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From "Hiroshi Ikeda (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 Fri, 21 Mar 2014 06:23:46 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13942838#comment-13942838
] 

Hiroshi Ikeda commented on HBASE-10656:
---------------------------------------

Sorry I just guess it by some trials of my counters with replacing ID and hashcode, and I
don't have practical scale HBase for my tests.

If in actual usages in HBase the performance overhead of ThreadLocal is not so apparent, I
prefer the last counter because of its durability in general situtations in the current and
near future HBase. Even if the measuerd consumed memory is low, it may still depend on situations
and luck (though using the sequential ID gives more adaptability to restricted situations).


>  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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