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To: Karoly Negyesi <karoly@negyesi.net>
In-Reply-To: <7e270cea0810191211w2cb77075y5e0ad78c2f7306f7@mail.gmail.com>
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Date: Mon, 20 Oct 2008 13:09:34 -0700
References: <7e270cea0810191211w2cb77075y5e0ad78c2f7306f7@mail.gmail.com>
Subject: Re: [PHP-DEV] An optimization idea
From: shire@tekrat.com (shire)


On Oct 19, 2008, at 12:11 PM, Karoly Negyesi wrote:

> Hi,
>
> I think zend_hash_compare could get a healthy speed boost in some
> cases if first it would check whether the two variables passed to it
> are actually the same (because of "reference counting"). Sorry, my C
> skills are way too rusty to write the patch which is likely to be just
> a few lines long.
>


A quick patch/test seems to agree with you, I'd be interested to know  
if you/others  are able to apply this patch and see any real-world  
savings with your web application.  The following was done with a  
debug build of PHP so results are likely exaggerated.  I'm also using  
non-recursive array with 256 byte strings below, results with numeric  
values are less significant of course (approx a 25% gain)...

I'll also look into applying this to some other functions like  
compare_function where it's likely to yield a larger savings in a  
general application.


patch against php-5.2 CVS head
--------------------------
iff --git a/Zend/zend_hash.c b/Zend/zend_hash.c
index a1d7071..d11785f 100644
--- a/Zend/zend_hash.c
+++ b/Zend/zend_hash.c
@@ -1327,16 +1327,14 @@ ZEND_API int zend_hash_compare(HashTable *ht1,  
HashTable *ht2, compare_func_t co
         IS_CONSISTENT(ht1);
         IS_CONSISTENT(ht2);

-       HASH_PROTECT_RECURSION(ht1);
-       HASH_PROTECT_RECURSION(ht2);
-
         result = ht1->nNumOfElements - ht2->nNumOfElements;
-       if (result!=0) {
-               HASH_UNPROTECT_RECURSION(ht1);
-               HASH_UNPROTECT_RECURSION(ht2);
+       if (ht1 == ht2 || result!=0) {
                 return result;
         }

+       HASH_PROTECT_RECURSION(ht1);
+       HASH_PROTECT_RECURSION(ht2);
+
         p1 = ht1->pListHead;
         if (ordered) {
                 p2 = ht2->pListHead;



simple test script
-------------------------------
<?php

$arr1 = array();
for ($i=0; $i < 10000; $i++) {
   $arr1[$i] = str_repeat('x', 256);
}
$arr2 = array();
for ($i=0; $i < 10000; $i++) {
   $arr2[$i] = str_repeat('x', 256);
}
$arr3 = $arr1;

$count = 0;
$start = microtime(true);
for ($i = 0; $i < 1000; $i++) {
   if ($arr1 == $arr2) {
     $count++;
   }
}
$stop = microtime(true);
echo "different array time: ".($stop-$start)."\n";
echo "count: $count \n";

$count = 0;
$start = microtime(true);
for ($i = 0; $i < 1000; $i++) {
   if ($arr1 == $arr3) {
     $count++;
   }
}
$stop = microtime(true);
echo "identical array time: ".($stop-$start)."\n";
echo "count: $count \n";
-------------------------------

(un-patched php build)
shire@shirebook:~/data/php/git/php$ ./sapi/cli/php.vanilla test.php
different array time: 4.2019698619843
count: 1000
identical array time: 2.4957029819489
count: 1000

(patched build)
shire@shirebook:~/data/php/git/php$ ./sapi/cli/php test.php
different array time: 4.059928894043
count: 1000
identical array time: 0.00043511390686035
count: 1000


-shire