Tại sao G1 Full GC được kích hoạt dường như không cần thiết?

Question

Tôi đang sử dụng

java version "1.7.0_09" 
Java(TM) SE Runtime Environment (build 1.7.0_09-b05) 
Java HotSpot(TM) 64-Bit Server VM (build 23.5-b02, mixed mode) 

với nhà sưu tập G1 rác. JVM argumens là

-server -Xss4096k -XX:MaxPermSize=512m -XX:PermSize=512m -Xms30G 
-Xmx30G -Xnoclassgc -XX:+UseNUMA -XX:+UseFastAccessorMethods 
-XX:ReservedCodeCacheSize=48m -XX:+UseStringCache 
-XX:+UseGCOverheadLimit -Duser.timezone=EET 
-Xmaxf1 -XX:+UseCompressedOops -XX:+DisableExplicitGC 
-XX:+AggressiveOpts -XX:CMSInitiatingOccupancyFraction=70 
-XX:+ParallelRefProcEnabled -XX:+UseAdaptiveSizePolicy 
-XX:MaxGCPauseMillis=500 -XX:+UseG1GC 
-XX:InitiatingHeapOccupancyPercent=0 
-XX:GCPauseIntervalMillis=10000 -XX:+PrintGCDetails 
-XX:+PrintHeapAtGC -XX:+PrintGCDateStamps -Xloggc:gc.log 

Tuy nhiên, tôi đang gặp phải việc quét toàn bộ GC mà không có lý do rõ ràng, cách loại bỏ chúng?

log GC với một số đuôi từ các sự kiện trước:

