As load climbs, long Garbage Collection pauses are often observed on production servers, very often in the 10-30 second range, but sometimes much higher: customer have seen 180 seconds, and their system administrators report occurences of 900 seconds.

The hardware setup for the test kit is a SUN Netra:

bash-2.03$ uname -a
SunOS averia 5.8 Generic_108528-23 sun4u sparc SUNW,UltraAX-i2

bash-2.03$ psrinfo -v
Status of processor 0 as of: 09/18/03 14:08:53
  Processor has been on-line since 09/18/03 10:34:37.
  The sparcv9 processor operates at 500 MHz,
        and has a sparcv9 floating point processor.

CPU states: 99.2% idle, 0.0% user, 0.8% kernel, 0.0% iowait, 0.0%
swap Memory: 2048M real, 989M free, 1493M swap in use, 1191M swap free

Running with the following options the long pauses times are seen.
-server -Xmx768m -Xms768m -XX:NewSize=256m -XX:MaxNewSize=256m -XX:SurvivorRatio=2 -XX:TargetSurvivorRatio=90 -XX:PermSize=128m -XX:MaxPermSize=128m -XX:+PrintTenuringDistribution -verbose:gc
-XX:+DisableExplicitGC

[GC Desired survivor size 60397976 bytes, new threshold 32 (max 32)
- age 1: 4395464 bytes, 4395464 total
- age 2: 4355928 bytes, 8751392 total
- age 3: 5033640 bytes, 13785032 total
- age 4: 4649080 bytes, 18434112 total
- age 5: 6494632 bytes, 24928744 total
 151501K->24344K(720896K), 11.6820641 secs]
[GC
Desired survivor size 60397976 bytes, new threshold 32 (max 32)
- age 1: 3259272 bytes, 3259272 total
- age 2: 3649848 bytes, 6909120 total
- age 3: 4353200 bytes, 11262320 total
- age 4: 5031600 bytes, 16293920 total
- age 5: 4648912 bytes, 20942832 total
- age 6: 6491704 bytes, 27434536 total
 155416K->26791K(720896K), 23.4025614 secs]
Desired survivor size 60397976 bytes, new threshold 32 (max 32)
- age 1: 1539792 bytes, 1539792 total
- age 2: 2045880 bytes, 3585672 total
- age 3: 3607016 bytes, 7192688 total
- age 4: 4351832 bytes, 11544520 total
- age 5: 5028312 bytes, 16572832 total
- age 6: 4648912 bytes, 21221744 total
- age 7: 6491704 bytes, 27713448 total
 157863K->27063K(720896K), 101.4247403 secs]
Desired survivor size 60397976 bytes, new threshold 32 (max 32)
- age 1: 1007208 bytes, 1007208 total
- age 2: 663184 bytes, 1670392 total
- age 3: 2026504 bytes, 3696896 total
- age 4: 3600344 bytes, 7297240 total
- age 5: 4351832 bytes, 11649072 total
- age 6: 5005384 bytes, 16654456 total
- age 7: 4641888 bytes, 21296344 total
- age 8: 6439832 bytes, 27736176 total
 158135K->27086K(720896K), 1.3596074 secs]
[GC
Desired survivor size 60397976 bytes, new threshold 32 (max 32)
- age 1: 911200 bytes, 911200 total
- age 2: 182840 bytes, 1094040 total
- age 3: 659800 bytes, 1753840 total
- age 4: 2026504 bytes, 3780344 total
- age 5: 3594128 bytes, 7374472 total
- age 6: 4331816 bytes, 11706288 total
- age 7: 4998288 bytes, 16704576 total
- age 8: 4641584 bytes, 21346160 total
- age 9: 6407320 bytes, 27753480 total
 158158K->27103K(720896K), 1.7949328 secs]

The pstacks, GC and thread dumps are in the attachment.