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Remko Popma commented on LOG4J2-1434: ------------------------------------- I don't think I misread. :-) I don't really see how the original question could have been interpreted differently. But no problem. Thanks for the clarification, I see what you mean and you have a good point. The way I would address this is in the above {{getStringBuilder()}} method, check the size of the StringBuilder before setting its length to zero, and trimming it to MAX_SIZE if it has grown too much. This allows us to do the check in a single place, with the drawback that the memory will not be freed in the case that a thread logs a very large message and then never logs anything again. I think that's a reasonable trade off. > StringBuffer in ThreadLocal can cause excessive memory usage after large log > messages > ------------------------------------------------------------------------------------- > > Key: LOG4J2-1434 > URL: https://issues.apache.org/jira/browse/LOG4J2-1434 > Project: Log4j 2 > Issue Type: Bug > Affects Versions: 2.6.1 > Reporter: Luke Butters > Assignee: Remko Popma > > In an effort to speed up logging ThreadLocals have been introduced see > LOG4J2-1125 however this does causes memory issues. > The problem of the ThreadLocal occurs when threads are re-used which is an > absolutely valid way of using java. For example an executor service can > re-use threads as well as Jetty. > Below I demonstrate a contrived example of the memory leak: > {code} > int stringSize = 1024*1024*10; //~10MB maybe 20MB for UTF-16 > StringBuilder sb = new StringBuilder(stringSize); > for(int i = 0; i < stringSize; i++) { > sb.append('a' + i % 5); > } > > String largeString = sb.toString(); > > sb = null; //Let it be GC'ed > ExecutorService es = Executors.newFixedThreadPool(100); > final CountDownLatch countDownLatch = new CountDownLatch(100); > for(int i = 0; i < 100; i++) { > es.execute(()-> { > //Log the big string to demonstrate the issue. > log.fatal(largeString); > > //Ensure we use all 100 of our threads by not releasing this > thread yet. > countDownLatch.countDown(); > }); > > //We sleep for 2s so we more easily watch memory growth > Thread.sleep(2000); > } > {code} > I recommend that log4j2 immediately remove the ThreadLocal as a small gain in > performance does not outweigh the problems associated with memory leaks. > Finally other options for caching the StringBuilder with a ThreadLocal could > be considered for example we might re-use StringBuilders that are no larger > than 3k while removing the ones which are larger than 3k. -- This message was sent by Atlassian JIRA (v6.3.4#6332) --------------------------------------------------------------------- To unsubscribe, e-mail: log4j-dev-unsubscr...@logging.apache.org For additional commands, e-mail: log4j-dev-h...@logging.apache.org