The following is Tip #3 from "25 Exchange 2003 Tips in 25 minutes." This content is excerpted from Scott Schnoll's book, "Microsoft Exchange Server 2003 Distilled," brought to you by © (2004) Pearson Education, Inc. Publishing as Addison-Wesley Professional.
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As the name suggests, Directory Service Access (DSAccess) is an internal component in Exchange that controls how all Exchange components access Active Directory. The primary function of DSAccess is to keep tabs on various directory-related things. For example, DSAccess discovers the Active Directory topology and detects the state of domain controllers and global catalog servers (up or down). In addition, all directory queries are routed through DSAccess, such as recipient resolution, configuration setting lookups, and others. As part of its job, DSAccess maintains an in-memory cache of the results of some of these queries so that if the same information is requested twice, it can be retrieved from the DSAccess cache instead of through another LDAP query against Active Directory. The size of the inmemory cache is configurable, in that you can set a maximum size for various cached items.
Many administrators found that on larger Exchange 2000 servers, the out-of-the-box values for the maximum cache size for recipient look-ups and the maximum cache size for configuration look-ups were not always optimized for their servers. On systems with an undersized DSAccess cache, it was common for local message delivery and/or address book resolution to be slow. Once the maximum size of the recipient cache was increased and the size of the configuration cache was decreased, performance would improve. The DSAccess cache tuning parameters for the configuration data cache and the user object cache were represented in the registry as follows.
In Exchange 2000, each cache pool (e.g., the configuration cache, the recipient cache, and
so on) was initially set at 25MB in size. To improve performance, the default values for the
configuration and recipient caches have been optimized in Exchange 2003. The configuration
data cache, which more often than not never needed anywhere near 25MB, now
defaults to 5MB. The user object cache, which was often undersized for larger systems, now
defaults to 140MB. Therefore, you should remove the
registry entries prior to upgrading from Exchange 2000 to Exchange 2003.
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About the author: Scott Schnoll, an Expert on SearchExchange.com, is an MCT, MCSA and a long-time Microsoft Most Valuable Professional (MVP).
In addition to writing "Microsoft Exchange Server 2003 Distilled," he is a co-author of the upcoming "Exchange 2003 Resource Kit from Microsoft Press" and lead author for "Exchange 2000 Server: The Complete Reference."
Scott has written numerous articles for Exchange & Outlook Magazine, and is a regular speaker at Microsoft conferences, including MEC and TechEd, as well as industry conferences such as Comdex and MCP TechMentor, where he covers topics such as Exchange, clustering, Internet Information Services and security.