title: Rapid Young G1 Evacuation Collections
body: <p>I'm working with an application that was recently upgraded and I'm seeing new behavior that I can't quite explain. The pattern of collections seems decent but then will perform in excess of 10 G1 Evacuation Collections (Young) in a row, within a few seconds. They seem to be clearing up the Eden memory, but I don't understand why it's filling up so quickly. </p>
  
  <p>Is this a complex problem or am I doing something wrong? (If I have posted too much detail, I can edit and remove it).</p>
  
  <pre><code>-XX:+UseG1GC -Xms10240m -Xmx10240m -XX:NewRatio=2 -XX:NewSize=1792m -XX:G1ReservePercent=30 -XX:+AggressiveOpts
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/OQYV9.png" rel="nofollow noreferrer">GCViewer</a>
  If you look at this screenshot, you can see nearly solid blue lines where the young gen collections happen in rapid succession.</p>
  
  <pre>
  
      2017-03-02T12:27:08.527-0800: 48187.087: [GC pause (G1 Evacuation Pause) (young)
      Desired survivor size 299892736 bytes, new threshold 15 (max 15)
      - age   1:    6684488 bytes,    6684488 total
      - age   2:   15234432 bytes,   21918920 total
      - age   3:    5530024 bytes,   27448944 total
      - age   4:    5502152 bytes,   32951096 total
      - age   5:    4490976 bytes,   37442072 total
      - age   6:    1736456 bytes,   39178528 total
      - age   7:    2849184 bytes,   42027712 total
      - age   8:    2600504 bytes,   44628216 total
      - age   9:    1793032 bytes,   46421248 total
      - age  10:    1996752 bytes,   48418000 total
      - age  11:     876104 bytes,   49294104 total
      - age  12:    2233720 bytes,   51527824 total
      - age  13:    1218392 bytes,   52746216 total
      - age  14:     903760 bytes,   53649976 total
      - age  15:    1774480 bytes,   55424456 total
      , 0.0369978 secs]
         [Parallel Time: 32.2 ms, GC Workers: 8]
            [GC Worker Start (ms): Min: 48187087.1, Avg: 48187087.2, Max: 48187087.3, Diff: 0.2]
            [Ext Root Scanning (ms): Min: 4.4, Avg: 6.5, Max: 12.0, Diff: 7.7, Sum: 51.9]
            [Update RS (ms): Min: 4.0, Avg: 8.5, Max: 9.6, Diff: 5.6, Sum: 68.3]
               [Processed Buffers: Min: 8, Avg: 13.4, Max: 19, Diff: 11, Sum: 107]
            [Scan RS (ms): Min: 0.1, Avg: 0.2, Max: 0.3, Diff: 0.2, Sum: 1.9]
            [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
            [Object Copy (ms): Min: 15.4, Avg: 16.6, Max: 17.8, Diff: 2.4, Sum: 132.5]
            [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
               [Termination Attempts: Min: 1, Avg: 1.0, Max: 1, Diff: 0, Sum: 8]
            [GC Worker Other (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.1, Sum: 0.8]
            [GC Worker Total (ms): Min: 31.9, Avg: 31.9, Max: 32.0, Diff: 0.2, Sum: 255.6]
            [GC Worker End (ms): Min: 48187119.1, Avg: 48187119.2, Max: 48187119.3, Diff: 0.1]
         [Code Root Fixup: 0.4 ms]
         [Code Root Purge: 0.0 ms]
         [Clear CT: 0.7 ms]
         [Other: 3.7 ms]
            [Choose CSet: 0.0 ms]
            [Ref Proc: 0.8 ms]
            [Ref Enq: 0.0 ms]
            [Redirty Cards: 0.2 ms]
            [Humongous Register: 0.2 ms]
            [Humongous Reclaim: 0.1 ms]
            [Free CSet: 1.8 ms]
         [Eden: 4508.0M(4508.0M)->0.0B(4516.0M) Survivors: 68.0M->64.0M Heap: 7036.0M(10.0G)->2524.1M(10.0G)]
       [Times: user=0.26 sys=0.00, real=0.04 secs] 
  
