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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4178) Use of Random.nextLong() in HRegionServer.addScanner(...)
Date Tue, 09 Aug 2011 20:42:28 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4178?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13081908#comment-13081908
] 

Lars Hofhansl commented on HBASE-4178:
--------------------------------------

So in summary an AtomicLong that resets (naturally) when the region server restarts should
work, but it is not clear that this is actually a worthwhile problem to fix.

I am happy to do the trivial AtomicLong fix, or to just close issue... Leaning towards the
latter.


> Use of Random.nextLong() in HRegionServer.addScanner(...)
> ---------------------------------------------------------
>
>                 Key: HBASE-4178
>                 URL: https://issues.apache.org/jira/browse/HBASE-4178
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.90.3
>            Reporter: Lars Hofhansl
>            Priority: Minor
>
> ScannerIds are currently assigned by getting a random long. While it would be a rare
occurrence that two scanners received the same ids on the same region server the results would
seem to be... Bad.
> A client scanner would get results from a different server scanner, and maybe only from
some of the region servers.
> A safer approach would be using an AtomicLong. We do not have to worry about running
of numbers: If we got 10000 scanners per second it'd take > 2.9m years to reach 2^63.
> Then again the same reasoning would imply that this collisions would be happening too
rarely to be of concern (assuming a good random number generator). So maybe this is a none-issue.
> AtomicLong would also imply a minor performance hit on multi core machines, as it would
force a memory barrier.

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