如何确保我们的.NET Core API清理数据库连接？

Question

We are running .NET Core 1.1 APIs in Docker containers on Ubuntu 14.04. The API's interact with various SQL Server databases through EF Core, and what we are seeing is that databases connections are not being cleaned up, nor are they being reused. We are quickly seeing thousands of connections on the database through the sp_who2 query.

1. All connections are created with the same connection string, so connection pooling should be able to work.
2. The LastBatch time on the connections does not update, so they do not appear to be being reused, as you'd expect if they were pooled.
3. Objects calling the database are defined with Scoped lifecycle, so should be cleaned up after each session.
4. The Hibernating Rhinos EF Profiler appears to show DbContexts being cleaned up consistently within EF.
5. The connection count does not increase every time the database is hit, so it may be specific code - we are still trying to nail that down.
6. Our testing shows that this does not happen when running on Windows under IIS or IIS Express, so it appears to be specific to Docker or Ubuntu.

Could this be by design in .NET Core? Or are we missing a trick? How could we force EF to do some connection cleanup?

Answer 1

We are now pretty sure that this is caused by a bug in the corefx System.Data.SqlClient which was fixed in version 4.3.1. We were running 4.3.0 and have now updated to 4.3.1, and initial testing indicates that the problem is resolved.

You can read more about the issue in the dotnet/corefx Github repository Issue #13422 .

In summary, it appears to be a Linux-specific bug where the connections were not being disposed.

I will confirm/mark as the answer when we have proved this solves the problem to my satisfaction.