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Log4J vs SLF4J simple vs Logback vs Java Util Logging vs LOG4J2

Logging is an age-old and intrinsic part of virtually every server-side application. It’s the primary method by which applications output live state in a persistent and readable manner. Some applications may only log a few megabytes a day, while others may log gigabytes of data or more in a matter of hours.

As logging usually involves IO to write data to disk (either blocking or async) – it comes at a cost. When logging large amounts of data over short periods of time, that cost can ramp up quickly. We decided to take a deeper look at the speed of some of today’s leading logging engines.

Most developers log data for three main reasons –

1. Monitoring – to see how code behaves in terms of throughput, scale, security, etc..

2. Debugging – to get access to the state that caused code to fail (variables, stack traces…). Takipi helps developers debug staging and production servers, and understand why code crashes and threads freeze.

3. Analytics – leverage live data from the app in order to derive conclusions about the way it’s being used.

Behind the facade. Most libraries today have logging built-in at key points in the code to provide visibility into their operations. To streamline this process and prevent different libraries from employing multiple logging methods in the same JVM, logging facades, which decouple code from the underlying engine, have come into the forefront. When we analyzed the top 100 software libraries for Java, SLF4J came up as the leading logging facade used by developers today.

The Competition

We decided to pick five of today’s most prominent logging engines, and see how they perform in a number of races. Now, before you take out the torches and pitchforks, I wanted to clarify that the point is not to say which is better, but to give a sense of the differences in throughput between the engines across a number of common logging tasks.

The Contestants

1. Log4J

2. Log4J2

3. Logback

4. SLF4J Simple Logging (SLF4J SL)

5. Java Util Logging (JUL)

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The Race

We wanted to see how the engines compare across a set of standard logging activities. Each logging operation includes a timestamp and a thread ID as its context.

These are the races:

1. Logging a string constant

2. Logging the .toString() value of a POJO

3. Logging a throwable object

4. Logging a string constant without time/tid context

The Track

We decided to hold five heats for each race to determine the best score, measuring the number of logging operations completed. In each test we gave the logging engines a task to perform across 10 threads in the space of a minute (the tests ran separately). We then took out the 2 heats with biggest deviation and averaged the results of the remaining three.

Between each individual logging operation we gave the CPU some work to do to put some space between the logging operations (checking whether a small random number is prime). The engines are all running behind SLF4J using their default configuration. The benchmarks were run on an Amazon m1.large EC2 instance.

Update: during our initial test Log4J2 was configured with a %C qualified class layout which increased its overhead. At the advice of @RemkoPopma we updated the configuration to %c (logger name) to conform with the other configuration, which gave Log4J2 a considerable performance boost, as you’ll see below. It’s definitely something worth paying attention to, and really highlights the cost of logging context data.

The Results

Pre conf change (%C):

Log olympics results

Post conf Change (%c):


To see the full dataset – Click here.

Race #1 – String constants

In this race the engines are logging a string constant along with thread and timestamp context. Log4J comes out the clear winner here, being able to write almost 270% more lines than JUL, 12.5% more than logback, 52% more than SLF4J SL. It was interesting to note that before we changed Log4J2’s configuration it was able to write 4X(!) less lines, with the switch boosting it up #3 with only 30% less lines written than logback.

Race #2 – .toString()

In this race the engines are logging a POJO (via its .toString) along with thread and timestamp context. The results here were much closer with Log4J2 coming in at #1 with a 25% advantage (post change) over SLF4J SL coming in at #2. Log4J and Logback are neck and neck for the #3 spot with JUL taking silver with 88% throughput of SLF4J SL.

Race #3 – Throwable

In this race the engines are logging an exception object and a description string along with thread and timestamp context. It’s in this race the Log4J2 is on fire, coming in at #1 logging more than 3X (!) times the rows when compared SLF4J SL at #5.

Log4J and Logback are also left in the dust, logging less than half the lines of our esteemed winner. JUL comes in at a solid #2, logging 82% of the lines compared to our winner – not too bad.

Race #4 (running barefoot) – .toString() minus context

When dealing with server logs, each entry’s context (e.g. thread ID, class context, time-stamp, etc…) is almost as important as the content of the entry itself. For the previous races we used two of the most common context elements you’ll find in most server log entries – thread ID and timestamp. We thought it’d be interesting to analyze the overhead of those by running a .toString() race without using any of the engines’ context appenders.

