2.10 - Hive Connector Limitations - Teradata QueryGrid

Teradata® QueryGrid™ Installation and User Guide

Teradata QueryGrid
September 2019
User Guide
The following limitations affect use of Hive connectors with Teradata QueryGrid:
  • Foreign function execution
  • 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 following Hive speculative properties are not supported and are disabled by default, unless the Support Hive Task Retries parameter is set to True:
    • mapreduce.map.speculative=false
    • mapreduce.reduce.speculative=false
    • tez.am.speculation.enabled=false
  • When using the Hive initiator:
    • Export is supported for Hive-on-Tez (Hive Execution Engine property = Tez) on HDP 3.0.1 or later only.
    • Export is not supported for 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 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), 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.
  • If Hive is upgraded or the location of standard Hive JARs are changed, a tdqg-node restart is required.
  • The default for Timestamp precision is nine (9); Teradata QueryGrid truncates data with more than six decimal places when using Hive-to-Teradata links.
  • Date literals used in WHERE clauses are not converted to the time zone of the remote system if the remote system time zone is different from the initiator system time zone.
  • UTF-16 supplementary characters exceeding more than 2 bytes in a table cause data truncation.
  • IMPORT is not supported on the VARCHAR, STRING, and CHAR columns of the Hive table if the table character set is something other than Latin or UTF-16.