v0.21.0

• ADO.NET: Added MinPoolSize setting to keep a minimum number of sessions ready in the PoolingSessionSource.
• ADO.NET: Added SessionIdleTimeout to remove idle sessions from the PoolingSessionSource automatically.
• ADO.NET: Made PoolingSessionSource faster and more reliable by using a lock-free LIFO stack.
• ADO.NET: Added BeginBulkUpsertImport for batch upsert operations with transaction checks and integration tests.
• Optimization: On BadSession, do not invoke the DeleteSession() method.
• Canceling AttachStream after calling the DeleteSession method.
• Fixed bug: fixed issue where session was not deleted (ClientTransportTimeout).
• Fixed bug: Grpc.Core.StatusCode.Cancelled was mapped to server's Canceled status.
• ADO.NET: PoolingSessionSource 2.0 based on Npgsql pooling algorithm.
• Added new ADO.NET options:
  • MinSessionPool: The minimum connection pool size.
  • SessionIdleTimeout: The time (in seconds) to wait before closing idle session in the pool if the count of all sessions exceeds MinSessionPool.
  • SessionPruningInterval: How many seconds the pool waits before attempting to prune idle sessions (see SessionIdleTimeout).
• Fixed bug Reader: unhandled exception in TryReadRequestBytes(long bytes).
• Handle YdbException on DeleteSession.
• Do not invoke DeleteSession if the session is not active.
• YdbException: Added cancellation token propagation support in CommitAsync and RollbackAsync.
• Deleted legacy exceptions: Driver.TransportException, StatusUnsuccessfulException and InitializationFailureException.
• Fixed bug: Unhandled exception System.Net.Http.HttpIOException has now been converted to YdbException (grpc-dotnet issue).
• Added 'x-ydb-client-pid' header to any RPC calls.
• Added DisableServerBalancer option to ADO.NET session creation; default false.

Full Changelog: v0.20.1...v0.21.0