  </pre>
  
  <pre>
  
      2017-03-02T12:27:09.078-0800: 48187.638: [GC pause (G1 Evacuation Pause) (young)
      Desired survivor size 301989888 bytes, new threshold 15 (max 15)
      - age   1:      31144 bytes,      31144 total
      - age   2:    6631192 bytes,    6662336 total
      - age   3:   15225176 bytes,   21887512 total
      - age   4:    5530024 bytes,   27417536 total
      - age   5:    5501976 bytes,   32919512 total
      - age   6:    4490976 bytes,   37410488 total
      - age   7:    1736456 bytes,   39146944 total
      - age   8:    2849184 bytes,   41996128 total
      - age   9:    2600504 bytes,   44596632 total
      - age  10:    1793032 bytes,   46389664 total
      - age  11:    1996752 bytes,   48386416 total
      - age  12:     876104 bytes,   49262520 total
      - age  13:    2233720 bytes,   51496240 total
      - age  14:    1218392 bytes,   52714632 total
      - age  15:     903760 bytes,   53618392 total
      , 0.0320568 secs]
         [Parallel Time: 28.0 ms, GC Workers: 8]
            [GC Worker Start (ms): Min: 48187638.4, Avg: 48187638.5, Max: 48187638.6, Diff: 0.2]
            [Ext Root Scanning (ms): Min: 3.8, Avg: 5.4, Max: 11.2, Diff: 7.4, Sum: 43.4]
            [Update RS (ms): Min: 2.4, Avg: 7.4, Max: 8.7, Diff: 6.3, Sum: 59.2]
               [Processed Buffers: Min: 7, Avg: 11.6, Max: 15, Diff: 8, Sum: 93]
            [Scan RS (ms): Min: 0.2, Avg: 0.2, Max: 0.3, Diff: 0.1, Sum: 1.9]
            [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
            [Object Copy (ms): Min: 13.6, Avg: 14.6, Max: 15.0, Diff: 1.3, Sum: 116.5]
            [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
               [Termination Attempts: Min: 1, Avg: 1.9, Max: 3, Diff: 2, Sum: 15]
            [GC Worker Other (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.1, Sum: 0.8]
            [GC Worker Total (ms): Min: 27.6, Avg: 27.7, Max: 27.8, Diff: 0.3, Sum: 221.9]
            [GC Worker End (ms): Min: 48187666.2, Avg: 48187666.3, Max: 48187666.3, Diff: 0.1]
         [Code Root Fixup: 0.3 ms]
         [Code Root Purge: 0.0 ms]
         [Clear CT: 0.7 ms]
         [Other: 3.0 ms]
            [Choose CSet: 0.0 ms]
            [Ref Proc: 0.5 ms]
            [Ref Enq: 0.0 ms]
            [Redirty Cards: 0.2 ms]
            [Humongous Register: 0.2 ms]
            [Humongous Reclaim: 0.1 ms]
            [Free CSet: 1.6 ms]
         [Eden: 4516.0M(4516.0M)->0.0B(4520.0M) Survivors: 64.0M->60.0M Heap: 7040.1M(10.0G)->2521.7M(10.0G)]
       [Times: user=0.23 sys=0.00, real=0.03 secs]
  
