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Example of Load Balancing for Improved Performance
Suppose that your directory must include 1,500,000 entries in support of 1,000,000
users, and each user performs ten directory lookups a day. Also assume that you
are using a messaging server that handles 25,000,000 mail messages a day, and that
performs five directory lookups for every mail message that it handles. Therefore,
you can expect 125,000,000 directory lookups per day just as a result of mail. Your
total combined traffic is, therefore, 135,000,000 directory lookups per day.
Assuming an eight-hour business day, and that your 1,000,000 directory users are
clustered in four time zones, your business day (or peak usage) across four time
zones is 12 hours long. Therefore you must support 135,000,000 directory lookups
in a 12-hour day. This equates to 3,125 lookups per second (135,000,000 /
(60*60*12)). That is:
1,000,000 users
25,000,000 messages
12-hour day includes
43,200 seconds
Now, assume that you are using a combination of CPU and RAM with your
Directory Servers that allows you to support 500 reads per second. Simple division
indicates that you need at least six or seven Directory Servers to support this load.
However, for enterprises with 1,000,000 directory users, you should add more
Directory Servers for local availability purposes.
You could, therefore, replicate as follows:
•
Place two Directory Servers in a multi-master configuration in one city to
handle all write traffic.
This configuration assumes that you want a single point of control for all
directory data.
•
Use these supplier servers to replicate to one or more hub suppliers.
The read, search and compare requests serviced by your directory should be
targeted at the consumer servers, thereby freeing the master servers to handle
write requests. For a definition of a hub supplier, refer to "Cascading
Replication," on page 103.
10 lookups per user =
5 lookups per message =
Total reads/day =
Total reads/second =
Chapter 6
Defining a Replication Strategy
10,000,000 reads/day
125,000,000 reads/day
135,000,000
3,125
Designing the Replication Process
113
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