Re: caching query results for all queries...?

Tim Martin-11 wrote:

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
>>>>>>>>
>>>>>>>>