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changes.mady.by.user Lefty Leverenz

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changes.mady.by.user Eugene Koifman

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  • BEGIN, COMMIT, and ROLLBACK are not yet supported.  All language operations are auto-commit.  The plan is to support these in a future release.
  • Only ORC file format is supported in this first release.  The feature has been built such that transactions can be used by any storage format that can determine how updates or deletes apply to base records (basically, that has an explicit or implicit row id), but so far the integration work has only been done for ORC.
  • By default transactions are configured to be off.  See the Configuration section below for a discussion of which values need to be set to configure it.
  • Tables must be bucketed to make use of these features.  Tables in the same system not using transactions and ACID do not need to be bucketed. External tables cannot be made ACID tables since the changes on external tables are beyond the control of the compactor (HIVE-13175).
  • Reading/writing to an ACID table from a non-ACID session is not allowed. In other words, the Hive transaction manager must be set to org.apache.hadoop.hive.ql.lockmgr.DbTxnManager in order to work with ACID tables.
  • At this time only snapshot level isolation is supported.  When a given query starts it will be provided with a consistent snapshot of the data.  There is no support for dirty read, read committed, repeatable read, or serializable.  With the introduction of BEGIN the intention is to support snapshot isolation for the duration of transaction rather than just a single query.  Other isolation levels may be added depending on user requests.
  • The existing ZooKeeper and in-memory lock managers are not compatible with transactions.  There is no intention to address this issue.  See Basic Design below for a discussion of how locks are stored for transactions.
  • Schema changes using ALTER TABLE is NOT supported for ACID tables. HIVE-11421 is tracking it.  Fixed in 1.3.0/2.0.0.
  • Using Oracle as the Metastore DB and "datanucleus.connectionPoolingType=BONECP" may generate intermittent "No such lock.." and "No such transaction..." errors.  Setting "datanucleus.connectionPoolingType=DBCP" is recommended in this case. 
  • LOAD DATA... statement is not supported with transactional tables.  (This was not properly enforced until HIVE-16732)

Streaming APIs

Hive offers APIs for streaming data ingest and streaming mutation:

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