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https://issues.apache.org/jira/browse/IMPALA-5200?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16530483#comment-16530483
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Joe McDonnell commented on IMPALA-5200:
---------------------------------------
This issue is something I encountered recently when looking at the total time
values in our runtime profiles. One way to fix this is to implement a special
Counter for time that has the start time field embedded. This moves the start
time from a stack variable to one that is accessible to other threads. The
start time would be zero (or some other invalid value) whenever the thread is
not in a wait. The value() function would look something like this:
{code:java}
int64_t value() {
int64_t ret_value = value_;
int64_t start_time = start_time_
if (start_time != 0) {
cur_time = GetCurrentTimeMicros();
ret_value += (cur_time - start_time);
}
return ret_value;
}{code}
This requires time calls on accessing the value, but it makes the counter
smooth. The other downside is that there is a timing window when the updating
thread comes out of the wait and is in the process of updating the counter. An
external reader at this point could undercount.
> 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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