Re: Cache Hit-Rate Statistics
Hi,
1.) Is there currently a proper and correct way of obtaining values for
the above four cache
performance metrics, that I am interested in, in order to monitor a
running application?
Basic L2 Cache statistics are available on later version of OpenJPA [1].
You can download [2] fairly stable nightly builds or 2-0.0-SNAPSHOT versions
for this facility.
[1]
http://openjpa.apache.org/builds/latest/docs/manual/manual.html#ref_guide_cache_statistics
[2] http://openjpa.apache.org/downloads.html
Regards --
Pinaki
Riaan wrote:
Hi,
I am new to Apache OpenJPA, but not new to the concept of persistence
layers in Java.
(I have played a little bit with Hibernate and TopLink in the past,
...without paying any attention to their cache schemes at the time.)
After beginning to understand the value of having an *extended* data cache
and query cache, I was drawn to Apache OpenJPA, because of the DataCache
and QueryCache features built into it.
I am busy writing my first proof-of-concept application using OpenJPA, and
I have written some Java code to interrogate the DataCache and QueryCache
instances at run-time. I find this very interesting, and the goal is to
gather *Cache Hit-Rate Statistics* from a running application.
What I would like to see, are the following four metrics:
Data Cache Hit Count:
Data Cache Miss Count:
Query Cache Hit Count:
Query Cache Miss Count:
In order to obtain values for the above four metrics, I downloaded the
OpenJPA 1.2.1 source code, and hacked in counters, and modified the source
code to update (increment) the counters when necessary.
This worked for me, and it gave me the information that I was looking for,
but my solution is (obviously) not ideal, because of the following
reasons:
a.) Any newer version of OpenJPA will not contain my hacks, and I would
have to modify the source code again.
b.) Because I don't fully understand the OpenJPA source code, my
modification may not be optimal. (This is an understatement.) Although it
works, and it gives me the answers I was looking for, I really don't feel
that confident about my source code changes.
c.) I suspect my changes may not even work properly the moment there are
more than one EntityManager or Persistence Unit in the same JVM. {I say
this, because my counters are defined as static attributes on some of the
OpenJPA classes. This is bad, I know.}
Anyway, here are my questions:
1.) Is there currently a proper and correct way of obtaining values for
the above four cache performance metrics, that I am interested in, in
order to monitor a running application?
2.) If there is currently no standard way in OpenJPA to get values for
these cache performance metrics, what is the chance that the OpenJPA
developers could add these in, so that these metrics can be used by all
OpenJPA users in the future?
3.) I guess what I am asking for, is probably not part of the Java EE
Persistence API specifications. What I am suggesting, is additional
features for Apache OpenJPA, ...if it is not already there. How does other
people feel about adding these features to the OpenJPA cache classes? I
would like to hear some thoughts on this from other users as well.
Just a few comments from my side:
A.] Database roundtrips are expensive, and it is a great win whenever a
database roundtrip can be avoided. (This is obviously a great benefit of
having data cache and query cache providers.)
B.] Because cache-hits are so precious, it makes good sense to monitor
cache-hits and cache-misses in a running application. The application
developer could write functions to extract these performance metrics on
demand.
C.] I would love to see Cache Performance Metrics (as listed above) as a
standard feature of OpenJPA, to be used by all OpenJPA users.
D.] I plan to use the persistence context in the *Extended* mode, as
opposed to per transaction or per session. In other words, for my
application, I want the data cache and the query cache to be available
throughout the full life cycle of the application back-end. This way, the
data cache and the query cache can be *shared* by *all* the application
users. This will hopefully save a lot of database roundtrips.
E.] Apache OpenJPA looks like a high-quality, feature-rich, open source
product. My thanks go out to the OpenJPA developers!
Regards
Riaan
South Africa
-
Pinaki
--
View this message in context:
http://n2.nabble.com/Cache-Hit-Rate-Statistics-tp4266362p4267778.html
Sent from the OpenJPA Users mailing list archive at Nabble.com.
Re: Cache Hit-Rate Statistics
Hi Pinaki, Thank you very much for this pointer! I am glad to see that the OpenJPA team has already thought of this! I will certainly look at these new features that are available in OpenJPA 2.0. Regards Riaan -- View this message in context: http://n2.nabble.com/Cache-Hit-Rate-Statistics-tp4266362p4267976.html Sent from the OpenJPA Users mailing list archive at Nabble.com.
Re: Cache Hit-Rate Statistics
Hi Riaan,
Apache OpenJPA looks like a high-quality, feature-rich, open source
product. My thanks go out to the
OpenJPA developers!
Good to know that you have found OpenJPA useful.
