[jira] [Resolved] (HBASE-8151) Decode memstoreTS in HFileReaderV2 only when necessary

["Lars Hofhansl (JIRA)" <ji...@apache.org>]

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

Lars Hofhansl resolved HBASE-8151.
----------------------------------

      Resolution: Fixed
    Hadoop Flags: Reviewed

Committed the first patch (handling #1) to 0.94, 0.95, and 0.96.
                
> Decode memstoreTS in HFileReaderV2 only when necessary
> ------------------------------------------------------
>
>                 Key: HBASE-8151
>                 URL: https://issues.apache.org/jira/browse/HBASE-8151
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>             Fix For: 0.95.0, 0.98.0, 0.94.7
>
>         Attachments: 8151-0.94.txt, 8151-0.94-v2.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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