Details
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Improvement
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Status: Open
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Major
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Resolution: Unresolved
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0.6 (pre-incubation)
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None
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None
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Important
Description
For single region, single row operations (both IDU DML as well as select) SQL will avoid beginning a transaction and perform the operation directly in HBase.
The feeling was that for single row operations a trasnaction was not necessary as HBase would make the operation atomic and provide the necessary guarantees. The problem is this circumvents the endpoint coprocessor and makes conflict detection with other concurrent transactions impossible.
For performance reasons we should try to approximate the autocommit behavior as much as possible while preserving the conflict detection. We can achieve this by implementing 'region transactions' whereby the region will create its own transaction identifier when a nontransactional operation arrives in the coprocessor. We will need to override all HTable nontransactional operations in both the TransactionalTable and SsccTransactionalTable classes. The override will create a new transaction identifier specific to the region transaction and then use that for all modifications as if it were issued by the DTM.
The transaction identifier needs to be unique so that other threads performing similar operations do not get confused at conflict resolution time. One possibility is to maintain an AtomicLong in the region that can be incremented whenever such a transaction is needed. This keeps all processing inside the region and eliminates any RPC to another server process.
