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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-6852) SchemaMetrics.updateOnCacheHit costs too much while full scanning a table with all of its fields
Date Fri, 21 Sep 2012 06:07:08 GMT

    [ https://issues.apache.org/jira/browse/HBASE-6852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13460253#comment-13460253
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Lars Hofhansl commented on HBASE-6852:
--------------------------------------

Interesting. Thanks Cheng. I wonder what causes the performance problem then. Is it the get/putIfAbsent
of the ConcurrentMap we store the metrics in?

I'd probably feel better if you set the threshold to 100 (instead of 2000) - you'd still reduce
the time used there by 99%.

Also looking at the places where updateOnCacheHit is called... We also increment an AtomicLong
(cacheHits), which is never read (WTF). We should remove that counter while we're at it (even
when AtomicLongs are not the problem).

                
> SchemaMetrics.updateOnCacheHit costs too much while full scanning a table with all of
its fields
> ------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-6852
>                 URL: https://issues.apache.org/jira/browse/HBASE-6852
>             Project: HBase
>          Issue Type: Improvement
>          Components: metrics
>    Affects Versions: 0.94.0
>            Reporter: Cheng Hao
>            Priority: Minor
>              Labels: performance
>             Fix For: 0.94.2, 0.96.0
>
>         Attachments: onhitcache-trunk.patch
>
>
> The SchemaMetrics.updateOnCacheHit costs too much while I am doing the full table scanning.
> Here is the top 5 hotspots within regionserver while full scanning a table: (Sorry for
the less-well-format)
> CPU: Intel Westmere microarchitecture, speed 2.262e+06 MHz (estimated)
> Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00
(No unit mask) count 5000000
> samples  %        image name               symbol name
> -------------------------------------------------------------------------------
> 98447    13.4324  14033.jo                 void org.apache.hadoop.hbase.regionserver.metrics.SchemaMetrics.updateOnCacheHit(org.apache.hadoop.hbase.io.hfile.BlockType$BlockCategory,
boolean)
>   98447    100.000  14033.jo                 void org.apache.hadoop.hbase.regionserver.metrics.SchemaMetrics.updateOnCacheHit(org.apache.hadoop.hbase.io.hfile.BlockType$BlockCategory,
boolean) [self]
> -------------------------------------------------------------------------------
> 45814     6.2510  14033.jo                 int org.apache.hadoop.hbase.KeyValue$KeyComparator.compareRows(byte[],
int, int, byte[], int, int)
>   45814    100.000  14033.jo                 int org.apache.hadoop.hbase.KeyValue$KeyComparator.compareRows(byte[],
int, int, byte[], int, int) [self]
> -------------------------------------------------------------------------------
> 43523     5.9384  14033.jo                 boolean org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(org.apache.hadoop.hbase.KeyValue)
>   43523    100.000  14033.jo                 boolean org.apache.hadoop.hbase.regionserver.StoreFileScanner.reseek(org.apache.hadoop.hbase.KeyValue)
[self]
> -------------------------------------------------------------------------------
> 42548     5.8054  14033.jo                 int org.apache.hadoop.hbase.KeyValue$KeyComparator.compare(byte[],
int, int, byte[], int, int)
>   42548    100.000  14033.jo                 int org.apache.hadoop.hbase.KeyValue$KeyComparator.compare(byte[],
int, int, byte[], int, int) [self]
> -------------------------------------------------------------------------------
> 40572     5.5358  14033.jo                 int org.apache.hadoop.hbase.io.hfile.HFileBlockIndex$BlockIndexReader.binarySearchNonRootIndex(byte[],
int, int, java.nio.ByteBuffer, org.apache.hadoop.io.RawComparator)~1
>   40572    100.000  14033.jo                 int org.apache.hadoop.hbase.io.hfile.HFileBlockIndex$BlockIndexReader.binarySearchNonRootIndex(byte[],
int, int, java.nio.ByteBuffer, org.apache.hadoop.io.RawComparator)~1 [self]

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