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From lars hofhansl <la...@apache.org>
Subject Re: one column family but lots of tables
Date Fri, 23 Aug 2013 05:35:03 GMT
You can think of it this way: Every region and column family is a "store" in HBase. Each store
has a memstore and its own set of HFiles in HDFS.
The more stores you have, the more there is to manage.

So you want to limit the number of stores. Also note that the word "Table" is somewhat a misnomer
in HBase it should have better been called "Keyspace".
The extra caution for the number of column families per table stems from the fact that HBase
flushes by region (which means all stores of that region are flushed). This in turn means
that unless are column families hold roughly the same amount of data you end up with very
lopsided distributions of HFile sizes.

-- Lars

 From: Koert Kuipers <koert@tresata.com>
To: user@hbase.apache.org; vrodionov@carrieriq.com 
Sent: Thursday, August 22, 2013 12:30 PM
Subject: Re: one column family but lots of tables

if that is the case, how come people keep warning about limiting the number
of column families to only a handful (with more hbase performance will
degrade supposedly), yet there seems to be no similar warnings for number
of tables? see for example here:

if a table means at least one column family then the number of tables
should also be kept to a minumum, no?

On Thu, Aug 22, 2013 at 1:58 PM, Vladimir Rodionov

> Nope. Column family is per table (its sub-directory inside your table
> directory in HDFS).
> If you have N tables you will always have , at least, N distinct CFs (even
> if they have the same name).
> Best regards,
> Vladimir Rodionov
> Principal Platform Engineer
> Carrier IQ, www.carrieriq.com
> e-mail: vrodionov@carrieriq.com
> ________________________________________
> From: Koert Kuipers [koert@tresata.com]
> Sent: Thursday, August 22, 2013 8:06 AM
> To: user@hbase.apache.org
> Subject: one column family but lots of tables
> i read in multiple places that i should try to limit the number of column
> families in hbase.
> do i understand it correctly that when i create lots of tables, but they
> all use the same column family (by name), that i am just using one column
> family and i am OK with respect to limiting number of column families ?
> thanks! koert
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