Use the Capacity Sizing worksheet to prepare your test plan and to derive your peak usage projections for load and throughput . Please refer to Chapter 6 for a complete description of the data and calculations in the worksheet. Also Chapter 10, the first part of the case study, provides an example using this worksheet. Input Data In order to estimate concurrent users and throughput, you need data provided by your marketing team and web site architect. The data includes expected user visits (per day), average user visit time, and pages per visit. Since you base all planning work on peak usage, you need a factor for estimating peak load over daily average load. The worksheets provide two methods to estimate peak load, as described in Chapters 6 and 10. | Input Data (Estimates) | Source of Data | Your Data | 1. | Number of user visits (day) | Marketing team | | | If you cannot estimate 2, provide estimates for 3 and 4 below. | 2. | Percent of daily users arriving in peak hour | Estimate | | | Provide 3 and 4 below only if you did not know 2. | 3. | Number of hours per day site is actively used | Estimate provided by marketing team (when in doubt, use 8 hours) | | 4. | Peak load increase over normal hour | Estimate (typically between 3 and 5) | | | Items 5 “7 must be provided to calculate throughput from user visits. | 5. | Average user visit time | Marketing team | | 6. | Average pages per visit | Marketing team | | 7. | Average static elements per page | Web site application architect | | Calculating Peak Load (Concurrent Users) For convenience, the worksheet provides space for all calculations in hours, minutes, and seconds. Obviously, multiplying the hours by 60 to get minutes, and by 60 again to get seconds derives these calculations. Express later calculations in hours, minutes or seconds, depending on your preference. | Calculated Data | Equation | Total (hr) | Total (min) | Total (sec) | | If you have data for 2, use the following calculation, otherwise skip to 9. | 8. | Number of user visits adjusted for peak load | Number of user visits * Percentage of users arriving at peak Line 1 * Line 2 | | | | | If you have data for 3 and 4, use the following calculations. | 9. | Number of user visits adjusted for length of day | Number of user visits / Hours in web site day Line 1 / Line 3 | | | | 10. | Number of user visits adjusted for peak load | Number of user visits adjusted for day * Peak load increase factor Line 9 * Line 4 | | | | | Do the following calculations (use the value from line 8 or line 10). | 11. | User arrival rate (new users per second) | User arrival rate = Line 8 or line 10 | | | | 12. | Concurrent users | User arrival rate * User visit time Line 11 * Line 5 | | | | Calculating Throughput (Page Rate and Request Rate) | Calculated Data | Equation | Total (hrs) | Total (min) | Total (sec) | 13. | Throughput: page rate | User arrival rate * Average pages per visit Line 11 * Line 6 | | | | 14. | Throughput: requests | Page rate + (Average static elements * Page rate) Line 13 + (Line 7 * Line 13) | | | | |