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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5930) Periodically flush the Memstore?
Date Thu, 24 Jan 2013 16:37:14 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5930?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13561739#comment-13561739
] 

Lars Hofhansl commented on HBASE-5930:
--------------------------------------

How can deferred log flush ever be as fast as not writing the WAL at all?
Considering only the latency of a single request that might be true in many cases, but it
will definitely not be true on a busy cluster since all data is written to the disks twice.
                
> Periodically flush the Memstore?
> --------------------------------
>
>                 Key: HBASE-5930
>                 URL: https://issues.apache.org/jira/browse/HBASE-5930
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Lars Hofhansl
>            Assignee: Devaraj Das
>            Priority: Minor
>             Fix For: 0.96.0
>
>         Attachments: 5930-1.patch, 5930-wip.patch
>
>
> A colleague of mine ran into an interesting issue.
> He inserted some data with the WAL disabled, which happened to fit in the aggregate Memstores
memory.
> Two weeks later he a had problem with the HDFS cluster, which caused the region servers
to abort. He found that his data was lost. Looking at the log we found that the Memstores
were not flushed at all during these two weeks.
> Should we have an option to flush memstores periodically. There are obvious downsides
to this, like many small storefiles, etc.

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