What does "[Pre-Login] initialisation=xyz" mean in an SQL Exception?

Question

What does the [Pre-Login] initialisation=A; handshake=B; [Login] initialization=C; authentication=D; [Post-Login] complete=E; portion mean in an SQL Timeout Exception?

For example, in the following SQL Timeout exception message, are they seconds, milliseconds, units or apples?

System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. This failure occurred while attempting to connect to the routing destination. The duration spent while attempting to connect to the original server was - [Pre-Login] initialization=28; handshake=24; [Login] initialization=0; authentication=0; [Post-Login] complete=1; ---> System.ComponentModel.Win32Exception: The wait operation timed out

Context

I'm trying to understand the root cause of an SQL Timeout on SQL Azure

Thanks.

Longer StackTrace

---> NHibernate.Exceptions.GenericADOException: could not execute batch command.[SQL: SQL not available] ---> System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. This failure occurred while attempting to connect to the routing destination. The duration spent while attempting to connect to the original server was - [Pre-Login] initialization=28; handshake=24; [Login] initialization=0; authentication=0; [Post-Login] complete=1; ---> System.ComponentModel.Win32Exception: The wait operation timed out --- End of inner exception stack trace --- at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction) at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) at System.Data.SqlClient.TdsParserStateObject.ReadSniError(TdsParserStateObject stateObj, UInt32 error) at System.Data.SqlClient.TdsParserStateObject.ReadSniSyncOverAsync() at System.Data.SqlClient.TdsParserStateObject.TryReadNetworkPacket() at System.Data.SqlClient.TdsParserStateObject.TryPrepareBuffer() at System.Data.SqlClient.TdsParserStateObject.TryReadByte(Byte& value) at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady) at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite, SqlDataReader ds, Boolean describeParameterEncryptionRequest) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite) at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite) at System.Data.SqlClient.SqlCommand.ExecuteNonQuery() at System.Data.SqlClient.SqlCommand.ExecuteNonQuery() at System.Data.SqlClient.SqlCommandSet.ExecuteNonQuery() at NHibernate.SqlAzure.ReliableSqlClientBatchingBatcher.ExecuteBatch(IDbCommand ps) --- End of inner exception stack trace --- at NHibernate.SqlAzure.ReliableSqlClientBatchingBatcher.ExecuteBatch(IDbCommand ps) at Microsoft.Practices.EnterpriseLibrary.TransientFaultHandling.RetryPolicy.<>c__DisplayClass1.<ExecuteAction>b__0() at Microsoft.Practices.EnterpriseLibrary.TransientFaultHandling.RetryPolicy.ExecuteAction[TResult](Func`1 func) at NHibernate.AdoNet.AbstractBatcher.ExecuteBatchWithTiming(IDbCommand ps) at NHibernate.AdoNet.AbstractBatcher.ExecuteBatch() at NHibernate.Engine.ActionQueue.ExecuteActions() at NHibernate.Event.Default.AbstractFlushingEventListener.PerformExecutions(IEventSource session) at NHibernate.Event.Default.DefaultFlushEventListener.OnFlush(FlushEvent event) at NHibernate.Impl.SessionImpl.Flush() at ____.Shared.NHibernate.NHibernateRepoSession.Dispose() in c:\\_____\\NHibernateRepoSession.cs:line 48 at ____.Store(String sourceId, String userId, ImageData imageData) in c:\\_____.cs:line 44 ...

Answer 1

I hunted down this issue and got a response from SQL support: A, B, C, D, and E represent the steps of a connection attempt:

[Pre-Login] initialization=A; handshake=B; [Login] initialization=C; authentication=D; [Post-Login] complete=E;

A. The connecting client and the server introduce themselves. The client and server let the other know how it intends to communicate.

B. A Secured Socket Layer connection is established.

C. The connecting client introduces itself to the Master database / database.

D. The Master database / database are referenced to complete authentication.

E. A connection has been successfully established.