2.06 - Hive Connector Limitations - Teradata QueryGrid

Teradata® QueryGrid™ Installation and User Guide

Product
Teradata QueryGrid
Release Number
2.06
Published
September 2018
Language
English (United States)
Last Update
2018-11-26
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The following limitations affect use of Hive connectors with Teradata QueryGrid:
  • Transaction semantics between systems is not supported.

    After data has been exported and committed to a remote system, any subsequent errors or aborts on the local system do not roll back the remote request.

  • The default for Timestamp precision is nine (9); Teradata QueryGrid truncates data with more than six decimal places when using Hive-to-Teradata links.
  • The following Hive speculative properties are not supported and are disabled by default.
    • mapreduce.map.speculative=false
    • mapreduce.reduce.speculative=false
    • tez.am.speculation.enabled=false
  • When using the Hive initiator:
    • Export is supported for Hive-on-MR only (Hive Execution Engine property = MR).
    • Export is not supported for Hive-on-Tez (Hive Execution Engine property = Tez) or Hive-on-Spark (Hive Execution Engine property = Spark)
    • The target server returns all columns and the initiator server processes any column projection.
    • The target server does not return query and plan data when using the Explain command.
    • The target server returns all columns when using the Count command; these then aggregate on the initiator server.
    • Sub-queries such as insert into 1st-non-native-table select from 2nd-non-native-table cannot be used.
  • By default, the Hive target connector returns a 1 as the number of rows exported regardless of how many rows were actually exported during a successful export query. Setting the Collect Approximate Activity Count connector property to true returns the number of rows exported with the following limitations:
    • If the Hive table statistics are inaccurate (this is uncommon – Hive table statistics are usually accurate), enabling this property can result in a performance overhead on the insert query.
    • If there are concurrent inserts on the Hive table, an inaccurate number of rows may be displayed, resulting in an approximate result rather than a precise number.