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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HBASE-2821) Keep young storefiles at lower replication
Date Wed, 07 Jul 2010 17:52:54 GMT

     [ https://issues.apache.org/jira/browse/HBASE-2821?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Todd Lipcon updated HBASE-2821:

    Attachment: lifetime-distribution.png

Here's a plot of the file lifetimes from an overnight data import. You can see that most of
the store files. Here's stats on the distribution:           
Min.   :    1  
1st Qu.:  569  
Median : 1353  
Mean   : 1801  
3rd Qu.: 2526  
Max.   :13342

So, 25% of store files last less than 10 minutes, and half of them last less than 22 minutes.

> Keep young storefiles at lower replication
> ------------------------------------------
>                 Key: HBASE-2821
>                 URL: https://issues.apache.org/jira/browse/HBASE-2821
>             Project: HBase
>          Issue Type: Improvement
>          Components: regionserver
>            Reporter: Todd Lipcon
>         Attachments: lifetime-distribution.png
> jgray and I were brainstorming some ideas about this:
> In a typical heavy-write scenario, many store files do not last very long. They're flushed
and then within a small number of seconds a compaction runs and they get deleted. For these
"short lifetime" store files, it's less likely that a failure will occur during the window
in which they're valid. So, I think we can consider some optimizations like the following:
> - Flush files at replication count 2. Scan once a minute for any store files in the region
that are older than 2 minutes. If they're found, increase their replication to 3. (alternatively,
queue them to avoid scanning)
> - More dangerous: flush files at replication count 1, but don't count them when figuring
log expiration. So, if they get lost, we force log splitting to recover.
> The performance gain here is that we avoid the network and disk transfer of writing the
third replica for a file that we're just about to delete anyway.

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