Hard Working DBA

How I collect network statistics during benchmarks.

by the hardworking DBA…

as of 2/17/2013

I am benchmarking an Oracle stored procedure these days. We have a 1 second SLA on this procedure. It returns a rather large payload, sometimes exceeding 10,000 records and 5MB of data. I have challenged the justification for that, and I am reassured that is what the application requires.

I was especially curious how many network packets it takes to move that much data. The ping command told me the average network round-trip speed between the server host and the client host is 0.14s. That might be OK for a small payload, but if it takes 250,000 packets per call, at 0.14ms per packet, that would threaten my SLA.

If I wanted to check the impact of this stored procedure on the network, how could I do that?

Linux has a command, “netstat –s”, that produces the report shown in Listing 1 below. It reports a lot of statistics about network usage. I could run that before and after, and compare the results, right?

The challenge is that the statistics are relative to when the machine last started. I only care about statistics during a short period of time. I cannot easily compare two 10-digit numbers that show total packets received, and tell if the difference is significant. And a lot of the statistics reported don’t change at all. I only care about the measures that changed.

The solution is to

1) take a “netstat –s” snapshot before the benchmark.

2) run the benchmark.

3) take a second “netstat –s” snapshot after the benchmark, and

4) report any differences in a meaningful, human-readable way.

The result is a report such as the one shown in Listing 2. While I was developing the script, I followed the netstat-differential report with some other statistics from sar and a list of the machines connected to my node. Those things have helped me talk to few other issues. It doesn’t hurt to know such things.

The script that produces Listing 2 is shown in Listing 3.

Check it out. Maybe that will give you an idea?

Best wishes to always have good network throughput!

~ the hard-working DBA

Listing 1 – Typical output from the netstat –s command.

> netstat -s

Ip:

1346387939 total packets received

2943839 with invalid addresses

0 forwarded

0 incoming packets discarded

1282689297 incoming packets delivered

3791124361 requests sent out

19013 outgoing packets dropped

6 fragments dropped after timeout

128 reassemblies required

26 packets reassembled ok

6 packet reassembles failed

136 fragments received ok

19012 fragments failed

422 fragments created

Icmp:

74159 ICMP messages received

255 input ICMP message failed.

ICMP input histogram:

destination unreachable: 24427

timeout in transit: 7

echo requests: 3238

echo replies: 46462

timestamp request: 17

address mask request: 8

93967 ICMP messages sent

0 ICMP messages failed

ICMP output histogram:

destination unreachable: 25376

echo request: 65521

echo replies: 3053

timestamp replies: 17

IcmpMsg:

InType0: 46462

InType3: 24427

InType8: 3238

InType11: 7

InType13: 17

InType17: 8

OutType0: 3053

OutType3: 25376

OutType8: 65521

OutType14: 17

Tcp:

18330381 active connections openings

10578845 passive connection openings

31217 failed connection attempts

804128 connection resets received

150 connections established

1104945674 segments received

3666265534 segments send out

2514600 segments retransmited

31 bad segments received.

242582 resets sent

Udp:

122170701 packets received

16624 packets to unknown port received.

0 packet receive errors

122252674 packets sent

TcpExt:

89760 invalid SYN cookies received

2411 resets received for embryonic SYN_RECV sockets

65 packets pruned from receive queue because of socket buffer overrun

211 ICMP packets dropped because they were out-of-window

14535660 TCP sockets finished time wait in fast timer

181501 time wait sockets recycled by time stamp

1370 packets rejects in established connections because of timestamp

126238132 delayed acks sent

43908 delayed acks further delayed because of locked socket

Quick ack mode was activated 1727250 times

372 times the listen queue of a socket overflowed

372 SYNs to LISTEN sockets ignored

521838861 packets directly queued to recvmsg prequeue.

