How to install cstore_fdw inside RDS postgres 9.6 cstore_fdw  is foreign data wrapper for columnar storage for postgresql. I want to install it inside RDS postgre 9.6 instance. Is it possible to install inside RDS instance? Thanks
No. It's not supported on RDS at this point. See https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_PostgreSQL.html#PostgreSQL.Concepts.General.FeatureSupport.Extensions.

If you really need cstore_fdw, you'll have to manage your own PG instance.