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From "Josh Elser" <josh.el...@gmail.com>
Subject Re: Review Request 19862: Design document for review on cross-cluster replication
Date Wed, 02 Apr 2014 15:15:25 GMT

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docs/src/main/resources/design/ACCUMULO-378-design.mdtext
<https://reviews.apache.org/r/19862/#comment71626>

    Thinking about this from a total ordering standpoint. Say we're replicating to two slaves,
and we have three rfiles to replicate (1, 2 and 3) to those two slaves.
    
    We replicate rfile1 to both, but then the link to slave2 goes down. We can still replicate
rfile2 and then rfile3 to slave1, while we try to send rfile2 to slave2.
    
    What, if instead of the link being down, we happen to communicate to an angry server inside
of slave2 which never completes the transfer. We don't want to transfer rfile3 to attempt
to better preserve global ordering.
    
    This can be restated as "we only want to replicate one 'file' to a slave at a time" so
that we preserve the original semantics of the replication "queue" (table). The problem is
that this could drastically slow down replication when the link between master and slave cannot
be saturated by one replication task at a time.
    
    This isn't anything that we can reliably guarantee now (without conditional mutations),
right? Is it worth trying to tackle? The one clear change I want to make is that we do want
to put the identifier for the slave in with the replication record rather than defer determination
of where a record should be replicated.


- Josh Elser


On April 1, 2014, 1:58 a.m., Josh Elser wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/19862/
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> 
> (Updated April 1, 2014, 1:58 a.m.)
> 
> 
> Review request for accumulo.
> 
> 
> Bugs: ACCUMULO-378
>     https://issues.apache.org/jira/browse/ACCUMULO-378
> 
> 
> Repository: accumulo
> 
> 
> Description
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> 
> Re-posting a version of the design doc that I own. Contains grammatical fixes from round
one, with a few extra clarifications. New content should be posted here, but I'll maintain
the old review as discussion progresses.
> 
> 
> Diffs
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> 
>   docs/src/main/resources/design/ACCUMULO-378-design.mdtext PRE-CREATION 
> 
> Diff: https://reviews.apache.org/r/19862/diff/
> 
> 
> Testing
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> 
> 
> Thanks,
> 
> Josh Elser
> 
>


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