3963876152 packets directly received from backlog

3457491267 packets directly received from prequeue

293190 packets dropped from prequeue

3307290762 packets header predicted

3884415728 packets header predicted and directly queued to user

886041005 acknowledgments not containing data received

1618307249 predicted acknowledgments

1 times recovered from packet loss due to fast retransmit

549898 times recovered from packet loss due to SACK data

3 bad SACKs received

Detected reordering 163 times using FACK

Detected reordering 3012 times using SACK

Detected reordering 613 times using time stamp

616 congestion windows fully recovered

7910 congestion windows partially recovered using Hoe heuristic

TCPDSACKUndo: 459

10024 congestion windows recovered after partial ack

2549350 TCP data loss events

TCPLostRetransmit: 28

1 timeouts after reno fast retransmit

5440 timeouts after SACK recovery

1123 timeouts in loss state

2193866 fast retransmits

93844 forward retransmits

99062 retransmits in slow start

71073 other TCP timeouts

TCPRenoRecoveryFail: 1

12967 sack retransmits failed

265222 times receiver scheduled too late for direct processing

17038 packets collapsed in receive queue due to low socket buffer

1721513 DSACKs sent for old packets

49 DSACKs sent for out of order packets

10316 DSACKs received

550 DSACKs for out of order packets received

29 connections reset due to unexpected SYN

770680 connections reset due to unexpected data

53290 connections reset due to early user close

4355 connections aborted due to timeout

IpExt:

InMcastPkts: 862471

InBcastPkts: 54622317

Listing 2 – An example of the output from the script.

================================================================================

Netstat Differential Report.

Ip:

total packets received: 8210

with invalid addresses: 1

incoming packets delivered: 8173

requests sent out: 8670

Icmp:

Icmp_input:

Icmp_output:

IcmpMsg:

Tcp:

active connections openings: 68

passive connection openings: 31

connection resets received: 2

segments received: 8012

segments send out: 8522

Udp:

packets received: 148

packets sent: 148

TcpExt:

TCP sockets finished time wait in fast timer: 53

delayed acks sent: 211

packets directly queued to recvmsg prequeue.: 4746

packets directly received from prequeue: 2240426

packets header predicted: 1601

packets header predicted and directly queued to user: 4731

acknowledgments not containing data received: 622

predicted acknowledgments: 5877

connections reset due to unexpected data: 2

IpExt:

InBcastPkts: 13

End of Netstat Differential Report.

================================================================================

Recent Network stats reported by SAR.

12:00:01 AM IFACE rxpck/s txpck/s rxbyt/s txbyt/s rxcmp/s txcmp/s rxmcst/s

07:50:01 PM lo 15.97 15.97 49533.85 49533.85 0.00 0.00 0.00

07:50:01 PM eth0 139.20 179.11 90875.86 131371.47 0.00 0.00 0.44

07:50:01 PM eth1 34.23 35.50 6752.12 18519.29 0.00 0.00 0.44

07:50:01 PM eth2 1.75 0.01 159.03 0.65 0.00 0.00 0.44

07:50:01 PM eth3 1.99 0.00 183.95 0.11 0.00 0.00 0.44

07:50:01 PM sit0 0.00 0.00 0.00 0.00 0.00 0.00 0.00

================================================================================

Connections are seen to the following hosts.

g3db2v.sys.cigna.com.

gvoz0858.internal.cigna.com.

localhost.

lsh1010a.sys.cigna.com.

lshnap001a.internal.cigna.com.

lshslx001a.sys.cigna.com.

lshslx002a.sys.cigna.com.

lshslx003a.sys.cigna.com.

lshslx014a.sys.cigna.com.

lshslx015a.sys.cigna.com.

psystcp1.sys.cigna.com.

Listing 3 – Korn-shell script that produces the netstat differential report shown above.

> cat netstat_differential_report.ksh

#!/bin/ksh

# This script simplifies taking a netstat snapshot before a benchmark, taking

# another netstat snapshot after a benchmark, and then reporting a

# comparison of just the network statistics that changed during the benchmark.

# See the show_usage function for more explanation.

# History

# Feb 2013 SWC Wrote it.

#==============================================================================

export NET_FILE_1

export NET_FILE_2

export NET_STRING_FILE

#==============================================================================

show_usage ()

{

cat <<-EOF

Usage:

$0 -n SNAPSHOT_NUMBER [-h|-?]

where

-n enables specification of a snapshot number.

When you say "-n 1", the script will run netstat -s and save the

output for future reference.

When you say "-n 2", the script will run netstat -s, and display a

report of the differences in network statistics since

the first snapshot was saved.

