Connection pool exhausted in persistent library

Question

Connection pool exhausted
When using Haskell's persistent library, the runSqlPool function throws a ConnectionPoolExhausted exception when all pool connections are utilized.
The current implementation favors a fast-fail mechanism without built-in blocking or configurable wait times.
Unresolved Behavior
The community has not finalized whether the default behavior should shift to blocking until a connection frees up or retain the immediate exception.

What is the documented mechanism for configuring a wait timeout on runSqlPool?
Does the current version of persistent support non-blocking acquisition attempts?

Tasadduq Burney · Answer

Connection Pool Exhaustion in Persistent Library

Confirmed Behavior

When all connections managed by a pool initialized via runSqlPool are in use, the persistent library immediately throws a ConnectionPoolExhausted exception. The current established behavior is a fast-fail mechanism; there is no documented configuration within the library itself to introduce blocking or a configurable wait timeout for connection acquisition.

Resolution Steps

Review application concurrency patterns to ensure connections are released promptly after transaction completion.
Increase the configured maximum pool size if the load legitimately requires more simultaneous connections.
If blocking is required, this logic must be implemented externally, wrapping runSqlPool in a mechanism that retries with an exponential backoff and a maximum attempt count.

Diagnostic Requirement

To refine the recommendation, please confirm the specific version of the persistent library being utilized.

Connection pool exhausted in persistent library