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From "Sandhya (JIRA)" <>
Subject [jira] Updated: (OPENJPA-738) QueryCache Improvement
Date Tue, 21 Oct 2008 22:58:44 GMT


Sandhya updated OPENJPA-738:

    Attachment: OPENJPA-738.8.patch

This patch has some changes to the coding style and some clean up to the code by removing
some string comparisons.

Sandhya Turaga

> QueryCache Improvement
> ----------------------
>                 Key: OPENJPA-738
>                 URL:
>             Project: OpenJPA
>          Issue Type: Improvement
>          Components: datacache
>    Affects Versions: 1.2.0, 1.2.1, 1.3.0
>            Reporter: Sandhya
>             Fix For: 1.3.0
>         Attachments: OPENJPA-738.2.patch, OPENJPA-738.3.patch, OPENJPA-738.6.patch, OPENJPA-738.7.patch,
OPENJPA-738.8.patch, OPENJPA-738.patch
> Hi All,
>       I have changed the jpa code to eliminate the scan of the jpa query cache to invalidate
cached queries that is triggered by entity bean values changes. The problem with the current
code is that whenever an entity bean value changes, the query cache needs to be scanned and
all the queries that are related to the changed entity bean should be invalidated. This is
resulting in poor performance when the querycache has too many queries in it. 
>       The new approach is to track the timestamp of the query and the timestamp of last
update for each entity class and compare the timestamps when retrieving the query for reuse.
 If the timestamp of the query result is older than the last update time of any entity in
the access path of the query,  the query result would not be reused and the query result would
be evicted from the query cache. 
>       I introduced a configurable attribute in the persistence.xml in QueryCache property
"evictOnTimestamp=true". Therefore the QueryCache property in persistence.xml file looks as
>       <property name="openjpa.QueryCache" value = "CacheSize=1000, evictOnTimestamp=true"
>       If the "evictOnTimestamp" value is set to true in the xml file the new code is
invoked otherwise the old code. The default behaviour would be the old code. That is the value
for "evictOnTimestamp" is false by default so that if this property is not set persistence.xml,
old code gets invoked. 
>       In the process of changing the code to evict the queries using the timestamp, I
had to introduce 4 methods in QueryCache interface. We want this change to be applied to JPA
trunk and 1.2.x branch. Anyone who is extending the QueryCache that implements this interface
would have to implement these 4 methods. Please respond as soon as possible if this interface
change is an issue. 

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