blocks|key|249799|text|是的，G1是Java1.7JVM中新的标准垃圾收集器。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|249800|Here您可以找到有关如何使用和配置新的垃圾收集器的大量信息：|offset|length|249801|使用G1+G1的|249802|仍被认为是实验性的，可以通过以下两个参数启用：|blockquote|249803|249804|-XX:%2BUnlockExperimentalVMOptions+-XX:%2BUseG1GC|249805|要设置GC暂停时间目标，请使用以下参数：|249806|-XX:MaxGCPauseMillis+=50+(暂停时间目标为50ms)|249807|使用G1，可以指定一个时间间隔，在此时间间隔内GC暂停的持续时间不应超过上面指定的时间：|249808|-XX:GCPauseIntervalMillis+=200+(对于200ms的暂停间隔目标)|249809|请注意，以上两个选项代表的是目标，而不是承诺或保证。它们可能在某些情况下工作得很好，但在另一些情况下却不是这样，GC可能并不总是能够遵守它们。|249810|或者，可以明确指定年轻一代的大小，以影响疏散暂停时间：|249811|-XX:%2BG1YoungGenSize=512m+(针对512兆字节的年轻一代)|249812|G1还使用等效的幸存空间，这自然是一组(可能不连续的)区域。它们的大小可以用通常的参数指定(例如，-XX:SurvivorRatio=6)。|249813|最后，为了最大限度地运行G1，请尝试设置这两个参数，这两个参数当前默认情况下是禁用的，因为它们可能会发现一种罕见的竞争条件：|249814|-XX:%2BG1ParallelRSetUpdatingEnabled+-XX:%2BG1ParallelRSetScanningEnabled|249815|另一件需要注意的事情是，当设置了-XX:%2BPrintGCDetails时，与其他HotSpot+GC相比，G1非常冗长。这是因为它打印每个GC线程的计时和其他信息，这些信息对分析和故障排除非常有帮助。如果您想要更简洁的GC日志，请切换到使用-verbosegc+(但建议获取更详细的GC日志)。|249816|249817|我也发现this文章对理解G1的内幕很有帮助。|249818|更多信息here。|249819|entityMap|0|LINK|mutability|MUTABLE|url|http://www.oracle.com/technetwork/java/javase/tech/g1-intro-jsp-135488.html|1|http://drdobbs.com/java/219401061?pgno=1|2|https://stackoverflow.com/questions/2254041/java-g1-garbage-collection-in-production^0|0|0|4|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|4|4|1|0|4|4|2|0^^$0|@$1|2|3|4|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1R|8|@]|9|@$D|1S|E|1T|1|1U]]|A|$]]|$1|F|3|G|5|6|7|1V|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|1W|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|1X|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|1Y|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|1Z|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|20|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|21|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|22|8|@]|9|@]|A|$]]|$1|V|3|W|5|6|7|23|8|@]|9|@]|A|$]]|$1|X|3|Y|5|6|7|24|8|@]|9|@]|A|$]]|$1|Z|3|10|5|6|7|25|8|@]|9|@]|A|$]]|$1|11|3|12|5|6|7|26|8|@]|9|@]|A|$]]|$1|13|3|14|5|6|7|27|8|@]|9|@]|A|$]]|$1|15|3|16|5|6|7|28|8|@]|9|@]|A|$]]|$1|17|3|18|5|6|7|29|8|@]|9|@]|A|$]]|$1|19|3|-4|5|6|7|2A|8|@]|9|@]|A|$]]|$1|1A|3|1B|5|6|7|2B|8|@]|9|@$D|2C|E|2D|1|2E]]|A|$]]|$1|1C|3|1D|5|6|7|2F|8|@]|9|@$D|2G|E|2H|1|2I]]|A|$]]|$1|1E|3|-4|5|6|7|2J|8|@]|9|@]|A|$]]]|1F|$1G|$5|1H|1I|1J|A|$1K|1L]]|1M|$5|1H|1I|1J|A|$1K|1N]]|1O|$5|1H|1I|1J|A|$1K|1P]]]]

Yes, G1 is the new standard garbage collector in Java 1.7 JVM.

