V8 idle notification is too aggressive

[haitaoli]

Since upgrading from node 0.10 to 4.2.3, the average response time of my app nearly doubled. It appears to be related to GC. I set up a test environment with 2 identical hosts, one running with --nouse_idle_notification and the other without. Then I count the number of requests that take more than 150ms to finish. The host without --nouse_idle_notification parameter accounts for more than 70% of the total slow responses. @jkrems pointed me to this link https://nodejs.org/en/blog/release/v0.10.0/#latency-and-idle-garbage-collection, which seems to indicate the idle notification has been removed a long time ago to improve performance. Was the idle notification turned back on in later versions?

• Version: v4.2.3
• Platform: Linux 2.6.18-238.el5 deps: update openssl to 1.0.1j #1 SMP Thu Jan 13 15:51:15 EST 2011 x86_64 GNU/Linux
• Subsystem:

[Fishrock123]

cc @bnoordhuis probably

[bnoordhuis]

Idle notifications are disabled in v4, if that is what you're asking. --nouse_idle_notification should not make a difference because node never posts idle notifications in the first place.

If you're wondering why, it's because V8's idle notifier is time-based ("Use the next 10 milliseconds to collect because nothing else is going to happen"), which works okay for applications that operate at discrete intervals - browsers with their repaint cycle - but is not so great for applications that are continuous, like node.

If you think lazy GC is your issue, start node with --expose_gc and call gc() at opportune times. You can also use https://github.com/bnoordhuis/node-idle-gc but see the trade-offs listed in the README.