  </pre>
  
  <pre>
  
      2017-03-02T12:27:09.618-0800: 48188.179: [GC pause (G1 Evacuation Pause) (young)
      Desired survivor size 301989888 bytes, new threshold 15 (max 15)
      - age   1:      47960 bytes,      47960 total
      - age   2:      26736 bytes,      74696 total
      - age   3:    6628208 bytes,    6702904 total
      - age   4:   15151304 bytes,   21854208 total
      - age   5:    5530024 bytes,   27384232 total
      - age   6:    5501976 bytes,   32886208 total
      - age   7:    4490976 bytes,   37377184 total
      - age   8:    1736456 bytes,   39113640 total
      - age   9:    2849184 bytes,   41962824 total
      - age  10:    2600504 bytes,   44563328 total
      - age  11:    1792992 bytes,   46356320 total
      - age  12:    1996752 bytes,   48353072 total
      - age  13:     876104 bytes,   49229176 total
      - age  14:    2233720 bytes,   51462896 total
      - age  15:    1218392 bytes,   52681288 total
      , 0.0347669 secs]
         [Parallel Time: 30.5 ms, GC Workers: 8]
            [GC Worker Start (ms): Min: 48188179.0, Avg: 48188179.0, Max: 48188179.1, Diff: 0.1]
            [Ext Root Scanning (ms): Min: 4.0, Avg: 6.2, Max: 14.5, Diff: 10.5, Sum: 49.9]
            [Update RS (ms): Min: 0.7, Avg: 8.2, Max: 10.1, Diff: 9.4, Sum: 65.9]
               [Processed Buffers: Min: 6, Avg: 12.5, Max: 22, Diff: 16, Sum: 100]
            [Scan RS (ms): Min: 0.1, Avg: 0.2, Max: 0.3, Diff: 0.2, Sum: 1.9]
            [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
            [Object Copy (ms): Min: 14.4, Avg: 15.4, Max: 15.8, Diff: 1.4, Sum: 123.1]
            [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
               [Termination Attempts: Min: 1, Avg: 1.6, Max: 3, Diff: 2, Sum: 13]
            [GC Worker Other (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.2, Sum: 0.9]
            [GC Worker Total (ms): Min: 30.2, Avg: 30.2, Max: 30.3, Diff: 0.1, Sum: 241.8]
            [GC Worker End (ms): Min: 48188209.2, Avg: 48188209.3, Max: 48188209.3, Diff: 0.2]
         [Code Root Fixup: 0.3 ms]
         [Code Root Purge: 0.0 ms]
         [Clear CT: 0.7 ms]
         [Other: 3.3 ms]
            [Choose CSet: 0.0 ms]
            [Ref Proc: 0.6 ms]
            [Ref Enq: 0.0 ms]
            [Redirty Cards: 0.4 ms]
            [Humongous Register: 0.2 ms]
            [Humongous Reclaim: 0.1 ms]
            [Free CSet: 1.5 ms]
         [Eden: 4520.0M(4520.0M)->0.0B(4520.0M) Survivors: 60.0M->60.0M Heap: 7041.7M(10.0G)->2525.3M(10.0G)]
       [Times: user=0.24 sys=0.00, real=0.03 secs]
  
   </pre>
  
  <pre>
  
      2017-03-02T12:27:10.264-0800: 48188.825: [GC pause (G1 Evacuation Pause) (young)
      Desired survivor size 301989888 bytes, new threshold 15 (max 15)
      - age   1:      48824 bytes,      48824 total
      - age   2:      18672 bytes,      67496 total
      - age   3:      17312 bytes,      84808 total
      - age   4:    6627608 bytes,    6712416 total
      - age   5:   15149168 bytes,   21861584 total
      - age   6:    5530024 bytes,   27391608 total
      - age   7:    5501976 bytes,   32893584 total
      - age   8:    4490848 bytes,   37384432 total
      - age   9:    1736456 bytes,   39120888 total
      - age  10:    2849184 bytes,   41970072 total
      - age  11:    2600504 bytes,   44570576 total
      - age  12:    1792992 bytes,   46363568 total
      - age  13:    1996752 bytes,   48360320 total
      - age  14:     876104 bytes,   49236424 total
      - age  15:    2233720 bytes,   51470144 total
      , 0.0343310 secs]
         [Parallel Time: 28.8 ms, GC Workers: 8]
            [GC Worker Start (ms): Min: 48188825.2, Avg: 48188825.3, Max: 48188825.5, Diff: 0.3]
            [Ext Root Scanning (ms): Min: 3.9, Avg: 5.9, Max: 12.0, Diff: 8.1, Sum: 47.5]
            [Update RS (ms): Min: 2.9, Avg: 8.0, Max: 9.3, Diff: 6.3, Sum: 63.6]
               [Processed Buffers: Min: 8, Avg: 11.8, Max: 21, Diff: 13, Sum: 94]
            [Scan RS (ms): Min: 0.1, Avg: 0.3, Max: 0.4, Diff: 0.3, Sum: 2.3]
            [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.0, Sum: 0.1]
            [Object Copy (ms): Min: 13.0, Avg: 14.2, Max: 14.9, Diff: 1.9, Sum: 113.3]
            [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
               [Termination Attempts: Min: 1, Avg: 1.5, Max: 2, Diff: 1, Sum: 12]
            [GC Worker Other (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.1, Sum: 0.7]
            [GC Worker Total (ms): Min: 28.3, Avg: 28.4, Max: 28.6, Diff: 0.4, Sum: 227.5]
            [GC Worker End (ms): Min: 48188853.7, Avg: 48188853.8, Max: 48188853.8, Diff: 0.1]
         [Code Root Fixup: 0.4 ms]
         [Code Root Purge: 0.0 ms]
         [Clear CT: 0.6 ms]
         [Other: 4.5 ms]
            [Choose CSet: 0.0 ms]
            [Ref Proc: 1.7 ms]
            [Ref Enq: 0.1 ms]
            [Redirty Cards: 0.3 ms]
            [Humongous Register: 0.3 ms]
            [Humongous Reclaim: 0.1 ms]
            [Free CSet: 1.7 ms]
         [Eden: 4520.0M(4520.0M)->0.0B(4524.0M) Survivors: 60.0M->56.0M Heap: 7045.3M(10.0G)->2522.1M(10.0G)]
       [Times: user=0.23 sys=0.00, real=0.03 secs]
  
