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Date: Fri, 17 Aug 2012 11:17:38 +1100 (NCT)
From: "Lars Hofhansl (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <423977086.21978.1345162658161.JavaMail.jiratomcat@arcas>
Subject: [jira] [Created] (HBASE-6603)
 RegionMetricsStorage.incrNumericMetric is called too often
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Lars Hofhansl created HBASE-6603:
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             Summary: RegionMetricsStorage.incrNumericMetric is called too often
                 Key: HBASE-6603
                 URL: https://issues.apache.org/jira/browse/HBASE-6603
             Project: HBase
          Issue Type: Bug
          Components: performance
            Reporter: Lars Hofhansl
            Assignee: Lars Hofhansl
             Fix For: 0.96.0, 0.94.2


Running an HBase scan load through the profiler revealed that RegionMetricsStorage.incrNumericMetric is called way too often.

It turns out that we make this call for *each* KV in StoreScanner.next(...).
Incrementing AtomicLong requires expensive memory barriers.

The observation here is that StoreScanner.next(...) can maintain a simple 
long in its internal loop and only update the metric upon exit. Thus the AtomicLong is not updated nearly as often.

That cuts about 10% runtime from scan only load (I'll quantify this better soon).

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