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From "Misha Dmitriev (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10656) high-scale-lib's Counter depends on Oracle (Sun) JRE, and also has some bug
Date Wed, 19 Oct 2016 00:22:59 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15587146#comment-15587146
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Misha Dmitriev commented on HBASE-10656:
----------------------------------------

To be more specific, our RegionServers end up with millions of Counter$Cell objects in memory:

{code}
 #instances     Shallow size     #instances    Shallow size       Class name
  garbage       garbage           live         live                         
----------------------------------------------------------------------------
 2,985,951   396,571K (32.8%)      766,919    101,856K (8.4%)     org.apache.hadoop.hbase.util.Counter$Cell
 2,985,949     69,983K (5.8%)      766,918     17,974K (1.5%)     org.apache.hadoop.hbase.util.Counter$Cell[]
{/code}

I think there is no point in talking about optimizations where we forcefully prevent two Cell
objects from sharing a single cache line where there are so many of them that they just cause
memory blowup.

A simple way of solving this problem would be to just remove the extra padding long fields.
However, I am totally new to HBase and don't know whether a large number of these objects
is always the case. Maybe in some setups there are very few of them. In that case, maybe it
would make sense to have two alternative implementations of Cell:
 - one that assumes a small number of objects and optimized for cache speed, as now
 - another that's just as compact as possible.

>  high-scale-lib's Counter depends on Oracle (Sun) JRE, and also has some bug
> ----------------------------------------------------------------------------
>
>                 Key: HBASE-10656
>                 URL: https://issues.apache.org/jira/browse/HBASE-10656
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Hiroshi Ikeda
>            Assignee: Hiroshi Ikeda
>            Priority: Minor
>             Fix For: 0.96.2, 0.98.1, 0.99.0
>
>         Attachments: 10656-098.v2.txt, 10656-trunk.v2.patch, 10656.096v2.txt, HBASE-10656-0.96.patch,
HBASE-10656-addition.patch, HBASE-10656-trunk.patch, MyCounter.java, MyCounter2.java, MyCounter3.java,
MyCounterTest.java, MyCounterTest.java, PerformanceTestApp.java, PerformanceTestApp2.java,
output.pdf, output.txt, output2.pdf, output2.txt
>
>
> Cliff's high-scale-lib's Counter is used in important classes (for example, HRegion)
in HBase, but Counter uses sun.misc.Unsafe, that is implementation detail of the Java standard
library and belongs to Oracle (Sun). That consequently makes HBase depend on the specific
JRE Implementation.
> To make matters worse, Counter has a bug and you may get wrong result if you mix a reading
method into your logic calling writing methods.
> In more detail, I think the bug is caused by reading an internal array field without
resolving memory caching, which is intentional the comment says, but storing the read result
into a volatile field. That field may be not changed after you can see the true values of
the array field, and also may be not changed after updating the "next" CAT instance's values
in some race condition when extending CAT instance chain.
> Anyway, it is possible that you create a new alternative class which only depends on
the standard library. I know Java8 provides its alternative, but HBase should support Java6
and Java7 for some time.



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