In a very high loaded Ubuntu/PHP web server I found that the PHP line:


sometimes takes ~5 secs.

Replacing the url with the ip address decreases the server load from ~20 to 0

My question is - where are the settings that effect the DNS caching for this? Is it in the server level or the memcache library ? How can I change it ?

Additional info: Ubuntu 10.04 lucid PHP: 5.3.2-1ubuntu4.10 Apache/2.2.14 (Ubuntu) Amazon EC2

Even more info per Celada's comment:

The DNS handling for the memcache server is done by scalr (the platform I use to manage the cloud resources). They have a client located on the instances and their own DNS servers.

/etc/nsswitch.conf - hosts: files dns /etc/resolv.conf: nameserver domain ec2.internal search ec2.internal

The domain is not in hosts.conf To check if I run nscd I used /etc/init.d/nscd stop and received 'no such file' so i guess I dont run nscd.

Thanks !

  • 2
    What are your hostname resolution settings ("hosts" line in /etc/nsswitch.conf and contents of /etc/resolv.conf)? Are you using a local DNS (e.g. in /etc/resolv.conf)? Does the hostname in question appear in /etc/hosts? Are you running nscd? By the way, the underscore character is not valid in host names.
    – Celada
    Mar 13, 2012 at 22:14
  • Please see post edit
    – Niro
    Mar 14, 2012 at 7:06

1 Answer 1


I ended up doing double buffering of the ip addresses in APC (PHP Cache) memory. This solves all the DNS timing issues.

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