Really simple queuing PL/SQL calcuations..

February 21, 2009


A couple of posts by Chen Shapira, (this one barbershop-queue-demo and this one random-thoughts-about-queues)  over at prodlife.wordpress.com regarding queuing in systems and queuing theory piqued my interest. Way back in the beginning of my career in IT I worked in an outsourced  call centre building reports, providing management information etc. one critical piece of this work was calculating requred staffing levels. A lot of this was based on a couple of pieces of maths the ErlangB and ErlangC Formulas as part of the reporting I ended up producing some PL/SQL to perform these calculations its not the best but if your interested its here queuing_calc_plsql.

This is based on the Excel erlangc calculator written by Lester Bromley at www.erlang.co.uk however my code has a couple of additional caveats, there is no error or input checking in the pl/sql I may add it a some point but then again I may not, it is therefore possible to get nonsensical responses or divide by zero errors.

Servicetime is defined in the functions as the time spent queuing not the queuing time+transaction time.

the PL/sql functions I wrote allow you to specify an interval rather than use a default of one hour, also the orgonal provides far more functions than i translated, I’ll probably get around to the others at some point but it may take a while.

The same conditions apply, you can use any of this code you like however do not sell rent or lease it out, also its provided as is and I’m not responsible for any loss or damages if its faulty or provides incorrect answers, also if you want to modify re-code into a different language feel free but it would be polite to contact Lester prior to publishing anything based on this as the original work is his.

Anyway back to the point, Chens post got me too thinking could this stuff be useful in an OTLP environment, my thoughts are possibly. It should be possible to estimate the number of cpus based on a given volume of transactions, cpu time required for each transaction and the desired service level. I suspect the model won’t be perfect as cpu usage for a transaction may be split into multiple chunks however hopefully I’ll get some time to produce a test case/simulation and see if it works aver the next week or so, if anyone has any bright ideas let me know..

Chris


How do I become a DBA?

January 6, 2009

My first post is my answer to this question, I see it get asked occasionally on the otn forums and elsewhere, unfortunately my answer probably doesn’t help anyone else, I got here by the following route:-

After leaving school I took Physics at university for the same reasons most 18 year olds take a university degree, I had no idea what career I actually wanted to follow but was good at physics and maths and all my friends were also heading off to University so I figured I didn’t want to be the only one staying in my hometown and getting a job.

Four years later (after a small hiccup and a change of university) I realised that I didn’t want work in the field I had just spent four years studying and the most likely alternative didn’t seem to attractive (apparently 50% of physics graduates end up as accountants), however I was really interested in computing so found myself starting out as an outsourced phone tech support agent for a large Internet provider, back in the days of dial up. Surprisingly this didn’t put me off a career in IT completely, trying to guide people through connecting to the Internet when they have just unpacked their first PC was a sometimes frustrating procedure especially as almost no one I spoke to had two telephone lines. After a year i moved into the IT department as an MIS analyst (OK the only MIS analyst) and spent a lot of time with Excel, over the next three years spent time working with crystal reports, oracle SQL and P/SQL and MS SQL Server, as well as assorted CTI and telephony technologies. Then in 2000 whilst my employer was between financial controllers and DBA’s my manager managed to get the 8i dba training courses approved for me and a colleague, the next four years I was a mix of DBA and developer working hours that I never want to repeat, until finally moving on in 2004, since then I’ve been a DBA covering both development and production dba roles.

Overall I have been very fortunate in working for a company that was setting up for the first time in the UK, I got to try lots of different IT roles and found the one that suits me and I enjoy, a more normal career path taking a computer science degree and entering a graduate training program may have been quicker but at least this way I know I’m in the role I enjoy most and one that I’m well suited too.

Hence my answer to the question is I don’t know how you become a DBA, I know how I got here but its not the most direct route and was the result of working for and with the right people at the right time.