Joe McDonnell created IMPALA-15333:
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Summary: "Release admission control resources" delays returning
query results
Key: IMPALA-15333
URL: https://issues.apache.org/jira/browse/IMPALA-15333
Project: IMPALA
Issue Type: Improvement
Components: Backend
Affects Versions: Impala 5.0.0
Reporter: Joe McDonnell
In the query timeline, the "Released admission control resources" is sometimes
a noticeable part of query execution time. This event happens when the
coordinator reaches the end of the result. Prior to returning the last rows to
the client, it does multiple things including releasing admission control
resources that all count towards this particular event. In spite of its name,
the time usage may not be in admission control. For some short queries with a
lot of fragments, this is a noticeable percentage of query time (e.g. 10%).
Here are some examples from TPC-DS 10TB:
|Query|Runtime|Time to release admission control resources|Percent|
|Q10|1s719ms|271.582ms|15.7%|
|Q12|854.545ms|60.219ms|7%|
|Q19|1s366ms|153.358ms|11%|
|Q21|557.227ms|54.152ms|9.7%|
|Q30|2s987ms|288.498ms|9.6%|
|Q69|1s806ms|339.064ms|18.7%|
|Q77|1s969ms|362.502ms|18.2%|
|Q80|3s716ms|347.306ms|9.3%|
|Q83|1s654ms|175.222ms|10%|
|Q8|1s549ms|188.056ms|12%|
|Q91|533.831ms|160.045ms|30%|
We should investigate where exactly the time goes and get it off of the
critical path. One theory is that the time is spent waiting for fragments to
complete so that the profile is complete. If that is the case, we would rather
return the results and have this wait happen asynchronously. A request to get
the profile should wait for this to complete.
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