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From Jean-Daniel Cryans <jdcry...@apache.org>
Subject Re: Number of column families vs Number of column family qualifiers
Date Thu, 14 Oct 2010 17:55:17 GMT
> So, even if I use get.addColumn(byte[] family, byte[] qualifier) for a
> certain cell, the HBase will have to traverse from the beginning of
> the column family to the qualifier I defined? Is it because HBase has
> to traverse all the blocks in the HFile to find the row key or the
> qualifier?

The answer is different for 0.20 and 0.90, but the short version would
be: sometimes yes and sometimes not all of the KVs will be read. HBase
is getting better at this but there's still work to do.

> I am confused here, in the keyvalue pairs in the data block, does the
> key refer to the row key or it refer to qualifier? Where is the row
> key and where is the qualifier?
> This has bothered me for a while. It would be nice to figure it out.
> Many thanks.
>

Down in the HBase internals we use KeyValue where the key is basically
row + family + qualifier + timestamp. See
http://hbase.apache.org/docs/r0.89.20100924/apidocs/org/apache/hadoop/hbase/KeyValue.html

J-D

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