TomcatExpert

Explaining jdbc-pool, a High Concurrency Alternative to Connection Pooling Module

posted by fhanik on March 12, 2010 02:23 PM

Why another connection pool project

In this article we are going to explore one of the modules that is being developed in the Tomcat development trunk. The module named, jdbc-pool, is exactly that, an implementation of pooling of JDBC resources.

Connection pools have been around for a long time. I wrote one myself in 1997 when I first was introduced to Java, and used that for a long time in different projects I worked on. When JDBC came up, developers quickly realized that pooling JDBC connections would be beneficial for performance, and also a way to siphon connections and control the resource usage on the database server. This was especially important in horizontally scaled clusters where the database was always a risk of being overloaded. In those days we typically ran 1, 2 and sometimes 4 CPU machines for the application servers.

Connection pooling quickly became something that J2EE vendors developed in-house to integrate with their transaction services and became proprietary and integrated into the server itself. Outside of the J2EE containers a number of open source projects popped up. A few examples are Proxool, Apache Commons DBCP, C3P0 and Poolman. These are the most common ones we encounter in the field. Apache Tomcat has for very many years relied on DBCP to provide Tomcat users with a connection pooling implementation.

All of these open source projects have their pros and cons, but they all have something in common. They have become fairly stagnant and the code bases have not continued to evolve to meet new features in the Java language and are not optimized for multicore hardware that is increasingly becoming the common platform to deploy Java applications on. Some of the projects have also suffered from unneeded complexity in the source code, most likely one of the main reasons the project code is not moving forward, making it hard to maintain and easy to break.

Out of the four open source projects mentioned above, the two we see in Apache Tomcat deployments today are Commons DBCP and C3P0. A short summary of these two projects would be:

Commons DBCP

  • Ships with Apache Tomcat, used because it is readily available
  • Fairly stable code base
  • Plagued by dead locks for a very long time
  • Customer on lower clock speed but higher parallelism often complain about throughput bottlenecks

C3P0

  • Often used instead of DBCP
  • Based on our experience in the field, still fairly buggy
  • Reputation to perform better than DBCP, albeit our results show different

Both of these implementations are fairly complex. DBCP is built on top of the Apache Commons Pool project, and all together forms a code base of over 60 source files. C3P0 has grown to over 200 source files. Yet both pools fall short on features, to mention a few:

  • Pools are often statically tied to a Java version, meaning if the pool was written for Java 5, it wont have the java.sql and javax.sql interfaces compatible with Java 6. A user would typically receive a NoSuchMethodException when trying to execute one of the newer interface methods.
  • The pools are limited to java.sql.Driver interface, making it impossible to pool resources from a javax.sql.DataSource
  • No support for XA data sources
  • No flexibility for plugging in new features

So back to our question, why yet another pool project? The answer was simple, we needed better performance and more features. We also believed that taking on one of the legacy implementations would require rewriting a majority of the code base. So, it came to make a judgement call, do we want to rewrite 60+ sources files, or even 200+.

I know what you're probably thinking, here is yet another engineer that believes in rewriting from scratch rather than contributing to the existing code base. In almost every case, I prefer to reuse and fix than rewrite. However, after carefully judging the following questions:

  • How many lines of code do we actually need to provide the exact same implementation of Commons DBCP?
  • Can we make my implementation flexible enough to expose all the methods of java.sql.Connection that the driver exposes?
  • Can we provide a framework for exposing additional features?
  • Can we make the implementation scale in multi core environments/?

The next challenge we faced with such a project, within the Apache Software Foundation, was how to build a community around the project. Community is often grown by having lots of code that is not quite finished, meaning, there is work to be done in multiple areas making it enjoyable for a group to work together.

By this time, we had a prototype, it was 8 source files, and provided all the features of the other pools combined. Not all that exciting for a group of Java developers. Trying to fire off a separate project would probably not be very fruitful from a community perspective. We've since then grown it to 24 source files mostly by creating prebuilt addons that can be configured.

And so the jdbc-pool module was started.

The jdbc-pool did get some early adoption and the number of bugs was very low. Most early bugs were actual workarounds for typical use of the java.sql interfaces, calling close multiple times on a connection etc.

Today we see jdbc-pool, even in its unreleased state, several cases of production use. SpringSource ships the pool module with its tc Server product and you can already read about it in blog posts.

The jdbc-pool has an almost identical configuration as the Commons DBCP pool, in order to provide an easy migration path. For users already using Apache Tomcat and DBCP, the only difference would be the factory attribute  factory="org.apache.tomcat.jdbc.pool.DataSourceFactory".

