Thursday, March 20, 2014

Packt Publishing now has 2000 titles and a great sale.


Packt is celebrating it's 2000th title and has a cool buy one get one free offer.  This is a great time to add to your personal library and start learning some new tech skills.  Its also a great time to grab a copy of my ActiveMQ book at Packt.

The sale ends 26th-Mar-2014 so don't wait to long.

Thursday, March 6, 2014

Packt's Learning Apache Maven 3 Video Course

I took some time recently to watch the latest Maven 3 video course offered by Packt publishing.  I wasn't sure what to expect since I have seen any of their other video courses.  I was pleasantly surprised by the depth of coverage and the well thought out organization of the course.

The course walks you through the ins and outs of using maven 3 which is great if you are a new user.  What's also great is that it shows you how to integrate development with maven into different IDE's like Eclipse and IntelliJ. 

If you've never used maven or you haven't spent much time using it inside an IDE this course is a great tool to get you started.  There's a lot of good tips in there even for those who already use maven as well.

Thursday, December 19, 2013

Christmas time at Packt Books


The $5 eBook Bonanza is here! Treat yourself to the eBook or Video of your choice for just $5 and get as many as you like until January 3rd 2014.  This is a great time to add to your personal library and start learning some new tech skills.  Its also a great time to grab a copy of my ActiveMQ book at Packt.

Wednesday, October 16, 2013

Get 50% Off of my Instant Apache ActiveMQ book plus many more


Packt Publishing is giving everyone the chance to explore its full range of over 1600 DRM-free eBooks this Columbus Day at a massive 50% off at www.packtpub.com, for 4 whole days. Customers simply use the code COL50 in their cart – as many times as they like until Thursday October 17th.  Use the following link to find out more. http://bit.ly/1bqvB29
You can take advantage of this sale to get an eBook copy of Instant Apache ActiveMQ Application development along with the upcoming Apache Camel cookbook.

Monday, September 9, 2013

ActiveMQ-CPP v3.8.0 Released

Its official, AcitveMQ-CPP v3.8.0 has now been released.

This is a new patch release of ActiveMQ-CPP which contains bug fixes for issues that were found since v3.7.1 was released and also some new features and build improvements for Windows users.  The windows project files are moving on to Visual Studio v2010 from this point on.  We kept around the vs2008 project files for now but will remove them in a later release just to try and make the transition a bit easier.

Here's a list of what's been fixed or added in this release.

 * 3.7.0 does not compile with gcc-4.4.7 on CentOS-6
 * APR-Util header include missed in latest release.
 * CMS FailoverTransport Leaks Socket Descriptors
 * closing a connection stalled in start because of failover should
   stop the transport safely.
 * Compilation Error Fix for Sun Studio under Solaris 10
 * Exception lifetime confusion can cause the application to crash
 * Connection didn't switch to the slave broker when the master broker
   is down
 * Committing a session with a deleted consumer causes access violation
 * Compilation of 3.7.0 fails for Linux systems (Redhat 5.8 and SuSE
   SLES 10)
 * Client doesn't work on Linux Red Hat 6.4 systems, fails when setting
   thread priority
 * Exception "attempt to unlock read lock, not locked by current
   thread" when doing performance testing
 * For SSL connections ensure the SNI field is set.
 * Can't send to temporary queues created by name
 * Added Visual Studio 2010 project files for the project.
 * Added Destination Source events based listener interfaces to the CMS API.

Tuesday, July 23, 2013

Coming in ActiveMQ 5.9 a new way to abort slow consumers.

The topic of how to deal with a slow consumer in ActiveMQ comes up on the mail list from time to time.  In the current releases there is a strategy class that allows you to configure a time interval after which a slow consumer is closed (some nice documentation can be found here).  The AbortSlowConsumerStrategy detects a consumer is slow by looking at its prefetch buffer and checking if its been to full for to long. When the consumer is aborted the messages that were in its prefetch buffer can then be sent on to other consumers on the same destination.

The AbortSlowConsumerStrategy works well when you have consumers whose prefetch limit is set to a value greater than one, but for those cases where you've set a value of zero or one the consumer may never get marked as slow by the broker so the strategy might never kick in to abort the slow consumers. 

To solve the problem of slow consumers with small prefetch values we've introduced the AbortSlowAckConsumerStrategy.  This strategy works by checking the time since a consumer last acknowledged a message as apposed to the time that the consumer has had a full prefetch buffer.  The strategy will poll all the consumers of destination at a configurable rate to determine if the consumer is slow and if the consumer meets the configured criteria for abort then it will be given the boot and any prefetched messages will be redispatched. 

The AbortSlowAckConsumerStrategy is configured in the XML configuration file as follows:

This configuration adds the AbortSlowAckConsumerStrategy with default options and applies it only to Topic consumers, for Queues you just need to replace the word 'topic' with 'queue' in the policy entry.

There are various options that can be set on the strategy to determine when it aborts a slow consumer.

Table 2. Settings for Abort Slow Consumer Strategy
AttributeDefaultDescription
maxTimeSinceLastAck30000Specifies the amount of time that must elapse since the last message acknowledge before a consumer is marked as slow.
ignoreIdleConsumerstrueSpecifies whether the time since last acknowledge is applied to consumer that has no dispatched messages.  If set false this strategy can be used to abort any consumer after the time since last acknowledge interval has expired.
maxSlowCount-1Specifies the number of times a consumer can be considered slow before it is aborted. -1 specifies that a consumer can be considered slow an infinite number of times.
maxSlowDuration30000Specifies the maximum amount of time, in milliseconds, that a consumer can be continuously slow before it is aborted.
checkPeriod30000Specifies, in milliseconds, the time between checks for slow consumers.
abortConnectionfalseSpecifies whether the broker forces the consumer connection to close. The default value specifies that the broker will send a message to the consumer requesting it to close its connection. true specifies that the broker will automatically close the consumer's connection.

If you read through the options above you should notice that it's possible to use this strategy not only to abort slow consumers that are receiving messages from the broker but also you can use this as a way to abort any consumer after a specified time interval. To accomplish this all you need to do is set the ignoreIdleConsumers option to false and the strategy will treat any consumer that hasn't acknowledged a message since the configured maxTimeSinceLastAck regardless of whether its had a message dispatched to it or not.

Lets look at an example of how to abort any topic consumer that hasn't acknowledged a message in the last 60 seconds:

Friday, July 12, 2013

ActiveMQ-CPP v3.7.1 Released

This is a new patch release of ActiveMQ-CPP, a lot of bugs have been fixed that were found in the v3.7.0 release which should reduce memory consumption and improve overall stability. Several compilation fixes were made as well so things should be better on a number of platforms. Fixes of note:
  • 3.7.0 does not compile with gcc-4.4.7 on CentOS-6
  • APR-Util header include missed in latest release.
  • CMS FailoverTransport Leaks Socket Descriptors
  • closing a connection stalled in start because of failover should stop the transport safely.
  • Compilation Error Fix for Sun Studio under Solaris 10
  • Exception lifetime confusion can cause the application to crash
  • Connection didn't switch to the slave broker when the master broker is down
  • Commiting a session with a deleted consumer causes access violation
  • Compilation of 3.7.0 fails for Linux systems (Redhat 5.8 and SuSE SLES 10)
  • Cient doesn't work on Linux Red Hat 6.4 systems, fails when setting thread priority