Steven Rand created YARN-7391:
---------------------------------
Summary: Consider square root instead of natural log for
size-based weight
Key: YARN-7391
URL: https://issues.apache.org/jira/browse/YARN-7391
Project: Hadoop YARN
Issue Type: Improvement
Components: fairscheduler
Affects Versions: 3.0.0-beta1
Reporter: Steven Rand
Currently for size-based weight, we compute the weight of an app using this
code from
https://github.com/apache/hadoop/blob/trunk/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FairScheduler.java#L377:
{code}
if (sizeBasedWeight) {
// Set weight based on current memory demand
weight = Math.log1p(app.getDemand().getMemorySize()) / Math.log(2);
}
{code}
Because the natural log function grows slowly, the weights of two apps with
hugely different memory demands can be quite similar. For example, {{weight}}
evaluates to 14.3 for an app with a demand of 20 GB, and evaluates to 19.9 for
an app with a demand of 1000 GB. The app with the much larger demand will still
have a higher weight, but not by a large amount relative to the sum of those
weights.
I think it's worth considering a switch to a square root function, which will
grow more quickly. In the above example, the app with a demand of 20 GB now has
a weight of 143, while the app with a demand of 1000 GB now has a weight of
1012. These weights seem more reasonable relative to each other given the
difference in demand between the two apps.
The above example is admittedly a bit extreme, but I believe that a square root
function would also produce reasonable results in general.
The code I have in mind would look something like:
{code}
if (sizeBasedWeight) {
// Set weight based on current memory demand
weight = Math.sqrt(app.getDemand().getMemorySize());
}
{code}
Would people be comfortable with this change?
--
This message was sent by Atlassian JIRA
(v6.4.14#64029)
---------------------------------------------------------------------
To unsubscribe, e-mail: yarn-issues-unsubscr...@hadoop.apache.org
For additional commands, e-mail: yarn-issues-h...@hadoop.apache.org
