[OPENJPA-2078] Using external datacache - poor performance when trying to fetch a large resultSet

• Type: Question
• Status: Open
• Priority: Critical
• Resolution: Unresolved
• Affects Version/s: 2.1.0
• Component/s: datacache, performance
• Environment: Mysql, memcached, SLES 11
• Assignee: Unassigned
• Reporter: Dimitrios Iosifidis
• Created: 22/Nov/11 14:24
• Updated: 22/Nov/11 15:21

Description

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.