When I'm doing problem solving, its always good to have too much information rather than too little. With this in mind, I was quite interested in looking at SQL Server Extended Events (XEvent support) in SQL Server 2008.

You could always get diagnostic information in SQL Server through DBCC and SQL Trace/SQL Profiler. In SQL Server 2005 there are enhancements to SQL Profiler, dynamic management views (which enhanced and in some cases superceded DBCC information), DDL Triggers, and Event Notifications. There is also a WMI provide for events which uses event notifications internally. Event Notifications are sent to a SQL Server service broker queue and the events that are exposed are the same ones DDL triggers handle and most of the ones that SQL Profiler sees. In addition to all this info, there is an ETW (event tracing for Windows) provider for SQL Server. ETW support also appeared in System.Data.dll and the SNAC OLE DB provider/ODBC driver in SQL Server 2005/ADO.NET 2.0.

SQL Server 2008 adds support for XEvent (was codenamed Crimson), the new event system in Windows. The BOL provides info on this support, which works by creating and activating EVENT SESSIONs with DDL statements. Event sessions deal with items from event packages: events, targets, actions, types, predicates, and maps. You can mix and match the items from different packages in an EVENT SESSION.

So how do you get started? Create an event session (with CREATE SESSION DDL) and add items from the packages to your session (either in CREATE SESSION or in ALTER SESSION). You need at least one event and one target. You start/stop collecting by using ALTER EVENT SESSION…STATE=START/STOP.

- SQL Server 2008 ships with three packages: sqlserver, sqlos, and package0.
- There are lots of events. You can find them in sys.dm_xe_objects where object_type = 'event'.
- There are four targets, three of which work in the July CTP. The ones that work are:
    package0.asynchronous_bucketizer
    package0.pair_matching
    package0.etw_classic_sync_target

The first two targets write their info to sys.dm_xe_session_targets. You can join this to sys.dm_xe_sessions (after starting a session and collecting events) and look around. The fields in these DMVs are doc'd in BOL. Start with sys.dm_xe_session_targets.target_data.

The third target writes to an ETW session/file, providing compatibility with ETW. More on this one next.