Sean Broeder created TRAFODION-1435:
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Summary: SQL operations not always performed transactionally with
AUTOCOMMIT OFF
Key: TRAFODION-1435
URL: https://issues.apache.org/jira/browse/TRAFODION-1435
Project: Apache Trafodion
Issue Type: Improvement
Components: dtm
Affects Versions: 0.6 (pre-incubation)
Reporter: Sean Broeder
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.
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