   </pre>
  
  <pre>
  
      2017-03-02T12:27:10.866-0800: 48189.426: [GC pause (G1 Evacuation Pause) (young)
      Desired survivor size 301989888 bytes, new threshold 15 (max 15)
      - age   1:     579088 bytes,     579088 total
      - age   2:       9904 bytes,     588992 total
      - age   3:      18376 bytes,     607368 total
      - age   4:      14720 bytes,     622088 total
      - age   5:    6624344 bytes,    7246432 total
      - age   6:   11726288 bytes,   18972720 total
      - age   7:    5529984 bytes,   24502704 total
      - age   8:    5492072 bytes,   29994776 total
      - age   9:    4482976 bytes,   34477752 total
      - age  10:    1736360 bytes,   36214112 total
      - age  11:    2848368 bytes,   39062480 total
      - age  12:    2600504 bytes,   41662984 total
      - age  13:    1792992 bytes,   43455976 total
      - age  14:    1996752 bytes,   45452728 total
      - age  15:     876104 bytes,   46328832 total
      , 0.0350574 secs]
         [Parallel Time: 29.2 ms, GC Workers: 8]
            [GC Worker Start (ms): Min: 48189427.4, Avg: 48189427.5, Max: 48189427.6, Diff: 0.2]
            [Ext Root Scanning (ms): Min: 4.0, Avg: 5.8, Max: 11.5, Diff: 7.5, Sum: 46.0]
            [Update RS (ms): Min: 3.3, Avg: 8.2, Max: 9.6, Diff: 6.3, Sum: 65.8]
               [Processed Buffers: Min: 7, Avg: 13.0, Max: 22, Diff: 15, Sum: 104]
            [Scan RS (ms): Min: 0.1, Avg: 0.2, Max: 0.3, Diff: 0.2, Sum: 1.9]
            [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.1]
            [Object Copy (ms): Min: 13.2, Avg: 14.4, Max: 14.9, Diff: 1.7, Sum: 114.8]
            [Termination (ms): Min: 0.0, Avg: 0.3, Max: 0.3, Diff: 0.3, Sum: 2.1]
               [Termination Attempts: Min: 1, Avg: 3.8, Max: 7, Diff: 6, Sum: 30]
            [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.1, Sum: 0.4]
            [GC Worker Total (ms): Min: 28.8, Avg: 28.9, Max: 29.0, Diff: 0.2, Sum: 231.1]
            [GC Worker End (ms): Min: 48189456.4, Avg: 48189456.4, Max: 48189456.4, Diff: 0.1]
         [Code Root Fixup: 0.3 ms]
         [Code Root Purge: 0.0 ms]
         [Clear CT: 0.7 ms]
         [Other: 4.8 ms]
            [Choose CSet: 0.0 ms]
            [Ref Proc: 1.4 ms]
            [Ref Enq: 0.2 ms]
            [Redirty Cards: 0.3 ms]
            [Humongous Register: 0.9 ms]
            [Humongous Reclaim: 0.1 ms]
            [Free CSet: 1.5 ms]
         [Eden: 4524.0M(4524.0M)->0.0B(4524.0M) Survivors: 56.0M->56.0M Heap: 7046.1M(10.0G)->2525.3M(10.0G)]
       [Times: user=0.24 sys=0.00, real=0.03 secs]
  
