Wanted to point out that a Map keyed by SQL is not sufficient, because that
approach would not properly account for self-referential associations (the
same SQL).
The patch provided for HHH-1 is well thought out in terms of accounting for
all association scenarios. It does not, of course, handle multi-table
structures which require a much different type of solution given how
Hibernate groups the DML for these behind the persisters (I know the general
approach I will use to solve this one now, btw).
On Thursday 23 August 2007 01:32:02 am Max Rydahl Andersen wrote:
http://opensource.atlassian.com/projects/hibernate/browse/HHH-1
/max
> I thought his question was a little too technical for the general list,
> so I thought I¹d ask it here. Is there a technical reason why Hibernate
> does not or cannot support the batching of multiple (different) object
> insertions within the same session?
>
> I have code that is semantically equivalent to:
>
> Session session = sessionFactory.getCurrentSession();
> for (int i = 0; i < 1000; i++) {
> Foo foo = new Foo();
> session.save(foo);
>
> Bar bar = new Bar();
> session.save(bar);
> }
> session.flush();
>
> If Foo or Bar is not in the equation, batching occurs as desired.
> However, if both Foo and Bar are inserted during the session in
> alternating fashion the result is that in the ActionQueue the 'insertion
> list' is interleaved with Foo's and Bar's. This is natural enough it
> seems. However, when ActionQueue.executeActions() is called the
> following occurs...
>
> 1) executeAction() iterates through the insertion list calling execute()
> on each Executable in the list
> 2) the Executable.execute() method calls insert() on the associated
> persister, in the case a SingleTableEntityPersister. It seems to realize
> that it CAN batch these inserts and so ...
> 3) insert() calls the BatchingBatcher.prepareBatchStatement(sql) which is
> actually a method on AbstractBatcher. This is where things go "awry"...
>
> The prepareBatchStatement(sql) does this thing where it compares the SQL
> statement that was provided with the _last SQL that it executed_ and if
> they match it re-uses the _last PreparedStatement_ which it also hung
> onto, otherwise it closes the existing PreparedStatement and creates a
> new one -- effectively ending the current "batch".
>
> In this case, because the objects are interleaved in the insertion list
> the result is that the prepareBatchStatement() is called with:
>
> insert into foo (a, b, c) values (?, ?, ?)
> insert into bar (x, y, z) values (?, ?, ?)
> insert into foo (a, b, c) values (?, ?, ?)
> insert into bar (x, y, z) values (?, ?, ?)
> insert into foo (a, b, c) values (?, ?, ?)
> insert into bar (x, y, z) values (?, ?, ?)
> ...
>
> The result being that each subsequent statement terminates the statement
> prepared before it, preventing batching from occuring. Well, it logs a
> debug message saying "Executing batch size: 1" for each statement.
>
> So my question is this ... is there any reason not to use a Map<sql,
> PreparedStatement> construct in the BatchingBatcher such that the
> appropriate PreparedStatement can be located and re-used based on the
> incoming SQL rather than only retaining the _last_ SQL statement which is
> guaranteed to "flap" in the case of alternating (or multiple) objects?
>
> If there is no technical reason why this shouldn't be done or wouldn't
> work, I will be happy to make the change and submit a patch. [Can you
> tell how bad I need batching in this scenario?]
>
> Thanks,
> Brett Wooldridge
> The ZipTie Project
>
www.ziptie.org
>
>
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> hibernate-dev(a)lists.jboss.org
>
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