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 [[email protected]] 发送时间: 2013年2月21日 16:22 收件人: [email protected] 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 <[email protected]> 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 [[email protected]] > 发送时间: 2013年2月21日 15:32 > 收件人: [email protected] > 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 >