   </pre>
  
  <pre>
  
      2017-03-02T12:27:11.515-0800: 48190.075: [GC pause (G1 Evacuation Pause) (young)
      Desired survivor size 301989888 bytes, new threshold 15 (max 15)
      - age   1:     827320 bytes,     827320 total
      - age   2:      16496 bytes,     843816 total
      - age   3:       2352 bytes,     846168 total
      - age   4:      18176 bytes,     864344 total
      - age   5:      14528 bytes,     878872 total
      - age   6:    6577816 bytes,    7456688 total
      - age   7:   11698856 bytes,   19155544 total
      - age   8:    5520560 bytes,   24676104 total
      - age   9:    5492032 bytes,   30168136 total
      - age  10:    4482976 bytes,   34651112 total
      - age  11:    1736360 bytes,   36387472 total
      - age  12:    2848368 bytes,   39235840 total
      - age  13:    2600504 bytes,   41836344 total
      - age  14:    1792992 bytes,   43629336 total
      - age  15:    1996752 bytes,   45626088 total
      , 0.0353327 secs]
         [Parallel Time: 28.5 ms, GC Workers: 8]
            [GC Worker Start (ms): Min: 48190075.8, Avg: 48190075.9, Max: 48190076.1, Diff: 0.3]
            [Ext Root Scanning (ms): Min: 3.3, Avg: 6.0, Max: 11.7, Diff: 8.4, Sum: 47.7]
            [Update RS (ms): Min: 3.1, Avg: 7.5, Max: 8.7, Diff: 5.6, Sum: 60.4]
               [Processed Buffers: Min: 6, Avg: 13.0, Max: 23, Diff: 17, Sum: 104]
            [Scan RS (ms): Min: 0.1, Avg: 0.2, Max: 0.3, Diff: 0.2, Sum: 1.9]
            [Code Root Scanning (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.1]
            [Object Copy (ms): Min: 12.8, Avg: 14.0, Max: 14.7, Diff: 1.9, Sum: 111.8]
            [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum: 0.0]
               [Termination Attempts: Min: 1, Avg: 1.4, Max: 2, Diff: 1, Sum: 11]
            [GC Worker Other (ms): Min: 0.0, Avg: 0.4, Max: 2.1, Diff: 2.1, Sum: 2.9]
            [GC Worker Total (ms): Min: 28.0, Avg: 28.1, Max: 28.2, Diff: 0.3, Sum: 224.8]
            [GC Worker End (ms): Min: 48190103.9, Avg: 48190104.0, Max: 48190104.1, Diff: 0.2]
         [Code Root Fixup: 0.4 ms]
         [Code Root Purge: 0.0 ms]
         [Clear CT: 0.7 ms]
         [Other: 5.7 ms]
            [Choose CSet: 0.0 ms]
            [Ref Proc: 2.6 ms]
            [Ref Enq: 0.0 ms]
            [Redirty Cards: 0.3 ms]
            [Humongous Register: 0.2 ms]
            [Humongous Reclaim: 0.1 ms]
            [Free CSet: 1.9 ms]
         [Eden: 4524.0M(4524.0M)->0.0B(4512.0M) Survivors: 56.0M->60.0M Heap: 7049.3M(10.0G)->2529.7M(10.0G)]
       [Times: user=0.23 sys=0.00, real=0.04 secs] 
  
  </pre>