Apache 2.2/2.4 (was running 2.4 but currently back to 2.2 to try to fix below issues)
Server Version: Apache/2.2.29 (Unix) mod_ssl/2.2.29 OpenSSL/0.9.8e-fips-rhel5 mod_bwlimited/1.4 Apache mod_fcgid/2.3.9
PHP 5.4
Memcached 1.4.15, running locally on the same server.
I recently had some database slowness on my site related to queries on large table (120M rows) and noticed that phpMyAdmin -> Status -> Advisor said I should no longer use the mySQL Query cache. My site was 200 requests/second and the trigger was anything over 100/second.
I installed memcached per this guide I found Easy way to install Memcached and memcache in a cPanel server | CryBit - /http://crybit.com/easy-way-to-install-memcached-and-memcache-in-a-cpanel-server/
Everything was fine, it was installed, I could see it was live in phpinfo and via this command:
memcached-tool 127.0.0.1:11211 stats
After installation, I began switching my PHP code to use memcache.
Example:
I verified data was being loaded from the cache in my PHP page, and I also could see data being stored using the memcached-tool command noted above .
Soon after I began using memcached, Apache would lock up and go to 256 connections (my configured max through WHM) every 30 minutes or so. This time would vary, it was seemingly random. I could also see database queries massively backing up when viewed via:
mytop -d mysql
I thought it was database issues so I began caching more and more stuff in my code, converted some high update/select tables to INNODB, etc. This actually seemed to help as my site was faster but as I cached even more, my site became unusable as Apache would overload at shorter and shorter increments, down to only working from 5-10 minutes today. I finally decided to disable all memcaching just as a test and boom, site came back up everything is ok, barring the occasional high load/high # of Apache connections that I think is normal for my site, especially when I still have the mySQL cache off.
I would like to use memcached as I have a bunch of queries that are long-running, often taking 3-30 seconds, and occasionally my site will still run slow due to these queries.
What can I check and/or change to get memcached working reliably?
Edit #1:
After looking at a lot of PHP code samples, I see very few people doing this in examples:
This example is more common, where some text is appended:
Is there an issue with just using md5 alone to generate a key?
Edit #2:
My site is a medium sized site - it has 800-1000 people online most of the time. I wonder if calling md5() hundreds/times/second is an issue? The major pages that I initially optimized had 5-10 memcached and md5 calls each.
Edit #3:
I took out some md5() calls as a test and just used a simple key like 'users' and my site still began overloading fairly quickly.
As another test, I also removed MEMCACHE_COMPRESSED and replaced it with a 0 to disable any compression in case that was a speed issue. The data I am caching is an array and it was NOT cached. Possible bug?
Edit #4:
Is mod_fcgid an issue? I mean overall but here are my settings from Pre VirtualHost Include, All Versions, in case there is an issue with the settings:
Server Version: Apache/2.2.29 (Unix) mod_ssl/2.2.29 OpenSSL/0.9.8e-fips-rhel5 mod_bwlimited/1.4 Apache mod_fcgid/2.3.9
PHP 5.4
Memcached 1.4.15, running locally on the same server.
I recently had some database slowness on my site related to queries on large table (120M rows) and noticed that phpMyAdmin -> Status -> Advisor said I should no longer use the mySQL Query cache. My site was 200 requests/second and the trigger was anything over 100/second.
I installed memcached per this guide I found Easy way to install Memcached and memcache in a cPanel server | CryBit - /http://crybit.com/easy-way-to-install-memcached-and-memcache-in-a-cpanel-server/
Everything was fine, it was installed, I could see it was live in phpinfo and via this command:
memcached-tool 127.0.0.1:11211 stats
After installation, I began switching my PHP code to use memcache.
Example:
PHP:
$memcache = new Memcache;
$memcache->connect('127.0.0.1', '11211');
$sql = "SELECT ids from id_table WHERE id_type=5";
$ids = $memcache->get(md5($sql));
if (!$ids)
{
$ids = get_ids_from_database($sql);
if (count($ids))
{
$memcache->set(md5($sql), $ids, MEMCACHE_COMPRESSED, 60);
}
}Soon after I began using memcached, Apache would lock up and go to 256 connections (my configured max through WHM) every 30 minutes or so. This time would vary, it was seemingly random. I could also see database queries massively backing up when viewed via:
mytop -d mysql
I thought it was database issues so I began caching more and more stuff in my code, converted some high update/select tables to INNODB, etc. This actually seemed to help as my site was faster but as I cached even more, my site became unusable as Apache would overload at shorter and shorter increments, down to only working from 5-10 minutes today. I finally decided to disable all memcaching just as a test and boom, site came back up everything is ok, barring the occasional high load/high # of Apache connections that I think is normal for my site, especially when I still have the mySQL cache off.
I would like to use memcached as I have a bunch of queries that are long-running, often taking 3-30 seconds, and occasionally my site will still run slow due to these queries.
What can I check and/or change to get memcached working reliably?
Edit #1:
After looking at a lot of PHP code samples, I see very few people doing this in examples:
PHP:
$ids = $memcache->get(md5($sql));
PHP:
$ids = $memcache->get('sql:' . md5($sql));Edit #2:
My site is a medium sized site - it has 800-1000 people online most of the time. I wonder if calling md5() hundreds/times/second is an issue? The major pages that I initially optimized had 5-10 memcached and md5 calls each.
Edit #3:
I took out some md5() calls as a test and just used a simple key like 'users' and my site still began overloading fairly quickly.
As another test, I also removed MEMCACHE_COMPRESSED and replaced it with a 0 to disable any compression in case that was a speed issue. The data I am caching is an array and it was NOT cached. Possible bug?
Edit #4:
Is mod_fcgid an issue? I mean overall but here are my settings from Pre VirtualHost Include, All Versions, in case there is an issue with the settings:
Last edited:
