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From "Puri, Aseem" <Aseem.P...@Honeywell.com>
Subject RE: Many columns in 0.19
Date Tue, 10 Mar 2009 05:34:07 GMT
Hi

Thanks for help. 

So it means for a table if there are 10 column families then there are
10 HStore in a region and corresponding to it there are 10 map files.
Mapfile further have blocks inside it of 64K are stored by HDFS. 

Am I right?  

-Aseem Puri



-----Original Message-----
From: Jonathan Gray [mailto:jlist@streamy.com] 
Sent: Monday, March 09, 2009 7:24 PM
To: hbase-user@hadoop.apache.org
Subject: RE: Many columns in 0.19

A Table is made up of 1 to N HRegions and defined by its Column
Families.

Each HRegion is made up of an HStore per column family.  Each HStore is
then
made up of a single Memcache and 0 to M HStoreFiles.

So, the HStore is one column family in one region.  It houses that
families
Memcache and HStoreFiles for that particular region.

And yes, Bigtable stores one family of a region in one SSTable.  The
only
caveat to that is that they offer "Locality Groups", as mentioned by
Ryan,
that group different families together in a single SSTable (or HStore in
our
case).  Changes in 0.20 leave the door open for HBase to also implement
them
but it is not currently on the roadmap.

Hope that helps.

JG

> -----Original Message-----
> From: Puri, Aseem [mailto:Aseem.Puri@Honeywell.com]
> Sent: Monday, March 09, 2009 3:22 AM
> To: hbase-user@hadoop.apache.org
> Subject: RE: Many columns in 0.19
> 
> 
> Hi
> 
> I was reading Google BigTable article. Many thing oh hbase are similar
> to Bigatable. But I cant understand the concept of HStore. Is HStore
> means one column family in one map file?
> 
> Is BigTable also store one column family in one SStable?
> 
> -Aseem
> 
> -----Original Message-----
> From: Ryan Rawson [mailto:ryanobjc@gmail.com]
> Sent: Monday, March 09, 2009 3:20 PM
> To: hbase-user@hadoop.apache.org
> Subject: Re: Many columns in 0.19
> 
> Don't forget, each column family is another file on disk, and file
> open.
> Every column family is stored in it's own mapfile, and that increases
> the
> load on HDFS.
> 
> This particular restriction won't ever really go away (unless we
> introduce
> locality groups, even then, each locality group = N families = 1
file),
> but
> in 0.20 it should be more feasable to have thousands of columns per
> family,
> or more.
> 
> -ryan
> 
> On Mon, Mar 9, 2009 at 1:47 AM, Michael Dagaev
> <michael.dagaev@gmail.com>wrote:
> 
> > Thank you, Ryan
> >
> > On Mon, Mar 9, 2009 at 10:28 AM, Ryan Rawson <ryanobjc@gmail.com>
> wrote:
> > > Sadly this is still a limit.
> > >
> > > 0.20 should make things much better.
> > >
> > > -ryan
> > >
> > > On Mon, Mar 9, 2009 at 12:23 AM, Michael Dagaev <
> > michael.dagaev@gmail.com>wrote:
> > >
> > >> Hi , all
> > >>
> > >>    I remember it was not recommended to add many columns (column
> > >> qualifiers) in Hbase 0.18
> > >> Does Hbase 0.19.0 still have this limitation?
> > >>
> > >> Thank you for your cooperation,
> > >> M.
> > >>
> > >
> >


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