DataStoreFactory does not properly support multiple stores
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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
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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