The transport channel services manage client connections and I/O
processing for HTTP and JMS requests. These I/O services are based on the
non-blocking I/O (NIO) features that are available in Java. These
services provide a highly scalable foundation to WebSphere Application Server
request processing. Java NIO based architecture has limitations in terms of
performance, scalability and end user usability. Therefore, integration of
true asynchronous I/O is implemented. This implementation provides significant
benefits in usability, reduces the complexity of I/O processing and reduces
that amount of performance tuning you have to perform.
About this task
Key features of the new transport channel services include:
- Scalability, which enables the WebSphere Application Server to handle
many concurrent requests.
- Asynchronous request processing, which provides a many-to-one mapping
of client requests to Web container threads
- Resource sharing and segregation, which enables thread pools to be shared
between the Web container and a messaging service.
- Improved usability and
- Incorporation of autonomic tuning and configuration functions.
Changing the default values for settings on one or more of the transport
channels associated with a transport chain can improve the performance of
that chain.
Figure 1. Transport Channel Service
Procedure
- Adjust TCP transport channel settings. In the
administration console, click Servers > Application servers > server_name >
Ports. Then click View associated transports for the appropriate
port.
- Select the transport chain whose properties you are changing.
- Click on the TCP transport channel defined for that chain.
- Lower the value specified for the Maximum open connections property.
This parameter controls the maximum number of connections that are available
for a server to use. Leaving this parameter at the default value of 20000,
which is the maximum number of connections allowed, might lead to stalled
web sites under failure conditions, because the product continues to accept
connections, thereby increasing the connection, and associated work, backlog.
The default should be changed to a significantly lower number, such as 500,
and then additional tuning and testing should be performed to determine the
optimal value that you should specify for a specific Web site or application
deployment.
- If client connections are being closed without data being written
back to the client, change the value specified for the Inactivity timeout
parameter. This parameter controls the maximum number of connections
available for a server's use. Upon receiving a new connection, the TCP transport
channel waits for enough data to arrive to dispatch the connection to the
protocol specific channels above the TCP transport channel. If not enough
data is received during the time period specified for the Inactivity timeout
parameter, the TCP transport channel closes the connection.
The default
value for this parameter is 60 seconds, which is adequate for most applications.
You should increase the value specified for this parameter if your workload
involves a lot of connections and all of these connections can not be serviced
in 60 seconds.
Assign a thread pool to a specific HTTP
port. Each TCP transport channel is assigned to a particular thread
pool. Thread pools can be shared between one or more TCP transport channels
as well as with other components. The default settings for a TCP transport
channel is to have all HTTP based traffic assigned to the WebContainer thread
pool and all other traffic assigned to the Default thread
pool. Use the Thread pool pull-down to assign a particular thread pool to
each TCP transport channel. The default settings for this parameter has all
HTTP based traffic assigned to the WebContainer thread
pool and all other traffic is assigned to the Default thread
pool. (Thread pool collection describes
how to create additional thread pools.)
Tune the size of your thread pools.
By default, a thread pool can have a minimum of 10 threads and a maximum
of 50 maximum threads. To adjust these values, click on Thread pools > threadpool_name and
adjust the values specified for the Minimum Size and Maximum Size parameters
for that thread pool. Typical applications usually do not need more than
10 threads per processor. One exception is if there is some off server condition,
such as a very slow backend request, that causes a server thread to wait for
the backend request to complete. In such a case, CPU usage is usually low
and increasing the workload does not increase CPU throughput. Thread dumps
show nearly all threads in a call out to the backend resource. If this condition
exists, and the backend is tuned correctly, try increasing the minimum number
of threads in the pooll until you see improvements in throughput and thread
dumps show threads in other areas of the runtime besides the backend call.
The
setting for the Grow as needed parameter should not be changed unless your
backend is prone to hanging for long periods of time. This condition might
indicate that all of your runtime threads are blocked waiting for the backend
instead of processing other work that does not involve the hung backend.
- Adjust HTTP transport channel settings. In the
administration console, click Servers > Application servers > server_name >
Ports. Then click View associated transports for the appropriate
port.
- Select the transport chain whose properties you are changing.
- Click on the HTTP transport channel defined for that chain.
- Tune HTTP keep-alive. The Use persistent (keep-alive)
connections setting controls whether or not connections are left open between
requests. Leaving the connections open can save setup and teardown costs
of sockets if your workload has clients that send multiple requests. The default
value is true and is the optimal setting in most cases.
If your clients
only send single requests over substantially long periods of time, it is probably
better to disable this option and close the connections right away rather
than to have the HTTP transport channel setup the timeouts to close the connection
at some later time.
- Change the value specified for the Maximum persistent requests
parameter to increase the number of requests that can flow over a connection
before it is closed. When the Use persistent connections option
is enabled, the Maximum persistent requests parameter controls the number
of requests that can flow over a connection before it is closed. The default
value is 100. This value should be set to a value such that most, if not
all, clients always have an open connection when they make multiple requests
during the same session. A proper setting for this parameter helps to eliminate
unnecessary setting up and tearing down of sockets.
For test scenarios
in which the client will never close a socket or where sockets are always
proxy or Web servers in front of your application server, a value of -1 will
disable the processing which limits the number of requests over a single connection.
The persistent timeout will still shutdown some idle sockets and protect
your server from running out of open sockets.
