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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-8151) Small optimization in HFileReaderV2
Date Wed, 20 Mar 2013 20:39:15 GMT

     [ https://issues.apache.org/jira/browse/HBASE-8151?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Ted Yu updated HBASE-8151:
--------------------------

    Attachment: 8151-0.96-v3.txt

Patch v3 fixes the following compilation error:
{code}
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.5.1:compile
(default-compile) on project hbase-server: Compilation failure
[ERROR] /Users/tyu/trunk/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFile.java:[659,13]
cannot find symbol
[ERROR] symbol  : constructor Writer(org.apache.hadoop.fs.FileSystem,org.apache.hadoop.fs.Path,int,org.apache.hadoop.hbase.io.compress.Compression.Algorithm,org.apache.hadoop.hbase.io.hfile.HFileDataBlockEncoder,org.apache.hadoop.conf.Configuration,org.apache.hadoop.hbase.io.hfile.CacheConfig,org.apache.hadoop.hbase.KeyValue.KVComparator,org.apache.hadoop.hbase.regionserver.BloomType,long,org.apache.hadoop.hbase.util.ChecksumType,int)
[ERROR] location: class org.apache.hadoop.hbase.regionserver.StoreFile.Writer
{code}
                
> Small optimization in HFileReaderV2
> -----------------------------------
>
>                 Key: HBASE-8151
>                 URL: https://issues.apache.org/jira/browse/HBASE-8151
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>         Attachments: 8151-0.94.txt, 8151-0.96.txt, 8151-0.96-v2.txt, 8151-0.96-v3.txt
>
>
> HFiles V2 store the memstoreTS of each KV.
> In many cases all the KVs in an HFile will have a memstoreTS of 0 (that is the case when
at the time the HFile was written there are no KVs that were created after the oldest still
active scanner - which is frequently the case).
> In that case we:
> # do not need to decode the memstoreTS (a vlong), since we know its value is 0 and its
length is 1 byte.
> # when we compact HFiles and all of the involved files have only KVs with memstoreTS
= 0 we know ahead of time that all KVs meet this condition and we do not need to store the
memstoreTS in the new HFile.
> This issue will cover the first part. The performance improvement will be modest as it
is fairly cheap to decode vlongs of size 1.

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