{Heap before GC invocations=206 (full 8): 
garbage-first heap total 31457280K, used 18323299K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000) 
    region size 8192K, 768 young (6291456K), 31 survivors (253952K) 
compacting perm gen total 524288K, used 145771K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000) 
    the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465af18, 0x00007fce7465b000, 0x00007fce8b800000) 
No shared spaces configured. 
2013-01-16T11:45:31.290+0200: 20430.451: [GC pause (young), 0.54738500 secs] 
    [Parallel Time: 510.7 ms] 
     [GC Worker Start (ms): 20430451.7 20430451.8 20430451.8 20430451.8 
     Avg: 20430451.8, Min: 20430451.7, Max: 20430451.8, Diff: 0.1] 
     [Ext Root Scanning (ms): 22.3 68.3 21.8 20.8 
     Avg: 33.3, Min: 20.8, Max: 68.3, Diff: 47.5] 
     [Update RS (ms): 21.6 0.0 23.6 23.7 
     Avg: 17.3, Min: 0.0, Max: 23.7, Diff: 23.7] 
     [Processed Buffers : 77 0 18 55 
      Sum: 150, Avg: 37, Min: 0, Max: 77, Diff: 77] 
     [Scan RS (ms): 19.6 0.1 19.3 19.6 
     Avg: 14.7, Min: 0.1, Max: 19.6, Diff: 19.5] 
     [Object Copy (ms): 439.1 434.2 437.8 438.4 
     Avg: 437.4, Min: 434.2, Max: 439.1, Diff: 4.9] 
     [Termination (ms): 0.0 0.0 0.0 0.0 
     Avg: 0.0, Min: 0.0, Max: 0.0, Diff: 0.0] 
     [Termination Attempts : 1 1 1 1 
      Sum: 4, Avg: 1, Min: 1, Max: 1, Diff: 0] 
     [GC Worker End (ms): 20430954.5 20430954.6 20430954.5 20430954.4 
     Avg: 20430954.5, Min: 20430954.4, Max: 20430954.6, Diff: 0.1] 
     [GC Worker (ms): 502.7 502.8 502.7 502.6 
     Avg: 502.7, Min: 502.6, Max: 502.8, Diff: 0.2] 
     [GC Worker Other (ms): 8.0 8.0 8.0 8.1 
     Avg: 8.0, Min: 8.0, Max: 8.1, Diff: 0.1] 
    [Clear CT: 2.6 ms] 
    [Other: 34.1 ms] 
     [Choose CSet: 0.1 ms] 
     [Ref Proc: 27.4 ms] 
     [Ref Enq: 0.2 ms] 
     [Free CSet: 5.4 ms] 
    [Eden: 5896M(5896M)->0B(5688M) Survivors: 248M->456M Heap: 17893M(30720M)->12208M(30720M)] 
[Times: user=2.12 sys=0.02, real=0.55 secs] 
Heap after GC invocations=207 (full 8): 
garbage-first heap total 31457280K, used 12501684K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000) 
    region size 8192K, 57 young (466944K), 57 survivors (466944K) 
compacting perm gen total 524288K, used 145771K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000) 
    the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465af18, 0x00007fce7465b000, 0x00007fce8b800000) 
No shared spaces configured. 
} 
{Heap before GC invocations=207 (full 8): 
garbage-first heap total 31457280K, used 19058524K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000) 
    region size 8192K, 727 young (5955584K), 57 survivors (466944K) 
compacting perm gen total 524288K, used 145775K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000) 
    the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465bdd8, 0x00007fce7465be00, 0x00007fce8b800000) 
No shared spaces configured. 
2013-01-16T11:46:26.619+0200: 20485.781: [GC pause (mixed), 1.42356500 secs] 
    [Parallel Time: 1385.9 ms] 
     [GC Worker Start (ms): 20485786.6 20485786.6 20485786.6 20485786.7 
     Avg: 20485786.6, Min: 20485786.6, Max: 20485786.7, Diff: 0.1] 
     [Ext Root Scanning (ms): 22.1 70.0 22.2 21.3 
     Avg: 33.9, Min: 21.3, Max: 70.0, Diff: 48.7] 
     [Update RS (ms): 9.9 0.0 10.9 11.2 
     Avg: 8.0, Min: 0.0, Max: 11.2, Diff: 11.2] 
     [Processed Buffers : 13 0 25 17 
      Sum: 55, Avg: 13, Min: 0, Max: 25, Diff: 25] 
     [Scan RS (ms): 324.6 276.4 324.6 324.6 
     Avg: 312.5, Min: 276.4, Max: 324.6, Diff: 48.2] 
     [Object Copy (ms): 1021.1 1031.2 1019.8 1020.5 
     Avg: 1023.1, Min: 1019.8, Max: 1031.2, Diff: 11.4] 
     [Termination (ms): 0.0 0.0 0.0 0.0 
     Avg: 0.0, Min: 0.0, Max: 0.0, Diff: 0.0] 
     [Termination Attempts : 6 5 5 1 
      Sum: 17, Avg: 4, Min: 1, Max: 6, Diff: 5] 
     [GC Worker End (ms): 20487164.3 20487164.3 20487164.3 20487164.3 
     Avg: 20487164.3, Min: 20487164.3, Max: 20487164.3, Diff: 0.0] 
     [GC Worker (ms): 1377.7 1377.6 1377.6 1377.6 
     Avg: 1377.7, Min: 1377.6, Max: 1377.7, Diff: 0.1] 
     [GC Worker Other (ms): 8.2 8.3 8.3 8.3 
     Avg: 8.3, Min: 8.2, Max: 8.3, Diff: 0.1] 
    [Clear CT: 4.4 ms] 
    [Other: 33.3 ms] 
     [Choose CSet: 5.5 ms] 
     [Ref Proc: 5.0 ms] 
     [Ref Enq: 0.2 ms] 
     [Free CSet: 9.1 ms] 
    [Eden: 5360M(5688M)->0B(5784M) Survivors: 456M->360M Heap: 18616M(30720M)->11359M(30720M)] 
[Times: user=5.56 sys=0.01, real=1.42 secs] 
Heap after GC invocations=208 (full 8): 
garbage-first heap total 31457280K, used 11632594K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000) 
    region size 8192K, 45 young (368640K), 45 survivors (368640K) 
compacting perm gen total 524288K, used 145775K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000) 
    the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465bdd8, 0x00007fce7465be00, 0x00007fce8b800000) 
No shared spaces configured. 
} 
{Heap before GC invocations=208 (full 8): 
garbage-first heap total 31457280K, used 11632594K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000) 
    region size 8192K, 45 young (368640K), 45 survivors (368640K) 
compacting perm gen total 524288K, used 145775K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000) 
    the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465bdd8, 0x00007fce7465be00, 0x00007fce8b800000) 
No shared spaces configured. 
2013-01-16T11:46:28.060+0200: 20487.222: [Full GC 11359M->8807M(30720M), 32.4879420 secs] 
[Times: user=45.41 sys=0.21, real=32.48 secs] 
Heap after GC invocations=209 (full 9): 
garbage-first heap total 31457280K, used 9019206K [0x00007fc6eb800000, 0x00007fce6b800000, 0x00007fce6b800000) 
    region size 8192K, 0 young (0K), 0 survivors (0K) 
compacting perm gen total 524288K, used 145775K [0x00007fce6b800000, 0x00007fce8b800000, 0x00007fce8b800000) 
    the space 524288K, 27% used [0x00007fce6b800000, 0x00007fce7465bdd8, 0x00007fce7465be00, 0x00007fce8b800000) 
No shared spaces configured. 
} 

