Conn.Pool Formula : T * (C-1)+1

[sandhya menon]

Dear Friends,
I have seen this formula widely quoted for defining Pool Size parameters.
As per this T- Stands for number of Threads.
This is sligtly confusing. Is this No of Max Connection defined at WAS Servlet Engine or is it no of JSP where DB operations are happening.
And as per my understanding C stands fro avg. no of Connection objects used per JSP (?)
I have defined Max Conn at Servlet Engine as 75 and no of jsp are 30 so in this if I use First
then my pool sixe would 75*(2-1)+1=76
(poor in maths pardon me !!! i have to think atleast 4 times to say 2+2 makes 5 !!! hahahaah)
Else if use second case id no of JSP as T then it would be 30*(2-1)+1 = 31 (!!)
So which should be exact one. Or if anyother case is ther ..pls advise

[sandhya menon]

hi any one ther to guide me !!
Kyle .......???

[Kyle Brown]

Where did you hear that formula quoted? There is NO application that I can think of that needs 76 database connections. That's insane. Most applications need no more than 10 or 20.
All that would happen with a lower number is that some threads would wait temporarily. Big whoop. That will be more than offset by the lower memory requirements of having fewer threads. Also -- not every thread will be simultaneously using a connection!
My advice is TRY your application and tune the numbers from watching its performance under load. When you start to see performance gains level off, then stop adding new connections. If the graph looks linear and goes up beyond about 20 connections, then you need to tune your application to use the connections less agressively (e.g. make sure they are only held while they are in actual use).
Kyle

[sandhya menon]

Kyle Thanks for that Suggestion.
But the formula I had quoted is taken from following Websphere Tuning Guide .
a] WebSphere Conn.Pooling by Deb Erickson,Shawn Lauzon,Melissa Modjeski (PDF) Page 42 Paragraph Tuning Connection Pooling.
b] Another Big PDF (3125 kb) called as IBM WebSphere Application Server Std and Advanced Editon( Now i noticed - No authour but a collection of Tuning Papers -includes Some Notes by Gennaro(Jerry)Cuomo on Websphere Queing System)
It is from these books i got thsi formula.
I think some has to put things straight forward otherwise these PDF may be misleadeing too..
Pls reply.
Regards.

[sandhya menon]

Mr.Kyle,
I am still wating for expert opinion. Pls advise soon.
Regards

[Kyle Brown]

OK, I read Melissa's paper again. In this case your first assessment, which is that T Is this Number of Max Connection defined at WAS Servlet Engine is correct. However, I'd probably not set the upper bound that high.
The reason is that each Database connection takes up approximately 1 MB of space in memory. So, if you think about your case, that means 76MB would be spent in connections alone!
So, I'd probably say set it a bit lower (say 40 or 50) and just live with the wait times... As always, though there are no magic formulas (not even this one). Test it and find out what you see for your application.
Kyle

[sandhya menon]

Thanks Kyle,
Thansk for that expert comments. I plan to go for a Stress Test around 300-400 hits with 30 first.
Regards