<a href="http://www.oracle.com/technetwork/java/javase/tech/g1-intro-jsp-135488.html" rel="nofollow noreferrer">Here</a> you can find plenty of information on how to use and configre the new garbage collector:

<blockquote>
 Using G1 G1 is still considered experimental and can be enabled with
 the following two parameters:
 
 -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC
 
 To set a GC pause time goal, use the following parameter:
 
 -XX:MaxGCPauseMillis =50 (for a pause time target of 50ms)
 
 With G1, a time interval can be specified during which a GC pause
 should last no longer than the time given above:
 
 -XX:GCPauseIntervalMillis =200 (for a pause interval target of 200ms)
 
 Note that the above two options represent goals, not promises or
 guarantees. They might work well in some situations but not in others,
 and the GC might not always be able to obey them.
 
 Alternatively, the size of the young generation can be specified
 explicitly to impact evacuation pause times:
 
 -XX:+G1YoungGenSize=512m (for a 512 megabyte young generation)
 
 G1 also uses the equivalent of survivor spaces, which are, naturally,
 a set of (potentially non-contiguous) regions. Their size can be
 specified with the usual parameters (e.g., -XX:SurvivorRatio=6).
 
 Finally, to run G1 at its full potential, try setting these two
 parameters which are currently disabled by default because they may
 uncover a rare race condition:
 
 -XX:+G1ParallelRSetUpdatingEnabled -XX:+G1ParallelRSetScanningEnabled
 
 One more thing to note is that G1 is very verbose compared to other
 HotSpot GCs when -XX:+PrintGCDetails is set. This is because it prints
 per-GC-thread timings and other information very helpful in profiling
 and trouble-shooting. If you want a more concise GC log, please switch
 to using -verbosegc (though it is recommended that the more detailed
 GC log be obtained).
</blockquote>

I have also found <a href="http://drdobbs.com/java/219401061?pgno=1" rel="nofollow noreferrer">this</a> article very helpful in understanding the inners of G1.

Even more info <a href="https://stackoverflow.com/questions/2254041/java-g1-garbage-collection-in-production">here</a>.

blocks|key|248171|text|在我的Java+1.7.0_01安装中，G1垃圾收集器不是默认的。您可以通过使用一些额外的命令行选项来亲自查看：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|248172|>+java+-XX:%2BPrintCommandLineFlags+-XX:%2BPrintGCDetails+-version
-XX:InitialHeapSize=132304640+-XX:MaxHeapSize=2116874240+-XX:ParallelGCThreads=4+-XX:%2BPrintCommandLineFlags+-XX:%2BPrintGCDetails+-XX:%2BUseCompressedOops+-XX:-UseLargePagesIndividualAllocation+-XX:%2BUseParallelGC
java+version+"1.7.0_01"
Java(TM)+SE+Runtime+Environment+(build+1.7.0_01-b08)
Java+HotSpot(TM)+64-Bit+Server+VM+(build+21.1-b02,+mixed+mode)
Heap
+PSYoungGen++++++total+37696K,+used+1293K+[0x00000007d5eb0000,+0x00000007d88c0000,+0x0000000800000000)
++eden+space+32320K,+4%25+used+[0x00000007d5eb0000,0x00000007d5ff3408,0x00000007d7e40000)
++from+space+5376K,+0%25+used+[0x00000007d8380000,0x00000007d8380000,0x00000007d88c0000)
++to+++space+5376K,+0%25+used+[0x00000007d7e40000,0x00000007d7e40000,0x00000007d8380000)
+PSOldGen++++++++total+86144K,+used+0K+[0x0000000781c00000,+0x0000000787020000,+0x00000007d5eb0000)
++object+space+86144K,+0%25+used+[0x0000000781c00000,0x0000000781c00000,0x0000000787020000)
+PSPermGen+++++++total+21248K,+used+2032K+[0x000000077ca00000,+0x000000077dec0000,+0x0000000781c00000)
++object+space+21248K,+9%25+used+[0x000000077ca00000,0x000000077cbfc288,0x000000077dec0000)|code-block|syntax|javascript|248173|不过，您不再需要启用实验选项即可打开G1收集器：|248174|>+java+-XX:%2BPrintCommandLineFlags+-XX:%2BPrintGCDetails+-XX:%2BUseG1GC+-version
-XX:InitialHeapSize=132304640+-XX:MaxHeapSize=2116874240+-XX:%2BPrintCommandLineFlags+-XX:%2BPrintGCDetails+-XX:%2BUseCompressedOops+-XX:%2BUseG1GC+-XX:-UseLargePagesIndividualAllocation
java+version+"1.7.0_01"
Java(TM)+SE+Runtime+Environment+(build+1.7.0_01-b08)
Java+HotSpot(TM)+64-Bit+Server+VM+(build+21.1-b02,+mixed+mode)
Heap
+garbage-first+heap+++total+130048K,+used+0K+[0x000000077ca00000,+0x0000000784900000,+0x00000007fae00000)
++region+size+1024K,+1+young+(1024K),+0+survivors+(0K)
+compacting+perm+gen++total+20480K,+used+2032K+[0x00000007fae00000,+0x00000007fc200000,+0x0000000800000000)
+++the+space+20480K,+++9%25+used+[0x00000007fae00000,+0x00000007faffc288,+0x00000007faffc400,+0x00000007fc200000)
No+shared+spaces+configured.|248175|我不知道你在哪里能找到好的文档。|248176|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

