how to design Hbase schema? - rdbms

Question

suppose that I have this RDBM table (Entity-attribute-value_model):
col1: entityID
col2: attributeName
col3: value
and I want to use HBase due to scaling issues.
I know that the only way to access Hbase table is using a primary key (cursor). you can get a cursor for a specific key, and iterate the rows one-by-one .
The issue is, that in my case, I want to be able to iterate on all 3 columns.
for example :
for a given an entityID I want to get all its attriutes and values
for a give attributeName and value I want to all the entitiIDS
...
so one idea I had is to build one Hbase table that will hold the data (table DATA, with entityID as primary index), and 2 "index" tables one with attributeName as a primary key, and the other one with value
each index table will hold a list of pointers (entityIDs) for the DATA table.
Is it a reasonable approach ? or is is an 'abuse' of Hbase concepts ?
In this blog the author say:
HBase allows get operations by primary
key and scans (think: cursor) over row
ranges. (If you have both scale and
need of secondary indexes, don’t worry
- Lucene to the rescue! But that’s another post.)
Do you know how Lucene can help ?
-- Yonatan

Answer 1

Secondary indexes would indeed be useful for many potential applications of HBase, and I believe the developers are in fact looking at it. Checkout http://www.mail-archive.com/hbase-dev#hadoop.apache.org/msg04801.html.
In the mean time though, if your application data storage can be modelled as a star schema (see http://en.wikipedia.org/wiki/Star_schema) you might like to checkout the solution that Hypertable proposes for secondary index-type needs http://markmail.org/message/rphm4q6cbar2ycgp

Answer 2

I recommend having two different flat tables: one for looking up attributes+values given entityID, and one for looking up the entityID given attributes+values.
Table 1 would look like this:
entityID1 {
attribute1: value1;
attribute2: value2;
...
}
and Table 2:
attribute1_value1 {
entityID1;
}
attribute2_value2 {
entityID1;
}