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Date: Tue, 28 Feb 2012 17:33:48 +0000 (UTC)
From: "Todd Lipcon (Commented) (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-3023) Optimize entries in edits log for
 persistBlocks calls
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    [ https://issues.apache.org/jira/browse/HDFS-3023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13218384#comment-13218384 ] 

Todd Lipcon commented on HDFS-3023:
-----------------------------------

bq. though why does updating block info also now update mod time and access time

I just moved the following code:
{code}
-    // Update the salient file attributes.
-    file.setAccessTime(addCloseOp.atime);
-    file.setModificationTimeForce(addCloseOp.mtime);
{code}
since OP_ADD contains those pieces of info, but OP_UPDATE_BLOCKS doesn't.
                
> 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
>         Attachments: hdfs-3023-HDFS-1623.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 transaction

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