I plan to use the persistence context in the *Extended* mode, as opposed
to per transaction or per session. In other words, for my application,
I want the data cache and the query cache to be available throughout the
full life cycle of the application back-end.
By definition, DataCache or L2 cache lifetime is bound to persistence unit
(a.k.a EntityManagerFactory) and not to a persistence context (a.k.a
EntityManager). Extended mode refers to lifetime of L1 cache which is not
the same as L2 cache.
You can find some discussion on their differences in [1].
[1]
http://ppoddar.blogspot.com/2009/10/l2-cache-in-jpa-20-and-openjpa-plug-in.html
Riaan wrote:
Hi,
I am new to Apache OpenJPA, but not new to the concept of persistence
layers in Java.
(I have played a little bit with Hibernate and TopLink in the past,
...without paying any attention to their cache schemes at the time.)
After beginning to understand the value of having an *extended* data cache
and query cache, I was drawn to Apache OpenJPA, because of the DataCache
and QueryCache features built into it.
I am busy writing my first proof-of-concept application using OpenJPA, and
I have written some Java code to interrogate the DataCache and QueryCache
instances at run-time. I find this very interesting, and the goal is to
gather *Cache Hit-Rate Statistics* from a running application.
What I would like to see, are the following four metrics:
Data Cache Hit Count:
Data Cache Miss Count:
Query Cache Hit Count:
Query Cache Miss Count:
In order to obtain values for the above four metrics, I downloaded the
OpenJPA 1.2.1 source code, and hacked in counters, and modified the source
code to update (increment) the counters when necessary.
This worked for me, and it gave me the information that I was looking for,
but my solution is (obviously) not ideal, because of the following
reasons:
a.) Any newer version of OpenJPA will not contain my hacks, and I would
have to modify the source code again.
b.) Because I don't fully understand the OpenJPA source code, my
modification may not be optimal. (This is an understatement.) Although it
works, and it gives me the answers I was looking for, I really don't feel
that confident about my source code changes.
c.) I suspect my changes may not even work properly the moment there are
more than one EntityManager or Persistence Unit in the same JVM. {I say
this, because my counters are defined as static attributes on some of the
OpenJPA classes. This is bad, I know.}
Anyway, here are my questions:
1.) Is there currently a proper and correct way of obtaining values for
the above four cache performance metrics, that I am interested in, in
order to monitor a running application?
2.) If there is currently no standard way in OpenJPA to get values for
these cache performance metrics, what is the chance that the OpenJPA
developers could add these in, so that these metrics can be used by all
OpenJPA users in the future?
3.) I guess what I am asking for, is probably not part of the Java EE
Persistence API specifications. What I am suggesting, is additional
features for Apache OpenJPA, ...if it is not already there. How does other
people feel about adding these features to the OpenJPA cache classes? I
would like to hear some thoughts on this from other users as well.
Just a few comments from my side:
A.] Database roundtrips are expensive, and it is a great win whenever a
database roundtrip can be avoided. (This is obviously a great benefit of
having data cache and query cache providers.)
B.] Because cache-hits are so precious, it makes good sense to monitor
cache-hits and cache-misses in a running application. The application
developer could write functions to extract these performance metrics on
demand.
C.] I would love to see Cache Performance Metrics (as listed above) as a
standard feature of OpenJPA, to be used by all OpenJPA users.
D.] I plan to use the persistence context in the *Extended* mode, as
opposed to per transaction or per session. In other words, for my
application, I want the data cache and the query cache to be available
throughout the full life cycle of the application back-end. This way, the
data cache and the query cache can be *shared* by *all* the application
users. This will hopefully save a lot of database roundtrips.
E.] Apache OpenJPA looks like a high-quality, feature-rich, open source
product. My thanks go out to the OpenJPA developers!
Regards
Riaan
South Africa
-
Pinaki
--
View this message in context:
http://n2.nabble.com/Cache-Hit-Rate-Statistics-tp4266362p4268214.html
Sent from the OpenJPA Users mailing list archive at Nabble.com.
Re: Cache Hit-Rate Statistics
Hi Pinaki, Thank you very much for this information. I must admit, I did not realize there were two distinct caches (L1 and L2). Furthermore, I am not that familiar with JPA 2.0 yet. (I will look into it.) As you say in your article: Everyone loves cache, and I am certainly excited about it. I can feel that I still need to learn quite a bit about JPA (v1.0 and v2.0), and therefore I appreciate your pointers greatly! Thank you very much for your support. Regards Riaan -- View this message in context: http://n2.nabble.com/Cache-Hit-Rate-Statistics-tp4266362p4268700.html Sent from the OpenJPA Users mailing list archive at Nabble.com.