The G1 garbage collector is not the default in my installation of Java, version 1.7.0_01. You can see for yourself by using with some extra command line options:

<pre><code>&gt; java -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -version
-XX:InitialHeapSize=132304640 -XX:MaxHeapSize=2116874240 -XX:ParallelGCThreads=4 -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC
java version "1.7.0_01"
Java(TM) SE Runtime Environment (build 1.7.0_01-b08)
Java HotSpot(TM) 64-Bit Server VM (build 21.1-b02, mixed mode)
Heap
 PSYoungGen total 37696K, used 1293K [0x00000007d5eb0000, 0x00000007d88c0000, 0x0000000800000000)
 eden space 32320K, 4% used [0x00000007d5eb0000,0x00000007d5ff3408,0x00000007d7e40000)
 from space 5376K, 0% used [0x00000007d8380000,0x00000007d8380000,0x00000007d88c0000)
 to space 5376K, 0% used [0x00000007d7e40000,0x00000007d7e40000,0x00000007d8380000)
 PSOldGen total 86144K, used 0K [0x0000000781c00000, 0x0000000787020000, 0x00000007d5eb0000)
 object space 86144K, 0% used [0x0000000781c00000,0x0000000781c00000,0x0000000787020000)
 PSPermGen total 21248K, used 2032K [0x000000077ca00000, 0x000000077dec0000, 0x0000000781c00000)
 object space 21248K, 9% used [0x000000077ca00000,0x000000077cbfc288,0x000000077dec0000)
</code></pre>

You don't need to enable experimental options to turn on the G1 collector any more, though:

<pre><code>&gt; java -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseG1GC -version
-XX:InitialHeapSize=132304640 -XX:MaxHeapSize=2116874240 -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseCompressedOops -XX:+UseG1GC -XX:-UseLargePagesIndividualAllocation
java version "1.7.0_01"
Java(TM) SE Runtime Environment (build 1.7.0_01-b08)
Java HotSpot(TM) 64-Bit Server VM (build 21.1-b02, mixed mode)
Heap
 garbage-first heap total 130048K, used 0K [0x000000077ca00000, 0x0000000784900000, 0x00000007fae00000)
 region size 1024K, 1 young (1024K), 0 survivors (0K)
 compacting perm gen total 20480K, used 2032K [0x00000007fae00000, 0x00000007fc200000, 0x0000000800000000)
 the space 20480K, 9% used [0x00000007fae00000, 0x00000007faffc288, 0x00000007faffc400, 0x00000007fc200000)
No shared spaces configured.
</code></pre>

I don't know where you can find any good documentation.

blocks|key|251162|text|在http://www.oracle.com/technetwork/java/javase/tech/g1-intro-jsp-135488.html+(由Wojtek提供的链接)上提供的文档似乎是唯一的官方信息链接，但信息似乎过时了，因为提到的一些标志只在测试版本中可用，它们不再存在于生产版本中。Oracle的某个人应该提供一些关于G1+GC的更新文档。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|251163|entityMap|0|LINK|mutability|MUTABLE|url|http://www.oracle.com/technetwork/java/javase/tech/g1-intro-jsp-135488.html^0|1|23|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

