Using Hibernate's ScrollableResults to slowly read 90 million records

Using setFirstResult and setMaxResults is your only option that I'm aware of.

Traditionally a scrollable resultset would only transfer rows to the client on an as required basis. Unfortunately the MySQL Connector/J actually fakes it, it executes the entire query and transports it to the client, so the driver actually has the entire result set loaded in RAM and will drip feed it to you (evidenced by your out of memory problems). You had the right idea, it's just shortcomings in the MySQL java driver.

I found no way to get around this, so went with loading large chunks using the regular setFirst/max methods. Sorry to be the bringer of bad news.

Just make sure to use a stateless session so there's no session level cache or dirty tracking etc.

EDIT:

Your UPDATE 2 is the best you're going to get unless you break out of the MySQL J/Connector. Though there's no reason you can't up the limit on the query. Provided you have enough RAM to hold the index this should be a somewhat cheap operation. I'd modify it slightly, and grab a batch at a time, and use the highest id of that batch to grab the next batch.

Note: this will only work if other_conditions use equality (no range conditions allowed) and have the last column of the index as id.

select * 
from person 
where id > <max_id_of_last_batch> and <other_conditions> 
order by id asc  
limit <batch_size>

You should be able to use a ScrollableResults, though it requires a few magic incantations to get working with MySQL. I wrote up my findings in a blog post (http://www.numerati.com/2012/06/26/reading-large-result-sets-with-hibernate-and-mysql/) but I'll summarize here:

"The [JDBC] documentation says:

To enable this functionality, create a Statement instance in the following manner:
stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,
                java.sql.ResultSet.CONCUR_READ_ONLY);
stmt.setFetchSize(Integer.MIN_VALUE);

This can be done using the Query interface (this should work for Criteria as well) in version 3.2+ of the Hibernate API:

Query query = session.createQuery(query);
query.setReadOnly(true);
// MIN_VALUE gives hint to JDBC driver to stream results
query.setFetchSize(Integer.MIN_VALUE);
ScrollableResults results = query.scroll(ScrollMode.FORWARD_ONLY);
// iterate over results
while (results.next()) {
    Object row = results.get();
    // process row then release reference
    // you may need to evict() as well
}
results.close();

This allows you to stream over the result set, however Hibernate will still cache results in the Session, so you’ll need to call session.evict() or session.clear() every so often. If you are only reading data, you might consider using a StatelessSession, though you should read its documentation beforehand."

Using Hibernate's ScrollableResults to slowly read 90 million records

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