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

[Emmanuel Bernard]

Sanne, I wonder if that could be used as a way to get rid of the weak
identity hash map we have in Hibernate Search. (I think we got rid of
all ThreadLocal already).

Steve, do you think I could (ab)use these as Session level cache? I
think OGM could benefit from such feature in a couple of situations.
That would require that from an eventsource, I could reach the list of
listeners to access the state I suppose.

Emmanuel

On Wed 2013-11-13 15:16, Steve Ebersole wrote:
> 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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