One of the benefits with U2 Data servers is that it can be extremely quick to turn-around a new system. The unfortunate downside is that this makes it extremely easy to ignore the architecture of your system. This can lead to future system performance issues and harder to maintain programs.
Here I’ll be looking at the set up of your files and records (tables and columns for those still grasping UniData/UniVerse). Your system revolves around your data, so if you don’t get it right to start with it inevitably leads to a sub-optimal system. What I won’t be discussing here is the usual modulo/block-size related maintenance of your files; there is already literature in the manuals for this topic.
To start with, you should have already read my previous post about correctly setting up the layout of your files and the need to create all the relevant D-type dictionary items. With that in mind, I have a story for you…
This story is about Johnny and Alicia, who are both admin staff working for a sales company back in the 1930’s. Both have a large set of contracts that they store in folders in a filing cabinet.
Occasionally their managers will ask them to find a contract that is being handled by a certain sales rep. Although they hate this task, each time they manually search through the stack of contracts to retrieve it. Funnily enough, in the time it takes Johnny to find one, Alicia can usually find at least two.
Curiosity gets the better of Johnny who eventually asks Alicia how she was so fast.
“It’s easy, I have moved the page with the sale rep’s name to the front of the contract”
Dang! So simple! Johnny realised having to dig ten pages deep on each contract was so senseless!
Fortunately, admin staff can now use digital retrieval systems, so they don’t have to think about this sort of small detail any more. The need to pay attention to this detail hasn’t gone away though. Now it rests with us.
Not only should you ensure the layout of data is in the correct format, but you should also pay attention to the order of your data. It should be organised with the most frequently searched upon and utilised data earlier on in the record. Since the record fields are separated by delimiters, using and querying later attributes requires the engine to scan every character up until to the requested attribute to determine where it starts. By moving the most frequently used data to the being of a record, you reduce the amount of work required to initial find the data.
Here are some timings from a simple test run I performed on our system.
The setup: A file with modulo 10007, pre-filled with records keyed from 10000 to 99999. Attributes 1, 2, … up until 29 are each set to the key. I have created a D-type attribute for each one timed (D1, D2 & D29).
The test: Perform a select on the file with the attribute equal to a value (E.g. SELECT TIMINGS WITH D1=”12345″). Repeat this 1000 times for each attribute tested.
Data in <1>: 338655 (100.00%)
Data in <2>: 342134 (101.03%)
Data in <29>: 471811 (139.32%)
Even with these small records, you can see the difference you can achieve by having your data in the correct order. Scale this up to larger files with bigger records, more complex select statements combined with the processing of these records in your subroutine and it can provide a significant difference in the execution times across a system.