Microsoft Exchange is due out by year's end. Last year it was also due out by year's end. Why the delay? If you asked Lotus, the company might say that Microsoft underestimated how difficult the replication process is until they tried to implement it.
With regard to replication, Exchange's most prominent deviation from Notes is that it works on a mail-based paradigm (see the figure
"Exchange Replication"
). "Our philosophy is to define the messaging infrastructure first and then use this infrastructure to build groupware applications," says Exchange Server product manager Elaine Sharp.
Since it's mail-based, replication in Exchange will not require that two
servers establish a session with each other. Each "public folder"--the analog of a Notes database--will know which servers it is distributed to, while users will not. The internal distribution list helps determine what other servers the update should be routed to whenever a public folder is modified. Synchronization within Exchange could occur on a continuous basis or according to a schedule.
Folder distribution, according to Microsoft, should be decided dynamically, based on statistical usage patterns. If the level of requests to access a folder from a given site crosses a predetermined threshold, a copy of the folder can be put on a server at that site.
There's a significant difference in the ways Exchange and Notes handle message routing. In Exchange, if message routing from server A to server C passes through server B, a public folder shared by servers A and C need not reside on server B for updates to get through.
There is obvious appeal to this paradigm. The only question that remai
ns is how well it will work. The industry's experience with Notes may well be why Microsoft appears to be taking performance seriously. Says Sharp: "We are planning to be very up-front with our customers about how important it is for them to plan and monitor the topology and schedule."
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How Exchange Handles Replication
