[jira] [Updated] (IMPALA-7969) Always admit trivial queries immediately

["Joe McDonnell (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IMPALA-7969?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Joe McDonnell updated IMPALA-7969:
----------------------------------
    Target Version: Impala 4.0  (was: Impala 3.4.0)

> Always admit trivial queries immediately
> ----------------------------------------
>
>                 Key: IMPALA-7969
>                 URL: https://issues.apache.org/jira/browse/IMPALA-7969
>             Project: IMPALA
>          Issue Type: Improvement
>          Components: Backend
>            Reporter: Tim Armstrong
>            Assignee: Bikramjeet Vig
>            Priority: Major
>              Labels: admission-control
>
> Here are two common query types that consume minimal resources:
> * {{select ... from ... limit 0}}, which is used by some clients to determine column types
> * {{select <expr1>, <expr2>, <expr3>}}, which just evaluates some constant expressions on the coordinator
> Currently these queries get queued if there are existing queued queries or the number of queries limit is exceeded, which is inconvenient for use cases where latency is important. I think the planner should identify trivial queries and admission controller should admit immediately.
> Here's an initial thought on the definition of a trivial query:
> * Must have PLAN ROOT SINK as the root
> * Can contain UNION and EMPTYSET nodes only



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