Le vendredi 04 f�vrier 2005 � 12:18 +0100, Erik Bruchez a �crit :
Simple: there is no caching.
Simple indeed!
Can I suggest two possible strategies that would improve things without being too difficult to implement?
The first one would be to provide a timeout parameter associated with the XQuery request that would define the expected validity of the query.
Of course, that could create a delay between the moment an update is done on the DB and the moment it shows out on the site, but when the update rate is low that could be acceptable.
The second one would be to store, for each collection, the timestamp of
the last update and to use that information to manage the cache. That
would be reliable for databases that are not updated directly (out of
the control of Presentation Server) such as embedded eXist databases.
Do you think these options would be worth RFEs?
Absolutely, in fact this would work for the SQL processor as well, or any processor doing database reads.
Just a precision about caching in OPS: it doesn't cache XML data circulating in a pipeline. Rather, it's a generic object cache that caches objects such as transformers, configurations, and serializer results through a mechanism of keys.
So if a page is built from an XML:DB query only, and that caching information is produced by the XML:DB processor naively, what will happen will be that the resulting page will be stored in the cache. But, if that resulting page happens to depend on some non-cacheable information as well, then it won't be cached, and the XML:DB query will have to be re-run again to produce the page.
That is, unless some more work is done in the XML:DB processor itself, like actually storing the result of the query in the cache. This would be closer from what the URL generator, which is able to store a parsed document in the OPS cache.
The bottom line is that it is not necessarily trivial to implement a good caching strategy.
Just added one RFE:
http://sourceforge.net/tracker/index.php?func=detail&aid=1116160&group_id=116683&atid=675663
-Erik
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