I'm a big fan of Stack Overflow and I tend to contribute regularly (am currently in the top 0.X%). In this category (stackoverflow) of posts I will will be posting my top rated questions and answers. This, btw, is allowed as explained in the meta thread here.
My question was:
I have a situation where I would have to query the database for some data which is the same for all users and changes daily, so I figured I could make a file in which I would save this data (once per day) and then load it from that file each time a user visits my site.
Now, I know that this is a common practice (caching) when the requests from database are big but the data I'm about to write to the file is a simple 3 digit number, so my question is should this still be faster or is it just an overkill and I should stick with the database query?
The answer, by Dukeling, was:
Caching, when done right, is always faster.
It depends how long storing and retrieving data from the file takes and how long requests to the database takes.
If the database query to get the number takes long, then caching may be a good idea, since the data is small.
If you were to do a search (e.g. sequential) in a file with lots of cached data (which doesn't seem to be the case), it would take long.
Disk I/O could be slower than database I/O (which is unlikely, unless it's a local DB).
Bottom line - benchmark.
For your scenario, caching is probably a good idea, but if it's only a single 3-digit number for all users then I'd just try to stick it in RAM rather than in a file.