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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 03:13:43 GMT
That's an excellent idea.  I would still like to distill the information
into a talk, but it would be nice if the information was also in the code.




On Tue, Jun 24, 2014 at 10:53 PM, Sean Busbey <busbey@cloudera.com> wrote:

> 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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