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From "Sean Busbey (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-2932) Increased control over write durability
Date Fri, 20 Jun 2014 16:49:25 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-2932?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14039013#comment-14039013
] 

Sean Busbey commented on ACCUMULO-2932:
---------------------------------------

It would be preferable to prevent tablets that have different durability configurations from
using the same WAL. Presuming that the user configuring things tunes down durability on some
table because they need the performance gain.

Should we really *always* sync the WALs involved in accumulo.metadata? I can see defaulting
to it or even requiring that changing it be done at the table level (presuming we still ahve
some system-wide default used for tables). But what if the user has stable backup power and
isn't worried about other sources of sudden machine loss?

> Increased control over write durability
> ---------------------------------------
>
>                 Key: ACCUMULO-2932
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2932
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: tserver
>            Reporter: Josh Elser
>
> ACCUMULO-2842 introduced the ability to configure the HDFS method that is use to sync
WALs. This was mainly done as a means to investigate the performance characteristic of hflush
and hsync. As such, it was was trivially done system-wide.
> However, there is also practical application to allowing this configuration, in addition
to some internal concerns.
> # We should *always* sync WALs involved in {{accumulo.metadata}}
> # Data loss may be acceptable on some user tables and not on others (we may want to use
hflush for some tables, hsync for other). The option must have the granularity to specify
at least on the table (if not locality group).
> When multiple tablets are using a WAL with differing durability guarantees, we should
choose the higher durability.
> If we compare this to HBase, we could also implement it on the per Mutation level, however
that's beyond the scope here.



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