AFTER INSERT Trigger Takes Forever On A Large Table (20 Million Rows)

I have a row that is being used log track plays on our website.

Here's the table:


CREATE TABLE [dbo].[Music_BandTrackPlays](
[ListenDate] [datetime] NOT NULL DEFAULT (getdate()),
[TrackId] [int] NOT NULL,
[IPAddress] [varchar](20)
) ON [PRIMARY]


There's a CLUSTERED INDEX on ListenDate ASC and a NON CLUSTERED INDEX on the TrackId.

I have a TRIGGER on the Music_BandTrackPlays table that looks like the following:


CREATE TRIGGER [trig_Increment_Music_BandTrackPlays_PlayCount]
ON [dbo].[Music_BandTrackPlays] AFTER INSERT
AS
UPDATE
Music_BandTracks
SET
Music_BandTracks.PlayCount = Music_BandTracks.PlayCount + TP.PlayCount
FROM
(SELECT TrackId, COUNT(*) AS PlayCount
FROM inserted
GROUP BY TrackId) AS TP
WHERE
Music_BandTracks.TrackId = TP.TrackId


When a simple INSERT statement is done on the Music_BandTrackPlays table, it can take quite a long time. When I remove the TRIGGER the INSERTs are immediate. The Execution plan for the TRIGGER shows that a 'Inserted Scan' is taking up most of the resources.

How exactly is the pseudo 'inserted' table formed?

For now, I think the easiest thing to do is update my logging page so it performs 2 queries. One to UPDATE the Music_BandTracks table and increment the counter, and perform the INSERT into the Music_BandTrackPlays table seperately.

I'm ok with that solution but I would really like to understand why the TRIGGER is taking so long. The 'inserted' pseudo table will be 1 row 99% of the time. Does SQL Server perform a table scan on all 20 million rows in order to determine what's new and put it in the inserted pseudo table?

Thanks!