CODEWITHSUNDEEP
javalog4jbuffer
Amos
Amos

Reputation: 1433

How do you flush a buffered log4j FileAppender?

In log4j, when using a FileAppender with BufferedIO=true and BufferSize=xxx properties (i.e. buffering is enabled), I want to be able to flush the log during normal shutdown procedure. Any ideas on how to do this?

Upvotes: 24

Views: 42200

Answers (8)

Ferran Maylinch
Ferran Maylinch

Reputation: 11539

The only solution that worked for me is waiting for a while:

private void flushAppender(Appender appender) {
    // this flush seems to be useless
    ((AbstractOutputStreamAppender<?>) appender).getManager().flush(); 
    try {
        Thread.sleep(500); // wait for log4j to flush logs
    } catch (InterruptedException ignore) {
    }
}

Upvotes: 1

Amos
Amos

Reputation: 1433

When shutting down the LogManager:

LogManager.shutdown();

all buffered logs get flushed.

Upvotes: 56

Станислав Борисов
Станислав Борисов

Reputation: 11

Sharing my experience with using "Andrey Kurilov"'s code example, or at least simmilar.

What I actually wanted to achieve was to implement an asynchronous log entries with manual flush (immediateFlush = false) to ensure an idle buffers content will be flushed before the bufferSize is reached.

The initial performance results were actually comparable with the ones achieved with the AsyncAppender - so I think it is a good alternative of it.

The AsyncAppender is using a separate thread (and additional dependency to disruptor jar), which makes it more performant, but with the cost of more CPU and even more disk flushing(no matter with high load flushes are made on batches).

So if you want to save disk IO operations and CPU load, but still want to ensure your buffers will be flushed asynchronously at some point, that is the way to go.

Upvotes: 1

Andrey Kurilov
Andrey Kurilov

Reputation: 51

public static void flushAll() {
    final LoggerContext logCtx = ((LoggerContext) LogManager.getContext());
    for(final org.apache.logging.log4j.core.Logger logger : logCtx.getLoggers()) {
        for(final Appender appender : logger.getAppenders().values()) {
            if(appender instanceof AbstractOutputStreamAppender) {
                ((AbstractOutputStreamAppender) appender).getManager().flush();
            }
        }
    }
}

Upvotes: 5

ewramner
ewramner

Reputation: 6278

I have written an appender that fixes this, see GitHub or use name.wramner.log4j:FlushAppender in Maven. It can be configured to flush on events with high severity and it can make the appenders unbuffered when it receives a specific message, for example "Shutting down". Check the unit tests for configuration examples. It is free, of course.

Upvotes: 0

Ondra Žižka
Ondra Žižka

Reputation: 46914

Maybe you could override WriterAppender#shouldFlush( LoggingEvent ), so it would return true for a special logging category, like log4j.flush.now, and then you call:

LoggerFactory.getLogger("log4j.flush.now").info("Flush")

http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/WriterAppender.html#shouldFlush%28org.apache.log4j.spi.LoggingEvent%29

Upvotes: 1

Niv
Niv

Reputation: 86

public static void flushAllLogs()
{
    try
    {
        Set<FileAppender> flushedFileAppenders = new HashSet<FileAppender>();
        Enumeration currentLoggers = LogManager.getLoggerRepository().getCurrentLoggers();
        while(currentLoggers.hasMoreElements())
        {
            Object nextLogger = currentLoggers.nextElement();
            if(nextLogger instanceof Logger)
            {
                Logger currentLogger = (Logger) nextLogger;
                Enumeration allAppenders = currentLogger.getAllAppenders();
                while(allAppenders.hasMoreElements())
                {
                    Object nextElement = allAppenders.nextElement();
                    if(nextElement instanceof FileAppender)
                    {
                        FileAppender fileAppender = (FileAppender) nextElement;
                        if(!flushedFileAppenders.contains(fileAppender) && !fileAppender.getImmediateFlush())
                        {
                            flushedFileAppenders.add(fileAppender);
                            //log.info("Appender "+fileAppender.getName()+" is not doing immediateFlush ");
                            fileAppender.setImmediateFlush(true);
                            currentLogger.info("FLUSH");
                            fileAppender.setImmediateFlush(false);
                        }
                        else
                        {
                            //log.info("fileAppender"+fileAppender.getName()+" is doing immediateFlush");
                        }
                    }
                }
            }
        }
    }
    catch(RuntimeException e)
    {
        log.error("Failed flushing logs",e);
    }
}

Upvotes: 7

rsp
rsp

Reputation: 23383

Try:

LogFactory.releaseAll();

Upvotes: 0

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