Bounds
db_pool_size for checkout may be set from 5 to 40. The database allows 100 connections in total across all services; staying at or under 40 keeps room for the others.
When it helps
When the pool is saturated by real load (more concurrent requests than connections) and the database itself is healthy. It does not fix a leak, it only moves the ceiling.
How
Set the config value through the platform's config action. The change applies to the running process without a restart. Watch db_pool_in_use and database query latency for ten minutes; if query latency rises, the database is the bottleneck and the pool should go back down.