[hibernate-dev] Delay the identity generation to flush-time for transactional contexts too

[Vlad Mihalcea]

HI,

I always wandered why the identity generator needs to assign an identifier
prior to flushing.
Because of this behavior, the JDBC batching is disabled which is bad news
for MySQL where most setups use IDENTITY instead of TABLE generation type.

Since the AbstractSaveEventListener supports the shouldDelayIdentityInserts
option for when there is no transaction n progress, we could make this a
default anyway.

If the inserts are delayed to flush-time, we could batch them based on the
current dialect. Only the SQL Server dialect and Oracle 11g don't allow
fetching the resulting keys from a batch. But Oracle 12c (which supports
IDENTITY), PostgreSQL and MySQL can save a batch of inserts and fetch the
generated keys.

If I judge from a Stack Overflow perspective, most questions are in the
context of MySQL, so many Hibernate users use MySQL in fact.

What do you think? Should we make this change and allow MySQL users to
batch JDBC inserts even for IDENTITY.

Vlad