Hi,
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
<GX> creative online development B.V.
t: 024 - 3888 261
f: 024 - 3888 621
e: [EMAIL PROTECTED]
Wijchenseweg 111
6538 SW Nijmegen
http://www.gx.nl/
