Angler

Angler is a utility for monitoring the performance of UDP and TCP message-processing in the Linux kernel.

Maintainer

Mark Price

What can it tell me?

Angler will notify registered listeners of buffer-depths, packet drops and receive errors of individual UDP and TCP sockets.

System-wide UDP receive metrics will also be supplied if requested.

Current metric sources are:

/proc/net/udp

1. socket queue (transmit & receive) depth
2. socket drop count

/proc/net/snmp

1. UDP queue errors
2. UDP buffer overflows
3. UDP checksum errors

/proc/net/softnet_stat

1. network events processed
2. time squeeze events
3. drop events

/proc/net/tcp

1. socket queue (transmit & receive) depth

Monitoring these metrics can be useful when trying to track down the source of packet-loss in high-throughput traffic scenarios.

How do I use it?

The simplest use-case for Angler is to monitor socket queue depth and drop counts:

// begin monitoring
private final UdpSocketMonitor udpSocketMonitor = new UdpSocketMonitor(monitoringCallback);

udpSocketMonitor.beginMonitoringOf(new InetSocketAddress("127.0.0.1", 19889));

Executors.newSingleThreadScheduledExecutor().
        scheduleAtFixedRate(() -> udpSocketMonitor.poll(loggingStatsHandler),
                0L, 1L, TimeUnit.SECONDS)

Implement a handler for the socket statistics:

private static class LoggingUdpSocketStatisticsHandler implements UdpSocketStatisticsHandler
{
    @Override
    public void onStatisticsUpdated(final InetAddress inetAddress, final int port,
                                    final long socketIdentifier, final long inode,
                                    final long transmitQueueDepth, final long receiveQueueDepth,
                                    final long drops)
    {
        if(drops != 0)
        {
            log("Socket [%s:%d], queued: %d, drops: %d",
                    inetAddress.toString(), port, receiveQueueDepth, drops);
        }
    }
}

The handler will be notified if the socket's queue-depths or drop-count changes between invocations of the poll method.

See the ExampleApplication for further details.

To test functionality, check out the project and run ./gradlew runExample.

Performance notes

Angler will not generate garbage once in a steady-state.

Adding and removing sockets from the monitored set will cause allocation. Large changes in the number of active UDP or TCP sockets on the system will cause one-time allocation of a larger read-buffer for datasources.

Road map

• Report relevant TCP statistics
• Support IPv6 sockets

Change log

1.0.5

• Report TCP socket transmit and receive buffer depth
• Upgrade to Agrona 0.5.3

1.0.4

• Bugfixes to file handling routine
• Report UDP socket transmit buffer depth

1.0.3

• Bugfixes to file handling routines

1.0.2

• Upgrade to Agrona 0.5.1