON_TIME then 1 else 1/0 end
from V$SESSION where AUDSID = userenv('SESSIONID')</check-valid-connection-sql>
This may involve some slow down in process of obtaining connections from pool. Make sure to test this under load.