những cái tương tự khác:

{Heap before GC invocations=105 (full 4): 
garbage-first heap total 31457280K, used 12638024K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000) 
    region size 8192K, 56 young (458752K), 56 survivors (458752K) 
compacting perm gen total 524288K, used 147352K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000) 
    the space 524288K, 28% used [0x00007fd2a2800000, 0x00007fd2ab7e61f8, 0x00007fd2ab7e6200, 0x00007fd2c2800000) 
No shared spaces configured. 
2013-01-14T10:31:31.240+0200: 14185.812: [Full GC 12341M->7092M(30720M), 25.3417840 secs] 
[Times: user=35.12 sys=0.21, real=25.33 secs] 
Heap after GC invocations=106 (full 5): 
garbage-first heap total 31457280K, used 7262578K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000) 
    region size 8192K, 0 young (0K), 0 survivors (0K) 
compacting perm gen total 524288K, used 147352K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000) 
    the space 524288K, 28% used [0x00007fd2a2800000, 0x00007fd2ab7e61f8, 0x00007fd2ab7e6200, 0x00007fd2c2800000) 
No shared spaces configured. 
} 

{Heap before GC invocations=248 (full 11): 
garbage-first heap total 31457280K, used 12262418K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000) 
    region size 8192K, 37 young (303104K), 37 survivors (303104K) 
compacting perm gen total 524288K, used 152608K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000) 
    the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2abd082e8, 0x00007fd2abd08400, 0x00007fd2c2800000) 
No shared spaces configured. 
2013-01-14T13:01:39.869+0200: 23194.441: [Full GC 11975M->7331M(30720M), 28.6147390 secs] 
[Times: user=40.31 sys=0.03, real=28.62 secs] 
Heap after GC invocations=249 (full 12): 
garbage-first heap total 31457280K, used 7507920K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000) 
    region size 8192K, 0 young (0K), 0 survivors (0K) 
compacting perm gen total 524288K, used 152608K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000) 
    the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2abd082e8, 0x00007fd2abd08400, 0x00007fd2c2800000) 
No shared spaces configured. 
} 

{Heap before GC invocations=399 (full 19): 
garbage-first heap total 31457280K, used 13016093K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000) 
    region size 8192K, 54 young (442368K), 54 survivors (442368K) 
compacting perm gen total 524288K, used 155475K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000) 
    the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2abfd4c70, 0x00007fd2abfd4e00, 0x00007fd2c2800000) 
No shared spaces configured. 
2013-01-14T15:31:36.484+0200: 32191.056: [Full GC 12711M->7543M(30720M), 29.secs] 
[Times: user=41.39 sys=0.06, real=29.50 secs] 
Heap after GC invocations=400 (full 20): 
garbage-first heap total 31457280K, used 7724994K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000) 
    region size 8192K, 0 young (0K), 0 survivors (0K) 
compacting perm gen total 524288K, used 155475K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000) 
    the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2abfd4c70, 0x00007fd2abfd4e00, 0x00007fd2c2800000) 
No shared spaces configured. 
} 

{Heap before GC invocations=476 (full 26): 
garbage-first heap total 31457280K, used 14622246K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000) 
    region size 8192K, 27 young (221184K), 27 survivors (221184K) 
compacting perm gen total 524288K, used 156716K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000) 
    the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2ac10b2b0, 0x00007fd2ac10b400, 0x00007fd2c2800000) 
No shared spaces configured. 
2013-01-14T18:46:41.545+0200: 43896.117: [Full GC 14279M->8107M(30720M), 31.6936770 secs] 
[Times: user=44.40 sys=0.18, real=31.69 secs] 
Heap after GC invocations=477 (full 27): 
garbage-first heap total 31457280K, used 8302054K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000) 
    region size 8192K, 0 young (0K), 0 survivors (0K) 
compacting perm gen total 524288K, used 156551K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000) 
    the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2ac0e1fa0, 0x00007fd2ac0e2000, 0x00007fd2c2800000) 
No shared spaces configured. 
} 

