Arrays, long considered the work horse of PHP have one flaw: they can be incredibly slow. There is however an alternative — at least, for a small subset of use cases.
SplFixedArray like so:
SplFixedArray class provides a super-fast, fixed size array implementation. There are some limitations however, first you must use numeric keys and secondly you cannot use anonymous assignment (i.e.
$array = 'value';).
You’ll notice one requirement was missing, that it should have a fixed size. While having a fixed size is what will bring you the speed increase it’s actually not a requirement that the size be fixed. Though you must specify a size to the constructor, you can change it (and lose most — if not all — speed benefits) at any time using
So, what sort of speed increase are we talking about? In my testing of arrays 100, 100… 1,000,000 elements, you will see a speed increase about 20-25%; for arrays smaller than 100, it will actually be slower by 25-40%.
The benchmarking was very simple, a comparison of a read and write iteration for both normal and fixed arrays of different sizes like so:
Additionally, the memory usage to run the benchmarks for array vs SplFixedArray is significantly different, regular arrays clock in at 198MB while SplFixedArray uses a mere 83MB, that’s a 59% memory saving.
In practical terms, you’re only going to be worried about the speed of arrays when you’re dealing with larger arrays anyway, so the speed loss for the lower digits isn’t a big concern… but where exactly could this be useful?
There is one common scenario where you will commonly be dealing with large numerically indexed arrays of data: Your database result sets. Using PDO, you can tell how many results you have before you retrieve the row data using
Unfortunately, it is not possible to set the result set container for
PDOStatement->fetchAll() to use
SplFixedArray — however, if someone wants to help (that is, someone who knows internals and… well, C), I’ve got an opening for a coach!
At the urging of my co-worker Helgi, I threw the arrays into a
FilterIterator and got some pretty interesting results. Using similar code to the first benchmark, but instead of just reading out the array, we created and used a custom
For regular arrays, we must first create an iterator:
For the SplFixedArray, we passed it straight into the
EvenFilterIterator, otherwise the code is the same.
Even with the extra overhead of creating the
ArrayIterator, the SplFixedArray is only marginally (1%) faster till it reaches the 10000 elements mark, and then it starts to become marginally slower (again 1%). So, I guess the take-away is: use with caution.