Because the data for an index is not all together(ie. Need a multi get to get the data). It is not contiguous.
The prefix in a partition they keep the data so all data for a prefix from what I understand is contiguous. QUESTION: What I don't get in the comment is I assume you are referring to CQL in which case we would need to specify the partition (in addition to the index)which means all that data is on one node, correct? Or did I miss something there. Thanks, Dean From: Ben Hood <0x6e6...@gmail.com<mailto:0x6e6...@gmail.com>> Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>> Date: Tuesday, October 2, 2012 11:18 AM To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>> Subject: Re: 1000's of column families Jeremy, On Tuesday, October 2, 2012 at 17:06, Jeremy Hanna wrote: Another option that may or may not work for you is the support in Cassandra 1.1+ to use a secondary index as an input to your mapreduce job. What you might do is add a field to the column family that represents which virtual column family that it is part of. Then when doing mapreduce jobs, you could use that field as the secondary index limiter. Secondary index mapreduce is not as efficient since you first get all of the keys and then do multigets to get the data that you need for the mapreduce job. However, it's another option for not scanning the whole column family. Interesting. This is probably a stupid question but why shouldn't you be able to use the secondary index to go straight to the slices that belong to the attribute you are searching by? Is this something to do with the way Cassandra is exposed as an InputFormat for Hadoop or is this a general property for searching by secondary index? Ben
