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Answers to frequently asked questions.

What happens when I hit my connection limit?

The connection (or client) limit is set by the default_max_clients on the tenant record or max_clients on the user.

Say your connection limit is 1000. When you try to connect client number 1001 this client will receive the error Max client connections reached which will be returned as a Postgres error to your client in the wire protocol and subsequently should show up in your exception monitoring software.

Does Supavisor support prepared statements?

As of 1.0 Supavisor supports prepared statements. Supavisor will detect prepare statements and issue those to all database connections. All clients will then be able to address those prepared statements by name when issuing execute statements.

Why do you route connections to a single Supavisor node when deployed as a cluster?

Supavisor can run as a cluster of nodes for high availability. The first node to receive a connection from a tenant spins up the connection pool on that node. Connections coming in to other nodes will route data do the owner node of the tenant pool.

We could run one pool per node and divide the database connection pool by N nodes but then we'd have to keep connection counts to the database in sync across all nodes. While not impossible at all, there could be some delay here temporarily causing more connections to the database than we want.

By running one pool on one node in a cluster for a tenant we can guarantee that the amount of connections to the database will be the default_pool_size set on the tenant.

Also running N pools on N nodes for N clients will not scale horizontally as well because all nodes will be doing all the same work of issuing database connections to clients. While not a lot of overhead, at some point this won't scale and we'd have to run multiple independant clusters and route tenants to clusters to scale horizontally.