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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