Location based caching system

Question

I like to have a location based data caching(on the server) system for supplying data for a mobile application. i.e., if some user requests data from a location (which is common to all the users from same area), i'll fetch the values from DB and show to them. But if a second user retrieves the same page within the next 5 mins from the same location, then i don't want to query the millions of records present in the DB and i can just take them if it is there in file cache. So any such things available now in PHP?

Answer 1

If all you are concerned about is the queries...one approach might be a db table that stores query results as json or serialized php objects along with whatever fields you need to match locations.

A cron job running on whatever interval best suits would clear out expired results

Answer 2

I am not aware of any such thing in PHP, but it's not too hard to make your own caching engine with PHP. You need to make a cache directory and based on the requests you get you have to check if a file corresponding to that request is there in your cache directory or not.

e.g your main parameters are lat and long. Suppose you get the request with lat = 123 and long =234 (taking some random values), you will check your cache folder is a file named 123_234.data is present or not. If it is present, instead of querying the database you read the file and send the content as the output, else you read from the database and before sending the response write that response in a file cache/123_234.data. This way you can serve the files later too without querying the database again.

Challenges:

1. Time: The cache will expire at some point or the other. So while checking if the file exists, you also need to check the last modified timestamp to ensure the cache is not expired. It depends on you application requirements if the cache expires in a minute, 10 minutes, hours, days or months.
2. Making intelligent cache file names in this case is going to be challenging as even for a distance of 100m, the lat,long combination will be different. One option for you might be to choose the file names by setting the precision. e.g a real lat long combination is of the form 28.631541,76.945281. You may want to make a cache file named 28.63154_76.94528.data (reducing precision value to 5 places after decimal). It again depends if you want to cache just for a single point on a globe or for a geographical region, and if a geographical region, then the radius of it.

I don't know why someone down voted the question, I believe it is a very good and intelligent question. There goes my upvote :)