Getting to Know Directory Usage Patterns: A Case Study

The ability to assess the potential load on Oracle Internet Directory is very important for developing an accurate capacity plan. Let us examine the e-mail messaging software employed by our hypothetical company, Acme Corporation. The e-mail messaging software in this example is based on Internet Message Access Protocol (IMAP). There are two main types of software that access Oracle Internet Directory:

• The IMAP clients, which will validate e-mail addresses within the company before sending the mail to the IMAP server. These clients include software programs like Netscape Messenger and Microsoft Outlook.

• The messaging software itself, also called the Mail Transfer Agent (MTA), which will look up the directory to route mail from the outside world to internal mailboxes as well as route internal mails to company-wide distribution lists.

Let us assume that the private aliases and private distribution lists of individual users are also stored in the directory. Let us further make the following assumptions, which will allow us to guess the size of the directory:

Table 20-1 Assumptions about Entry Types and Their Sizes

Entry Type	Size
Total user population	40,000
Average number of private aliases for each person	10
Average number of private distribution lists for each person	10
Total number of public distribution lists	4000
Total number of public aliases in the company	1000
Number of attributes in each entry in the directory related to this application	20
Number of cataloged attributes	10

Based on these assumptions, we can derive the overall count of entries in Oracle Internet Directory as:

Table 20-2 Overall Count of Entries

Entry Type	Size
User entries	40,000 (these represent the users themselves)
Private aliases of users	40,000 x 10 = 400,000 entries
Private distribution lists of users	40,000 x 10 = 400,000 entries
Company wide distribution lists	4000
Company wide aliases	1000

These assumptions will yield a directory population of about one million entries. Given the user population and the directory population, let us then analyze usage patterns so that we can derive performance requirements from them. A typical user tends to send an average of 10 e-mails everyday and receives an average of 10 e-mails a day from the outside world. Assuming that there are, on an average, five recipients for each e-mail being sent by a user, this would result in five directory lookups for each e-mail.

The following table summarizes all the possible directory lookups that can happen in one day:

Table 20-3  Directory Lookups in a Single Day

Type of Directory Lookup	Number of Directory Lookups In One Day
The Mail Transfer Agent (MTA) processing outbound mail from each user	5x10x40,000 = 2,000,000
The MTA processing mails from the outside world	10x40,000 = 400,000
All other directory lookups (like IMAP clients validating certain addresses, and so on)	800,000

Summing up, the total number of directory lookups everyday would be about 3,200,000 (3.2 million) directory lookups everyday. If these directory lookups were spread out uniformly along the day, it would require about 37 directory lookups every second (133,333 lookups every hour). Unfortunately, we will never have this case.

Usage analysis of the current e-mail system over a period of 24 hours shows the pattern illustrated in Figure 20-1.

Figure 20-1 Usage Analysis of Current E-mail System

Text description of the illustration oidag016.gif

The e-mail system and Oracle Internet Directory are maximally stressed in the mornings. There are other usage peaks as well--one close to lunch time, and one near the end of business day. However, it is in the mornings that the Oracle Internet Directory is stressed the most.

Let us assume that 90 percent of all the directory lookups happen during normal working hours. Let us now split up the working hour load into the following categories for an 8 hour workday:

Table 20-4  Working Hour Loads

Shift Load	Lookups
Morning load	65%: 0.90 x 0.65 x 3,200,000 = 1,872,000 lookups for 2 hours (936,000 lookups every hour)
Afternoon load	10%: 0.90 x 0.10 x 3,200,000 = 288,000 lookups for 1 hour (288,000 lookups every hour)
Evening load	20%: 0.90 x 0.20 x 3,200,000 = 576,000 lookups for 2 hours (288,000 lookups every hour)

These calculations indicate that the Oracle Internet Directory in this case should be designed to handle the peak load of 936,000 lookups every hour.

Now that we know the data-set size as well as the performance requirements, we can now look into individual components of the installation and estimate good values for each.