[hibernate-dev] Multiple-object batched inserts

[Brett Wooldridge]

Thanks for that.

-Brett

On 8/23/07 1:32 AM, "Max Rydahl Andersen" <max.andersen at redhat.com> 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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>