this is not an error. it is the default behavior of the c# driver. the driver only establishes the connection to the database server when the very first operation is initiated and will take a few hundred milliseconds to establish connection.
subsequent operations do not need to establish new connections because of the driver's connection pooling mechanisms. more connections will only be established only if they are really needed. if the app is not multi-threaded, the driver will usually open about 2 connections for the entirety of the app from what i have seen. if you inspect your mongodb log file, it will be apparent.
my suggestion is to just ignore the time it takes to initialize the connection if you're doing any kind of testing/ benchmarks.
UPDATE:
if your database is hosted across a network, something like a firewall may be interfering with idle connections. if that's the case you could try doing the following so that idle connections get recycled/renewed every minute.
MongoDefaults.MaxConnectionIdleTime = TimeSpan.FromMinutes(1)
if all else fails to work, the only remaining option i can think of is to fire off a keep-alive task like the following:
public void InitKeepAlive()
{
Task.Run(async () =>
{
while (true)
{
await client.GetCollection<Document>("Documents")
.AsQueryable()
.Select(d => d.Id)
.FirstOrDefaultAsync();
await Task.Delay(TimeSpan.FromMinutes(1));
}
});
}
