§Configuring netty

Play 2’s main server is built on top of Netty.

§Default configuration

Play uses the following default configuration:

play.server {

  # The server provider class name
  provider = "play.core.server.NettyServerProvider"

  netty {

    # The number of event loop threads. 0 means let Netty decide, which by default will select 2 times the number of
    # available processors.
    eventLoopThreads = 0

    # The maximum length of the initial line. This effectively restricts the maximum length of a URL that the server will
    # accept, the initial line consists of the method (3-7 characters), the URL, and the HTTP version (8 characters),
    # including typical whitespace, the maximum URL length will be this number - 18.
    maxInitialLineLength = 4096

    # The maximum length of the HTTP headers. The most common effect of this is a restriction in cookie length, including
    # number of cookies and size of cookie values.
    maxHeaderSize = 8192

    # The maximum length of body bytes that Netty will read into memory at a time.
    # This is used in many ways.  Note that this setting has no relation to HTTP chunked transfer encoding - Netty will
    # read "chunks", that is, byte buffers worth of content at a time and pass it to Play, regardless of whether the body
    # is using HTTP chunked transfer encoding.  A single HTTP chunk could span multiple Netty chunks if it exceeds this.
    # A body that is not HTTP chunked will span multiple Netty chunks if it exceeds this or if no content length is
    # specified. This only controls the maximum length of the Netty chunk byte buffers.
    maxChunkSize = 8192

    # Whether the Netty wire should be logged
    log.wire = false

    # The transport to use, either jdk or native.
    # Native socket transport has higher performance and produces less garbage but are only available on linux 
    transport = "jdk"

    # Netty options. Possible keys here are defined by:
    # Options that pertain to the listening server socket are defined at the top level, options for the sockets associated
    # with received client connections are prefixed with child.*
    option {

      # Set the size of the backlog of TCP connections.  The default and exact meaning of this parameter is JDK specific.
      # SO_BACKLOG = 100

      child {
        # Set whether connections should use TCP keep alive
        # SO_KEEPALIVE = false

        # Set whether the TCP no delay flag is set
        # TCP_NODELAY = false



§Configuring transport socket

Native socket transport has higher performance and produces less garbage but are only available on linux
You can configure the transport socket type in application.conf:

play.server {
  netty {
    transport = "native"

§Configuring channel options

The available options are defined in Netty channel option documentation.
If you are using native socket transport you can set additional options.

Next: Configuring Play's thread pools

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