Thursday, May 7, 2015

Application servers are dead. Apparently.

OK so you may be wondering what the title has to do with transactions. Well it's really because of this article I came across recently. It's slightly old and I'm not sure how I missed it the first time round (maybe I had better things to do at the time!) Anyway, I'm not going to argue about whether or not application servers are dead: you can find enough from me on that topic by searching on JBoss.org or elsewhere.

What I did want to focus on was the transactions references in the article. Basically the author looks at some of the capabilities that an application server provides and tries to show how the same things can be done outside of an application server or with other frameworks/stacks. Well you can probably guess how the comments on transactions went down with me! Let's start by deconstructing the paragraph - yes, it only deserved a paragraph on something I think is so fundamental to enterprise applications! But hey, maybe I'm just strange (don't go there!)

"2PC is used to coordinate multiple transaction resource that should take part in a single transaction. Whether this feature makes sense could be the subject of an article in its own right. " Now of course you could interpret the last sentence in a number of ways, but I'll give the author the benefit of the doubt. Yes, transactions aren't always the right thing to use and in some cases they've definitely been misused.

Then we have: "If 2PC is used to coordinate two databases the architecture might be wrong. Why is data distributed across two databases if it has such a close relation that it should be changed as part of a single transaction?" Erm, exsqueeze me?! Have you heard of separation of concerns? Or maybe different organisations? Or perhaps difference companies? Or what about different levels of security/encryption, so a company stores and updates data in different repositories/data stores with different levels? And of course there's that other example ... replication!

The next bit made be laugh and then cry: "If JMS and access to a database are done in the same transaction synchronization might be an alternative. It offers almost the same guarantees but is a lot less complex and resource consuming." I can almost imagine the conversation: "Yes sir, we lost your money transfer because the message got lost but we were assured the chances of it happening were so small we really didn't need transactions and could use something that was almost exactly the same thing!" Look, a Citroen Belingo is almost the same thing as a Ferrari but I know which one I'd prefer!

"And remember: Also 2 PC can fail – like any IT system." Yes, it can fail. But guess what? A good transaction system implementation will have something called crash recovery (or failure recovery) which will attempt to resolve things for you automatically so you, the developer or sys admin, don't have to. Catastrophic failures may be unrecoverable, but then that would be the case without transactions anyway.

Then it wraps up with: "In modern Systems that use technologies such as REST or NoSQL 2PC cannot be used anyway. These technologies do not support 2PC. So more often than not 2PC is not that useful." OK so what about things like REST Transactions (the clue's in the name!) and the work we've been doing on compensation transactions and NoSQL?

Look, in general the recommendation(s) to stay away from transactions is bogus and ill-informed. If you don't want to use an application server that doesn't mean you should throw away everything that you get from it such as transactions. For instance, you don't need to use Narayana in the scope of an application server - in fact it began life years before there was ever such a thing!
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