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From "Aaron T. Myers (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3023) Optimize entries in edits log for persistBlocks calls
Date Thu, 01 Mar 2012 18:23:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13220209#comment-13220209

Aaron T. Myers commented on HDFS-3023:

+1 for the delta.
> Optimize entries in edits log for persistBlocks calls
> -----------------------------------------------------
>                 Key: HDFS-3023
>                 URL: https://issues.apache.org/jira/browse/HDFS-3023
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node, performance
>    Affects Versions: HA branch (HDFS-1623), 0.23.2
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: HA branch (HDFS-1623)
>         Attachments: hdfs-3023-HDFS-1623.txt, hdfs-3023.txt
> One of the performance issues noticed in the HA branch is due to the much larger edit
logs, now that we are writing OP_ADD transactions to the edit log on every block allocation.
We can condense these calls down in two ways:
> 1) use variable-length integers for the block list length, size, and genstamp (most of
these end up fitting in far less than 8 bytes)
> 2) use delta-coding for the genstamp and block size for any blocks after the first block
(most blocks will be the same size and only slightly higher genstamps)
> 3) introduce a new OP_UPDATE_BLOCKS transaction that doesn't re-serialize metadata information
like lease owner, permissions, etc
> 4) allow OP_UPDATE_BLOCKS to only re-serialize the blocks that have changed for a given

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