The temporary files used by this script are saved in a subdirectory called logs.

Best wishes.

EOF

exit 1

}

#==============================================================================

# Parse the command line parameters.

if [ $# -eq 0 ]; then

show_usage

while getopts n: option

case $option in

n) SNAPSHOT_NUM=$OPTARG

;;

h) show_usage

;;

\?) show_usage

;;

esac

done

#==============================================================================

if [ "$SNAPSHOT_NUM." = "." ]; then

echo "Error: Please specify which snapshot_number to process."

show_usage

exit 1

DIR=`dirname $0`

cd $DIR

DIR=`pwd`

BASE=`basename $0 .ksh`

if [ ! -d $DIR/logs ]; then

mkdir $DIR/logs

#==============================================================================

# Use this version when the netstat statistic is at the start of the line.

report_netstat_diff_v1 ()

{

S=$1

grep "$S$" $NET_FILE_1 | awk '{print $1}' | read V1

grep "$S$" $NET_FILE_2 | awk '{print $1}' | read V2

let V=V2-V1

if [ $V -ne 0 ]; then

printf "%60.60s: %d\n" "$S" $V

echo $S >> $NET_STRING_FILE

}

#==============================================================================

# Use this version when the netstat statistic follows a colon.

report_netstat_diff_v2 ()

{

S=$1

grep "$S" $NET_FILE_1 | cut -f2 -d':' | read V1

grep "$S" $NET_FILE_2 | cut -f2 -d':' | read V2

let V=V2-V1

if [ $V -ne 0 ]; then

printf "%60.60s: %d\n" "$S" $V

echo $S >> $NET_STRING_FILE

}

#==============================================================================

# Use this version when the netstat statistic is in the middle of the line.

report_netstat_diff_v3 ()

{

S1=$1

FIELD_NUM=$2

S2=$3

grep "$S1" $NET_FILE_1 | grep "$S2" | cut -f$FIELD_NUM -d' ' | read V1

grep "$S1" $NET_FILE_2 | grep "$S2" | cut -f$FIELD_NUM -d' ' | read V2

let V=V2-V1

if [ $V -ne 0 ]; then

printf "%60.60s _ %s: %d\n" "$S1" "$S2" $V

echo $S >> $NET_STRING_FILE

}

#==============================================================================

if [ $SNAPSHOT_NUM -eq 1 ]; then

rm -f $DIR/logs/netstat.*

NET_FILE=$DIR/logs/netstat.1.log

netstat -s > $NET_FILE

if [ ! -f $NET_FILE ]; then

print "Error: Failed to save snapshot 1."

exit 1

print "`date`: Saved netstat snapshot number 1."

elif [ $SNAPSHOT_NUM -eq 2 ]; then

NET_FILE=$DIR/logs/netstat.2.log

netstat -s > $NET_FILE

print "`date`: Saved netstat snapshot number 2."

# Separate the file contents by section

for N in 1 2; do

cat $DIR/logs/netstat.$N.log |

while read LINE; do

if [ "$LINE" = "Ip:" ]; then

OUT_FILE=$DIR/logs/netstat.Ip.$N

elif [ "$LINE" = "Icmp:" ]; then

OUT_FILE=$DIR/logs/netstat.Icmp.$N

elif [ "$LINE" = "ICMP input histogram:" ]; then

OUT_FILE=$DIR/logs/netstat.Icmp_input.$N

elif [ "$LINE" = "ICMP output histogram:" ]; then

OUT_FILE=$DIR/logs/netstat.Icmp_output.$N

elif [ `echo "$LINE" | grep -c "ICMP messages sent"` -gt 0 ]; then

# Continue putting lines back in the regular Icmp file

OUT_FILE=$DIR/logs/netstat.Icmp.$N

elif [ "$LINE" = "IcmpMsg:" ]; then

OUT_FILE=$DIR/logs/netstat.IcmpMsg.$N

elif [ "$LINE" = "Tcp:" ]; then

OUT_FILE=$DIR/logs/netstat.Tcp.$N

elif [ "$LINE" = "Udp:" ]; then

OUT_FILE=$DIR/logs/netstat.Udp.$N

elif [ "$LINE" = "TcpExt:" ]; then

OUT_FILE=$DIR/logs/netstat.TcpExt.$N

elif [ "$LINE" = "IpExt:" ]; then

OUT_FILE=$DIR/logs/netstat.IpExt.$N

echo $LINE >> $OUT_FILE

done

printf "%80s\n" " " | tr ' ' '='

print "Netstat Differential Report."

