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https://issues.apache.org/jira/browse/HADOOP-8541?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13410690#comment-13410690
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Andrew Wang commented on HADOOP-8541:
-------------------------------------
Thanks for the very detailed review Aaron. The Eclipse auto-formatter should
have gotten the style comments, and I tried to address most of the rest.
For 11, since memory usage seemed to be a major concern, I wanted to avoid the
object overhead from using Longs instead of the primitive type. This is O(KBs)
though, so I can change it if you think it's not readable. The usage of the
array is pretty simple though, there isn't any weird iteration, and it's only
flushed completely.
For 13, I'd have to think about how to make this work. It's probably doable
(basically need to merge adjacent items instead of inserting), but I don't
think it'll yield that big of a performance boost. Again, I'll work on this if
you think it's worthwhile.
> Better high-percentile latency metrics
> --------------------------------------
>
> Key: HADOOP-8541
> URL: https://issues.apache.org/jira/browse/HADOOP-8541
> Project: Hadoop Common
> Issue Type: Improvement
> Components: metrics
> Affects Versions: 2.0.0-alpha
> Reporter: Andrew Wang
> Assignee: Andrew Wang
> Attachments: hadoop-8541-1.patch, hadoop-8541-2.patch,
> hadoop-8541-3.patch, hadoop-8541-4.patch
>
>
> Based on discussion in HBASE-6261 and with some HDFS devs, I'd like to make
> better high-percentile latency metrics a part of hadoop-common.
> I've already got a working implementation of [1], an efficient algorithm for
> estimating quantiles on a stream of values. It allows you to specify
> arbitrary quantiles to track (e.g. 50th, 75th, 90th, 95th, 99th), along with
> tight error bounds. This estimator can be snapshotted and reset periodically
> to get a feel for how these percentiles are changing over time.
> I propose creating a new MutableQuantiles class that does this. [1] isn't
> completely without overhead (~1MB memory for reasonably sized windows), which
> is why I hesitate to add it to the existing MutableStat class.
> [1] Cormode, Korn, Muthukrishnan, and Srivastava. "Effective Computation of
> Biased Quantiles over Data Streams" in ICDE 2005.
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