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From "Prashant kumar" <prashant.ku...@baypackets.com>
Subject problem in GC tuning
Date Sun, 25 May 2003 11:41:33 GMT
Hi All,
 
I m working on an sip application server and want to increase its
performance. at max load the CPU of my server machine is around 45-50%
free. The issue I am facing is that for a short period of time (for
around 7-10 sec), free CPU goes below 25%. My server has a constraint
that it must have at least 25% CPU free every time. So at the time when
CPU goes below 25%, my server starts dropping requests. This limits my
server performance.
 
The reason why CPU goes below 25% is garbage collector. When GC occurs,
CPU goes below 25%.
 
My queries are,
 
 1)  Is there any means  by which GC takes less CPU,  I mean that it
can take longer time to complete  its one cycle (as memory is not a
constraint) ? 
 
2)  Do writing of logs at higher loads have some impact on the
performance?
 
3)  As memory is not a constraint, until now, are there some options
which can exploit this information for the betterment of the
performance?
 
 
I m using following garbage collector and heap option in my application
server:
 
export MEM_OPTS="-Xmx3400m -Xms3400m -XX:NewSize=194m
-XX:MaxNewSize=194m -XX:+UseTLAB"
 
export GC_OPTS="${MEM_OPTS} -XX:+UseParNewGC -XX:+UseConcMarkSweepGC"
export GC_OPTS="${GC_OPTS} -XX:+CMSIncrementalMode
-XX:+CMSIncrementalPacing "
export GC_OPTS="${GC_OPTS} -Xloggc:<logFileName> -XX:+PrintGCDetails
-XX:+PrintGCTimeStamps"
 
The typical GC output looks like:
 
