On Sep 29, 2009, at 12:08 PM, Manik Surtani wrote:


On 29 Sep 2009, at 09:57, Mircea Markus wrote:

Hi,

Again, this is a feature from Coherence[1].

Basic idea is to execute a query against the cache, and hold the result object. This result object will always have up to date query result; this means that whenever something is modified in the cache the result itself is updated. Advantage: if one performs the same query very often(e.g. several times every millisecond) the response will be fast and the system will not be overloaded. 

Is it really faster?  Surely all you save is the construction of the various query objects, but the query itself would have to be re-run every time.  Or does it attach a listener to the cache and check whether any new additions/removals should be used to update the result set?
this is the way it works. It is a sort of a near-cache, just that instead of being invalidated it is updated whenever the cache is updated. The documentation also suggests that they are using listeners.
 I don't see how that could be much faster though.
I think it might be if the you are running *the same query* tons of times. Basically you don't do a map-reduce on all the nodes, but rather on every insertion (especially if the number of insertion is relative small compared to the number of same-query-bring-run) you updated (if necessary) the cached query result. 

Adding Hibernate-dev in cc so that the HIbernate Search guys can comment too.

E.g. 
Filter filter = new AndFilter(new EqualsFilter("getTrader", traderid),
                              new EqualsFilter("getStatus", Status.OPEN));
ContinuousQueryCache cacheOpenTrades = new ContinuousQueryCache(cache, filter);

Iterator iter = cacheOpenTrades.entrySet().iterator(); //*this entrySet call will be instant!*

FOr a full list of scenario in which this can be used take a look at [1].
Shall we consider adding something similar?

Cheers,
Mircea


[1] http://download.oracle.com/docs/cd/E14526_01/coh.350/e14509/continuousquery.htm#BABBEIAH
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Manik Surtani
Lead, Infinispan
Lead, JBoss Cache




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