On 07/03/2013 10:25 AM, Pat Erler wrote:
hi,
we see in our new relic console from time to time periods, where there
is a delay from the request to pound until the answer is served from the
(IIS) webserver (between 3 and 7 seconds).
a pound restart solves this.
we suspect it happened the first time after we installed 2.7b (because
it supports the neccessary security mechanisms for the PCI security
test). the machine itself is not the problem, RAM/Disk/CPU/network usage
is in the single digits to max 20%. all this in ubuntu 64bit.
what could we check if this happens next time?
You might see if the delays correlate with TCP retransmissions recorded
on the client or pound server or connection request drops on the
back-end web server. Three and 7 seconds happen to be along the
cumulative timeline for a contemporary Linux TCP's sequence of initial
retransmissions:
Timeout values for successive retransmissions:
1, 2, 4
Cumulative time:
1, 3, 7
If you client kernel is older though, the RTO sequence would be
3, 6, 12 with a cumulative of 3, 9, 17
When this is happening, you might try taking a packet trace on the
client or the pound server to be able to look at the TCP packets directly.
Here is what a sequence of TCP connection establishment packet (aka TCP
SYNchronize segment) retransmissions looks like in tcpdump output. The
'S' is what identifies it as a SYN segment. The "EW" you see there is
simply my system having TCP's use of Explicit Congestion Notification
enabled:
root@tardy:~# tcpdump -i eth0 host 1.2.3.4
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
15:10:12.536666 IP tardy.50331 > testname.telnet: Flags [SEW], seq
1436714364, win 14600, options [mss 1460,sackOK,TS val 133075933 ecr
0,nop,wscale 7], length 0
15:10:13.534479 IP tardy.50331 > testname.telnet: Flags [SEW], seq
1436714364, win 14600, options [mss 1460,sackOK,TS val 133076183 ecr
0,nop,wscale 7], length 0
15:10:15.538480 IP tardy.50331 > testname.telnet: Flags [SEW], seq
1436714364, win 14600, options [mss 1460,sackOK,TS val 133076684 ecr
0,nop,wscale 7], length 0
15:10:19.546456 IP tardy.50331 > testname.telnet: Flags [SEW], seq
1436714364, win 14600, options [mss 1460,sackOK,TS val 133077686 ecr
0,nop,wscale 7], length 0
15:10:27.554480 IP tardy.50331 > testname.telnet: Flags [SEW], seq
1436714364, win 14600, options [mss 1460,sackOK,TS val 133079688 ecr
0,nop,wscale 7], length 0
rick jones
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