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Oracle® Coherence Administrator's Guide
Release 3.7

Part Number E18679-01
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4 Performing a Network Performance Test

Coherence includes a datagram test utility that is used to test and tune network performance between two or more computers. The datagram test operates in one of three modes: either as a packet publisher, a packet listener, or both. When the utility is run, a publisher transmits UDP packets to the listener who then measures the throughput, success rate, and other statistics.

Tune the environment based on the results of these tests to achieve maximum performance. See Chapter 6, "Performance Tuning" for more information.

The following sections are included in this chapter:

4.1 Running the Datagram Test Utility

The datagram test utility is run from the command line using either the com.tangosol.net.DatagramTest class or by running the datagram-test script that is provided in the COHERENCE_HOME/bin directory. A script is provided for both Windows and UNIX-based platforms.

The following example demonstrates using the DatagramTest class:

java -server com.tangosol.net.DatagramTest <command value> <command value> ...

The following example demonstrates using the script:

datagram-test <command value> <command value> ...

Table 4-1 describes the available command line options for the datagram test utility.

Table 4-1 Command Line Options for the Datagram Test Utility

Command Required/Optional Applicability Description Default

-local

Optional

Both

The local address to bind to, specified as addr:port

localhost:9999

-packetSize

Optional

Both

The size of packet to work with, specified in bytes.

1468

-payload

Optional

Both

The amount of data to include in each packet. Use 0 to match packet size.

0

-processBytes

Optional

Both

The number of bytes (in multiples of 4) of each packet to process.

4

-rxBufferSize

Optional

Listener

The size of the receive buffer, specified in packets.

1428

-rxTimeoutMs

Optional

Listener

The duration of inactivity before a connection is closed.

1000

-txBufferSize

Optional

Publisher

The size of the transmit buffer, specified in packets.

16

-txRate

Optional

Publisher

The rate at which to transmit data, specified in megabytes.

unlimited

-txIterations

Optional

Publisher

Specifies the number of packets to publish before exiting.

unlimited

-txDurationMs

Optional

Publisher

Specifies how long to publish before exiting.

unlimited

-reportInterval

Optional

Both

The interval at which to output a report, specified in packets.

100000

-tickInterval

Optional

Both

The interval at which to output tick marks.

1000

-log

Optional

Listener

The name of a file to save a tabular report of measured performance.

none

-logInterval

Optional

Listener

The interval at which to output a measurement to the log.

100000

-polite

Optional

Publisher

Switch indicating if the publisher should wait for the listener to be contacted before publishing.

off

-provider

Optional

Both

The socket provider to use (system, tcp, ssl, file:xxx.xml)

system

arguments

Optional

Publisher

Space separated list of addresses to publish to, specified as addr:port.

none


4.2 How to Test Network Performance

The example in this section demonstrates how to test network performance between two servers— Server A with IP address 195.0.0.1 and Server B with IP address 195.0.0.2. One server acts as a packet publisher and the other as a packet listener. The publisher transmits packets as fast as possible and the listener measures and reports performance statistics.

First, start the listener on Server A. For example:

datagram-test.sh

After pressing ENTER, the utility displays that it is ready to receive packets. Example 4-1 illustrates sample output.

Example 4-1 Output from Starting a Listener

starting listener: at /195.0.0.1:9999
packet size: 1468 bytes
buffer size: 1428 packets
  report on: 100000 packets, 139 MBs
    process: 4 bytes/packet
        log: null
     log on: 139 MBs

The test, by default, tries to allocate a network receive buffer large enough to hold 1428 packets, or about 2 MB. The utility reports an error and exits if it cannot allocate this buffer. Either decrease the requested buffer size using the -rxBufferSize parameter, or increase the operating system's network buffer settings. Increase the operating system buffers for the best performance. See Chapter 7, "Production Checklist" for details on tuning an operating system for Coherence.

Start the publisher on Server B and direct it to publish to Server A. For example:

datagram-test.sh servera

After pressing ENTER, the test instance on Server B starts both a listener and a publisher. However, the listener is not used in this configuration. Example 4-2 demonstrates the sample output that displays in the Server B command window.

