Re: dnscache performance still applicable today?

James Sutherland wrote:
> On 24 May 2009, at 14:50, Rihad wrote:
> 
>> Why I asked: dnscache's log file has stats lines like:
>> 2009-05-24 18:42:48.254665500 stats 2098047 158736598 190 0
>>
>> According to dnscache log file description at 
>> http://www.dqd.com/~mayoff/notes/djbdns/dnscache-log.html#stats
>> the third number after stats (190) means:
>>
>> udp-active      The number of queries that dnscache has received via 
>> UDP but not yet responded to or dropped.
>>
>> Am I right in assuming that dnscache's single thread of execution 
>> becomes its main bottleneck, so it has to delay query execution while 
>> processing current requests?
>>
>> Probably when dnscache was written the load on the Internet was 
>> lighter, and SMP computers were rare, unlike today. Any advancements 
>> in this area?
> 
> No, this just means you have 190 queries currently waiting for something 
> to happen - presumably awaiting replies from remote DNS servers.
 > [...]
 > It certainly does handle multiple concurrent
> requests - indeed, at the moment that log entry was written, it was in 
> the process of handling 190 of them simultaneously!
OK, thanks to you and those who also gave the same explanation. Having 
read the logfile format explanation I thought dnscache hadn't had a 
chance to even start processing those 190 requests yet, and I wasn't 
aware it used async i/o, and in reality that number stood for the number 
of current request being handled.


> As another message 
> says, your 6% CPU usage is probably 6% of a single core, rather than 6% 
> of the total CPU capacity of the system.
> 
Yup. Late in the night I confused per process CPU load with top's 
overall load line at the top. There, if a task on a two quad-core box 
used 100% cpu, top would displays ~86% idle. But I wasn't expecting 
single core cpu load to be the problem anyway, because even 50% would be 
far from being overloaded.