How to optimize an ArrayIterator implementation in PHP? - php

Question

I have a long running PHP daemon with a collection class that extends ArrayIterator. This holds a set of custom Column objects, typically less than 1000. Running it through the xdebug profiler I found my find method consuming about 35% of the cycles.
How can I internally iterate over the items in an optimized way?
class ColumnCollection extends \ArrayIterator
{
public function find($name)
{
$return = null;
$name = trim(strtolower($name));
$this->rewind();
while ($this->valid()) {
/** #var Column $column */
$column = $this->current();
if (strtolower($column->name) === $name) {
$return = $column;
break;
}
$this->next();
}
$this->rewind();
return $return;
}
}

Answer 1

Your find() method apparently just returns the first Column object with the queried $name. In that case, it might make sense to index the Array by name, e.g. store the object by it's name as the key. Then your lookup becomes a O(1) call.
ArrayIterator implements ArrayAccess. This means you can add new items to your Collection like this:
$collection = new ColumnCollection;
$collection[$someCollectionObject->name] = $someCollectionObject;
and also retrieve them via the square bracket notation:
$someCollectionObject = $collection["foo"];
If you don't want to change your client code, you can simply override offsetSet in your ColumnCollection:
public function offsetSet($index, $newValue)
{
if ($index === null && $newValue instanceof Column) {
return parent::offsetSet($newValue->name, $newValue);
}
return parent::offsetSet($index, $newValue);
}
This way, doing $collection[] = $column would automatically add the $column by name. See http://codepad.org/egAchYpk for a demo.
If you use the append() method to add new elements, you just change it to:
public function append($newValue)
{
parent::offsetSet($newValue->name, $newValue);
}
However, ArrayAccess is slower than native array access, so you might want to change your ColumnCollection to something like this:
class ColumnCollection implements IteratorAggregate
{
private $columns = []; // or SplObjectStorage
public function add(Column $column) {
$this->columns[$column->name] = $column;
}
public function find($name) {
return isset($this->data[$name]) ? $this->data[$name] : null;
}
public function getIterator()
{
return new ArrayIterator($this->data);
}
}

Answer 2

I replaced the iterator method calls with a loop on a copy of the array. I presume this gives direct access to the internal storage since PHP implements copy-on-write. The native foreach is much faster than calling rewind(), valid(), current(), and next(). Also pre-calculating the strtolower on the Column object helped. This got performance down from 35% of cycles to 0.14%.
public function find($name)
{
$return = null;
$name = trim(strtolower($name));
/** #var Column $column */
foreach ($this->getArrayCopy() as $column) {
if ($column->nameLower === $name) {
$return = $column;
break;
}
}
return $return;
}
Also experimenting with #Gordon's suggestion of using an array keyed on name instead of using the internal storage. The above is working well for a simple drop-in replacement.