richardstartin commented on issue #7414: URL: https://github.com/apache/pinot/issues/7414#issuecomment-916270036
> `System.currentTimeMillis()` was more efficient than nanos This is the first time I have heard that and I must admit I am very skeptical about those articles' claims. On linux, `System.currentTimeMillis` delegates to `CLOCK_REALTIME` (see [here](https://github.com/openjdk/jdk/blob/20a373a0d00b72f0c6dceb19efca3b7cc34335e5/src/hotspot/os/posix/os_posix.cpp#L1387)) whereas `System.nanoTime()` delegates to `CLOCK_MONOTONIC` ([here](https://github.com/openjdk/jdk/blob/20a373a0d00b72f0c6dceb19efca3b7cc34335e5/src/hotspot/os/posix/os_posix.cpp#L1409)). There are [faster clocks](https://people.cs.rutgers.edu/~pxk/416/notes/c-tutorials/gettime.html) than `CLOCK_MONOTONIC` but Java users don't have access to them. Performance wise, the dominating factor in time measurement tends to be whether the `clock_gettime ` syscall is mapped into userspace by vDSO or not, and e.g. Xen doesn't do that, which can confound measurement. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: commits-unsubscr...@pinot.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@pinot.apache.org For additional commands, e-mail: commits-h...@pinot.apache.org
