Performance Tuning WebWizard

Expanation of Network

Networks are complex beyond the scope of this page really. Running a network take CPU in kernel mode (running the device drivers) and memory (some where to land the data as it arrives). Performance problems in networks can show up in very strange ways in you application - temporary glitches, lockups or just low throughput.

For real network problems you will need hardware/software tools to analyse the problem in detail.

These tuning tips shoudl let you see when you a pushing a good network to hard.

Network Bottleneck ???

Criteria: The network is transfering too much data or too many packets

lo looback not used!
en Ethernet 1Mbyte per second 256 packets per second
tr Token Ring 1.5 Mbytes per second 500 packets per second
cs SP Switch 500Mbytes per second 1000 packets per second
While monitoring processes do not worry about small 1 to 3 seconds bursts.

Network monitor Statistics

The Network usage is on the Network Screen of nmon.
The statisics break what the processes is doing into types

Read and Write kB/s K bytes per second This is the network transfer rate and how busy the network is. Check its in the direction you expect.
Packin and Packout number of packets This can tell you how much CPU will be used. Each packet will require the attension of the device driver.
insize and outsize The size of the packets (on average) This tells you what is being sent. Telnet uses very small packets 80 bytes -some only 1 byte of data. RDBMS uses middle size packets (SQL and answer rows). FTP uses bigger packets.

Notes:

Loopback - only used to talk to yourself - like telnet to your own host. If this is a problem do not do it!!
Push your network too hard really hurts - packets get dropped (lack of memory to save them) and collide (need resending) this adds yet more work to do.
MOnitor the NFS work load too as that might be the real network user.

What can you do to tune the Network?

Is the network load as expected? i.e. read/write ratio look right.
Check your network routes are as expected.
Try pinging if you think the network is slow.
Check someone is not FTPing large volumes of data - see process tuning.
Reduce the priority of network hungry transfers, if you can.
Run FTP at other times - night time!
Check that no one is running pointless processes - like programs that loop polling for information.
Check for process that continually output data to a users screen - even when they are not there (like "netscape" and "nmon"!!).
Check for hacker attacks and programs searching through the entire filesystem tree over NFS mounts like "find" as these take a lot of network.
Remember writing NFS files take four times the CPU of reading over NFS.
For the SP Switch check those network parameters and remember to set all the nodes to the same value.

lo	looback	not used!
en	Ethernet	1Mbyte per second	256 packets per second
tr	Token Ring	1.5 Mbytes per second	500 packets per second
cs	SP Switch	500Mbytes per second	1000 packets per second

Read and Write kB/s	K bytes per second	This is the network transfer rate and how busy the network is. Check its in the direction you expect.
Packin and Packout	number of packets	This can tell you how much CPU will be used. Each packet will require the attension of the device driver.
insize and outsize	The size of the packets (on average)	This tells you what is being sent. Telnet uses very small packets 80 bytes -some only 1 byte of data. RDBMS uses middle size packets (SQL and answer rows). FTP uses bigger packets.