Re: An optimization idea

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