[hibernate-dev] SessionEventsListener feature (HHH-8654)

[Gunnar Morling]

Hi,

This sounds very promising.

Regarding the suggested type names, I'd personally prefer SessionEventListener
(without the plural "s") and something like BaseSessionEventListener
instead of EmptySessionEventsListener, as "empty" implies a specific
behavior which a sub-class would not satisfy when overriding methods.

--Gunnar




2013/11/13 Steve Ebersole <steve at hibernate.org>

> I wanted to highlight a new feature in 4.3 as it came about from
> performance testing efforts.  Its a way to hopefully help track down
> potential performance problems in applications that use Hibernate. In
> this way it is similar to statistics, but it operates per-Session
> (though certainly custom impls could role the metrics up to a SF level).
>
> It revolves around the SessionEventsListener[1] interface which
> essentially defines a number of start/end pairs for the interesting
> events (for example starting to prepare a JDBC statement and ending that
> preparation).
>
> Multiple SessionEventsListener instances can be associated with the
> Session simultaneously.  You can add them programatically to a Session
> using Session#addEventsListeners(SessionEventsListener...) method.  They
> can also be added to the Session up-front via the
> SessionFactory#withOptions API for building Sessions.
>
> Additionally there are 2 settings that allow SessionEventsListener impls
> to be applied to all Sessions created:
>
> * 'hibernate.session.events.auto' allows you to name any arbitrary
> SessionEventsListener class to apply to all Sessions.
> * 'hibernate.session.events.log' refers to a particular built-in
> implementation of SessionEventsListener that applies some timings across
> the start/end pairs
> (org.hibernate.engine.internal.LoggingSessionEventsListener).  In fact
> this listener is added by default if (a) stats are enabled and (b) the
> log level (currently INFO) of LoggingSessionEventsListener is enabled.
> Below[2] is some sample output of LoggingSessionEventsListener.
>
> There is also a org.hibernate.EmptySessionEventsListener (no-op) class
> to help develop custom ones.
>
> Anyway, as much as anything I wanted to point it out so people can try
> it out and to get feedback.  I think the API covers most of the
> interesting events.  If you feel there are any missing, lets discuss
> here or on a Jira issue.
>
>
> [1] https://gist.github.com/sebersole/7438250
>
> [2]
> 14:40:20,017  INFO LoggingSessionEventsListener:275 - Session Metrics {
>      9762 nanoseconds spent acquiring 1 JDBC connections;
>      0 nanoseconds spent releasing 0 JDBC connections;
>      1020726 nanoseconds spent preparing 4 JDBC statements;
>      1442351 nanoseconds spent executing 4 JDBC statements;
>      0 nanoseconds spent executing 0 JDBC batches;
>      0 nanoseconds spent executing 0 L2C puts;
>      0 nanoseconds spent executing 0 L2C hits;
>      0 nanoseconds spent executing 0 L2C misses;
>      2766689 nanoseconds spent executing 1 flushes (flushing a total of
> 3 entities and 1 collections);
>      1096552384585007 nanoseconds spent executing 2 partial-flushes
> (flushing a total of 3 entities and 3 collections)
> }
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