Need help optimizing a lat/Lon geo search for mysql

Question

I have a mysql (5.0.22) myisam table with roughly 300k records in it and I want to do a lat/lon distance search within a five mile radius.

I have an index that cov

Answer 1

You really should avoid doing that much math in your select statement. That's probably the source of a lot of your slowdowns. Remember, SQL is a query language; it's really not optimized for trigonometric functions.

SQL will be faster and your overall results will be faster if you do a very naive distance search (which will return more results) and then winnow your results.

If you want to be using distance in your query, at the very least, use a squared distance calculation; sqrt calculations are notoriously slow. Squared distance is much easier to use. A squared distance calculation is simply using the square of the distance instead of the distance; it is much simpler. For cartesian coordinate systems, since the sum of the squares of the short sides of a right triangle equals the square of the hypotenuse, it's easier to calculate the square distance (just sum the two squares) than it is to calculate the distance; all you have to do is make sure that you're squaring the distance you want to compare to (so instead of finding the precise distance and comparing that to your desired distance (let's say 5), you find the square distance, and compare that to the square of the desired distance (25, if your desired distance was 5).