Linux udp buffer size

This section provides recommendations for optimal performance scaling server for the following server subsystems:

Processors

The GlassFish Server automatically takes advantage of multiple CPUs. In general, the effectiveness of multiple CPUs varies with the operating system and the workload, but more processors will generally improve dynamic content performance.

Static content involves mostly input/output (I/O) rather than CPU activity. If the server is tuned properly, increasing primary memory will increase its content caching and thus increase the relative amount of time it spends in I/O versus CPU activity. Studies have shown that doubling the number of CPUs increases servlet performance by 50 to 80 percent.

Memory

See the section Hardware and Software Requirements in the GlassFish Server Release Notes for specific memory recommendations for each supported operating system.

Disk Space

It is best to have enough disk space for the OS, document tree, and log files. In most cases 2GB total is sufficient.

Put the OS, swap/paging file, GlassFish Server logs, and document tree each on separate hard drives. This way, if the log files fill up the log drive, the OS does not suffer. Also, its easy to tell if the OS paging file is causing drive activity, for example.

OS vendors generally provide specific recommendations for how much swap or paging space to allocate. Based on Oracle testing, GlassFish Server performs best with swap space equal to RAM, plus enough to map the document tree.

Networking

To determine the bandwidth the application needs, determine the following values:

The number of peak concurrent users (N_peak) the server needs to handle.

The average request size on your site, r. The average request can include multiple documents. When in doubt, use the home page and all its associated files and graphics.

Decide how long, t, the average user will be willing to wait for a document at peak utilization.

Then, the bandwidth required is:

For example, to support a peak of 50 users with an average document size of 24 Kbytes, and transferring each document in an average of 5 seconds, requires 240 Kbytes (1920 Kbit/s). So the site needs two T1 lines (each 1544 Kbit/s). This bandwidth also allows some overhead for growth.

The server’s network interface card must support more than the WAN to which it is connected. For example, if you have up to three T1 lines, you can get by with a 10BaseT interface. Up to a T3 line (45 Mbit/s), you can use 100BaseT. But if you have more than 50 Mbit/s of WAN bandwidth, consider configuring multiple 100BaseT interfaces, or look at Gigabit Ethernet technology.

UDP Buffer Sizes

GlassFish Server uses User Datagram Protocol (UDP) for the transmission of multicast messages to GlassFish Server instances in a cluster. For peak performance from a GlassFish Server cluster that uses UDP multicast, limit the need to retransmit UDP messages. To limit the need to retransmit UDP messages, set the size of the UDP buffer to avoid excessive UDP datagram loss.

To Determine an Optimal UDP Buffer Size

The size of UDP buffer that is required to prevent excessive UDP datagram loss depends on many factors, such as:

The number of instances in the cluster

The number of instances on each host

The number of processors

The amount of memory

The speed of the hard disk for virtual memory

If only one instance is running on each host in your cluster, the default UDP buffer size should suffice. If several instances are running on each host, determine whether the UDP buffer is large enough by testing for the loss of UDP packets.

Note — On Linux systems, the default UDP buffer size might be insufficient even if only one instance is running on each host. In this situation, set the UDP buffer size as explained in To Set the UDP Buffer Size on Linux Systems.

Ensure that no GlassFish Server clusters are running.

Determine the absolute number of lost UDP packets when no clusters are running.

How you determine the number of lost packets depends on the operating system. For example:

On Linux systems, use the netstat -su command and look for the packet receive errors count in the Udp section.

On AIX systems, use the netstat -s command and look for the fragments dropped (dup or out of space) count in the ip section.

Start all the clusters that are configured for your installation of GlassFish Server.

Determine the absolute number of lost UDP packets after the clusters are started.

If the difference in the number of lost packets is significant, increase the size of the UDP buffer.

To Set the UDP Buffer Size on Linux Systems

On Linux systems, a default UDP buffer size is set for the client, but not for the server. Therefore, on Linux systems, the UDP buffer size might have to be increased. Setting the UDP buffer size involves setting the following kernel parameters:

Set the kernel parameters in the /etc/sysctl.conf file or at runtime.

If you set the parameters in the /etc/sysctl.conf file, the settings are preserved when the system is rebooted. If you set the parameters at runtime, the settings are not preserved when the system is rebooted.

To set the parameters in the /etc/sysctl.conf file, add or edit the following lines in the file:
To set the parameters at runtime, use the sysctl(8) command.

Example 5-1 Setting the UDP Buffer Size in the /etc/sysctl.conf File

This example shows the lines in the /etc/sysctl.conf file for setting the kernel parameters for controlling the UDP buffer size to 524288.

Example 5-2 Setting the UDP Buffer Size at Runtime

This example sets the kernel parameters for controlling the UDP buffer size to 524288 at runtime.

