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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-12934) Utilize Flash storage for flushing
Date Wed, 28 Jan 2015 02:08:36 GMT

    [ https://issues.apache.org/jira/browse/HBASE-12934?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14294592#comment-14294592
] 

Lars Hofhansl commented on HBASE-12934:
---------------------------------------

SSD wear is well documented. I am not sure it is an issue specifically, just a concern to
rule out. Would definitely use SSDs only for data that mostly read, especially with LSM trees.

The title of this jira is about utilizing flash for flushing. It only does flushes, and when
enabled does all flushes to SSDs. That just makes no sense to me. Why would I want to place
all HFiles resulting from flushes on SSDs across the board? I can't think of a single use
case where this is useful. It's the wrong way to slice this problem.
Flushes are asynchronous, they only become a problem when we reach the number of the blocking
store files, which is a problem of *compactions* not being able to keep, not flushes.

Now...
If you slice it the other way and say "all files written on behalf of this column family are
written to SSD", then we have a story. And that would *not* be about improving writes but
about *reads*. In that case you write all flushes and compaction of a specific column families
to SSDs.
This jira is not doing that, nor does it provide a path to get there.


> Utilize Flash storage for flushing
> ----------------------------------
>
>                 Key: HBASE-12934
>                 URL: https://issues.apache.org/jira/browse/HBASE-12934
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Ted Yu
>            Assignee: Ted Yu
>         Attachments: 12934-001.txt
>
>
> Store flushing should be able to make use of hdfs storage policy.
> One option is to allow setting storage policy for the directory path of the specified
column family.



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