what's log4j actually doing when we turn on or off some log places?

Question

We know we can config log4j to turn off log on specific places (class or package in Java) via its properties/configuration file. My questions are followed:

1. wha

Answer 1

I ran a simple benchmark to test.

    for (int j = 0; j < 5; j++) {
        long t1 = System.nanoTime() / 1000000;
        int iterations = 1000000;
        for (int i = 0; i < iterations; i++) {
            int test = i % 10;
            log.debug("Test " + i + " has value " + test);
        }
        long t2 = System.nanoTime() / 1000000;
        log.info("elapsed time: " + (t2 - t1));

        long t3 = System.nanoTime() / 1000000;
        for (int i = 0; i < iterations; i++) {
            int test = i % 10;
            if (log.isDebugEnabled()) {
                log.debug("Test " + i + " has value " + test);
            }
        }
        long t4 = System.nanoTime() / 1000000;
        log.info("elapsed time 2: " + (t4 - t3));
    }

elapsed time: 539
elapsed time 2: 17
elapsed time: 450
elapsed time 2: 18
elapsed time: 454
elapsed time 2: 19
elapsed time: 454
elapsed time 2: 17
elapsed time: 450
elapsed time 2: 19

With 1.6.0_18, which surprised me as I would have thought the inlining would have prevented this. Maybe Java 7 with escape analysis will.

However I still wouldn't wrap debug statements in an if clause unless time improvements of the order of half a microsecond get to be important!