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From Sean Busbey <bus...@cloudera.com>
Subject Re: Meaning of < in METADATA table [SEC=UNOFFICIAL]
Date Wed, 25 Jun 2014 02:53:50 GMT
Couldn't we add this kind of documentation to e.g. the MetadataSchema
class?

Or some developer focuses architecture docs?



On Jun 24, 2014 9:48 PM, "Eric Newton" <eric.newton@gmail.com> wrote:
>
> "<" means no end-row.  It's the last tablet, which is often called the
default tablet.
>
> So,
>
>> 3p< ~tab:~pr \x00
>
>
> You can decode this as a tablet covering (-inf, +inf) for tablet id 3p.
>
>> 3p;a ~tab:~pr \x00
>> 3p;m ~tab:~pr \x01a
>> 3p;z ~tab:~pr \x01m
>> 3p<  ~tab:~pr \x01z
>
>
> This table, id "3p" has splits: (-inf, a], (a, m], (m, z], (z, +inf).
 "pr" stands for "end-row of previous tablet", which we often shorten to
"prevrow". Tilde's sort late in UTF8, which is important for some race
conditions when a table is splitting.
>
> I'm putting together a new presentation on the decoding of the metadata
tables.  I need to get the presentation approved by my colleagues, so it's
going to be some time before it is ready.  I would like to write a shell
Formatter that would make the metadata more more human friendly.
>
> If you have any other questions about the metadata table, please ask.
 I'll make sure the answers are in the presentation.
>
> -Eric
>
>
>
>
> On Tue, Jun 24, 2014 at 10:21 PM, William Slacum <
wilhelm.von.cloud@accumulo.net> wrote:
>>
>> < is a byte used for doing an ordering on rows that share the same
prefix.
>>
>> There was a presentation floating around on the specifics of the
metadata table at one point. I believe that helps tablet information sort
before the last tablet, which is suffixed with '~', to force it to sort
after the other tablets. We'll probably get an Eric or Keith email soon
laying down the law, but that's what I remember.
>>
>>
>> On Tue, Jun 24, 2014 at 9:57 PM, Dickson, Matt MR <
matt.dickson@defence.gov.au> wrote:
>>>
>>> UNOFFICIAL
>>>
>>> When looking up rfile references in the metadata table we normally see
<tableid>;<range> for the rowid.   I've noticed some rowids are
<tableid><     eg.    3p<
>>>
>>> Is this because the table is small and hasn't been split or some other
reason?
>>
>>
>

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