{Heap before GC invocations=522 (full 34): 
garbage-first heap total 31457280K, used 16096219K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000) 
    region size 8192K, 30 young (245760K), 30 survivors (245760K) 
compacting perm gen total 524288K, used 156869K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000) 
    the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2ac1315d8, 0x00007fd2ac131600, 0x00007fd2c2800000) 
No shared spaces configured. 
2013-01-14T22:31:40.711+0200: 57395.283: [Full GC 15718M->11933M(30720M), 42.0857250 secs] 
[Times: user=60.13 sys=0.07, real=42.08 secs] 
Heap after GC invocations=523 (full 35): 
garbage-first heap total 31457280K, used 12219927K [0x00007fcb22800000, 0x00007fd2a2800000, 0x00007fd2a2800000) 
    region size 8192K, 0 young (0K), 0 survivors (0K) 
compacting perm gen total 524288K, used 156869K [0x00007fd2a2800000, 0x00007fd2c2800000, 0x00007fd2c2800000) 
    the space 524288K, 29% used [0x00007fd2a2800000, 0x00007fd2ac1315d8, 0x00007fd2ac131600, 0x00007fd2c2800000) 
No shared spaces configured. 
} 

báo cáo vấn đề tương tự khác:

http://grokbase.com/t/openjdk/hotspot-gc-use/1192sy84j5/g1c-strange-full-gc-behavior http://grokbase.com/p/openjdk/hotspot-gc-use/123ydf9c92/puzzling-why-is-a-full-gc-triggered-here http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2013-February/001484.html

Tôi đã phân tích vấn đề bằng cách sử dụng profiler appdynamics và tôi đã phát hiện ra rằng mỗi khi Full GC xảy ra, Code Cache (được cấu hình đến mức tối đa) đã đầy. Nó có vẻ giống như một lỗi trong GC.

Xem thêm hình ảnh hồ sơ, hai GC đầy đủ không cần thiết: s ở giữa 24/5 và 25/5. Quan trọng hơn, họ giết khả năng sử dụng máy chủ, vì họ kéo dài 60 giây cho mỗi:

Profiler log image http://eisler.vps.kotisivut.com/logs/g1gc-code-cache-full-gc-bug-illustration.png

Xem thêm thảo luận về GC pauseless Azul, họ dường như đã tìm ra loại vấn đề http://www.artima.com/lejava/articles/azul_pauseless_gc.html

Answer 1

Chúng tôi ghi nhận lỗi này trên 1,7 ._u06 và nâng cấp lên 1.7.0_21-b11 chỉ vài ngày trước và chúng tôi chưa thấy bất kỳ Full GC nào kể từ khi nâng cấp, vì vậy có vẻ như lỗi này đã được sửa trong JVM. Các cấu hình bộ nhớ cache của mã trông đẹp hơn nhiều trong trình lược tả. Trong quá khứ, vấn đề này từng là vấn đề hàng ngày, một lần đến nhiều lần mỗi ngày.

Nếu tình hình thay đổi, tôi sẽ báo cáo lại. Cho đến lúc đó, tôi xem vấn đề này đã được giải quyết với bản nâng cấp.

Answer 2

xin vui lòng xem trả lời của tôi trong G1GC long pause with initial-mark

mọi cài đặt của bạn phải có lý do chắc chắn để ở đây ... và rất tiếc một số thiết bị không có ví dụ-XX:+UseBiasedLocking (used for combination of tenured and young generation GCs, but G1GC is capable to handle both) -XX:+DisableExplicitGC (its unpredictable, in my experience its never restrict explicit gc calls)

xin vui lòng sử dụng/tinh chỉnh các thiết lập phù hợp dưới đây đề cập để có được kết quả tối ưu, tôi đem lại cho bạn cơ bản để di chuyển về phía trước, hy vọng như vậy các thiết lập này sẽ làm việc cho bạn: Java G1 garbage collection in production