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Date: Mon, 10 Nov 2008 16:09:29 -0800
Cc:  <internals@lists.php.net>
Subject: Re: [PHP-DEV] An optimization idea
From: shire@tekrat.com (shire)


On Nov 10, 2008, at 2:32 PM, Stan Vassilev | FM wrote:

>> I just ran a quick benchmark on this and I'm not seeing a  
>> significant real world change for Facebook's codebase. (definitely  
>> less than 1%) This was a pretty small test, without a lot of code  
>> execution, so I  could see other applications doing better.  I'm  
>> pretty neutral on this  one, it's not a really big change so might  
>> be worth adding if it's  going to give a few applications out there  
>> a gain, but I couldn't see  doing this everywhere of course.
>>
>> -shire
>
>
> Hi,
>
> Something that could give arrays a boost would be to:
>
> - pool all string literals in each file
> - give each stringl iteral an id (unique in the loaded environment)
> - bind early all array access with string literals (a common  
> occurence), so they don't need to be resolved with a hashmap lookup,  
> but rather, a direct stirng literal id lookup.
>
> The benefit of this approach are:
>
> - There's no need to generate a hashmap in the first place
> - String literal id-s are unique integers and have no conflicts, so  
> no need to do conflict resolution.



This wouldn't really help with the case here of "if ($array1 ==  
$array2)..." though right?  (not to say it's not good, just making  
sure I understand ;-) ).

It sounds like this would only work if the array contents where static  
though, as you're mapping a constant string to the contents of the  
hash (or did I misunderstand and you'd be mapping string const. values  
to hash IDs?).

I am at the point now where my #1 item CPU wise is my hash function.   
I'm working on finding a slightly faster implementation, but I'm also  
playing with having a hash value stored in every zval so that the hash  
function call can be skipped if we've already ran it once.  The  
problem that comes into play here is that there's no central code to  
update or clear the hash if the string or contents of the zval  
change.  Of course, doing this with constant values would be easier to  
accomplish and could be done at compile time, and like you say this is  
a pretty common scenario.

-shire