Thanks for sharing!
On Sunday, November 18, 2012 2:44:02 AM UTC-8, Niro wrote:
>
> Hi Guys,
>
> I thought you can benefit so I share this with the community.
>
> A few months ago I noticed that calls to Scalr DNS such as :
> $memcache->addServer("ext-memcached.memcached.yourdomain.net",11211);
> that happen on every script hit cost a lot in resources since the DNS can
> take up to a couple of seconds. Remember you have this also for databases
> etc...
>
> So I wrote the function below which uses APC (on php) to cache the IP in a
> smart and efficient way.
> This reduced my servers load from average of around 3 with peaks of around
> 16 to Zero (on a server doing ~100 hits/sec )
>
>
> Sample usage: $memcache->addServer(dns_resolve_cached_new("
> ext-memcached.memcached.yourdomain.net"),11211);
>
> Use at your own risk. See attached image for the effect in my case
>
> Enjoy
>
> Nir B
>
>
>
> // dns_resolve_cached_new
>
> // use APC to cache the ip address for servers like mysql and memcache
>
> // Handles multiple ip addresses for the same url (such as in multiple
> mysql slaves case)
>
> // every 10 seconds fetch IP address again and update APC so other threads
> wont fetch also
>
> function dns_resolve_cached_new($url){
> $now=time();
> $prefix='dnscache'; // so new version could work with older one
>
> $ips_array=apc_fetch($prefix.$url); // ips_array[ips][ip_addr]=last
> update; ips_array['checketime']=[timestamp for next check]
>
> if (empty ($ips_array['ips']) || ($now > $ips_array['checktime']) ) { //
> every X seconds fetch ip from DNS
>
> // immediately write to APC so other threads wont fetch IP as well
> $ips_array['checktime']=$now+10; // check again in 10 secs;
> apc_store ($prefix.$url, $ips_array, 1000);
>
> // fetch IP address from DNS
> $ip=gethostbyname($url);
> $ips_array['ips'][$ip]=$now;
>
> // if any of the ip addresses didnt get updated for the last 100 secs
> discard it
> foreach ($ips_array['ips'] as $tmp_ip=>$update_time)
> if (($now-$update_time) > 100 ) unset
> ($ips_array['ips'][$tmp_ip]);
>
> apc_store ($prefix.$url, $ips_array, 1000); // store updated (with
> new refresh timestamp and without discarded ips)
> }
>
> // get random ip if multiple ips for the url (multiple mysql slaves for
> example)
> return array_rand($ips_array['ips']);
> }
>
>
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