Initial request to server extremely slow after longer periods of inactivity

[Raimund Sacherer]

----- Original Message ----- 

> From: opendaddy at hushmail.com
> To: "Raimund Sacherer" <rs at logitravel.com>
> Cc: freebsd-questions at freebsd.org
> Sent: Saturday, April 11, 2015 5:19:45 PM
> Subject: Re: Initial request to server extremely slow after longer periods of
> inactivity

> Hello,

> On 10. april 2015 at 9:01 AM, "Raimund Sacherer" <rs at logitravel.com> wrote:
> >
> >Then what I would do in your case is open a few ssh sessions, run
> >top with cpu focus in one, top with IO focus in another and in a
> >third i would take a tcpdump written to a file. Maybe another
> >session with vmstat to check on pagin/pageout, etc.
> >
> >Then I'd wait the appropriate amount of time and try a web
> >connection, if it takes long, I'l check the top's if there is
> >something going on (lot's of CPU, lot's of IO, pages etc.) and
> >check the tcpdump in wireshark to see if there are problematic DNS
> >queries which maybe are timing out, etc.

> Wouldn't SSH sessions act as "continuous feedback loops" preventing the
> server from going unresponsive in the first place?

Yes, that could be, but you would be able to rule it out rather quickly, if you do not seem to get the system in the "unresponsive" state then I would execute them in a screen or tmux session so they are available for you to check out later. In this case a top won't do you much good and you have to use some form of vmstat or similar to check out what had happened (cpu, paging, interrupt storm, context switches, IO-wait, etc.). If none of those indicates problems, and the tcpdump does not reveal DNS problems it may be an issue with the VPS host (if you use a virtually shared hosted service). 

Best
Ray

> Also, how can I do stuff like `traceroute` or `mtr` knowing beforehand that
> the server is indeed unresponsive? Since it's only unresponsive on first
> requests, if I send a request to check, things will have returned to normal
> by the time I get to run those commands.

> Thanks!

> O.D.

-- 

-- 

Raimund Sacherer 
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