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Bug #59199 cas() and set() extremely slow
Submitted: 2010-05-08 11:49 UTC Modified: 2012-03-07 17:32 UTC
From: abodera at gmail dot com Assigned:
Status: Analyzed Package: memcached (PECL)
PHP Version: 5.3.2 OS: Fedora 12
Private report: No CVE-ID: None
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From: abodera at gmail dot com
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 [2010-05-08 11:49 UTC] abodera at gmail dot com
Description:
------------
The cas() operation is extremely slow with php-memcached.
Below are timings taken from xdebug profiler:

Function             a.self a.cum  t.slf. t.cum calls
php::Memcached->cas    15ms  15ms  238ms    238    16
php::Memcached->get    0,2ms 0,2ms 0,2ms     16    90
php::Memcached->add    0,1s  0,1ms   1ms     1ms    9

cas() individual self time peaks up to 40ms, while similar set() and add() operations are always < 0.5ms in the same application and thread.

Tested and consistent under:
 - 1.0.1 + libmemcached 0.38
 - 1.0.2 + libmemcached 0.40

Memcached ver 1.4.4

Reproduce code:
---------------
Values stored are small (count() < 20) arrays.
Env: apache php module
Profiler: xdebug  2.0.5
Connection to memcached: 127.0.0.1, loopback via TCP

Expected result:
----------------
cas() self time < 1ms (including overhead).




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 [2010-05-08 14:38 UTC] abodera at gmail dot com
Just verified the same with set().
I've dumped cas() code completely and replaced it with plain set(). The lag is enormous...

For example:
php::Memcached->set
  avg.self: 18ms 
  total: 1933ms (105 calls)

Just tested, for comparison, the same code but with memcache (persistent, compression disabled):
php::Memcache->set
  avg.self: <0,1ms
  total: 3,9ms (59 calls)

php-memcache: Version => 2.2.5
php-memcached: Version => 1.0.2
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 [2012-03-07 17:32 UTC] andrei@php.net
Can you try with newer version of libmemcached and php-memcached?
 [2012-03-07 17:32 UTC] andrei@php.net
-Status: Open +Status: Analyzed
 
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