Example 4-2 Datagram Test—Starting a Listener and a Publisher on a Server

starting listener: at /195.0.0.2:9999
packet size: 1468 bytes
buffer size: 1428 packets
  report on: 100000 packets, 139 MBs
    process: 4 bytes/packet
        log: null
     log on: 139 MBs

starting publisher: at /195.0.0.2:9999 sending to servera/195.0.0.1:9999
packet size: 1468 bytes
buffer size: 16 packets
  report on: 100000 packets, 139 MBs
    process: 4 bytes/packet
      peers: 1
       rate: no limit

no packet burst limit
oooooooooOoooooooooOoooooooooOoooooooooOoooooooooOoooooooooOoooooooooOoooooooooO

The series of o and O marks appear as data is (O)utput on the network. Each o represents 1000 packets, with O indicators at every 10,000 packets.

On Server A, a corresponding set of i and I marks, representing network (I)nput. This indicates that the two test instances are communicating.

4.2.1 Performing a Bidirectional Test

The test can also be run in bidirectional mode where both servers act as publishers and listeners. Restart the test instances and supply the instance on Server A with the address for Server B. For example on Server A run:

datagram-test.sh -polite serverb

The -polite parameter instructs this test instance to not start publishing until it starts to receive data. Run the same command as before on Server B.

datagram-test.sh servera

4.2.2 Performing a Distributed Test

The test can be run with more than two computers. For example, setup two publishers to target a single listener. This style of testing is far more realistic then simple one-to-one testing and may identify network bottlenecks that may not otherwise be apparent.

The following example runs the datagram test among 4 computers:

On Server A:

datagramtest.sh -txRate 100 -polite serverb serverc serverd

On Server B:

datagramtest.sh -txRate 100 -polite servera serverc serverd

On Server C:

datagramtest.sh -txRate 100 -polite servera serverb serverd

On Server D:

datagramtest.sh -txRate 100 servera serverb serverc

This test sequence causes all nodes to send a total of 100MB per second to all other nodes (that is, 33MB/node/second). On a fully switched 1GbE network this should be achievable without packet loss.

To simplify the execution of the test, all nodes can be started with an identical target list, they obviously transmit to themselves as well, but this loopback data can easily be factored out. It is important to start all but the last node using the -polite switch, as this causes all other nodes to delay testing until the final node is started.

4.3 Understanding Report Statistics

Each side of the test (publisher and listener) periodically report performance statistics. The publisher simply reports the rate at which it is publishing data on the network. For example:

Tx summary 1 peers:
   life: 97 MB/sec, 69642 packets/sec
    now: 98 MB/sec, 69735 packets/sec

The report includes both the current transmit rate (since last report) and the lifetime transmit rate.

Table 4-2 describes the statistics that can be reported by the listener.

Table 4-2 Listener Statistics

Element Description

Elapsed

The time interval that the report covers.

Packet size

The received packet size.

Throughput

The rate at which packets are being received.

Received

The number of packets received.

Missing

The number of packets which were detected as lost.

Success rate

The percentage of received packets out of the total packets sent.

Out of order

The number of packets which arrived out of order.

Average offset

An indicator of how out of order packets are.


As with the publisher, both current and lifetime statistics are reported. The following example demonstrates a typical listener report:

Lifetime:
Rx from publisher: /195.0.0.2:9999
             elapsed: 8770ms
         packet size: 1468
          throughput: 96 MB/sec
                      68415 packets/sec
            received: 600000 of 611400
             missing: 11400
        success rate: 0.9813543
        out of order: 2
          avg offset: 1


Now:
Rx from publisher: /195.0.0.2:9999
             elapsed: 1431ms
         packet size: 1468
          throughput: 98 MB/sec
                      69881 packets/sec
            received: 100000 of 100000
             missing: 0
        success rate: 1.0
        out of order: 0
          avg offset: 0

The primary items of interest are the throughput and success rate. The goal is to find the highest throughput while maintaining a success rate as close to 1.0 as possible. A rate of around 10 MB/second should be achieved on a 100 Mb network setup. A rate of around 100 MB/second should be achieved on a 1 Gb network setup. Achieving these rates require some throttle tuning.

Throttling

The publishing side of the test may be throttled to a specific data rate expressed in megabytes per second by including the -txRate M parameter, when M represents the maximum MB/second the test should put on the network.