* use only required session variables in multiplexed queries for subscriptions
This will reduce the load on Postgres when the result of a subscription
is not dependent on the session variables of the request
* add DerivingVia to the project wide extension list
* expose a more specific function to filter session variables
* improve documentation of session variables of a cohort
Co-Authored-By: Alexis King <lexi.lambda@gmail.com>
* fix bad rebase
* add test for checking only required session variables are used to make query
Co-authored-by: Alexis King <lexi.lambda@gmail.com>
Co-authored-by: Karthikeyan Chinnakonda <karthikeyan@hasura.io>
This fixes an issue where queries could incorrectly be considered
reusable if a variable was used in two positions: one where it affected
SQL generation and one where it did not.
