This is a bit of a silly question, but I'm curious to know:

What does hibernate use as the default transaction isolation (under 1.2.x), assuming I fail to provide one in the hibernate.properties file?

Thanks,

Ken

Whatever your database defaults to ;)

Hehe, so somewhere between TRANSACTION_READ_UNCOMMITTED and TRANSACTION_SERIALIZABLE. I know you're a DB2 guy Gavin (I'm stuck with DB2/400, which is a different engine but should be similar), do you know what the DB2 default is off the top of your head?

Thanks

err I have not used db2 in the past year except for Hibernate testing - and never on AS/400 - but anyway, IIRC, the default is actually what DB2 calls "repeatable read", which is what ANSI calls serializable. You probably want to change it to "cursor stability" (read committed) or "read stability" (repeatable read) if you want high concurrency. If you are using Hibernate, I would go for read committed, especially if you are

(a) using versioning (optimistic locking)
(b) using the second-level cache

This is hilarious, actually:



wtf?

Some digging around deep in the JDBC drivers (which are a byzantine mess as you might imagine) and it *looks* like they're defaulting to TRANSACTION_READ_UNCOMMITTED. I'll look into using READ_COMMITTED though, since we are in fact making heavy use of optimistic locking via <timestamp>.

Thanks!

eh? Read uncommitted is evil! You mean that your jdbc driver defaults to this??


Note that it is possible to change the default transaction isolation level by editing one of db2's config files....

Yep, the IBM JDBC driver for the AS/400 defaults to READ_UNCOMMITTED. I finally gave up trying to trace through exactly why I was unable to set any value via hibernate.connection.isolation (message board seems to indicate that they've tied the autocommit and isolation level props together in some way, and just to use URL props), and am just setting it via a connection property on the URL.

Thanks for the help