Examples of org.apache.log4j.net.SocketAppender

• org.apache.log4j.net.SocketAppender
  Sends {@link LoggingEvent} objects to a remote a log server, usually a {@link SocketNode}.

  The SocketAppender has the following properties:

  • If sent to a {@link SocketNode}, remote logging is non-intrusive as far as the log event is concerned. In other words, the event will be logged with the same time stamp, {@link org.apache.log4j.NDC}, location info as if it were logged locally by the client.
  • SocketAppenders do not use a layout. They ship a serialized {@link LoggingEvent} object to the server side.
  • Remote logging uses the TCP protocol. Consequently, if the server is reachable, then log events will eventually arrive at the server.

  • If the remote server is down, the logging requests are simply dropped. However, if and when the server comes back up then event transmission is resumed transparently. This transparent reconneciton is performed by a connector thread which periodically attempts to connect to the server.

  • Logging events are automatically buffered by the native TCP implementation. This means that if the link to server is slow but still faster than the rate of (log) event production by the client, the client will not be affected by the slow network connection. However, if the network connection is slower then the rate of event production, then the client can only progress at the network rate. In particular, if the network link to the the server is down, the client will be blocked.

    On the other hand, if the network link is up, but the server is down, the client will not be blocked when making log requests but the log events will be lost due to server unavailability.

  • Even if a SocketAppender is no longer attached to any category, it will not be garbage collected in the presence of a connector thread. A connector thread exists only if the connection to the server is down. To avoid this garbage collection problem, you should {@link #close} the the SocketAppender explicitly. See also next item.

    Long lived applications which create/destroy many SocketAppender instances should be aware of this garbage collection problem. Most other applications can safely ignore it.

  • If the JVM hosting the SocketAppender exits before the SocketAppender is closed either explicitly or subsequent to garbage collection, then there might be untransmitted data in the pipe which might be lost. This is a common problem on Windows based systems.

    To avoid lost data, it is usually sufficient to {@link #close} the SocketAppender either explicitly or by calling the {@link org.apache.log4j.LogManager#shutdown} method before exiting the application.

  @author Ceki Gülcü @since 0.8.4

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