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From "Junping Du (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-3816) [Aggregation] App-level Aggregation for YARN system metrics
Date Tue, 21 Jul 2015 18:05:08 GMT

    [ https://issues.apache.org/jira/browse/YARN-3816?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14635513#comment-14635513
] 

Junping Du commented on YARN-3816:
----------------------------------

Thanks [~sjlee0] for review and comments!
bq. If I understand correctly, this patch basically does a time integral of a given metric,
or "the area under the curve" for the metric as a function of time. For example, if the underlying
metric is a container CPU usage, the "aggregated" metric according to TimelineMetric.aggregateTo()
would be a cumulative CPU usage over time for that container (in the units of CPU-millis).
That's correct. As a poc patch for app aggregation, we only pick up some metric to aggregated
in some way to demonstrate overall end-to-end flow. I understand there could be more important
aggregated metrics there and I will try to add more in following patches.

bq. While this is certainly a useful number to keep track of, this was not the app-level aggregation
I had in mind. IMO, the app-level aggregation (or any aggregation for that matter) is all
about rolling metrics up from child entities to the parent entity. I would have thought that
it would be the first thing we want to get to. It looks, however, as though that aggregation
is not done in this patch. I don't see any code that rolls up values from containers to the
application. Are you planning to introduce that soon?
Yes. I should add that part in poc v2 patch for taking a "snapshot" for resource consumption
on an application. Previous area value is also kept for different purpose (resource billing/charge,
etc.).

bq. This type of time integral works only if the underlying metric is a gauge. For example,
for any counter-like metric (e.g. HDFS bytes read) which is cumulative in nature, the time
integral does not make sense. We will need to introduce another type dimension to the metrics
that signifies whether it is a counter or a gauge, but this is just to note that the time
integral works only for gauges.
I agree that we should differentiate counter with gauge. For the previous one, we are more
focus on its cumulative property while the later one is more focus on "snapshot". However,
in practice, there are cases that some aggregated metrics has both properties, like "area"
value here - we do need its cumulative values and also could be interested in getting values
within a given time interval. Isn't it?

bq. Also, this is pretty similar to what we talked about during the offline meeting as "average/max"
for gauges, except that it's not divided over time. We discussed that we want to introduce
time averages and maxes for gauges (see "time average & max" in https://issues.apache.org/jira/secure/attachment/12743390/aggregation-design-discussion.pdf).
Are we thinking of replacing that with this?
No. Nothing get changed on the design since our last discussions. The average and max is also
important but I just haven't get bandwidth to add in poc stage as adding existing things could
be more straight-forward. I will add it later.

bq. In the specific case of container CPU usage, it seems to me that emitting the actual CPU
time millis directly would be a far easier and more accurate way to capture this info. I believe
it's readily available, and it would be a counter-like metric instead of a gauge. Therefore
the time integral doesn't apply (as it already is one). But all you need to do at the app-level
aggregation for it is just to sum it up. I recognize that this time integral would be useful
for other things, but just wanted to point that out.
Thanks for pointing that out. I agree this is more precisely and will update this in following
patch.

> [Aggregation] App-level Aggregation for YARN system metrics
> -----------------------------------------------------------
>
>                 Key: YARN-3816
>                 URL: https://issues.apache.org/jira/browse/YARN-3816
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: timelineserver
>            Reporter: Junping Du
>            Assignee: Junping Du
>         Attachments: Application Level Aggregation of Timeline Data.pdf, YARN-3816-poc-v1.patch,
YARN-3816-poc-v2.patch
>
>
> We need application level aggregation of Timeline data:
> - To present end user aggregated states for each application, include: resource (CPU,
Memory) consumption across all containers, number of containers launched/completed/failed,
etc. We need this for apps while they are running as well as when they are done.
> - Also, framework specific metrics, e.g. HDFS_BYTES_READ, should be aggregated to show
details of states in framework level.
> - Other level (Flow/User/Queue) aggregation can be more efficient to be based on Application-level
aggregations rather than raw entity-level data as much less raws need to scan (with filter
out non-aggregated entities, like: events, configurations, etc.).



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