# Now compare the different sections one at a time.

for TYPE in Ip Icmp Icmp_input Icmp_output IcmpMsg Tcp Udp TcpExt IpExt; do

NET_FILE_1=$DIR/logs/netstat.$TYPE.1

NET_FILE_2=$DIR/logs/netstat.$TYPE.2

NET_STRING_FILE=$DIR/logs/netstat.strings.txt

rm -f $NET_STRING_FILE

touch $NET_STRING_FILE

print "$TYPE:"

case $TYPE in

Ip)

report_netstat_diff_v1 'total packets received'

report_netstat_diff_v1 'with invalid addresses'

report_netstat_diff_v1 'forwarded'

report_netstat_diff_v1 'incoming packets discarded'

report_netstat_diff_v1 'incoming packets delivered'

report_netstat_diff_v1 'requests sent out'

report_netstat_diff_v1 'outgoing packets dropped'

report_netstat_diff_v1 'fragments dropped after timeout'

report_netstat_diff_v1 'reassemblies required'

report_netstat_diff_v1 'packets reassembled ok'

report_netstat_diff_v1 'packet reassembles failed'

report_netstat_diff_v1 'fragments received ok'

report_netstat_diff_v1 'fragments failed'

report_netstat_diff_v1 'fragments created'

;;

Icmp)

report_netstat_diff_v1 'ICMP messages received'

report_netstat_diff_v1 'input ICMP message failed.'

report_netstat_diff_v1 'ICMP messages sent'

report_netstat_diff_v1 'ICMP messages failed'

;;

Icmp_input)

report_netstat_diff_v2 'destination unreachable'

report_netstat_diff_v2 'timeout in transit'

report_netstat_diff_v2 'echo requests'

report_netstat_diff_v2 'echo replies'

report_netstat_diff_v2 'timestamp request'

report_netstat_diff_v2 'address mask request'

;;

Icmp_output)

report_netstat_diff_v2 'destination unreachable'

report_netstat_diff_v2 'echo request'

report_netstat_diff_v2 'echo replies'

report_netstat_diff_v2 'timestamp replies'

;;

IcmpMsg)

report_netstat_diff_v2 'InType0'

report_netstat_diff_v2 'InType3'

report_netstat_diff_v2 'InType8'

report_netstat_diff_v2 'InType11'

report_netstat_diff_v2 'InType13'

report_netstat_diff_v2 'InType17'

report_netstat_diff_v2 'OutType3'

report_netstat_diff_v2 'OutType8'

report_netstat_diff_v2 'OutType14'

;;

Tcp)

report_netstat_diff_v1 'active connections openings'

report_netstat_diff_v1 'passive connection openings'

report_netstat_diff_v1 'failed connection attempts'

report_netstat_diff_v1 'connection resets received'

report_netstat_diff_v1 'connections established'

report_netstat_diff_v1 'segments received'

report_netstat_diff_v1 'segments send out'

report_netstat_diff_v1 'segments retransmited'

report_netstat_diff_v1 'bad segments received.'

report_netstat_diff_v1 'resets sent'

;;

Udp)

report_netstat_diff_v1 'packets received'

report_netstat_diff_v1 'packets sent'

report_netstat_diff_v1 'packet receive errors'

report_netstat_diff_v1 'packets to unknown port received.'