The documentation available at <a href="http://www.oracle.com/technetwork/java/javase/tech/g1-intro-jsp-135488.html" rel="nofollow">http://www.oracle.com/technetwork/java/javase/tech/g1-intro-jsp-135488.html</a> (the link provided by Wojtek) seems to be the only official link with info but the info seems outdated as some of the flags mentioned there were only available in the test builds, they no longer exist in the production releases. Some one from Oracle should provide some updated documentation on the G1 GC.

blocks|key|246250|text|在jdk+1.7.0_02中，No+G1不是默认的垃圾收集器。默认垃圾收集器取决于机器的类别。如果机器属于Server类，那么默认的垃圾收集器是吞吐量收集器。如果机器属于客户端类，那么默认的垃圾收集器是串行收集器。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|246251|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

No G1 is not default garbage collector in jdk 1.7.0_02.
The default garbage collector depends upon the class of machine.
If the machine is of Server class then the default garbage collector is Throughput Collector.
If the machine is of Client class then the default garbage collector is Serial Collector.

blocks|key|3140285|text|甲骨文终于在Java7+U4中正式发布了G1：http://www.oracle.com/technetwork/java/javase/7u4-relnotes-1575007.html|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3140286|描述：http://docs.oracle.com/javase/7/docs/technotes/guides/vm/G1.html|3140287|命令行选项：http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html#G1Options|3140288|不过，我不认为它是Java+7中的默认收集器。对于服务器，默认的收集器是Java+6中的并行收集器。|3140289|entityMap|0|LINK|mutability|MUTABLE|url|http://www.oracle.com/technetwork/java/javase/7u4-relnotes-1575007.html|1|http://docs.oracle.com/javase/7/docs/technotes/guides/vm/G1.html|2|http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html#G1Options^0|N|1Z|0|0|3|1S|1|0|6|2E|2|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@$A|W|B|X|1|Y]]|C|$]]|$1|D|3|E|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|F|3|G|5|6|7|13|8|@]|9|@$A|14|B|15|1|16]]|C|$]]|$1|H|3|I|5|6|7|17|8|@]|9|@]|C|$]]|$1|J|3|-4|5|6|7|18|8|@]|9|@]|C|$]]]|K|$L|$5|M|N|O|C|$P|Q]]|R|$5|M|N|O|C|$P|S]]|T|$5|M|N|O|C|$P|U]]]]

Oracle finally made G1 official in Java 7 U4:
<a href="http://www.oracle.com/technetwork/java/javase/7u4-relnotes-1575007.html">http://www.oracle.com/technetwork/java/javase/7u4-relnotes-1575007.html</a>

Description:
<a href="http://docs.oracle.com/javase/7/docs/technotes/guides/vm/G1.html">http://docs.oracle.com/javase/7/docs/technotes/guides/vm/G1.html</a>

Command line options:
<a href="http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html#G1Options">http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html#G1Options</a>

Still, I do not think it is the default collector in Java 7. For servers the default is the Parallel Collector as in Java 6.

