It's not a Postgres variant at all. Postgres is emulated as an interface to the columnar ParAccel database underneath. ParAccel does neat things (compiles your SQL into a program that it runs to answer the question, for instance) and really rips if you can order your data on good keys up front (and then use those keys in your query, of course).
Source: I helped build a very high speed network data analytical tool on top of ParAccel (before it was bought by Amazon and rolled into redshift).
Source: I helped build a very high speed network data analytical tool on top of ParAccel (before it was bought by Amazon and rolled into redshift).