Log4J2 is the winner here (post conf change, getting a 180% boost) with a clear 25% lead over by both Logback and JUL. SLF4J SL are trailing behind. It was puzzling to see that across the five different heats, SLF4J SL did better with the appenders than without (would love to hear your thoughts on it in the comments).

Log4J saw the biggest bump with a 15% increase in throughput. JUL, while not performing as well as Log4J or Log4J2 in this race, deliver almost the exact same results with and without the context data.

I’d love to hear your comments and inputs. You can also check out the code on GitHub.

Further reading: 

blog_boat (1)

The 7 Log Management Tools Java Developers Should Know

Tal is the CEO of OverOps. Tal has been designing scalable, real-time Java and C++ applications for the past 15 years. He still enjoys analyzing a good bug though, and instrumenting code. In his free time Tal plays Jazz drums.
  • BelSoft

    You should probably run these benchmark on your local machine.
    There are many things that can happen on Amazon instances that could modify the results.

  • Java Developer

    Wow, interesting benchmarks. Clearly no single winner. However its annoying that mix of these libraries create a lot of pain. Specially if you have a dependency that uses one of them.

    Thanks for sharing the results.

    I would also want to know if you could run this on a single machine/laptop and see results. Amazon is all VMs so results may vary, but they are still useful since we use a lot of amazon cloud.

  • Pablo Fernandez

    Just as a sidenote, on applications that log too much (either because there are too many log calls, too many requests or both) we found that most file appenders have a explicit lock that gets *heavily* contended, sometimes becoming the application bottleneck.

    For these scenarios most logging implementations provide an AsyncAppender that uses a nonblocking data structure and discards lower level (INFO, DEBUG, TRACE) log lines when full.

    • Zangetsu zangetsu

      I actually got to this post because I was disheartened to find at least 4 of these contenders used interchangeably in the same product (historic reasons) and was trying to find an overriding reason for so much choice. There is just no good reason for all these upper-hand efforts to decide who is the ultimate wrapper and the ultimate implementation when it leads to competing code changes. I admire the geekness built into logback and log4j2, but I often wonder if it wouldn’t just have been wiser to implement them as Handlers and Formatters under JUL.

      JDK 4 came out in 2002, OpenJdk has been out in 2008. These forks do far more harm than good to the overall ecosystem.

      • Peter Hansson

        So true. The arguments for using something else than JUL (since at least Java 1.5) seem to be circular. I’m still trying to get to the bottom of what are the true benefits of logging framework X over JUL. It all seems to be historical reasons.

        • HaakonKL

          The argument shouldn’t be this vs that. It should be “slf4j + whatever you want” so that we don’t have to have this argument *again*. That’s the beauty of slf4j: What logging framework to use? YOU decide. Just set it up somehow, and I’ll tell it what I need logged, and we’re all happy.

          • Peter Hansson

            Still, this is history. Facades only exist because at some point people started diverting in all sorts of directions because the default implementation they were provided with – in this case JUL – just wasn’t good enough. (meaning there are very good historical reasons why it happened). However, if the default implementation provided by the JDK *is* good enough, then the facade just creates unnecessary complexity which is unused because everyone uses the default implementation anyway. My point is: Would someone invent Log4j, Commons Logging, logback,etc, TODAY? (given what JUL can do in Java8 and onwards). If not, then there’s also nobody who would invent slf4j or argue for a facade. Don’t get me wrong. I’m not against facades. But JUL is itself an abstraction over Handlers and Formatters where you can create your own and the operator can change these without involving the developer (meaning with only config change). And then a facade on top of that??. Bottom line: the facade concept exist because – at some point – the default just wasn’t good enough. But now that it is, then what? As an example: I do not consider putting a facade in front of Java’s collections framework so that the default JDK collections framework can be swapped for something else. Why? Because the default implementation is good enough and the collections facade would be an unnecessary abstraction for a need that would very unlikely arise.

            Young programmers who enters the Java world today will look at all these frameworks (and thus the need for a facade) and ask why? We – the old-timers – will answer: “It’s history, kid, you are too young to understand”. 🙂

  • Remko Popma

    Dear Takipi, your test is unfairly biased against Log4j2.

