Question

Our DBA just came back with a long running query against our SQL server database. He thought we should review that query and see if we could optimize.

The problem is that the query doesn’t come from our application code. It is loading a number of records from a single table by their primary key, nine to be exact, and we NEVER have any queries to that table by primary key from our application. It is also definitely a hibernate query by the name mangling that hibernate does and the loading of all of the properties.

So I’m wondering if hibernate does some predictive caching, like pulling records it thinks I might want later. Any input on this?

Thanks.

Answer 1

This is probably a query that is executed due to batch fetching:

Using batch fetching, Hibernate can load several uninitialized proxies
if one proxy is accessed. Batch fetching is an optimization of the
lazy select fetching strategy.

Batch fetching for classes/entities is easier to understand. Consider
the following example: at runtime you have 25 Cat instances loaded in
a Session, and each Cat has a reference to its owner, a Person. The
Person class is mapped with a proxy, lazy=”true”. If you now iterate
through all cats and call getOwner() on each, Hibernate will, by
default, execute 25 SELECT statements to retrieve the proxied owners.
You can tune this behavior by specifying a batch-size in the mapping
of Person:

<class name="Person" batch-size="10">...</class>

Hibernate will now execute only three queries: the pattern is 10, 10,
5.