Skip to main content

Mysql deadlock during delete query and index

I had written a hierachical lock manager using mysql and once a thread finishes it was unlocking by deleting the locks.  The 20 thread perf test was fine but daily some 100-200 of deadlock exceptions would come randomly on some nodes. Now each thread is working in isolation so it doesnt makes sense to get deadlock, the query was like

delete from hie_path_locks where customer_id=? and thread_id= ?

Finally after some hit and try and troubleshooting I found that we had an index on customer_id only and when 10 thread on same workgroup would try to read locks to detect conflicts they would do 

select * from hie_path_locks where customer_id=? and thread_id= ?

apparently mysql default isolation of REPEATABLE_READ would take locks on even rows that are read, check

Adding an index on customer_id,thread_id instead of just customer_id  solved the random deadlocks.


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()