    Specifically, the configuration pattern layout used in the test is %C (caller class) for Log4j2 only. All other logging frameworks are tested with pattern layout %c or %logger (logger name). This means that Log4j2 (and only Log4J2) is forced to walk the stack trace to collect location information on the caller. (This is 1.3-5 times slower than not including location information, as documented several times in the Log4J2 docs.)

    Can you correct this error and re-run the tests?

    A few more requests:

    Could you do some warmup before starting the measurements? The current code in com.takipi.benchmark.logging.BM includes the initialization time in the measurement. (Logging frameworks that take more time to read config files etc when they start up are presented as less performant.) Initialization time is probably not what you want to measure. May I suggest creating a separate BaseTest instance and letting this instance run for 15+ seconds (and delete its output so it doesn’t get counted) before starting the threadpool that does the measurements?

    Could you include a test that uses Log4j2’s RandomAccessFileAppender instead of the FileAppender? RandomAccessFileAppender is many times faster than FileAppender.

    Could you mention that the test only measures synchronous logging, and does not include asynchronous logging? This is important because asynchronous logging can give much, much better performance than synchronous logging. (See the graphs here: )

    • Tal Weiss

      Hi Remko,

      We’ve gone ahead and updated the post to reflect the change in configuration. Thanks for the heads up!

      Re warmup. you’re right in that a warmup period can yield better results in terms of JVM / IO readiness, but as a race between the frameworks I thought it’d be interesting to see how they go from 0 to 100mph.

      Re sync vs. async, as most developers usually log synchronously in relation to their code I thought I’d focus on that. You’re totally right that in high scale situations diverting the logging operation to a background / dedicated thread can help yield better throughput.

      If you’re interested in taking the test, modifying it and running it again, I’d be happy to link and share your results.

      Thanks for the great input.

      • Remko Popma

        Hi Tal,

        Thanks for re-running the test and updating the article so quickly. And on Christmas eve! Much appreciated!

        Re warmup, I understand that your first priority was fixing the configuration and I appreciate the quick response, but I would like to ask you to reconsider. I think many of your readers are interested in this post because it may help them choose between logging frameworks. If the startup/initialization time skews the results then the article may not be as useful to your readers because it does not reflect how logging frameworks will perform in production.

        Please don’t take this the wrong way, I realize how much work you’ve put into this already.

        If it is useful I can make the code changes for the warmup and send you a pull request.

        By the way, just curious, according to the Log4j2 docs, RandomAccessFileAppender can be about twice as fast as FIleAppender ( ). I would be really interested to see if those numbers hold out in your test as well. Wouldn’t you want to use the fastest appender when doing a performance test? I would think that RandomAccessFileAppender would be a more natural choice for this test than FileAppender…

        • Dan Eloff

          Doh, back to Google, this benchmark may not have meaningful results, it can’t be used as the basis of a decision.

        • Juan Liska

          One problem may be that the Log4j2 documentation is too big and the chaff gets mixed in with the wheat. If these benchmark results are real, then it is surprising that logback is so much more popular — based on github stars, etc, than log4j

  • Deepak Pant

    Thanks for nice detailed article. Have you tried any benchmarks which involves wrapper library like Apache Commons or JBoss Logging and uses Log4j2 or SL4j.

  • Zangetsu zangetsu
  • Denilson N.

    A few comments:

    1. update to the git repo …

    The git settings for log4j2 do not reflect the blog updates:

    2. The “toString” results should not be a surprise. The cost of “toString” is not as significant when placed next to things like creating an ArrayList, multiple calls to “rand” or the implicit string formatting and parameter replacement built into the “” call.

    3. the JulFormatter class has a couple of problems: (a) the “pw” stream is not closed and (b) you probably should write the initial value into the writer, thus avoiding the string concatenation after that point:

    More like this

    if (t != null) {
    StringWriter sw = new StringWriter();
    PrintWriter pw = new PrintWriter(sw);
    try {
    formattedRecord = sw.toString();
    } finally {

  • Roman

    I dont think Slf4J’s SimpleLogger is production-recommended and thus worth evaluation. Usually Slf4J is used with logger implementation like Logback or Log4j.