If it's sparsely populated you'll get the same benefit from the schema definition. You don't pay for fields you don't use.
> On Nov 24, 2015, at 12:17 PM, Jack Krupansky <jack.krupan...@gmail.com> wrote: > > Are all or ost of the 1000+ columns populated for a given row? If they are > sparse you can replace them with a single map collection column which would > only occupy the entries that are populated. > > -- Jack Krupansky > > On Tue, Nov 24, 2015 at 11:04 AM, Jack Krupansky <jack.krupan...@gmail.com > <mailto:jack.krupan...@gmail.com>> wrote: > As always, your queries should drive your data model. Unless you really need > 1000+ columns for most queries, you should consider separate tables for the > subsets of the columns that need to be returned for a given query. > > The new 3.0 Materialized View feature can be used to easily create subsets of > a base table, although that begs the question of whether you ever really need > all 1000+ columns in the same table. > > -- Jack Krupansky > > On Tue, Nov 24, 2015 at 10:45 AM, Kai Wang <dep...@gmail.com > <mailto:dep...@gmail.com>> wrote: > Hi all, > > If I have the following table: > CREATE TABLE t ( > pk int, > ck int, > c1 int, > c2 int, > ... > PRIMARY KEY (pk, ck) > ) > > There are lots of non-clustering columns (1000+). From time to time I need to > do a query like this: > > SELECT c1 FROM t WHERE pk = abc AND ck > xyz; > > How efficient is this query compared to SELECT * ...? Apparently SELECT c1 > would save a lot of network bandwidth since only c1 needs to be transferred > on the wire. But I am more interested in the impact on disk IO. If I > understand C* storage engine correctly, one CQL row is clustered together on > disk. That means c1 from different rows are stored apart. In the case of > SELECT c1, does C* do multiple seeks to only lift c1 of each row from disk or > lift the whole row into memory and return c1 from there? > > From comments on https://issues.apache.org/jira/browse/CASSANDRA-5762 > <https://issues.apache.org/jira/browse/CASSANDRA-5762> it seems C* lifts the > whole row as of 1.2.7. Is this still the case on 2.1.*? > > Thanks. > >
