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From Hari Sreekumar <hsreeku...@clickable.com>
Subject Clarification regarding HBase reads
Date Sun, 20 Feb 2011 14:38:58 GMT

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 ?


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