The isolation level has an important role to play in the lock activities of the database system. It specifies whether locks are requested or released implicitly, and how.
The isolation level has consequences for whether concurrent transactions can be executed in parallel, and affects the consistency of the data. The lower the chosen value of the isolation level, the higher the degree of concurrency and the lower the guaranteed level of consistency. If transactions are competing for access to the same data, then different isolation levels can cause different inconsistent phenomena.
You can specify the isolation level with the CONNECT statement when, for example, you open a database session.
The following isolation levels exist:
· Isolation level 0 (uncommitted)
· Isolation level 1 or 10 (committed)
· Isolation level 2 or 20 (repeatable)
· Isolation level 3 or 30 (serializable)
1 and 10 are just different ways of writing the same isolation level; there is no difference in meaning. The same applies to 1 and 20 and to 3 and 30.