Strange STW pauses

[Nick Chadwick]

Hi,

My Java application is suffering from long (5s+) STW pauses. Latency is a
priority for the application, so I need to get to the bottom of what's going
on.

With all the usual JVM options on, I see the following in the logs:

[deflating idle monitors, 0.0000102 secs]
[updating inline caches, 0.0000149 secs]
[compilation policy safepoint handler, 0.0000005 secs]
[mark nmethods, 0.0000549 secs]
[purging class loader data graph, 0.0000002 secs]
         vmop                    [threads: total initially_running
wait_to_block]    [time: spin block sync cleanup vmop] page_trap_count
915.696: no vm operation                  [      24          1             
1    ]      [     0     0  7303     0     0    ]  1
Total time for which application threads were stopped: 0.0002608 seconds,
Stopping threads took: 0.0001250 seconds

[deflating idle monitors, 0.0000110 secs]
[updating inline caches, 0.0000706 secs]
[compilation policy safepoint handler, 0.0000006 secs]
[mark nmethods, 0.0000576 secs]
[purging class loader data graph, 0.0000003 secs]
         vmop                    [threads: total initially_running
wait_to_block]    [time: spin block sync cleanup vmop] page_trap_count
1051.564: no vm operation                  [      24          0             
1    ]      [     0     0  1652     0     0    ]  0
Total time for which application threads were stopped: 0.0002285 seconds,
Stopping threads took: 0.0000414 seconds

[deflating idle monitors, 0.0000135 secs]
[updating inline caches, 0.0000083 secs]
[compilation policy safepoint handler, 0.0000005 secs]
[mark nmethods, 0.0000894 secs]
[purging class loader data graph, 0.0000002 secs]
         vmop                    [threads: total initially_running
wait_to_block]    [time: spin block sync cleanup vmop] page_trap_count
1056.223: no vm operation                  [      24          0             
0    ]      [     0     0     0  5704     0    ]  0
Total time for which application threads were stopped: 5.7042454 seconds,
Stopping threads took: 0.0000270 seconds

[deflating idle monitors, 0.0000116 secs]
[updating inline caches, 0.0000093 secs]
[compilation policy safepoint handler, 0.0000005 secs]
[mark nmethods, 0.0000540 secs]
[purging class loader data graph, 0.0000001 secs]
         vmop                    [threads: total initially_running
wait_to_block]    [time: spin block sync cleanup vmop] page_trap_count
1756.475: no vm operation                  [      24          0             
0    ]      [     0     0     0  4402     0    ]  0
Total time for which application threads were stopped: 4.4023833 seconds,
Stopping threads took: 0.0000268 seconds

I've done some reading up, here and elsewhere, on "guaranteed safepoints"
etc, but am stumped as to what it's spending its time doing.

Please can anyone give me a clue?

Thanks,
Nick



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