# Receiving massive amounts of messages with high performance

## Use Case

You are receiving syslog messages via UDP and or TCP at a very high data rate. You want to tune the system so that it can process as many messages as possible. All messages shall be written to a single output file.

## Sample Configuration

    # load required modules
    module(load="imudp" threads="2"
           timeRequery="8" batchSize="128")
    module(load="imptcp" threads="3")

    # listeners
    # repeat blocks if more listeners are needed
    # alternatively, use array syntax:
    # port=["514","515",...]
    input(type="imudp" port="514"
          ruleset="writeRemoteData")
    input(type="imptcp" port="10514"
          ruleset="writeRemoteData")

    # now define our ruleset, which also includes
    # threading and queue parameters.
    ruleset(name="writeRemoteData"
            queue.type="fixedArray"
            queue.size="250000"
            queue.dequeueBatchSize="4096"
            queue.workerThreads="4"
            queue.workerThreadMinimumMessages="60000"
           ) {
        action(type="omfile" file="/var/log/remote.log"
               ioBufferSize="64k" flushOnTXEnd="off"
               asyncWriting="on")
    }

## Notes on the suggested config

It is highly suggested to use a recent enough Linux kernel that supports the recvmmsg() system call. This system call improves UDP reception speed and decreases overall system CPU utilization.

We use the imptcp module for tcp input, as it uses more optimal results. Note, however, that it is only available on Linux and does currently not support TLS. If imptcp cannot be used, use imtcp instead (this will be a bit slower).

When writing to the output file, we use buffered mode. This means that full buffers are written, but during processing file lines are not written until the buffer is full (and thus may be delayed) and also incomplete lines are written (at buffer boundary). When the file is closed (rsyslogd stop or HUP), the buffer is completely flushed. As this is a high-traffic use case, we assume that buffered mode does not cause any concerns.

## Suggested User Performance Testing

Each environment is a bit different. Depending on circumstances, the imudp module parameters may not be optimal. In order to obtain best performance, it is suggested to measure performance level with two to four threads and somewhat lower and higher batchSize. Note that these parameters affect each other. The values given in the config above should usually work well in high-traffic environments. They are sub-optimal for low to medium traffic environments.

## See Also

imptcp, imtcp, imudp, ruleset()