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From Eric Newton <eric.new...@gmail.com>
Subject Re: Meaning of < in METADATA table [SEC=UNOFFICIAL]
Date Wed, 25 Jun 2014 02:47:44 GMT
"<" 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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