WebSphere® Application
Server uses the TCP/IP sockets communication mechanism extensively.
For a TCP/IP socket connection, the send and receive buffer sizes
define the receive window. The receive window specifies the amount
of data that can be sent and not received before the send is interrupted.
If too much data is sent, it overruns the buffer and interrupts the
transfer. The mechanism that controls data transfer interruptions
is referred to as flow control. If the receive window size for TCP/IP
buffers is too small, the receive window buffer is frequently overrun,
and the flow control mechanism stops the data transfer until the receive
buffer is empty.
About this task
TCP/IP can be the source of some significant remote
method delays.
To change the system wide
value, perform the following steps:
Procedure
Tune the TCP/IP buffer sizes.
- First, ensure that you have defined enough sockets to
your system and that the default socket time-out of 180 seconds is
not too high. To allow enough sockets, update the BPXPRMxx parmlib
member:
- Set MAXSOCKETS for the AF_INET filesystem high enough.
- Set MAXFILEPROC high enough.
We recommend setting MAXSOCKETS and MAXFILEPROC to at least
5000 for low-throughput, 10000 for medium-throughput, and 35000 for
high-throughput WebSphere transaction
environments. Setting high values for these parameters should not
cause excessive use of resources unless the sockets or files are actually
allocated.
Example:
/* Open/MVS Parmlib Member */
/* CHANGE HISTORY: */
/* 01/31/02 AEK Increased MAXSOCKETS on AF_UNIX from 10000 to 50000*/
/* per request from My Developer */
/* 10/02/01 JAB Set up shared HFS */
/* KERNEL RESOURCES DEFAULT MIN MAX */
/* ======================== =================== === =========== */
.
.
MAXFILEPROC(65535) /* 64 3 65535 */
.
.
NETWORK DOMAINNAME(AF_INET) DOMAINNUMBER(2) MAXSOCKETS(30000)
.
- Next check the specification of the port in TCPIP profile
dataset to ensure that NODELAYACKS is
specified as follows:
PORT 8082 TCP NODELAYACKS
In your runs, changing this could improve throughput by as
much as 50% (this is particularly useful when dealing with trivial
workloads). This setting is important for good performance when running
SSL.
- You should ensure that your DNS configuration is optimized
so that lookups for frequently-used servers and clients are being
cached.
Caching is sometimes related to the name server's
Time To Live (TTL) value. On the one hand, setting the TTL high will
ensure good cache hits. However, setting it high also means that,
if the Daemon goes down, it will take a while for everyone in the
network to be aware of it.
A good way to verify that your DNS
configuration is optimized is to issue the oping and onslookup USS
commands. Make sure they respond in a reasonable amount of time. Often
a misconfigured DNS or DNS server name will cause delays of 10 seconds
or more.
- Increase the size of the TCPIP send and receive buffers
from the default of 16K to at least 64K. This is the size of the buffers
including control information beyond what is present in the data that
you are sending in your application. To do this specify the following:
TCPCONFIG TCPSENDBFRSIZE 65535
TCPRCVBUFRSIZE 65535
Note: It is unreasonable, in some cases, to specify
256 KB buffers.
- Increase the default listen backlog. This is used to
buffer spikes in new connections which come with a protocol like HTTP.
The default listen backlog is 10 requests. We recommend that you increase
this value to something larger. For example:
protocol_http_backlog=100
protocol_https_backlog=100
protocol_iiop_backlog=100
protocol_ssl_backlog=100
- Reduce the finwait2 time. In the most demanding
benchmarks you may find that even defining 65K sockets and file descriptors
does not give you enough 'free' sockets to run 100%. When a socket
is closed abnormally (for example, no longer needed) it is not made
available immediately. Instead it is placed into a state called finwait2
(this is what shows up in the netstat -s command). It waits there
for a period of time before it is made available in the free pool.
The default for this is 600 seconds.
Note: Unless you
have trouble using up sockets, we recommend that you leave this set
to the default value.
If you are using z/OS® V1.2 or above, you can control the amount
of time the socket stays in finwait2 state by specifying the following
in the configuration file:
FINWAIT2TIME 60
Results
Repeat this
process until you determine the ideal buffer size.
What to do next
The TCP/IP
buffer sizes are changed. Repeat this process until you determine
the ideal buffer size.