选择事务隔离级别

Question

I don't have a specific example here, I was just trying to understand the different levels of transaction isolation and how one might go about deciding which is best for a given situation.

I'm trying to think of situations in which I would want a transaction that is not serializable, other than to possibly increase performance in situations where I'm willing to give up a little data integrity.

Can anybody provide an example of a situation in which "read uncommitted", "read committed", and/or "repeatable read" would be the preferable isolation level?

Answer 1

Using the serializable isolation level does not only have advantages, but also disadvantages:

• You have to accept increased performance overhead.

• You have to handle serialization errors by redoing transactions, which complicates your application code and hurts performance if it happens often.

I'll come up with use cases for the other transaction levels. This list is of course not complete:

1. READ UNCOMMITTED : If you request this isolation level, you will actually get READ COMMITTED . So this isolation level is irrelevant. On database systems that use read locks, you use that isolation level to avoid them.

2. READ COMMITTED : This is the best isolation level if you are ready to deal with concurrent transactions yourself by locking rows that you want to be stable. The big advantage is that you never have to deal with serialization errors (except when you get a deadlock).

3. REPEATABLE READ : This isolation level is perfect for long running read-only transactions that want to see a consistent state of the database. The prime example is pg_dump .