This may have occurred because all pooled connections were in use and max pool size was reached.

ERROR Message:

```
System.InvalidOperationException: Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.
at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection)
at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
at System.Data.SqlClient.SqlConnection.Open()
at Hangfire.SqlServer.SqlServerStorage.CreateAndOpenConnection()
at Hangfire.SqlServer.SqlServerStorage.UseConnection[T](DbConnection dedicatedConnection, Func`2 func)
at Hangfire.SqlServer.SqlServerStorage.UseConnection(DbConnection dedicatedConnection, Action`1 action)
at Hangfire.SqlServer.SqlServerConnection.Heartbeat(String serverId)
at Hangfire.Server.ServerHeartbeatProcess.Execute(BackgroundProcessContext context)
```

I have modified the Hangfire source code. The database password will be changed from time to time, so the project needs to dynamically obtain the database password. change code as below:

``` csharp
internal DbConnection CreateAndOpenConnection()
{
using (_options.ImpersonationFunc?.Invoke())
{
DbConnection connection = null;

try
{
connection = new SqlConnection(ConnectionString); //_existingConnection ?? _connectionFactory();

if (connection.State == ConnectionState.Closed)
{
connection.Open();
}

return connection;
}
catch
{
ReleaseConnection(connection);
throw;
}
}
}
```
When adding doWork to a project, this is done every 2 minutes. A connection pooling error occurs after 5 hours. Do not know where is not releasing the connection, please help me

Start with Hangfire.SqlServer.SqlServerStorage.CreateAndOpenConnection and its UseConnection callers, then trace the Heartbeat path through SqlServerConnection. Reproduce the connection-pool timeout with the reported two-minute workload and inspect whether connections remain in use; done means identifying the leak or lifecycle failure and confirming the pool remains healthy over the same interval.

Written by the indexing model from the issue text.