Skip to main content

Oracle TM contention

Assume there exists a table DEPARTMENT. Table EMPLOYEE references DEPARTMENT using field SYS_DEPT_ID. When SYS_DEPT_ID is not indexed, and EMPLOYEE has large no of rows, this can cause long-running TM lock on delete of a DEPARTMENT row because oracle has to figure out if there are any employees working on this department or not. You can use Oracle Grid control to see the wait events and if you see a TM contention wait event than use the following query to identify these types of missing indexes so they can be added.

SELECT c.table_name, cc.column_name, cc.position column_position
FROM user_constraints c, user_cons_columns cc
WHERE c.constraint_name = cc.constraint_name
AND c.constraint_type = 'R'
SELECT i.table_name, ic.column_name, ic.column_position
FROM user_indexes i, user_ind_columns ic
WHERE i.index_name = ic.index_name
ORDER BY table_name, column_position;


Popular posts from this blog

RabbitMQ java clients for beginners

Here is a sample of a consumer and producer example for RabbitMQ. The steps are
Download ErlangDownload Rabbit MQ ServerDownload Rabbit MQ Java client jarsCompile and run the below two class and you are done.
This sample create a Durable Exchange, Queue and a Message. You will have to start the consumer first before you start the for the first time.

For more information on AMQP, Exchanges, Queues, read this excellent tutorial
import com.rabbitmq.client.Connection; import com.rabbitmq.client.Channel; import com.rabbitmq.client.*; public class RabbitMQProducer { public static void main(String []args) throws Exception { ConnectionFactory factory = new ConnectionFactory(); factory.setUsername("guest"); factory.setPassword("guest"); factory.setVirtualHost("/"); factory.setHost(""); factory.setPort(5672); Conne…

Spring query timeout or transaction timeout

If you are using spring to manage transactions then you can specify default transaction timeout using

    <bean id="transactionManager"
        <property name="dataSource" ref="dataSource" />
        <property name="defaultTimeout" value="30" /> <!--30 sec--->             

or you can override the timeout in the annotation

    @Transactional(readOnly = false, timeout=30)

or if you are doing it programatic transactions then you can do

DataSourceTransactionManager transactionManager = new DataSourceTransactionManager(dataSource);

 or you can override the timeout for one particular transaction

TransactionTemplate transactionTemplate = new TransactionTemplate();

Python adding pid file

I have a thumbnail generator that launches multiple processes and the correct way to shut it down is to send kill -HUP to the parent process. To automate I had to write a pid file from python, it was a piece of cake
def writePidFile(): pid = str(os.getpid()) f = open('', 'w') f.write(pid) f.close()