Thomas Tauber-Marshall created IMPALA-8597:
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Summary: Improve session maintenance timing logic
Key: IMPALA-8597
URL: https://issues.apache.org/jira/browse/IMPALA-8597
Project: IMPALA
Issue Type: Improvement
Reporter: Thomas Tauber-Marshall
Currently, the coordinator maintains a list of the timeout lengths for all
sessions that have an idle_session_timeout set. The original intention of this
was to have the thread that checks for timeouts wake up at an interval of <the
shortest currently registered timeout> / 2, but this resulted in IMPALA-5108
The fix for that bug changed the session maintenance thread wake up every 1
second if any timeout is registered, but we still maintain the list of timeout
values even though only the length of the list is ever used.
Given that the default config is for there to be no session timeouts and that
the maintenance thread is somewhat inefficient in holding the
session_state_map_ lock for almost its entire execution, we may want to keep
the behavior of only waking up once per second if there are any registered
timeouts, in which case it would be more efficient to just maintain a count of
timeouts instead of the list.
Or, we may want to just simplify the logic and have the thread always wake up
once per second, without tracking the registered timeouts at all (esp. with the
new work in IMPALA-1653 which adds closing of disconnected sessions to the
maintenance thread), in which case we might want to consider ways to avoid
holding the session_state_map_ lock for so long, eg. by sharding it the way we
did with the client_request_state_map_
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