How to prevent Hibernate from flushing in list?

Question

I have a simple Hibernate query like:

from MyEntity where name = ?

Nothing fancy, but it's called many times in a fairly big transaction (lasts one second, may load dozens or hundreds of entities). Profiler shows that a lot of time is spent in:

org.hibernate.internal.SessionImpl.autoFlushIfRequired(SessionImpl.java:1185)
org.hibernate.internal.SessionImpl.list(SessionImpl.java:1240)
org.hibernate.internal.QueryImpl.list(QueryImpl.java:101)

In other words - flushing changes before running the actual query.

Can I somehow prevent Hibernate from doing this flush at all?

If not, what can I do to make it faster?

Answer 1

By default hibernate flushes before issuing a query during a session (FlushMode.AUTO), and chews up lots of CPU time doing it. It is particularly painful if you have a session where many queries and updates run alternately.

If the query is likely to select back data that you have inserted/updated/deleted during the current session then you need these flushes. This may also be the case even if you haven't modified anything in the current transaction but are using a transaction-isolation level like read-uncommitted.

Assuming you don't want uncommitted reads, etc., there are two ways around this that I know of:

1. Select everything you'll need during the session before you make any modifications (ie., re-order things so that all your queries are issued before any modifications are made).

2. If you know for sure that you are selecting data that has not been modified in this session then you can explicitly set the flush-mode to something which won't trigger the flush, like this:

   Query query = session.getNamedQuery(SOME_QUERY_NAME);
   query.setFlushMode(FlushMode.COMMIT);