Tim Armstrong created IMPALA-7969:
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Summary: 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
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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