Since fixing CONF-3507, customers are meant to be able to run DB2 with a transaction isolation level of "read committed" (2 in JDBC speak, "cursor stability" in DB2). However, in Confluence 2.5.6, that level causes deadlocks. Customers must again set their transaction isolation level to "read uncommitted" (1 in JDBC).

The setting can be made by adding the following line to confluence.cfg.xml:

<property name="hibernate.connection.isolation">1</property>