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https://issues.apache.org/jira/browse/IMPALA-5200?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16663037#comment-16663037
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Joe McDonnell commented on IMPALA-5200:
---------------------------------------
Regardless of whether we have something equivalent to the counters I described
previously, we can do a better job of implementing
RuntimeProfile::ComputeTimeInProfile() to make it more sensible while a query
is executing. This function should take advantage of the fact that a profile
includes all of its childrens' time. Specifically, if a profile's total time is
profile_total_time and its summed childrens' total time is children_total_time,
then a profile's total time is max(children_total_time, profile_total_time). If
a profile's total time is 0 because of the SCOPED_TIMER issue described above,
it can sensibly use the total time of its children. This prevents it from
reporting the local time percentage as 100% when it is stuck in child code.
A pseudocode recursive version looks something like this (this ignores locking,
custom local times, and probably other things):
{code:java}
void computeTimeInProfile() {
// Recurse and process children so that they are up to date
for child in children_:
child.computeTimeInProfile();
// All the children have up-to-date total time. Iterate and sum it.
children_total_time = 0;
for child in children_:
children_total_time += child.total_time();
profile_total_time = total_time_counter()->value();
total_time = max(children_total_time, profile_total_time);
// For profiles that have the SCOPED_TIMER condition described above, this
condition means that local_time is 0 and local_time_percentage = 0, which is
more sensible than 100%.
local_time = total_time - children_total_time;
local_time_percentage = (100 * local_time) / total_time;
}{code}
If the leaf node is waiting in an indefinite wait (and thus is not updating its
counters), then this will not help. That's ok, because that is a small subset
of the issues that we encounter.
> Profile timers not updated during long-running sort
> ---------------------------------------------------
>
> Key: IMPALA-5200
> URL: https://issues.apache.org/jira/browse/IMPALA-5200
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Affects Versions: Impala 2.9.0
> Reporter: Tim Armstrong
> Priority: Minor
> Labels: observability, ramp-up, supportability
>
> If you have a query plan with a long-running sort operation (e.g. minutes),
> the profile timers are not updated to reflect the time spent in the sort
> until the sort starts returning rows.
> E.g. this is a summary from a sort query that was running for a few hours
> (!). The summary was misleading and the "heat map" plan in the debug web UI
> is misleading - it showed the join as the "hot" operator. It would be ideal
> if we could somehow at least periodically update the time spent in the
> operator.
> {code}
> Operator #Hosts Avg Time Max Time #Rows Est. #Rows
> Peak Mem Est. Peak Mem Detail
> ----------------------------------------------------------------------------------------------------------------------------
> 05:MERGING-EXCHANGE 1 0.000ns 0.000ns 0 635.58M
> 0 -1.00 B UNPARTITIONED
> 03:SORT 1 0.000ns 0.000ns 0 635.58M
> 47.86 GB 800.00 MB
> 02:HASH JOIN 1 4s859ms 4s859ms 771.02M 635.58M
> 162.11 MB 16.03 MB INNER JOIN, BROADCAST
> |--04:EXCHANGE 1 38.988ms 38.988ms 247.20K 247.20K
> 0 0 BROADCAST
> | 01:SCAN HDFS 1 8s089ms 8s089ms 247.20K 247.20K
> 3.79 MB 32.00 MB product b
> 00:SCAN HDFS 1 209.997ms 209.997ms 15.09M 635.58M
> 185.27 MB 176.00 MB sales a
> {code}
> http://community.cloudera.com/t5/Interactive-Short-cycle-SQL/Impala-join-query-running-slow
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