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From "Lewis John McGibbney (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GORA-105) DataStoreFactory does not properly support multiple stores
Date Thu, 08 Mar 2012 18:39:58 GMT

    [ https://issues.apache.org/jira/browse/GORA-105?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13225373#comment-13225373
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Lewis John McGibbney commented on GORA-105:
-------------------------------------------

This arguement you've created here in this issue is about flexibility and usability and is
a real great catch at this late stage in the day so to speak.
I've followed your commentary as above and only have the following comments:
* Would be great to see the new static createProps() annotated with something along the lines
of "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. ", this provides a neat justification
for the change.
* Can you please expand on what you mean by {bq} We can always reintroduce caching functionality
when we can implement a proper key. {bq}?
Does this require us to log the issue just now and act on it at a later stage?

All in all I'm very happy with the issue and of course the proposed solution. It's a real
nice catch and can only get better once it's implemented and tested more.
                
> 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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