Interesting (mysql?) problem 2006-02-15 - By Tom Sightler
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On Wed, 2006-02-15 at 20:56 -0500, Ken Snider wrote:
> However, for some reason, with mysql is under load, interactive response on
> that server becomes "choppy", that is, pauses of a few seconds here and
> there can be seen in connections. Also, a connection to the mysql server is
> usually subsecond, however every 5-10 seconds connections will take 3-4
> seconds to establish, for no reason I can make out.
>
> In short, this box is bored - it's doing nearly nothing and I cannot find a
> resource contention issue of any sort - yet it would appear that, for
> whatever reason, delays keep popping up on connect. I'm beginning to think
> I'm hitting a TCP stack limitation of some sort. Any ideas?
Well, at first glance it doesn't seem like 100-150 connections a second
would be enough to cause problems, however, when thinking about this I
wonder if it is possible that you are seeing some performance issues
because of sockets in time wait state. Running 'netstat -an' should
show this easily.
If that is the case then you might want to By default the local port
range is set for 32768-61000. That's a lot of ports and the default
time wait is 60 seconds, however, I've seen performance issues once
there are more the 1000 sockets in time wait which you could easily be
seeing. You might try setting tcp_fin_timeout to something lower, like
15 seconds, and potentially increase the port range by setting
ip_local_port_range.
Of course, that's assuming it really is a tcp problem which is at this
moment unproven, however, it shouldn't be difficult to tell by watching
netstat output.
Later,
Tom
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