For users of dependency injection frameworks, like the Spring Framework it's easy to just configure the org.apache.tomcat.jdbc.pool.DataSource bean.

Folks, that is why we have yet another pool module for JDBC connections. Over the next few articles, I will be digging deeper into:

  • Performance of jdbc-pool
  • The feature set, how and when to use it
  • The actual implementation and why it scales
  • How to build extensions

Filip Hanik is a Senior Software Engineer for the SpringSource Division of VMware, Inc. (NYSE: VMW) and a key participant in the company's Apache Tomcat initiatives. Filip brings 15 years of extensive experience in architecture, design and development of distributed application frameworks and containers and is recognized for his top-quality system development skills and continuous participation of Open Source development projects. Filip is an Apache Software Foundation member and a committer to the Apache Tomcat project where he is a leading authority on Tomcat clustering and a key contributor to the core of the platform. Filip has made contributions to software initiatives for Walmart.com, Sony Music, France Telecom and has held a variety of senior software engineering positions with technology companies in both the United States and Sweden. He received his education at Chalmers University of Technology in Gothenburg, Sweden where he majored in Computer Science and Computer Engineering.

Comments

Switching from C3P0...

Hi Filip.


I'm using C3P0 in a product I work on. I occasionally have problems with deadlocks, but in general it works pretty well. Do you think jdbc-pool is mature enough to start considering an eventual switch?



--Matt

RE: Switching from C3P0...

Hi Matt, absolutely. The jdbc-pool has faired very well in many environments that we've seen. So go for the switch.
What we see as common pitfalls, is that some code doesn't have proper closure of statements, for that they would use the StatementFinalizer, or applications don't reset auto commit and read only values, and for that they would use the ConnectionState interceptor.
We have an upcoming article about configuration, that will talk more in depth about these issues.

If you run into any problems, you can ping me on my apache.org email, my id is fhanik, or ask a question on the tomcat user mailing list.

best
Filip

RE: Switching from C3P0...

Thanks Filip. I'm working on a product that's about to have a release. Once that's out, I'll give jdbc-pool a try. Maybe I'll be able to include it in the next release. :)

--Matt

Sorry for the slow reply - for some reason my dev build of Chrome is consistently unhappy with the reply page. It took me a few days to get around to writing it in Firefox. ;)

On this page, you'll see my

On this page, you'll see my profile, please read this information. Save The Marriage System

On this page, you'll see my

On this page, you'll see my profile, please read this information. Ways To Get Your Ex Back

Welcome to the party of my

Welcome to the party of my life here you will learn everything about me. Survive In Bed

This is helpful, nonetheless

This is helpful, nonetheless it can be crucial so that you can check out the following website: audiometry

This is very appealing,

This is very appealing, however , it is very important that will mouse click on the connection: How To Give A Hand Job

During this website, you will

During this website, you will see this shape, i highly recommend you learn this review. f4x bodybuilding rebelmouse

You possess lifted an

You possess lifted an essential offspring..Blesss for using..I would want to study better latest transactions from this blog..preserve posting.. How to Turn a Guy On

There you can download for

There you can download for free, see the first of these data. sexosur

Very interesting information,

Very interesting information, worth recommending. However, I recommend this: sexosur

Mmm.. estimable to be here in

Mmm.. estimable to be here in your report or notify, whatever, I repute I should moreover process strong for my have website want I play some salubrious further updated busy in your location. sexonorte

This is important, though

This is important, though it's necessary to help you head over to it weblink: zonaescort.cl

On this page you can read

On this page you can read my interests, write something special. The Bonding Code Review

great post

hello all, introduce me from Indonesia.
I manage the best quality wholesale furniture business, for those of you who are in need of furniture can directly contact me. http://www.karyafurniturejepara.com

mebel murah mebel jati furniture online kursi tamu

Good dear!

Blessings come in many disguises. There's always something to learn from everything we go through. http://goatripsindia.com/goa-new-year-packages

Beautifully written article.

Beautifully written article. This is exactly why I've bookmarked your blog. I always want to read your articles, new or old. I hope you will keep this going on.
Ink Cartridges

sl786982

I believe your site is precisely exactly what I've been searching for; this solutions a lot of associated with my personal queries. michael spencer gilroy

sl786982

Thanks for publishing this

Thanks for publishing this amazing post today. You've been doing a really good job for the past few months and check interesting article. I just hope that you will keep doing the same job!!

