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HBase, mail # user - one column family but lots of tables


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Re: one column family but lots of tables
Michael Segel 2013-08-23, 14:33
I think the issue which a lot of people miss is why do you want to use a column family in the first place.

Column families are part of the same table structure, and each family is kept separate.

So in your design, do you have tables which are related, but are not always used at the same time?

The example that I use when I teach about HBase or do a lecture/presentation is an Order Entry system.
Here you have an order being entered, then you have  one or many pick slips being generated, same for shipping then there's the invoicing.
All separate processes which relate back to the same order.

So here it makes sense to use column families.

Other areas could be metadata is surrounding a transaction. Again... few column families are tied together.

Does this make sense?
On Aug 23, 2013, at 12:35 AM, lars hofhansl <[EMAIL PROTECTED]> wrote:

> 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
>>
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The opinions expressed here are mine, while they may reflect a cognitive thought, that is purely accidental.
Use at your own risk.
Michael Segel
michael_segel (AT) hotmail.com