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From Ed Korthof>
Subject Re: Patch to slow down children's deaths
Date Wed, 08 Jan 1997 00:19:27 GMT
On Tue, 7 Jan 1997, Cliff Skolnick wrote:
> On Tue, 7 Jan 1997, Ed Korthof wrote:
> I think apache should print a warning, since these values conflict with
> each other in a logic sense to me and aparently apache does not like it
> either. 

Yeah -- if we don't do a patch of some sort, I'd also like to see a
warning about this.
> Also can someone explain why a large start servers is better than letting
> apache start more as the load rises?  I would think you simply trade off a
> few seconds of unavaliablity at startup for a slightly higher latency on
> http requests untila steady state is reached. 

Well, here's my reasoning.  Apache isn't designed to deal with a rapidly
increasing load, but that is exactly the conditions a server experiences
at start up time.  With a large server, load will rise extremely fast
until there are sufficiently many servers in existence; if the server has
a reasonably fast CPU, it could have easily forked the extra children
(which doesn't take all that long) at start up time, but since it's
finished the start up procedure, the 1 fork per second limitation will
slow things down significantly. If there aren't enough servers, then
additional requests are simply delayed until more are created. 

The server I help administer is fairly large; after a restart, when I
attempt to load a page -- any page -- there is a delay of at least 10-15
seconds.  Clearly not everyone will experience that (after restarting, it
takes about 5 seconds to request the page), but I'm confident that the
average delay is 5 seconds or more during the 30 seconds starting about 3
seconds after server restart.  I'm afraid I don't have any hard data,
however, other than my observation that the servers increase at one per
second for more than a minute.  I'm inclined to try avoid these delays
wherever possible.

I do know that we reach equilibrium at more than 256 servers (mostly
Keep-Alives, but we get more than 20 hits per second). 

Anyway, on a dedicated server, MaxSpareServers can be made high to
compensate, but then what's the point of having StartServers at all?

> --
> Cliff Skolnick, Technical Consultant
> Steam Tunnel Operations
>, 415.297.5938

     -- Ed Korthof        |  Web Server Engineer --
     --    |  Organic Online, Inc --
     -- (415) 278-5676    |  Fax: (415) 284-6891 --

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