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5 Tuning the Operating System and Platform

This chapter discusses tuning the operating system (OS) for optimum performance. It discusses the following topics:

Server Scaling

This section provides recommendations for optimal performance scaling server for the following server subsystems:

Processors

Memory

See the section Hardware and Software Requirements in the GlassFish Server Release Notes for specific memory recommendations for each supported operating system.

Disk Space

It is best to have enough disk space for the OS, document tree, and log files. In most cases 2GB total is sufficient.

Networking

To determine the bandwidth the application needs, determine the following values:

The number of peak concurrent users ( N _peak) the server needs to handle.

The average request size on your site, r . The average request can include multiple documents. When in doubt, use the home page and all its associated files and graphics.

Decide how long, t , the average user will be willing to wait for a document at peak utilization.

Then, the bandwidth required is:

UDP Buffer Sizes

To Determine an Optimal UDP Buffer Size

The size of UDP buffer that is required to prevent excessive UDP datagram loss depends on many factors, such as:

The number of instances in the cluster

The number of instances on each host

The number of processors

The amount of memory

The speed of the hard disk for virtual memory

On Linux systems, the default UDP buffer size might be insufficient even if only one instance is running on each host. In this situation, set the UDP buffer size as explained in To Set the UDP Buffer Size on Linux Systems.

Ensure that no GlassFish Server clusters are running.

If necessary, stop any running clusters as explained in «To Stop a Cluster» in Oracle GlassFish Server High Availability Administration Guide .

Determine the absolute number of lost UDP packets when no clusters are running.

How you determine the number of lost packets depends on the operating system. For example:

On Linux systems, use the netstat -su command and look for the packet receive errors count in the Udp section.

On AIX systems, use the netstat -s command and look for the fragments dropped (dup or out of space) count in the ip section.

Start all the clusters that are configured for your installation of GlassFish Server.

Start each cluster as explained in «To Start a Cluster» in Oracle GlassFish Server High Availability Administration Guide .

Determine the absolute number of lost UDP packets after the clusters are started.

If the difference in the number of lost packets is significant, increase the size of the UDP buffer.

To Set the UDP Buffer Size on Linux Systems

Set the kernel parameters in the /etc/sysctl.conf file or at runtime.

If you set the parameters in the /etc/sysctl.conf file, the settings are preserved when the system is rebooted. If you set the parameters at runtime, the settings are not preserved when the system is rebooted.

To set the parameters in the /etc/sysctl.conf file, add or edit the following lines in the file:

To set the parameters at runtime, use the sysctl command.

Example 5-1 Setting the UDP Buffer Size in the /etc/sysctl.conf File

This example shows the lines in the /etc/sysctl.conf file for setting the kernel parameters for controlling the UDP buffer size to 524288.

Example 5-2 Setting the UDP Buffer Size at Runtime

This example sets the kernel parameters for controlling the UDP buffer size to 524288 at runtime.

Solaris 10 Platform-Specific Tuning Information

Solaris Dynamic Tracing (DTrace) is a comprehensive dynamic tracing framework for the Solaris Operating System (OS). You can use the DTrace Toolkit to monitor the system. The DTrace Toolkit is available through the OpenSolaris project from the DTraceToolkit page.

Tuning for the Solaris OS

Tuning Parameters

Tuning Solaris TCP/IP settings benefits programs that open and close many sockets. Since the GlassFish Server operates with a small fixed set of connections, the performance gain might not be significant.

The following table shows Solaris tuning parameters that affect performance and scalability benchmarking. These values are examples of how to tune your system for best performance.

Table 5-1 Tuning Parameters for Solaris

Limit of process open file descriptors. Set to account for expected load (for associated sockets, files, and pipes if any).

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How do I increase the UDP receive buffer size?

I have a computer that communicates with a camera via UDP connected with a physical cable (no router or switch). The camera acts as the UDP server with the computer as client. Once in a while my Java APP hangs while an image is being transferred, line by line. My Java software waits for a line of the image that is never received and I believe this could be caused by receive buffer overflow.

I’ve tried to increase the receive buffer maximum size in /etc/sysctl.conf :

My program requests 7000000 bytes but at runtime reports that it received only 212992 bytes.

When I try to ask the OS the min, default, and maximum size:

How do I get a larger buffer? Is sysctl even being read?

2 Answers 2

This sets the max OS receive buffer size for all types of connections.

Resolving Slow UDP Traffic

If your server does not seem to be able to receive UDP traffic as fast as it can receive TCP traffic, it could be because Linux, by default, does not set the network stack buffers as large as they need to be to support high UDP transfer rates. One way to alleviate this problem is to allow more memory to be used by the IP stack to store incoming data. For instance, use the commands:

to increase the read buffer memory max and default to 262143 (256k — 1) from defaults of max=131071 (128k — 1) and default=65535 (64k — 1). These variables will increase the amount of memory used by the network stack for receives, and can be increased significantly more if necessary for your application.

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Parameter	Scope	Default	Tuned Value	Comments