Research + Implement Citus Sharding/Tenancy

[toastercup]

After speaking with Citus, it appears their open source solution is relevant to Cortex's needs. It can ensure multitenant data integrity, simplify our code via use of their gem, and increase performance via sharding. It can be modified to support nested tenancy, and we can use Citus Reference Tables to share data across shards/tenants.

This Issue is a placeholder to contain research and implementation notes for Citus.

[toastercup]

This module from Citus's activerecord-multi-tenant gem is pretty neat; it lets you wrap an ActiveRecord transaction in a block that auto-magically scopes the data to a tenant. It could cut down on mistakes and boilerplate.

Not useful for ElasticSearch. But there it is.

[toastercup]

PS we could write something very similar for our ES queries (very easily)