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From "Jonathan Gray" <jl...@streamy.com>
Subject RE: Many columns in 0.19
Date Mon, 09 Mar 2009 13:54:11 GMT
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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