Connection Pool Size Limits in Meteor: Unresolved Exhaustion Behavior

Goal

Diagnose intermittent "MongoError: connection pool exhausted" incidents in a Meteor application.

Constraints

Current Meteor releases default to 10 MongoDB connections per process, adjustable via MONGO_CONNECTION_POOL_SIZE. The pool exhaustion error propagates to clients without built‑in back‑pressure or retry logic.

Unresolved Question

While the environment variable can increase the pool, it is unclear whether there is an upper practical limit or whether Meteor provides graceful degradation when the pool is exceeded. The behavior under sustained high concurrency remains undocumented.

Specific Questions

1. What is the maximum pool size that Meteor reliably supports in version 1.12 and later?
2. Does setting MONGO_CONNECTION_POOL_SIZE above the default ever lead to unstable behavior or crashes?
3. Is there any built‑in mechanism for back‑pressure or retry when the connection pool is exhausted?