Understand Concurrent mark and sweep output

Question

Hello There,
We are working on production issue where different processes stopped almost 5 mins and I thing GC stop the world occurred. But when I analysed/parsed gc logs I haven't seen much interesting. I analysed gc logs and found user: fields showing aroud 3 mins time. I don't understand what Times: field explaining.
Times: user=0.45 sys=0.00, real=0.09 secs
what USER/SYS/REAL indicates please?
--Venkat                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       

Answer 1

This are the typical OS timings (you also know from the times tool) and measure time in seconds for the GC threads. user is the accumulated CPU time spent in user mode, sys is the time spent in kernel mode and real is the wall clock time.
Note that usr+sys is measured in CPU seconds, so if you have 8 cores and 6 are doing 1s long calculating something (like memory reachability) and 2 are in kernel page handlers the real time will be 1s and the user time will be 6s.
Typically for GC you should not see large sys times at all and the real time should be small and the usr time should be parallelity-times more than real clock.
Bernd