This post is part of a series exploring the unique aspects and capabilities of WebSphere Liberty when running on z/OS.
We'll also explore considerations when moving from WebSphere traditional on z/OS to Liberty on z/OS.
To start at the beginning, follow this link to the first post.
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The ability to easily wrap application operations in a transaction is one of the great benefits of running in an application server like Liberty (although you can certainly do it yourself and people have been for ages). Transactions allow you to group multiple operations involving one or more resource managers (think databases, but it can be other stuff) into a single thing that either does or doesn’t happen. The classic example is moving money from one account to another. The debit and credit either both have to happen or neither one should happen. It is bad if only one of them happens.
There are, of course, thousands and thousands (I’m having a low-budget Carl Sagan moment) of other examples. I won’t try to list them here even though it would make this post a more reasonable length.
Here we are, of course, more interested in the messages in messages.log that relate to transactions. There are actually quite a few and if you go browsing in the neighborhood of the message IDs I’ll mention shortly you can see some of them. They mostly relate to error situations and I’m going to be optimistic and just look at the happy ones.
If you have your server configured to use z/OS RRS then you’re probably going to see CWLIB0103I at startup. That message indicates that Liberty has managed to connect to RRS. It will tell you the resource manager name, which probably starts with ‘BBG’ and ends with ‘IBM’. It will also tell you the number of unresolved recovery units. These are probably transactions that were in flight when a previous instance of this server went down. Hopefully the number is zero, but if it isn’t then the Liberty transaction service will try to sort them out and you’ll probably see other messages relating to that.
Once everything is settled you’ll see message CWLIB0104I which tells you that recovery processing is completed for any outstanding transactions (‘outstanding’ here means those that needed recovery and is not an indication of the relative quality of the transaction…I’m sure all your transactions are just marvelous – you may do your Billy Crystal impression while reading that if you like).