Details regarding java garbage collection (GC) messages

Solution Verified - Updated -

Issue

The following messages were output:

[Full GC (Metadata GC Threshold) <time>: 42000.838: [CMS: 49033K->49033K(524288K), 0.2266686 secs] 51829K->49033K(996160K), [Metaspace: 99893K->99893K(370688K)], 0.2270268 secs] [Times: user=0.21 sys=0.00, real=0.23 secs] 
[Full GC (Metadata GC Threshold) <time>: 42001.342: [CMS: 49033K->45547K(524288K), 0.2349651 secs] 54644K->45547K(996160K), [Metaspace: 99893K->99893K(370688K)], 0.2398863 secs] [Times: user=0.24 sys=0.00, real=0.24 secs]

[Full GC (Last ditch collection) <time>: 41997.525: [CMS: 49033K->49033K(524288K), 0.2266774 secs] 49033K->49033K(996160K), [Metaspace: 99893K->99893K(370688K)], 0.2269730 secs] [Times: user=0.21 sys=0.00, real=0.23 secs] 
[Full GC (Last ditch collection) <time>: 41998.005: [CMS: 49033K->49033K(524288K), 0.2017113 secs] 49033K->49033K(996160K), [Metaspace: 99893K->99893K(370688K)], 0.2021881 secs] [Times: user=0.20 sys=0.00, real=0.20 secs]
[GC (Allocation Failure) <time>: 32569.530: [ParNew: 419456K->17149K(471872K), 0.1212009 secs] 476088K->73782K(996160K), 0.1214609 secs] [Times: user=0.06 sys=0.00, real=0.12 secs] 
[GC (Allocation Failure) <time>: 32651.806: [ParNew: 436597K->18949K(471872K), 0.0744025 secs] 493230K->75582K(996160K), 0.0746680 secs] [Times: user=0.06 sys=0.00, real=0.08 secs]
[GC (GCLocker Initiated GC) <time>: 41211.366: [ParNew: 75K->40K(471872K), 0.0052672 secs] 51010K->50975K(996160K), 0.0054723 secs] [Times: user=0.01 sys=0.00, real=0.01 secs] 
[GC (GCLocker Initiated GC) <time>: 41250.440: [ParNew: 25K->33K(471872K), 0.0070864 secs] 50981K->50990K(996160K), 0.0072657 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] 
[GC (CMS Initial Mark) [1 CMS-initial-mark: 49029K(524288K)] 51917K(996160K), 0.0031067 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 
[GC (CMS Initial Mark) [1 CMS-initial-mark: 49029K(524288K)] 49029K(996160K), 0.0033349 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[GC (CMS Final Remark) [YG occupancy: 12 K (471872 K)]2021-01-08T15:12:11.972+0900: 39824.096: [Rescan (parallel) , 0.0028905 secs] <time>: 39824.099: [weak refs processing, 0.0000553 secs]2021-01-08T15:12:11.975+0900: 39824.099: [class unloading, 0.0262626 secs]<time>: 39824.126: [scrub symbol table, 0.0116444 secs]2021-01-08T15:12:12.013+0900: 39824.137: [scrub string table, 0.0016910 secs][1 CMS-remark: 51522K(524288K)] 51535K(996160K), 0.0427001 secs] [Times: user=0.04 sys=0.00, real=0.05 secs] 
[GC (CMS Final Remark) [YG occupancy: 56 K (471872 K)]<time>: 40096.885: [Rescan (parallel) , 0.0056038 secs]<time>: 40096.890: [weak refs processing, 0.0000792 secs]<time>: 40096.890: [class unloading, 0.0283725 secs]<time>: 40096.919: [scrub symbol table, 0.0126654 secs]<time>: 40096.932: [scrub string table, 0.0018464 secs][1 CMS-remark: 51357K(524288K)] 51413K(996160K), 0.0487658 secs] [Times: user=0.05 sys=0.01, real=0.05 secs]

Please tell us the following three questions about the above messages:

  • meaning of each message
  • condition of each message
  • how to identify the memory area being reclaimed by the corresponding garbage collection

Environment

  • Red Hat Enterprise Linux (RHEL) 7
  • java-1.8.0-openjdk-1.8.0.232.b09-0.el7_7

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