;;

TcpExt)

report_netstat_diff_v1 'invalid SYN cookies received'

report_netstat_diff_v1 'resets received for embryonic SYN_RECV sockets'

report_netstat_diff_v1 'packets pruned from receive queue because of socket buffer overrun'

report_netstat_diff_v1 'ICMP packets dropped because they were out-of-window'

report_netstat_diff_v1 'TCP sockets finished time wait in fast timer'

report_netstat_diff_v1 'time wait sockets recycled by time stamp'

report_netstat_diff_v1 'packets rejects in established connections because of timestamp'

report_netstat_diff_v1 'delayed acks sent'

report_netstat_diff_v1 'delayed acks further delayed because of locked socket'

report_netstat_diff_v3 'Quick ack mode was activated' 6 'times'

report_netstat_diff_v1 'times the listen queue of a socket overflowed'

report_netstat_diff_v1 'SYNs to LISTEN sockets ignored'

report_netstat_diff_v1 'packets directly queued to recvmsg prequeue.'

report_netstat_diff_v1 'packets directly received from backlog'

report_netstat_diff_v1 'packets directly received from prequeue'

report_netstat_diff_v1 'packets dropped from prequeue'

report_netstat_diff_v1 'packets header predicted'

report_netstat_diff_v1 'packets header predicted and directly queued to user'

report_netstat_diff_v1 'acknowledgments not containing data received'

report_netstat_diff_v1 'predicted acknowledgments'

report_netstat_diff_v1 'times recovered from packet loss due to fast retransmit'

report_netstat_diff_v1 'times recovered from packet loss due to SACK data'

report_netstat_diff_v1 'bad SACKs received'

report_netstat_diff_v3 'Detected reordering' 3 'times using FACK'

report_netstat_diff_v3 'Detected reordering' 3 'times using SACK'

report_netstat_diff_v3 'Detected reordering' 3 'times using time stamp'

report_netstat_diff_v1 'congestion windows fully recovered'

report_netstat_diff_v1 'congestion windows partially recovered using Hoe heuristic'

report_netstat_diff_v2 'TCPDSACKUndo'

report_netstat_diff_v1 'congestion windows recovered after partial ack'

report_netstat_diff_v1 'TCP data loss events'

report_netstat_diff_v2 'TCPLostRetransmit'

report_netstat_diff_v1 'timeouts after reno fast retransmit'

report_netstat_diff_v1 'timeouts after SACK recovery'

report_netstat_diff_v1 'timeouts in loss state'

report_netstat_diff_v1 'fast retransmits'

report_netstat_diff_v1 'forward retransmits'

report_netstat_diff_v1 'retransmits in slow start'

report_netstat_diff_v1 'other TCP timeouts'

report_netstat_diff_v2 'TCPRenoRecoveryFail'

report_netstat_diff_v1 'sack retransmits failed'

report_netstat_diff_v1 'times receiver scheduled too late for direct processing'

report_netstat_diff_v1 'packets collapsed in receive queue due to low socket buffer'

report_netstat_diff_v1 'DSACKs sent for old packets'

report_netstat_diff_v1 'connections reset due to unexpected SYN'

report_netstat_diff_v1 'connections reset due to unexpected data'

report_netstat_diff_v1 'connections reset due to early user close'

report_netstat_diff_v1 'connections aborted due to timeout'

;;

IpExt)

report_netstat_diff_v2 'InMcastPkts'

report_netstat_diff_v2 'InBcastPkts'

;;

esac

# Show any strings that might have been missed in the case-statement above.

diff $NET_FILE_1 $NET_FILE_2 |

grep -v '\-\-\-' |

grep -v '[0-9],[0-9]' |

grep -v '[0-9]c[0-9]' |

grep -v -f $NET_STRING_FILE

done

print "End of Netstat Differential Report."

printf "%80s\n" " " | tr ' ' '='

print "Recent Network stats reported by SAR."

sar -n DEV | grep IFACE | head -1

sar -n DEV | grep -v Average | tail -6

printf "%80s\n" " " | tr ' ' '='

print "Connections are seen to the following hosts."

IP_FILE=$DIR/logs/$$.ip

netstat -nat | awk '{ print $5}' | cut -d: -f1 | sed -e '/^$/d' | sort -u > $IP_FILE

NS_FILE=$DIR/logs/$$.ns

grep '\.' $IP_FILE |

while read IP; do

nslookup $IP 2>&1 | grep name | cut -f2 -d'=' >> $NS_FILE

done

sort -u $NS_FILE

# Cleanup

rm $NS_FILE

rm $IP_FILE

rm $DIR/logs/netstat.*

…End of another blog by the hardworking DBA!

Sunday, February 17, 2013

How I collect network statistics during benchmarks.