I had been having some

I had been having some problems on this topic, but after reading this tremendously written blog post, all my queries have vanished. Good job! learn how to save energy

I really impressed after read

I really impressed after read this because of some quality work and informative thoughts . I just wanna say thanks for the writer and wish you all the best for coming!.
carry on sizes

Great content material and

Great content material and great layout. Your website deserves all of the positive feedback it’s been getting.
typseri.top

Most of the time I don’t make

Most of the time I don’t make comments on websites, but I'd like to say that this article really forced me to do so. Really nice post!
where to buy spartagen xt

I like this post,And I guess

I like this post,And I guess that they having fun to read this post,they shall take a good site to make a information,thanks for sharing it to me.
nyc flower delivery

I had an amazing time reading

I had an amazing time reading this post. This has to be one of the best posts that I've read in recent times. I am really thankful to you for giving us this. I just hope you'll keep this going on. Halaman utama

jams

Its a great pleasure reading your post.Its full of information I am looking for and I love to post a comment that "The content of your post is awesome" Great work.
rear extension architect

I am happy to find this post

I am happy to find this post very useful for me, as it contains lot of information. I always prefer to read the quality content and this thing I found in you post. Thanks for sharing.
Stanford Pelage Blog

sl786982

This will be to an incredible degree noteworthy for me when I get an opportunity to begin my blog. Photo débutant

sl786982

Your articles are always a

Your articles are always a joy to read. The information that I collected from this article was very helpful for me to complete my project on this topic. I just hope that you will continue to give more stuff like this. débarras maison gratuit

I really loved reading your

I really loved reading your blog. It was very well authored and easy to understand. Unlike other blogs I have read which are really not that good.Thanks alot!
kyle

Wow, cool post. I’d like to

Wow, cool post. I’d like to write like this too – taking time and real hard work to make a great article… but I put things off too much and never seem to get started. Thanks though.
versicherungdrohne.de

I would like to say that this

I would like to say that this blog really convinced me to do it! Thanks, very good post. minecraft pocket edition gratuit /
free netflix accounts

Nice post! This is a very

Nice post! This is a very nice blog that I will definitively come back to more times this year! Thanks for informative post.
vobizen wise 5 booking

This type of message always

This type of message always inspiring and I prefer to read quality content, so happy to find good place to many here in the post, the writing is just great, thanks for the post.
diabetesdestroyer.strikingly.com

Thanks for posting this info.

Thanks for posting this info. I just want to let you know that I just check out your site and I find it very interesting and informative. I can't wait to read lots of your posts.
duckness.net – Best Home Interior and Decoration Ideas

I have not any word to

I have not any word to appreciate this post.....Really i am impressed from this post....the person who create this post it was a great human..thanks for shared this with us.
redmi note 4 flipkart

I was looking at some of your

I was looking at some of your posts on this website and I conceive this web site is really instructive! Keep putting up..
Canadian online pharmaceuticals

sl786982

Wow! Such an amazing and helpful post this is. I really really love it. It's so good and so awesome. I am just amazed. Feldco facebook

sl786982

sl786982

I concur With your choices and your future will energetically expect redesign. Feldco twitter page

sl786982

sl786982

I am overwhelmed by your post with such a nice topic. Usually I visit your blogs and get updated through the information you include but today’s blog would be the most appreciable. Well done! feldco jobs

sl786982

sl786982

The post is written in very a good manner and it contains many useful information for me. feldco youtube page

sl786982

sl786982

I was getting bore since morning but as soon as I got this link & reached at this blog, I turned into fresh and also joyful too. feldco linkedin

sl786982

I think that thanks for the

I think that thanks for the valuabe information and insights you have so provided here. building inspectirs

You completed a few fine

You completed a few fine points there. I did a search on the subject and found nearly all persons will go along with with your blog.
James Bond Sprectre Jacket

I am happy to find your

I am happy to find your distinguished way of writing the post. Now you make it easy for me to understand and implement the concept. Thank you for the post.
Grandeur Park CEL near Singapor Expo

I am definitely enjoying your

I am definitely enjoying your website. You definitely have some great insight and great stories. pages

This is a great inspiring

This is a great inspiring article.I am pretty much pleased with your good work.You put really very helpful information. Keep it up. Keep blogging. Looking to reading your next post. cbtf

Hi, I find reading this

Hi, I find reading this article a joy. It is extremely helpful and interesting and very much looking forward to reading more of your work..
hanson

Thanks a lot for sharing us

Thanks a lot for sharing us about this update. Hope you will not get tired on making posts as informative as this.
Spielhaus Sandkasten

Post new comment

CAPTCHA
This question is for testing whether you are a human visitor and to prevent automated spam submissions.