Sorting Projects list leads to "Transaction was rolled back in a different thread!" and many other errors

On translate.zanata.org (which has a large number of projects), sorting the Projects table (by clicking on a column header) eventually leads to a transaction timeout and many varied errors on subsequent requests, all of which seem to have the same cause.

• javax.persistence.TransactionRequiredException: No active JTA transaction on joinTransaction call

• javax.resource.ResourceException: IJ000459: Transaction is not active: tx=TransactionImple < ac, BasicAction: 0:ffff0a196a24:731414b0:57a9f41b:54ed8 status: ActionStatus.ABORTED >

• org.hibernate.HibernateException: Logical connection is closed

• org.hibernate.HibernateException: Transaction was rolled back in a different thread!

• javax.resource.ResourceException: IJ000460: Error checking for a transaction

I think this may be the most important stack trace, because it shows that a richfaces component triggered an in-memory merge sort, during which a database operation was invoked (very bad):

In the short term, I think we need to disable sorting on the projects list.