Is this a “white knuckle” time of the year for your organization? If you are in banking or retail, the holiday season is the peak time for point of sale transactions. It is the time when the most money (transaction value) is flowing through your systems. For our clients it is literally tens of thousands of dollars per second. It is also the time when these systems and networks are most susceptible to capacity problems.
As a performance manager or capacity planner, you must know and plan for the holiday peak. For some organizations, that may be only 40% to 50% higher than the non-holiday traffic. For other organizations, it may be two or three times normal. We had one client where their holiday peak was five times normal!
So, “white knuckles” or “cool and calm?” Are you nervous because so much is at stake if something breaks? Are you “flying blind” and simply don’t know if you have enough capacity? Or are you confident that your systems are ready?
Successful capacity managers know that they need to plan for only one half-hour peak a year. If they have configured, optimized, and balanced for that peak time, the rest of the year will take care of itself.
So let’s talk about how to prepare for the peak.
First, count the transactions going through the system. All of them. Not just when you think the peak half-hour happens each week or month. Our clients have proved that the peak half-hour moves. Sometimes it’s noon, sometimes it’s 5:30 p.m. Sometimes it’s Saturday, sometimes Monday, sometimes Friday. Expect the unexpected. Count continuously.
Why do we use a half-hour? Our experience is that POS transactions arrive in a nice bell-shaped curve over the course of a day. Occasionally we’ll see a bell with two peaks depending on the characteristics of the business. Our experience also shows that the peak minute’s traffic is usually within 10% of the half-hour average traffic. A half-hour interval gives 48 counts in a day, and that’s convenient to work with.
Now you have the data you need to analyze and do projections. We look at multiple growth ratios (and one additional factor) to try to figure out what the future will bring. We look at:
· Average transaction day each month, month-to-month growth, and growth over last year;
· Year to date transaction growth such as January – October this year versus the same period last year;
· Peak transaction day each month and growth over last year;
· Peak transaction half-hour each month and growth over last year.
Yes, this gives us several numbers to use, none of which agree. So then we have to bring in the “additional factor:” Knowledge of the business! Is growth happening because of a merger? What does the business partner say? Are there more business changes coming? Will there be a special promotion? What does s/he think the season will bring?
After reviewing all of the above, pick the most probable growth number using an educated guess.
One of our clients had a severe problem one year because they didn’t talk to their business partner. They added a gift card product, and didn’t adequately plan for how successful the card would be. Everything was in place for the card, but it was so wildly successful that the day after Christmas, when people came into the stores to use the card, the communications link to the authorizer didn’t have enough bandwidth and the system had severe problems.
OK, so now you have a number for growth. Apply it to last year’s peak half-hour to come up with this year’s target. And do one more thing: Take last year’s December over October ratio, and apply it to this October. How do the two numbers compare? Take the larger.
What do you do with the new target?
Over the last year we have been collecting the details of the system during each month’s peak transaction half-hour. We know CPU, disk, memory, communications, and process usage for each month. What’s more, we use these numbers to compute the usage per transaction (or transaction per second) each month.
From this we have:
· Basic numbers to use for modeling, and
· An indication of whether the application is getting more or less efficient.
We once had a client who added velocity file synchronization between two active systems. They did unit testing, but when they installed in production we showed them that the number of disk I/Os per transaction had doubled. We worked with them to rebalance the system.
So, it is reasonable to expect that if the transaction counts are expected to increase by 50% over October’s, it is also reasonable that all the other usage factors will do likewise. If October’s CPU was 40% busy, we should expect to see 60%. If the busiest disk in October was 70% busy, it will be 105%! Oops! Not good. Time to look more closely at that disk and offload or stripe it. If your legacy communications (SNA or X.25) will go over 50% of the bandwidth, time to upgrade it. And so on…
Click here for sample of our peak half-hour analysis for the HP NonStop and Stratus VOS architectures. These reports don't include the process detail.
If you use our techniques your pagers will stay quiet during the holidays.
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