blocks|key|2925979|text|1.+G1是Java7中的默认收集器吗(...)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2925980|this+Java+5+page上的规则仍然适用于Java7(以及AFAIK、Java8)：|offset|length|2925981|2925982|在运行服务器VM的server-class计算机上，垃圾收集器(GC)已从以前的串行收集器(-XX:%2BUseSerialGC)更改为并行收集器(-XX:%2BUseParallelGC)。|blockquote|2925983|2925984|2925985|但也要考虑：|2925986|2925987|64位JVM不随-client+VM一起提供，因此自Java7以来，始终是|unordered-list-item|style|CODE|2925988|，使用-XX:%2BUseParallelGC+(无论是设置的还是隐含的)还意味着-XX:%2BUseParallelOldGC+(即，除非显式禁用)|2925989|2925990|例如，如果在Windows+x64上运行...|2925991|对于64位的|2925992|Java7，默认情况下会得到并行GC+(既适用于年轻一代，也适用于老一代)。|2925993|Java8+32位，默认情况下获得串行GC+(两代)|2925994|2925995|1.+(...)如何开通G1？|2925996|从Java7开始，只需使用-XX:%2BUseG1GC。也许你也会感兴趣的是你想要的when：|2925997|如果应用程序具有以下一个或多个特征，则使用内容管理系统或ParallelOld垃圾收集器运行的|2925998|应用程序将有利于切换到G1。|2925999|2926000|2926001|2926002|超过50%25的Java堆被实时数据占用。|2926003|对象分配率或提升的速率因长时间垃圾收集或压缩暂停(大于0.5到1秒)而异|2926004|2926005|2.+Java7中g1有哪些可选设置？|2926006|我自己没有使用过G1，但我使用了I+gather，因为它遵循用于调优其他并行收集器的相同的基本“吞吐量/人体工程学”标志。在我使用并行GC的经验中，-XX:GCTimeRatio在提供预期的速度和内存折衷方面起到了关键作用。YMMV.|2926007|here中列出了特定于G1的选项|2926008|3.+(...)有变化吗？是cms还是Java+7中的并行收集器？|2926009|不知道，but...|2926010|2926011|+G1计划作为并发标记-清除收集器(CMS)的长期替代产品|2926012|2926013|2926014|4.在哪里可以找到关于Java+7中垃圾回收的好文档？|2926015|这可能是一个痛苦的发现，不是吗？也许我找到的最好的“中心”页面是这个：|2926016|http://www.oracle.com/technetwork/java/javase/tech/index-jsp-140228.html|2926017|需要一些深入的阅读，但如果您需要进行一些调整，则值得花费时间。特别有见地的是：Garbage+Collector+Ergonomics|2926018|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/1.5.0/docs/guide/vm/gc-ergonomics.html|1|http://docs.oracle.com/javase/1.5.0/docs/guide/vm/server-class.html|2|http://docs.oracle.com/javase/7/docs/technotes/guides/vm/G1.html|3|http://bugs.sun.com/view_bug.do?bug_id=6937160|4|http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html|5|6|7|http://www.oracle.com/technetwork/java/javase/gc-tuning-6-140523.html^0|0|0|G|0|0|0|9|C|1|0|0|0|0|0|8|7|0|0|0|0|0|0|0|0|0|D|C|14|4|2|0|0|0|0|0|0|0|0|0|0|22|F|G|8|3|0|0|4|4|0|0|4|6|5|0|0|0|0|0|0|0|0|20|6|0|13|S|7|0^^$0|@$1|2|3|4|5|6|7|2S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|2T|8|@]|9|@$D|2U|E|2V|1|2W]]|A|$]]|$1|F|3|-4|5|6|7|2X|8|@]|9|@]|A|$]]|$1|G|3|H|5|I|7|2Y|8|@]|9|@$D|2Z|E|30|1|31]]|A|$]]|$1|J|3|-4|5|6|7|32|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|33|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|34|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|35|8|@]|9|@]|A|$]]|$1|O|3|P|5|Q|7|36|8|@$D|37|E|38|R|S]]|9|@]|A|$]]|$1|T|3|U|5|Q|7|39|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|3A|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|3B|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|3C|8|@]|9|@]|A|$]]|$1|10|3|11|5|Q|7|3D|8|@]|9|@]|A|$]]|$1|12|3|13|5|Q|7|3E|8|@]|9|@]|A|$]]|$1|14|3|-4|5|6|7|3F|8|@]|9|@]|A|$]]|$1|15|3|16|5|6|7|3G|8|@]|9|@]|A|$]]|$1|17|3|18|5|6|7|3H|8|@$D|3I|E|3J|R|S]]|9|@$D|3K|E|3L|1|3M]]|A|$]]|$1|19|3|1A|5|6|7|3N|8|@]|9|@]|A|$]]|$1|1B|3|1C|5|I|7|3O|8|@]|9|@]|A|$]]|$1|1D|3|-4|5|6|7|3P|8|@]|9|@]|A|$]]|$1|1E|3|-4|5|6|7|3Q|8|@]|9|@]|A|$]]|$1|1F|3|-4|5|6|7|3R|8|@]|9|@]|A|$]]|$1|1G|3|1H|5|Q|7|3S|8|@]|9|@]|A|$]]|$1|1I|3|1J|5|Q|7|3T|8|@]|9|@]|A|$]]|$1|1K|3|-4|5|6|7|3U|8|@]|9|@]|A|$]]|$1|1L|3|1M|5|6|7|3V|8|@]|9|@]|A|$]]|$1|1N|3|1O|5|6|7|3W|8|@$D|3X|E|3Y|R|S]]|9|@$D|3Z|E|40|1|41]]|A|$]]|$1|1P|3|1Q|5|6|7|42|8|@]|9|@$D|43|E|44|1|45]]|A|$]]|$1|1R|3|1S|5|6|7|46|8|@]|9|@]|A|$]]|$1|1T|3|1U|5|6|7|47|8|@]|9|@$D|48|E|49|1|4A]]|A|$]]|$1|1V|3|-4|5|6|7|4B|8|@]|9|@]|A|$]]|$1|1W|3|1X|5|I|7|4C|8|@]|9|@]|A|$]]|$1|1Y|3|-4|5|6|7|4D|8|@]|9|@]|A|$]]|$1|1Z|3|-4|5|6|7|4E|8|@]|9|@]|A|$]]|$1|20|3|21|5|6|7|4F|8|@]|9|@]|A|$]]|$1|22|3|23|5|6|7|4G|8|@]|9|@]|A|$]]|$1|24|3|25|5|6|7|4H|8|@]|9|@$D|4I|E|4J|1|4K]]|A|$]]|$1|26|3|27|5|6|7|4L|8|@]|9|@$D|4M|E|4N|1|4O]]|A|$]]|$1|28|3|-4|5|6|7|4P|8|@]|9|@]|A|$]]]|29|$2A|$5|2B|2C|2D|A|$2E|2F]]|2G|$5|2B|2C|2D|A|$2E|2H]]|2I|$5|2B|2C|2D|A|$2E|2J]]|2K|$5|2B|2C|2D|A|$2E|2L]]|2M|$5|2B|2C|2D|A|$2E|2N]]|2O|$5|2B|2C|2D|A|$2E|2J]]|2P|$5|2B|2C|2D|A|$2E|25]]|2Q|$5|2B|2C|2D|A|$2E|2R]]]]

