If each indexed value has very few matching rows, then querying using SASI (or any impl of secondary index) may scan the whole cluster.
This is because the index are "distributed" e.g. the indexed values stay on the same nodes as the base data. And even SASI with its own data-structure will not help much here. One should understand that the 2nd index query has to deal with 2 layers: 1) The cluster layer, which is common for any impl of 2nd index. Read my blog post here: http://www.planetcassandra.org/blog/cassandra-native-secondary-index-deep-dive/ 2) The local read path, which depends on the impl of 2nd index. Some are using Lucene library like Stratio impl, some rolls in its own data structures like SASI If you have a 1-to-1 relationship between the index value and the matching row (or 1-to-a few), I would recommend using materialized views instead: http://www.slideshare.net/doanduyhai/sasi-cassandra-on-the-full-text-search-ride-voxxed-daybelgrade-2016/25 Materialized views guarantee that for each search indexed value, you only hit a single node (or N replicas depending on the used consistency level) However, materialized views have their own drawbacks (weeker consistency guarantee) and you can't use range queries (<, >, ≤, ≥) or full text search on the indexed value On Sat, Oct 15, 2016 at 11:55 AM, Kant Kodali <k...@peernova.com> wrote: > Well I went with the definition from wikipedia and that definition rules > out #1 so it is #2 and it is just one matching row in my case. > > > > On Sat, Oct 15, 2016 at 2:40 AM, DuyHai Doan <doanduy...@gmail.com> wrote: > > > Define precisely what you mean by "high cardinality columns". Do you > mean: > > > > 1) a single indexed value is present in a lot of rows > > 2) a single indexed value has only a few (if not just one) matching row > > > > > > On Sat, Oct 15, 2016 at 8:37 AM, Kant Kodali <k...@peernova.com> wrote: > > > >> I understand Secondary Indexes in general are inefficient on high > >> cardinality columns but since SASI is built from scratch I wonder if the > >> same argument applies there? If not, Why? Because I believe primary > keys in > >> Cassandra are indeed indexed and since Primary key is supposed to be the > >> column with highest cardinality why not do the same for secondary > indexes? > >> > > > > >
