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From Ted Yu <yuzhih...@gmail.com>
Subject Re: Clarification regarding HBase reads
Date Sun, 20 Feb 2011 15:17:56 GMT
>> Does this mean that a store instance is opened for all tables present in
>> HBase irrespective of which table we are querying and for all
>> columnfamilies?
No. The blog says Store instance is for each family.

You should generally avoid multiple column families. But we can help you
analyze your use case.
If you read through https://issues.apache.org/jira/browse/HBASE-3149, you
would better understand current implementation.

On Sun, Feb 20, 2011 at 6:38 AM, Hari Sreekumar <hsreekumar@clickable.com>wrote:

> Hi,
>
> I was going through the HBase architecture blog by Lars George (
> http://www.larsgeorge.com/2009/10/hbase-architecture-101-storage.html) and
> I just wanted a clarification regarding how HBase reads data. The blog
> mentions that :
>
> Next the HRegionServer opens the region it creates a corresponding
> HRegion object.
> When the HRegion is "opened" it sets up a Store instance for each
> HColumnFamily for every table as defined by the user beforehand. Each of
> the Store instances can in turn have one or more StoreFile instances, which
> are lightweight wrappers around the actual storage file called HFile. A
> HRegion also has a MemStore and a HLog instance. We will now have a look at
> how they work together but also where there are exceptions to the rule.
>
> Does this mean that a store instance is opened for all tables present in
> HBase irrespective of which table we are querying and for all
> columnfamilies? Is this why I generally see people avoiding large number of
> tables/large number of column families. If not, what is the reason for
> that?
> Is it true at all that we should avoid too many tables/CFs ?
>
> Thanks,
> Hari
>

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