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From "HBase Review Board (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2468) Improvements to prewarm META cache on clients
Date Fri, 28 May 2010 17:58:46 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12873079#action_12873079
] 

HBase Review Board commented on HBASE-2468:
-------------------------------------------

Message from: "Benoit Sigoure" <tsunanet@gmail.com>

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This is an automatically generated e-mail. To reply, visit:
http://review.hbase.org/r/78/#review91
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src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment515>

    Remove the spurious spaces around the parenthesis.



src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment516>

    No space before `[]' on this line and the previous line.



src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment517>

    Move the declaration of this variable to line 675 where it's initialized.



src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment518>

    I'm not sure I understand this comment but it could be because I'm not very familiar with
this part of the code.



src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment519>

    Do this instead:
    
    if (value == null) {
      return true;  // don't cache it
    }
    final String serverAddress = Bytes.toString(value);



src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment520>

    I don't understand the last part of the comment ("fetch ahead number of rows in META").



src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment521>

    No space before `[]'.



src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment522>

    Wrap the `else' on the previous line.



src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment523>

    Instead of doing `+ e.getMessage()', pass `e' in second argument.



src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment524>

    No space before `[]'.



src/main/java/org/apache/hadoop/hbase/client/HConnectionManager.java
<http://review.hbase.org/r/78/#comment525>

    Remove the second part of the check (tableLogs.values() == null).  This can't happen.
 If it happens, there's a bug in SoftValueSortedMap and we shouldn't hide it.



src/test/java/org/apache/hadoop/hbase/client/TestFromClientSide.java
<http://review.hbase.org/r/78/#comment526>

    No space before `[]'.


- Benoit





> Improvements to prewarm META cache on clients
> ---------------------------------------------
>
>                 Key: HBASE-2468
>                 URL: https://issues.apache.org/jira/browse/HBASE-2468
>             Project: HBase
>          Issue Type: Improvement
>          Components: client
>            Reporter: Todd Lipcon
>            Assignee: Mingjie Lai
>             Fix For: 0.21.0
>
>         Attachments: HBASE-2468-trunk.patch
>
>
> A couple different use cases cause storms of reads to META during startup. For example,
a large MR job will cause each map task to hit meta since it starts with an empty cache.
> A couple possible improvements have been proposed:
>  - MR jobs could ship a copy of META for the table in the DistributedCache
>  - Clients could prewarm cache by doing a large scan of all the meta for the table instead
of random reads for each miss
>  - Each miss could fetch ahead some number of rows in META

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