On 13/03/15 12:37, Andy Seaborne wrote:
To check my understanding, let me put that in my own words: This is
essentially fronting the Fuseki server with another webapp that
intercepts all requests to the Fuseki server. ("All requests" because
it has to see update to manage the cache).
[...]
Both will work - personally, I'd go for option 2 because the
Sparql_Cache servlet can have detailed access to the internals of
Fuseki, for example the service registry and the admin interface. It
can be integrated into the UI (in Fuseki2) so the admin console can be
extended to manage the cache. See the stats page in the Fuseki2 UI. If
its external, the management will be a separate function.
I agree with Andy. I don't see much of a benefit for option 1 (an
external service) since you can already deploy a reverse proxy such as
Varnish or nginx in front of Fuseki and get pretty much the same
benefits. See my quick tutorial for installing Varnish in front of
Fuseki [1]. (this simple configuration will not cache POST requests, but
it is possible to tweak Varnish to cache those as well)
The problem with an external cache is that it cannot easily be made
aware of changes in the data. So when anything in the data changes, you
have to arrange to flush the cache - in most cases the entire cache,
since it's very difficult to know whether it has affected the results of
a particular query.
Where I can see the benefit is basically option 2 that is integrated to
the Fuseki servlet and is aware of updates. Even just flushing the
entire cache when an update comes in would be an improvement on using an
external cache, since at least there would be no possibility of stale
data being served. But if the cache could somehow be made aware of which
parts of the data (perhaps on a graph level, if not triple level)
contributed to the cached results of a particular query, it could
perhaps do even smarter invalidation and not throw away everything when
a single triple changes.
-Osma
[1] https://github.com/NatLibFi/Skosmos/wiki/FusekiTuning#http-caching
--
Osma Suominen
D.Sc. (Tech), Information Systems Specialist
National Library of Finland
P.O. Box 26 (Teollisuuskatu 23)
00014 HELSINGIN YLIOPISTO
Tel. +358 50 3199529
[email protected]
http://www.nationallibrary.fi
