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 <[email protected]> To: [email protected]; [email protected] 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: http://comments.gmane.org/gmane.comp.java.hadoop.hbase.user/27616 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 <[email protected]>wrote: > 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: [email protected] > > ________________________________________ > From: Koert Kuipers [[email protected]] > Sent: Thursday, August 22, 2013 8:06 AM > To: [email protected] > 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 > > Confidentiality Notice: The information contained in this message, > including any attachments hereto, may be confidential and is intended to be > read only by the individual or entity to whom this message is addressed. If > the reader of this message is not the intended recipient or an agent or > designee of the intended recipient, please note that any review, use, > disclosure or distribution of this message or its attachments, in any form, > is strictly prohibited. If you have received this message in error, please > immediately notify the sender and/or [email protected] and > delete or destroy any copy of this message and its attachments. >
