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https://issues.apache.org/jira/browse/OPENJPA-2078?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13155201#comment-13155201
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Rick Curtis commented on OPENJPA-2078:
--------------------------------------
First off, we'd prefer to have you wait until we have identified that a code
change is necessary before opening a JIRA. For future reference, could you use
the users/dev mailing lists to ask questions?
Now on to answering your questions.
> 1) Is there a relevance between query cache and data cache?
Yes, the openja.QueryCache(QueryResultsCache) can be thought of as a mapping of
SQL (and params) to a collection of oids. While it is possible to use the query
cache without a data cache, that usage doesn't make much sense for most users.
> This means subsequently that this type of query cannot benefit from caching
> techniques?
Honestly, I'm not 100% on the meaning of that message, but I'm fairly certain
it is a noisy message coming from another one of the internal OpenJPA query
caches.... I think it can be safely ignored.
> 2) Is there a way to get all ids of the PO's from openjpa that consist the
> resultlist of a specific query?
Yes, that is how the data is stored in the QueryCache. [key] -> Collection<PO>
> 3) In this particular example, enabling the default cache (openJPA's):
I believe this statement supports my previous comment that the indicated
message is just noise.
> 4) Is there a mechanism to trigger using the "bulk" getAll, loadAll() etc
> methods?
Unfortunately there isn't... but I would think that we could do something along
these lines. As you may have noticed, OpenJPA is quite bad at it's cache usage.
We issue lots and lots of remote calls.
Hopefully this answers a majority of your questions.
Thanks,
Rick
> Using external datacache - poor performance when trying to fetch a large
> resultSet
> ----------------------------------------------------------------------------------
>
> Key: OPENJPA-2078
> URL: https://issues.apache.org/jira/browse/OPENJPA-2078
> Project: OpenJPA
> Issue Type: Question
> Components: datacache, performance
> Affects Versions: 2.1.0
> Environment: Mysql, memcached, SLES 11
> Reporter: Dimitrios Iosifidis
> Priority: Critical
>
> In our application, we have extended the AbstractDataCache/AbstractQueryCache
> in order to introduce our own caching implementation using Memcached.
> However, during testing it has been found that performance has dramatically
> degraded. Analysis has shown that the main reason for this is the fact that
> openjpa calls the
>
> protected DataCachePCData getInternal(final Object arg0)
> method instead (probably) of the:
> Map<Object, DataCachePCData> getAll(List<Object> arg0)
> For a result set of 40000 records for example, 40000 get requests are issued
> to the external cache, resulting in poor performance. Instead, if the
> getAll(..) method (overrided from AbstractDataCache) was to be called, then
> the cache would have a decent performance (as a consequence of a single
> request).
> So, my question consists of the following:
> 1) Is there a relevance between query cache and data cache? The query I am
> experimenting on is like:
> SELECT user FROM UserPO AS user WHERE user.domain.fname = :domainName
> for which I get at the console output:
> "WARN [Runtime] Query "SELECT user FROM UserPO AS user WHERE
> user.domain.fname = :domainName" is removed from cache excluded permanently.
> Query "SELECT user FROM UserPO AS user WHERE user.domain.fname = :domainName"
> is not cached because its result is not obtained by executing a select
> statement. This can happen if the query was evaluated in-memory. The result
> was provided by
> org.apache.openjpa.datacache.QueryCacheStoreQuery$CachingResultObjectProvider.
> "
> This means subsequently that this type of query cannot benefit from caching
> techniques?
> 2) Is there a way to get all ids of the PO's from openjpa that consist the
> resultlist of a specific query?
> 3) In this particular example, enabling the default cache (openJPA's):
> <property name="openjpa.DataCache" value="true"/>
> <property name="openjpa.QueryCache" value="true"/>
> seems to work fine (in respect of performance)
> The above queries are issued two times, but only one reached the database.
> Taking into account that the same warning is displayed (Query "SELECT user
> FROM UserPO AS user WHERE user.domain.fname = :domainName" is removed from
> cache excluded permanently.....) how this works?
> 4) Is there a mechanism to trigger using the "bulk" getAll, loadAll() etc
> methods?
> Any hints are highly appreciated!
> Thank you in advance,
> Dimitris.
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