Cloudera Docs

Query execution finished in Hue but shows as executing on Cloudera Manager Impala Queries Page

Cloudera Manager and the Impala demon web page may show a query in an executing or In Flight state even though the query has finished executing on the Hue web UI. This can happen due to various reasons.

The three main reasons why the completed Hue query still shows as "executing" are:
  • Hue does not close the connection to Impala until you click on the Results page.

    Clicking the Results page in Hue executes the fetchresults call to Impala.

  • Impala queries are client-driven. Therefore, the query still remains in a running state until the client sends a fetch command to complete fetching the entire result set.
  • If a query has not been closed or unregistered, Impala shows the same in the In Flight section on its web UI. Cloudera Manager shows all In Flight queries in the Executing state.

Impala query life cycle

When you submit Impala queries, they are first registered by the system. The system identifies the queries with the help of a coordinator. They also have a state, such as CREATED, INITIALIZED, RUNNING, FINISHED, EXCEPTION, and some metadata.

  • FINISHED implies that the rows are available but not all rows are ready to be fetched. It is possible that Impala daemons are still executing the query.
  • EXCEPTION implies that an error has occurred. For example, if the system runs out of memory, then the query transitions to the EXCEPTION state.

    The query can also go into an EXCEPTION state if it is cancelled.

Query cancellations may be triggered explicitly with a HiveServer2/Beeswax call or if the query times out. Query time-out may be set through a process-wide impalad argument or with a per-query option.

Currently, Impala does not have a state that explicitly indicates whether all Impala daemons have finished executing the query and that all results have been fetched. Let us call it as End of Statement (EOS), temporarily.

When a query is in the EOS (FINISHED) or EXCEPTION state, the query is not doing any more processing, but the query remains registered. It needs to remain registered because clients may need to access the state.

The query is unregistered only in the following two cases:
  • The query is explicitly closed by a Close() API call
  • The session associated with the query is closed explicitly or the session time-out is set and the session times out
To optimize resource utilization, configure the Impala daemon to stop the idle sessions by setting the session timeout value in the --idle_session_timeout impalad argument:
  1. Sign in to Cloudera Manager as an Administrator.
  2. Go to Clusters > Impala service > Configuration.
  3. Specify the following in the Impala Command Line Argument Advanced Configuration Snippet (Safety Valve) field:
    --idle_session_timeout=<maximum lifetime of your queries in seconds>
    For example, 
    --idle_session_timeout=3600

    In this case, the query will time out after one hour.