7760.617: [CMS-concurrent-mark-start]
7765.387: [GC 7765.387: [ParNew: 198272K->0K(198464K), 0.1787951 secs]
996415K->812092K(3481408K) icms_dc=10 , 0.1790065 secs]
7774.972: [GC 7774.972: [ParNew: 198272K->0K(198464K), 0.1910697 secs]
1010364K->827429K(3481408K) icms_dc=10 , 0.1913241 secs]
7784.586: [GC 7784.586: [ParNew: 198272K->0K(198464K), 0.1910507 secs]
1025701K->842794K(3481408K) icms_dc=10 , 0.1912954 secs]
7792.251: [GC 7792.251: [ParNew: 198272K->0K(198464K), 0.1595620 secs]
1041066K->854987K(3481408K) icms_dc=10 , 0.1597866 secs]
7801.843: [GC 7801.843: [ParNew: 198272K->0K(198464K), 0.1900005 secs]
1053259K->870350K(3481408K) icms_dc=10 , 0.1902646 secs]
7806.146: [CMS-concurrent-mark: 5.022/45.529 secs]
7806.147: [CMS-concurrent-preclean-start]
7811.467: [GC 7811.467: [ParNew: 198272K->0K(198464K), 0.1943446 secs]
1068622K->885726K(3481408K) icms_dc=10 , 0.1945964 secs]
7820.015: [GC 7820.015: [ParNew: 198272K->0K(198464K), 0.1667043 secs]
1083998K->898767K(3481408K) icms_dc=10 , 0.1669592 secs]
7828.807: [GC 7828.807: [ParNew: 198272K->0K(198464K), 0.1982581 secs]
1097039K->914071K(3481408K) icms_dc=10 , 0.1984625 secs]
7838.324: [GC 7838.324: [ParNew: 198272K->0K(198464K), 0.2005505 secs]
1112343K->929384K(3481408K) icms_dc=10 , 0.2008112 secs]
7842.719: [CMS-concurrent-preclean: 4.244/36.572 secs]
7842.719: [GC7843.155: [weak refs processing, 0.0032912 secs] [1
CMS-remark: 929384K(3282944K)] 1021754K(3481408K), 0.4391301 secs]
7843.159: [CMS-concurrent-sweep-start]
7847.798: [GC 7847.798: [ParNew: 198272K->0K(198464K), 0.1952376 secs]
1113089K->929939K(3481408K) icms_dc=10 , 0.1954940 secs]
7855.450: [GC 7855.450: [ParNew: 198272K->0K(198464K), 0.1753630 secs]
1108874K->922848K(3481408K) icms_dc=10 , 0.1756148 secs]
7865.105: [GC 7865.105: [ParNew: 198272K->0K(198464K), 0.2015532 secs]
1092061K->909155K(3481408K) icms_dc=10 , 0.2018162 secs]
7874.678: [GC 7874.678: [ParNew: 198272K->0K(198464K), 0.1859961 secs]
1058045K->875118K(3481408K) icms_dc=10 , 0.1862536 secs]
7883.184: [GC 7883.184: [ParNew: 198272K->0K(198464K), 0.1593874 secs]
1003006K->818082K(3481408K) icms_dc=10 , 0.1596041 secs]
7891.866: [GC 7891.866: [ParNew: 198272K->0K(198464K), 0.1977762 secs]
963983K->781405K(3481408K) icms_dc=10 , 0.1979563 secs]
7896.965: [CMS-concurrent-sweep: 5.086/53.806 secs]
7896.965: [CMS-concurrent-reset-start]
7901.469: [GC 7901.469: [ParNew: 198272K->0K(198464K), 0.1865064 secs]
924647K->741740K(3481408K) icms_dc=10 , 0.1867165 secs]
7905.936: [CMS-concurrent-reset: 0.356/8.971 secs]
7911.426: [GC 7911.426: [ParNew: 198272K->0K(198464K), 0.1802738 secs]
940012K->757357K(3481408K) icms_dc=10 , 0.1805271 secs]
7913.587: [GC [1 CMS-initial-mark: 757357K(3282944K)] 846861K(3481408K),
0.2955865 secs]
7913.883: [CMS-concurrent-mark-start]
7918.611: [GC 7918.611: [ParNew: 198272K->0K(198464K), 0.1589979 secs]
955629K->768902K(3481408K) icms_dc=10 , 0.1592427 secs]
7928.066: [GC 7928.066: [ParNew: 198272K->0K(198464K), 0.1978113 secs]
967174K->784280K(3481408K) icms_dc=10 , 0.1980187 secs]
7937.656: [GC 7937.656: [ParNew: 198272K->0K(198464K), 0.1959725 secs]
982552K->799658K(3481408K) icms_dc=10 , 0.1962251 secs]
7945.307: [GC 7945.307: [ParNew: 198272K->0K(198464K), 0.1633872 secs]
997930K->811865K(3481408K) icms_dc=10 , 0.1636053 secs]
7954.925: [GC 7954.925: [ParNew: 198272K->0K(198464K), 0.1972658 secs]
1010137K->827248K(3481408K) icms_dc=10 , 0.1974907 secs]
7964.609: [GC 7964.610: [ParNew: 198272K->0K(198464K), 0.2009350 secs]
1025520K->842638K(3481408K) icms_dc=10 , 0.2011559 secs]
7968.873: [CMS-concurrent-mark: 5.773/54.990 secs]
7968.873: [CMS-concurrent-preclean-start]
7974.834: [GC 7974.835: [ParNew: 198272K->0K(198464K), 0.1811506 secs]
1040910K->855650K(3481408K) icms_dc=10 , 0.1813716 secs]
7981.902: [GC 7981.902: [ParNew: 198272K->0K(198464K), 0.2050517 secs]
1053922K->870454K(3481408K) icms_dc=10 , 0.2052528 secs]
7991.449: [GC 7991.449: [ParNew: 198272K->0K(198464K), 0.1999756 secs]
1068726K->885800K(3481408K) icms_dc=10 , 0.2002290 secs]
8001.095: [GC 8001.095: [ParNew: 198272K->0K(198464K), 0.1956788 secs]
1084072K->901229K(3481408K) icms_dc=10 , 0.1958831 secs]
8005.477: [CMS-concurrent-preclean: 3.660/36.604 secs]
8005.478: [GC8005.879: [weak refs processing, 0.0033165 secs] [1
CMS-remark: 901229K(3282944K)] 1010055K(3481408K), 0.4045541 secs]
8005.883: [CMS-concurrent-sweep-start]
8008.666: [GC 8008.666: [ParNew: 198272K->0K(198464K), 0.1572205 secs]
1099394K->913209K(3481408K) icms_dc=10 , 0.1574554 secs]
8018.200: [GC 8018.200: [ParNew: 198272K->0K(198464K), 0.1762875 secs]
1029950K->846961K(3481408K) icms_dc=10 , 0.1764872 secs]
8027.796: [GC 8027.796: [ParNew: 198272K->0K(198464K), 0.1764513 secs]
1018796K->835879K(3481408K) icms_dc=10 , 0.1766460 secs]
8036.182: [GC 8036.183: [ParNew: 198272K->0K(198464K), 0.1496021 secs]
1005163K->819861K(3481408K) icms_dc=10 , 0.1498642 secs]
8045.035: [GC 8045.035: [ParNew: 198272K->0K(198464K), 0.1714910 secs]
969596K->786671K(3481408K) icms_dc=10 , 0.1716964 secs]
8049.630: [CMS-concurrent-sweep: 4.484/43.747 secs]
8049.630: [CMS-concurrent-reset-start]
8049.974: [CMS-concurrent-reset: 0.344/0.344 secs]
8054.626: [GC 8054.626: [ParNew: 198272K->0K(198464K), 0.1614032 secs]
920368K->737444K(3481408K) icms_dc=10 , 0.1616091 secs]
8058.849: [GC [1 CMS-initial-mark: 737444K(3282944K)] 828209K(3481408K),
0.3487117 secs]
 
 
Thanks and Regards
Prashant Kumar
 

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