mmm, but I think that only refreshes the results for
the returned objects ? Is that a correct assumption ?
it wouldnt remove all results for all param values from the cache
for that named query - meaning that the caller thats creating the
named query would need to know to force a refresh - but it doesnt
know as its not responsible for doing the updates...
our current scenario is :
static data updated generically in one ejb
when real business processing logic needs to get a piece of static
data it's read by entity specific dao's
when a static data entity is updated I want to clear the caches
(I'm happy to completely clear all caches at this point as it's
very infrequent).
so I was hoping to call a short helper function that would do that
- initially by calling something like this here which would
invalidate everything
genericUpdateDao.clearQueryCaches(){
List<String> qNames =
Helper.getCachedQueryNames();
for each qName {
Query q =
em.createQuery(qName)
q.query.setHint("eclipselink.query-results-cache.size",1)
q.getResultList();
}
On 12/03/2012 15:38, Tom Ware wrote:
I
suggest you use the refresh query hint. That should refresh the
cache.
On 12/03/2012 11:09 AM, Tim Martin wrote:
Is there anyway to force a cache clear - I
can see that
query.setHint(""eclipselink.query-results-cache.size",1)
and then calling the query with parameters that would never
return a result
would clear the cache, BUT is there a better way ?
On 12/03/2012 13:12, Tom Ware wrote:
The query cache will not know to refresh
when a different persistence
operation changes one of the results held in the cache.
-Tom
On 12/03/2012 4:58 AM, Tim Martin wrote:
Tom - one further question re
queryResults caching -
if I run queryA which returns object X,Y,Z which are cached
and then and update one of those objects, does the query
results cache know or
get told enough to clear the results for queryA so re
running it will go to the
database instead of returning a stale result ?
thanks
http://wiki.eclipse.org/Introduction_to_EclipseLink_Queries_%28ELUG%29#How_to_Cache_Query_Results_in_the_Query_CacheHow
to Cache Query Results in the Query Cache
In addition to EclipseLink's object cache, EclipseLink also
supports a query
cache. There is the following distinction between the two:
* The /object cache/ indexes objects by their primary key,
allowing primary
key queries to obtain cache hits. By using the object
cache, queries that
access the data source can avoid the cost of building
the objects and their
relationships if the object is already present.
* The /query cache/ is distinct from the object cache. The
query cache is
indexed by the query and the query parameters–not the
object's primary key.
This allows for any query executed with the same
parameters to obtain a
query cache hit and return the same result set.
On 09/03/2012 14:14, Tom Ware wrote:
The hint can be added to all
queries. Obviously it will improve performance
more for queries that are executed more often. (named
queries are a good
candidate here)
Queries are actually cloned before we apply query hints to
them, so the
SessionCustomizer option listed below may be what you want
for certain
queries. (since it will affect the query every time it is
looked up rather
than just the instance you get from em.createQuery()).
BTW: Some doc:
http://wiki.eclipse.org/Introduction_to_EclipseLink_Queries_(ELUG)#How_to_Cache_Query_Results_in_the_Query_Cache
-Tom
On 09/03/2012 8:49 AM, Tim Martin wrote:
Just to check - the hint can only
be added to named ? not those built on
the fly
(which of course we are doing are best to avoid :)
On 09/03/2012 13:45, Tom Ware wrote:
There is no setting to do this
universally for a whole persistence unit. It
should be possible to do this using EclipseLink-native
API in a
SessionCustomizer by iterating through the queries
defined in the query
manager and calling the required native API to set it
up. The timeouts could
be set in the same code.
The reason there is no universal setting is that it is
not clear that this
would be desirable in most use-cases. EclipseLink
already has a cache that
provides quite a bit of performance boost and the
query results cache is
intended to provide an additional performance boost
for selected queries.
Using the query cache requires an understanding about
the degree to which
results may be stale when they come back.
-Tom
On 09/03/2012 8:16 AM, Tim Martin wrote:
Hi - anyone know if there is a
valid property to use in the
persistence.xml to
cache all query results by name and parameter
values.
So rather than putting a hint on the queries we can
do something like
<property name="eclipselink.query-results-cache"
value="true"/>
I've come across it searching in google - but not
come across anything
defintive...
If so - how would we configure expiration of the
cache ? something simple
like
expire everything every x minutes would do to start
with..
Thanks
Tim
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