1. Is G1 the default collector in Java 7 (...)

The rule on <a href="http://docs.oracle.com/javase/1.5.0/docs/guide/vm/gc-ergonomics.html">this Java 5 page</a> is still applicable in Java 7 (and AFAIK, Java 8):

<blockquote>
 On <a href="http://docs.oracle.com/javase/1.5.0/docs/guide/vm/server-class.html">server-class</a> machines running the server VM, the garbage collector (GC) has changed from the previous serial collector (-XX:+UseSerialGC) to a parallel collector (-XX:+UseParallelGC).
</blockquote>

But also consider: 

<ul>
<li>64-bit JVMs do not come with a <code>-client</code> VM, so are always "server class"</li>
<li>Since Java 7, using -XX:+UseParallelGC (whether set or implied) additionally implies -XX:+UseParallelOldGC (i.e. unless explicitly disabled)</li>
</ul>

For example, if on Windows x64 you run...

<ul>
<li>Java 7 64-bit, you get Parallel GC (for both young and old generations) by default. </li>
<li>Java 8 32-bit, you get Serial GC (for both generations) by default</li>
</ul>

1. (...) how do I activate G1?

As of Java 7, simply <code>-XX:+UseG1GC</code>. Perhaps also of interest is <a href="http://docs.oracle.com/javase/7/docs/technotes/guides/vm/G1.html">when</a> you would want to:

<blockquote>
 Applications running today with either the CMS or the ParallelOld garbage collector would benefit switching to G1 if the application has one or more of the following traits.
 
 <ul>
 <li>More than 50% of the Java heap is occupied with live data.</li>
 <li>The rate of object allocation rate or promotion varies significantly.</li>
 <li>Undesired long garbage collection or compaction pauses (longer than 0.5 to 1 second)</li>
 </ul>
</blockquote>

2. What optional settings does g1 have in Java7?

I've not used G1 myself, but <a href="http://bugs.sun.com/view_bug.do?bug_id=6937160">I gather</a> that it adheres to the same basic "throughput / ergonomic" flags used to tune the other parallel collectors. In my experience with the Parallel GC, <code>-XX:GCTimeRatio</code> has been the pivotal one in providing the expected speed-memory tradeoff. YMMV.