- Change the value specified for the Persistent timeout parameter
to increase the length of time that a connection is held open before being
closed due to inactivity. The Persistent timeout parameter controls
the length of time that a connection is held open before being closed because
there is no activity on that connection. The default value is 30 seconds
This parameter should be set to a value that keeps enough connections open
so that most clients can obtain a connection available when they need to make
a request.
- If clients are having trouble completing a request because it
takes them more than 60 seconds to send their data, change the value specified
for the Read timeout parameter. Some clients pause more than 60
seconds while sending data as part of a request. To ensure they are able to
complete their requests, change the value specified for this parameter to
a length of time in seconds that is sufficient for the clients to complete
the transfer of data. Be careful when changing this value that you still protect
the server from clients who send incomplete data and thereby utilize resources
(sockets) for an excessive amount of time.
- If some of your clients require more than 60 seconds to receive
data being written to them, change the value specified for the Write timeout
parameter. Some clients are slow and require more than 60 seconds
to receive data that is sent to them. To ensure they are able to obtain all
of their data, change the value specified for this parameter to a length of
time in seconds that is sufficient for all of the data to be received. Be
careful when changing this value that you still protect the server from malicious
clients.
- Adjust Web container transport channel settings. In
the administration console, click Servers > Application servers > server_name >
Ports. Then click View associated transports for the appropriate
port.
- Select the transport chain whose properties need to be changed.
- Click on the Web container transport channel defined for that
chain.
- If multiple writes are required to handle responses to the client,
change the value specified for the Write buffer size parameter to a value
that is more appropriate for your clients. The Write buffer size
parameter controls the maximum amount of data per thread that the Web container
buffers before sending the request on for processing. The default value is
32768 bytes, which is sufficient for most applications. If the size of a
response is greater than the size of the write buffer, the response is chunked
and written back in multiple TCP writes.
If you need to change the value
specified for this parameter, make sure the new value enables most requests
to be written out in a single write. To determined an appropriate value for
this parameter, look at the size of the pages that are returned and add some
additional bytes to account for the HTTP headers.
- Adjust the settings for the bounded buffer.
Even though the default bounded buffer parameters are optimal for
most of the environments, you might need to change the default values in certain
situations and for some operating systems to enhance performance. Changing
the bounded buffer parameters can degrade performance. Therefore, make sure
that you tune the other related areas, such as the Web container and ORB thread
pools, before deciding to change the bounded buffer parameters.
To change
the bounded buffer parameters:
- In the administrative console, click Servers > Application
Servers > server.
- Under Server Infrastructure, click Java and Process Management
> Process Definition > Java Virtual Machine.
- Specify one of the following parameters in the Generic JVM arguments
field.
- Click Apply or OK.
- Enter one of the following custom properties in the Name field
and an appropriate value in the Value field, and then click Apply to
save the custom property and its setting.
- com.ibm.ws.util.BoundedBuffer.spins_take=value
Specifies the
number of times a Web container thread is allowed to attempt to retrieve a
request from the buffer before the thread is suspended and enqueued. This
parameter enables you to trade off the cost of performing possibly unsuccessful
retrieval attempts, with the cost to suspending a thread and activating it
again in response to a put operation.
Default: |
4 |
Recommended: |
Any non-negative integer value is allowed. In practice an integer
between 2 and 8 have shown the best performance results. |
Usage: |
com.ibm.ws.util.BoundedBuffer.spins_take=6. Six attempts are made
before the thread is suspended. |
- com.ibm.ws.util.BoundedBuffer.yield_take=true or false
Specifies that
a thread yields the CPU to other threads after a set number of attempts to
take a request from the buffer. Typically a lower number of attempts is preferable.
Default: |
false |
Recommended: |
The effect of yield is implementation specific for individual platforms. |
Usage: |
com.ibm.ws.util.BoundedBuffer.spins_take=boolean value |
- com.ibm.ws.util.BoundedBuffer.spins_put=value
Specifies the number
of attempts an InboundReader thread makes to put a request into the buffer
before the thread is suspended and enqueued. This value allows to trade off
between the cost of repeated, possibly unsuccessful, attempts to put a request
into the buffer with the cost to suspend a thread and reactivate it in response
to a take operation.
Default: |
4 |
Recommended: |
Any non-negative integer value is allowed. In practice an integer
between 2 and 8 have shown the best performance results. |
Usage: |
com.ibm.ws.util.BoundedBuffer.spins_put=6. Six attempts are made
before the thread is suspended. |
- com.ibm.ws.util.BoundedBuffer.yield_put=true or false
Specifies that
a thread yields the CPU to other threads after a set number of attempts to
put a request into the buffer. Typically a lower number of attempts is preferable.
Default: |
false |
Recommended: |
The effect of yield is implementation specific for individual platforms. |
Usage: |
com.ibm.ws.util.BoundedBuffer.yield_put=boolean value |
- com.ibm.ws.util.BoundedBuffer.wait=number of milliseconds
Specifies
the maximum length of time, in milliseconds, that a request might unnecessarily
be delayed if the buffer is completely full or if the buffer is empty.
Default: |
10000 milliseconds |
Recommended: |
A value of 10000 milliseconds usually works well. In rare instances
when the buffer becomes either full or empty, a smaller value guarantee a
more timely handling of requests, but there is usually a performance impact
to using a smaller value. |
Usage: |
com.ibm.ws.util.BoundedBuffer.wait=8000. A request might unnecessarily
be delayed up to 8000 milliseconds. |
- Click Apply and then Save to save these changes.