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From "Ferdy Galema (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GORA-105) DataStoreFactory does not properly support multiple stores
Date Thu, 08 Mar 2012 20:13:57 GMT

    [ https://issues.apache.org/jira/browse/GORA-105?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13225456#comment-13225456

Ferdy Galema commented on GORA-105:

"the new static createProps() annotated"
That's a good idea. It's going to be an important method after all. Will include it in the
next patch.

"Does this require us to log the issue just now and act on it at a later stage? "
Yes that is what I propose. I will create an issue that is for implementing caching, the right
way. Because this needs to be very well thought out, I did not intend to include it with this
issue. Simply disabling cache should be right for now because this will prevent unexpected
behaviour. (Like the scenario I sketched above with the two different databases). I do not
expect this change to have negative impact.

In any case I am more than happy to also provide annotations for the "createDataStore" methods
to clarify their exact behaviour.
> DataStoreFactory does not properly support multiple stores
> ----------------------------------------------------------
>                 Key: GORA-105
>                 URL: https://issues.apache.org/jira/browse/GORA-105
>             Project: Apache Gora
>          Issue Type: Bug
>          Components: schema, storage
>            Reporter: Ferdy Galema
>            Priority: Blocker
>             Fix For: 0.2
>         Attachments: GORA-105.patch
> DataStoreFactory has a single, static properties field. This is completely unacceptable,
because that way when multiple stores are instantiated in the same JVM, the last store instance
will overwrite the "default.schema" property. This causes that all the previous stores will
read a misconfigured default schema property. Beside this it may cause several other nasty
future bugs. In my opinion this is a blocker because the methods on DataStoreFactory suggest
that it can handle multiple stores, when as a matter fact it doesn't. 
> I will attach and commit a patch that fixes this problem. It only modifies gora-core.
All stores directly benefit from this bugfix because of DataStoreBase. This patch fixes the
following property related problems.
> -It introduces a static method createProps in DataStoreFactory. This is the equivalent
of Configuration.create(). Everyone can create a new properties object and set everything
interesting on it and pass it on to whatever stores they like, instead of ALL stores.
> -It fixes the method javadoc of DataStoreBase#getSchemaName(String mappingSchemaName,
Class<?> persistentClass). The previous description was simply wrong.
> -It SERIALIZES the properties field of DataStoreBase instead of grabbing the static DataStoreFactory.properties
field. This has the additional benefit of making sure that the store can be used correctly
with runtime modified properties in a mapreduce context.
> -It removes the caching functionality of DataStoreFactory. Because of the dynamic configuration
in the Properties and Configuration object, it is very difficult to implement a correct key
hash for the cache. At the moment it only uses the triple {datastoreClass, keyClass,valueClass}
as a key hash. Multiple stores cannot be properly supported when the factory uses badly implemented
hash keys. (For example, one might instantiate 2 SqlStores, both using the exact same {datastoreClass,
keyClass,valueClass} triple, but pointing to different databases. When one is about the instantiate
the second datastore, it will faulty return the first datastore from cache). We can always
reintroduce caching functionality when we can implement a proper key.
> The patch passes all tests. Will commit when there are no objections.

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