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Date: Wed, 12 Dec 2012 13:17:47 -0500
Message-ID: 
 <CADczPYRunj-Gkto9eZVjvb+mD=PpFTVhA3jNjFFkZcQzEurdFA@mail.gmail.com>
Subject: Re: Table splitting
From: John Vines <vines@apache.org>
To: user@accumulo.apache.org
Content-Type: multipart/alternative; boundary=e89a8f3ba0dbc07d9804d0abd083

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When a file gets written to hdfs, there is a guarantee the file is local as
long as that systems disks are not full. Accumulo does not have a locality
guarantee as tablets will migrate on occasion. However, as data is added,
major compactions will occur which will restore locality.
On Dec 12, 2012 1:09 PM, "ameet kini" <ameetkini@gmail.com> wrote:

>
> Along these lines....
>
> Can someone help me understand how tablets map to files on disk in HDFS?
> From what I understand, after a compaction, there may be one (or more?)
> files on HDFS for a given tablet. Each file can consist of multiple HDFS
> blocks. Does Accumulo guarantee that the tablet serving a given data range
> finds all its blocks locally? If so, how does it keep this guarantee?
> Wouldn't HDFS distribute these blocks around based on HDFS balancing
> strategy?
>
> Thanks,
> Ameet
>
> On Tue, Dec 11, 2012 at 9:37 AM, William Slacum <
> wilhelm.von.cloud@accumulo.net> wrote:
>
>> Tablets will split automatically, down to the granularity of a row.
>>
>>
>> On Tue, Dec 11, 2012 at 9:32 AM, Mathias Herberts <
>> mathias.herberts@gmail.com> wrote:
>>
>>> Hi,
>>>
>>> I've read the user manual for v1.4.2 and I have not seen any mention of
>>> automatic tablet splitting. Is there such a thing in Accumulo or is
>>> pre-splitting the only way to split a table?
>>>
>>> Thanks,
>>>
>>> Mathias.
>>>
>>
>>
>

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<p dir=3D"ltr">When a file gets written to hdfs, there is a guarantee the f=
ile is local as long as that systems disks are not full. Accumulo does not =
have a locality guarantee as tablets will migrate on occasion. However, as =
data is added, major compactions will occur which will restore locality.</p=
>

<div class=3D"gmail_quote">On Dec 12, 2012 1:09 PM, &quot;ameet kini&quot; =
&lt;<a href=3D"mailto:ameetkini@gmail.com">ameetkini@gmail.com</a>&gt; wrot=
e:<br type=3D"attribution"><blockquote class=3D"gmail_quote" style=3D"margi=
n:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><br></div>Along these lines....<div><br></div><div>Can someone help me=
 understand how tablets map to files on disk in HDFS? From what I understan=
d, after a compaction, there may be one (or more?) files on HDFS for a give=
n tablet. Each file can consist of multiple HDFS blocks. Does Accumulo guar=
antee that the tablet serving a given data range finds all its blocks local=
ly? If so, how does it keep this guarantee? Wouldn&#39;t HDFS distribute th=
ese blocks around based on HDFS balancing strategy?</div>


<div><br></div><div>Thanks,</div><div>Ameet=A0<br><div><div><br><div class=
=3D"gmail_quote">On Tue, Dec 11, 2012 at 9:37 AM, William Slacum <span dir=
=3D"ltr">&lt;<a href=3D"mailto:wilhelm.von.cloud@accumulo.net" target=3D"_b=
lank">wilhelm.von.cloud@accumulo.net</a>&gt;</span> wrote:<br>



<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">Tablets will split automatically, down to th=
e granularity of a row.<div><div><br><br><div class=3D"gmail_quote">
On Tue, Dec 11, 2012 at 9:32 AM, Mathias Herberts <span dir=3D"ltr">&lt;<a =
href=3D"mailto:mathias.herberts@gmail.com" target=3D"_blank">mathias.herber=
ts@gmail.com</a>&gt;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">Hi,<div><br></div><div>I&#39;ve read the use=
r manual for v1.4.2 and I have not seen any mention of automatic tablet spl=
itting. Is there such a thing in Accumulo or is pre-splitting the only way =
to split a table?</div>




<div>
<br></div><div>Thanks,</div><div><br></div><div>Mathias.</div>
</blockquote></div><br>
</div></div></blockquote></div><br>
</div></div></div>
</blockquote></div>

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