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From 谢良 <xieli...@xiaomi.com>
Subject 答复: 答复: GC frequency
Date Thu, 21 Feb 2013 08:50:39 GMT
Here is a good formula to estimate: http://blog.ragozin.info/2011/06/understanding-gc-pauses-in-jvm-hotspots.html

Hope it helpful:)
发件人: Varun Sharma [varun@pinterest.com]
发送时间: 2013年2月21日 16:22
收件人: user@hbase.apache.org
主题: Re: 答复: GC frequency

What do you mean by normal size heap ? Here is JVM settings

-Xms11480m -Xmx11480m -XX:NewSize=512m -XX:MaxNewSize=512m
-XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=60
-XX:+UseCMSInitiatingOccupancyOnly -XX:ParallelGCThreads=4

I was told that for a 4 core machine, it typically takes 200ms to clean out
512m - now, the only thing that I am afraid with reducing the size of new
gen is higher frequency and the chances of more frequent promotion failures.

On Thu, Feb 21, 2013 at 12:10 AM, 谢良 <xieliang@xiaomi.com> wrote:

> Of course, you'll hit the nightmarish "CMS fragement" easier if NewSize
> too low:)
> Generally speaking, most of YGC should be less than 5ms for a normal size
> heap.
> maybe your load is too high or there're vm options be misconfigured ?
> ________________________________________
> 发件人: Varun Sharma [varun@pinterest.com]
> 发送时间: 2013年2月21日 15:32
> 收件人: user@hbase.apache.org
> 主题: GC frequency
> Hi,
> I have a system tuned with new Gen 512M with a lot write load. The system
> has 4 cores - ParNewGC and GCThreads is set to 4. I am using ConcMarkGC and
> CMSInitiating fraction is set to 60 %. I am observing the 90th/99th
> percentile of latency and see it highly correlated with GC pauses. There
> are times when I have a GC pause of ~ 200 ms every 4 seconds - the tail
> latency shoots up to 200 milliseconds for reads - most reads are being
> served out of cache. Looking at the GC log and tail latency pattern, there
> is direct correlation b/w the two. When the write load is low, and the GC
> pauses are like 100-150 ms every 6 seconds, the tail latency improves.
> After seeing this behaviour, I am intent on reducing the NewSize to 256M
> but I risk 100 ms pauses pretty much every 1-2 seconds and perhaps higher
> chance of promotion failures (MSLAB etc. is on). Does anyone know if
> frequent young gen collections can be a problem ?
> Thanks
> Varun
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