[jira] [Created] (IMPALA-5933) Compute incremental stats should always return a result set

["Alexander Behm (JIRA)" <ji...@apache.org>]

Alexander Behm created IMPALA-5933:
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             Summary: Compute incremental stats should always return a result set
                 Key: IMPALA-5933
                 URL: https://issues.apache.org/jira/browse/IMPALA-5933
             Project: IMPALA
          Issue Type: Bug
          Components: Backend, Frontend
    Affects Versions: Impala 2.8.0, Impala 2.6.0, Impala 2.7.0, Impala 2.9.0, Impala 2.10.0
            Reporter: Alexander Behm


Compute incremental stats should always return a result set that states which stats were computed/modified. Today, we have a shortcut in the code for compute incremental stats that does not return a result set when no new stats are computed because all partitions already have incremental stats.

The fact that the same command sometimes returns a result set and sometimes not depending on the state of a table is strange, and can confuse clients like JDBC/ODBC that might reasonably expect a result set for that statement.

The issue can be reproduced by running compute incremental stats twice in a row on the same table. The second run does not return a result set.

The culprit is in client-request-state.cc ClientRequestState::WaitInternal():
{code}
...
  if (catalog_op_type() == TCatalogOpType::DDL &&
      ddl_type() == TDdlType::COMPUTE_STATS && child_queries.size() > 0) {
    RETURN_IF_ERROR(UpdateTableAndColumnStats(child_queries));
  }
...
{code}

For a no-op incremental stats the number of child queries is 0, so we never set a result set or the result set metadata.




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