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https://issues.apache.org/jira/browse/HBASE-27224?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Bryan Beaudreault updated HBASE-27224:
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Fix Version/s: 2.6.0
> HFile tool statistic sampling produces misleading results
> ---------------------------------------------------------
>
> Key: HBASE-27224
> URL: https://issues.apache.org/jira/browse/HBASE-27224
> Project: HBase
> Issue Type: Improvement
> Reporter: Bryan Beaudreault
> Assignee: Bryan Beaudreault
> Priority: Major
> Labels: patch-available
> Fix For: 2.6.0, 2.5.1, 3.0.0-alpha-4
>
>
> HFile tool uses codahale metrics for collecting statistics about key/values
> in an HFile. We recently had a case where the statistics printed out that the
> max row size was only 25k. This was confusing because I was seeing bucket
> cache allocation failures for blocks as large as 1.5mb.
> Digging in, I was able to find the large row using the "-p" argument (which
> was obviously very verbose). Once I found the row, I saw the vlen was listed
> as ~1.5mb which made much more sense.
> First thing I notice here is that default codahale metrics histogram is using
> ExponentiallyDecayingReservoir. This probably makes sense for a long-lived
> histogram, but the HFile tool is run at a point in time. It might be best to
> use UniformReservoir instead.
> Secondly, we do not need sampling for min/max. Let's supplement the histogram
> with our own calculation which is guaranteed to be accurate for the entirety
> of the file.
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