Performance: caching negative results
-------------------------------------
Key: JCR-716
URL: https://issues.apache.org/jira/browse/JCR-716
Project: Jackrabbit
Issue Type: Improvement
Components: core
Reporter: Martijn Hendriks
We recently have been looking at the performance of JackRabbit and noted that
the SharedItemStateManager does not cache negative results. For instance, when
"hasItemState" returns false, then this negative result is not cached and a
subsequent call with the same ItemId will again query the database (if the item
has not been added and cached yet). We think, however, that caching such
negative results might improve the performance significantly for some
applications.
I've tried to add a simple negative-caching scheme. ItemIds are negatively
cached in the method "hasNonVirtualItemState" when the persistence manager
returns "false". Cache eviction occurs in the method "getNonVirtualItemState"
when a state is loaded. It also seems necessary to evict ItemIds in the methods
"stateCreated" and "has/getItemState" (when one of the virtual providers
returns something), because when an ItemId is neg-cached, it might still be
provided by one of the VISP. The negative cache can then be used in the method
"hasNonVirtualItemState" like this:
if (cache.isCached(id)) {
return true;
} else if (negativeCache.isCached(id)) {
return false;
}
Although all JackRabbit tests succeeded during compilation and our application
seemingly behaved ok, I still doubt that my implementation is completely
correct (I don't know the ins and outs of the SharedItemStateManager and made
some assumptions). We are, however, quite eager to investigate this further as
our application is 15% faster in an important use case with this very simple
negative caching scheme enabled.
Is there any previous work on something like this in JackRabbit? How difficult
is a solid implementation?
Regards,
Martijn Hendriks
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
