Why is the first SaveChanges slower than following calls? - ravendb

Question

I'm investigating some performance problems in an experimental scheduling application I'm working on. I found that calls to session.SaveChanges() were pretty slow, so I wrote a simple test.
Can you explain why the first iteration of the loop takes 200ms and subsequent loop 1-2 ms? How I can I leverage this in my application (I don't mind the first call to be this slow if all subsequent calls are quick)?
private void StoreDtos()
{
for (int i = 0; i < 3; i++)
{
StoreNewSchedule();
}
}
private void StoreNewSchedule()
{
var sw = Stopwatch.StartNew();
using (var session = DocumentStore.OpenSession())
{
session.Store(NewSchedule());
session.SaveChanges();
}
Console.WriteLine("Persisting schedule took {0} ms.",
sw.ElapsedMilliseconds);
}
Output is:
Persisting schedule took 189 ms. // first time
Persisting schedule took 2 ms. // second time
Persisting schedule took 1 ms. // ... etc
Above is for an in-memory database. Using a http connection to a Raven DB instance (on the same machine), I get similar results. The first call takes noticeably more time:
Persisting schedule took 1116 ms.
Persisting schedule took 37 ms.
Persisting schedule took 14 ms.
On Github: RavenDB 2.0 testcode and RavenDB 2.5 testcode.

Answer 1

The very first time that you call RavenDB, there are several things that have to happen.
We need to prepare the serializers for your entities, which takes time.
We need to create the TCP connection to the server.
On the next calls, we can reuse the connection that is already open and the created serializers.