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From "Eric Newton (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-578) consider using hdfs for the walog
Date Tue, 22 May 2012 13:31:40 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13280939#comment-13280939
] 

Eric Newton commented on ACCUMULO-578:
--------------------------------------

I did a quick measurement of the number of NN operations done over a short ingest period,
to evaluate if logging to HDFS would significantly increase pressure on the NN.

I pre-split the ingest table into 8 tablets and used goraci to ingest 80 million entries (240M
k-v).  I grabbed the jmx counters on the NN before the start of the map-reduce job, and then
10 minutes later.  That was enough time for the idle flush and the GC to run a couple of times.

As expected, the change was negligible.

I don't have a good sense of what the different costs of the different Ops might be... but
nothing stands out as horribly different.



                
> consider using hdfs for the walog
> ---------------------------------
>
>                 Key: ACCUMULO-578
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-578
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: logger, tserver
>    Affects Versions: 1.5.0-SNAPSHOT
>            Reporter: Eric Newton
>            Assignee: Eric Newton
>         Attachments: HDFS_WAL_states.pdf, NNOpsComparison.pdf, comparison.png
>
>
> Using HDFS for walogs would fix:
>  * ACCUMULO-84: any node can read the replicated files
>  * ACCUMULO-558: wouldn't need to monitor loggers
>  * ACCUMULO-544: log references wouldn't include hostnames
>  * ACCUMULO-423: wouldn't need to monitor loggers
>  * ACCUMULO-258: hdfs has load balancing already
> To implement it, we would need the ability to distribute log sorts.
> Continuing to use loggers helps us avoid:
>  * hdfs pipeline strategy
>  * we don't have fine-grained insight when a single node makes dfs slow
>  * additional namenode pressure
>  * flexibility: for example, we can add fadvise() calls to the logger before HDFS supports
it

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