XADM: Space Tree Fragmentation in Exchange Database Engine Can Degrade Server Performance (230691)

SYMPTOMS

Messages begin backing up and/or moving out slowly in the private information store queue in the Microsoft Exchange Message Transfer Agent (MTA).
The information store process CPU use (as seen by using Windows NT Performance Monitor) begins to increase as the length of the MTA queue increases.
A given number of threads belonging to the information store process Store.exe, (as seen by using Windows NT Performance Monitor) seem to be running at a high CPU percentage for a long period of time (that is, more than 30 percent).

CAUSE

Available space in the Exchange Server information store database is in the form of a list of pages that can be used to store new data. The available space is called a space tree. The space tree is held as binary tree that is searched whenever a block of new data needs to be added to the database.

The problems in the "Symptoms" section are caused when the space tree becomes very fragmented, causing the size of the binary tree to grow very large. This large space tree causes massive I/O when navigating through the binary tree looking for space. As a result, the performance of the server degrades as more and more information store threads navigate the space tree.

RESOLUTION

To resolve this problem, obtain the latest service pack for Exchange Server version 5.5. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

191014 XGEN: How to Obtain the Latest Exchange Server 5.5 Service Pack

The English version of this fix should have the following file attributes or later:

Component: JET

File name	Version
Ese.dll	5.5.2650.16

WORKAROUND

An offline defragmentation (eseutil /d ispriv |ispub) of the database will shrink the size of the space tree, and provide relief until the time the fragmentation builds up once more in the space tree.

STATUS

Microsoft has confirmed that this is a problem in Microsoft Exchange Server version 5.5. This problem was first corrected in Exchange Server 5.5 Service Pack 3.