G1-specific options are listed <a href="http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html">here</a>

3. Were there changes to (...) cms or the parallel collector in Java 7?

Don't know, <a href="http://docs.oracle.com/javase/7/docs/technotes/guides/vm/G1.html">but...</a> 

<blockquote>
 G1 is planned as the long term replacement for the Concurrent Mark-Sweep Collector (CMS)
</blockquote>

4. Where can I find good documentation on garbage collection in Java 7?

It can be a pain to find, can't it? Probably the best "hub" page I've found is this one:

<a href="http://www.oracle.com/technetwork/java/javase/tech/index-jsp-140228.html">http://www.oracle.com/technetwork/java/javase/tech/index-jsp-140228.html</a>

Some deep reading required, but worth the time if you need to do some tuning. Particularly insightful is: <a href="http://www.oracle.com/technetwork/java/javase/gc-tuning-6-140523.html">Garbage Collector Ergonomics</a>

blocks|key|249908|text|默认情况下，您并不真正想使用G1收集器，因为它并不比其他收集器更好。它只适用于特殊用途。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|249909|在低延迟的应用程序中，is比CMS好得多，因为它的暂停时间更短，更可预测。在交换中，吞吐量比交换中的CMS差得多。|249910|因此，只有在延迟很重要的情况下才是好的，但吞吐量根本不重要。如果两者都很重要，那么请继续使用CMS。|249911|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

By default you don't really want to use G1 collector, as it is not really better than the others. It is only good for special purposes.

In low latency application is is sligthly better than CMS, as it has a little bit shorter, and more predictable pause times. In exchange the throughput is much worse than CMS in exchange.

So it is only good if the latency is important, but the throughput is not important at all. If both are important, then stay with CMS.

blocks|key|246308|text|type|unstyled|depth|inlineStyleRanges|entityRanges|data|246309|blockquote|246310|246311|246312|是Java7中的默认收集器，如果不是，如何激活G1?|ordered-list-item|246313|246314|G1不是Java7中的默认收集器，-XX:%2BUseG1GC将启用G1GC|offset|length|style|CODE|246315|246316|246317|246318|246319|+g1在Java7中有哪些可选设置？|246320|246321|有很多。有关完整的信息，请参阅这篇oracle文章。|246322|246323|+G1+GC是一个自适应垃圾收集器，其默认设置使其无需修改即可高效工作。|246324|246325|246326|由于这个原因，自定义关键参数|BOLD|246327|-XX:MaxGCPauseMillis
-XX:G1HeapRegionSize
-XX:ParallelGCThreads
-XX:ConcGCThreads|code-block|syntax|javascript|246328|，并将所有其他参数保留为默认值。|246329|以下是重要选项及其默认值的列表。此列表适用于最新的Java+HotSpot+VM，build+24。您可以在G1命令行上调整和调优JVM设置。|246330|重要默认值：|246331|-XX:G1HeapRegionSize=n|246332|设置G1区域的大小。该值将是2的幂，范围从1MB到32MB。我们的目标是基于最小Java堆大小拥有大约2048个区域。|246333|-XX:MaxGCPauseMillis=200|246334|设置所需最大停顿时间的目标值。默认值为200毫秒。指定的值不适合您的堆大小。|246335|-XX:G1NewSizePercent=5|246336|设置要用作年轻代大小的最小值的堆的百分比。默认值是您的Java堆的5%25。|246337|-XX:G1MaxNewSizePercent=60|246338|设置堆大小的百分比，以用作年轻代大小的最大值。默认值是您的Java堆的60+%25。|246339|-XX:ParallelGCThreads=n|246340|设置STW工作线程的值。将n的值设置为逻辑处理器的数量。N的值与逻辑处理器的数量相同，最多不超过8。|246341|如果有8个以上的逻辑处理器，则将n的值设置为逻辑处理器的大约5/8。这在大多数情况下都是有效的，除了较大的SPARC系统，其中n的值可以大约是逻辑处理器的5/16。|246342|-XX:ConcGCThreads=n|246343|设置并行标记线程的数量。将n设置为并行垃圾回收线程(ParallelGCThreads)数量的大约1/4。|246344|-XX:InitiatingHeapOccupancyPercent=45|246345|设置触发标记周期的Java堆占用阈值。默认的占用率是整个Java堆的45+%25。|246346|-XX:G1MixedGCLiveThresholdPercent=65|246347|设置要包括在混合垃圾收集周期中的旧区域的占用阈值。默认占用率为65%25|246348|-XX:G1HeapWastePercent=10|246349|设置您愿意浪费的堆的百分比。当可回收百分比小于堆浪费百分比时，Java+HotSpot+VM不会启动混合垃圾收集周期。|246350|-XX:G1MixedGCCountTarget=8|246351|设置在标记周期后混合垃圾回收的目标数量，以收集最多包含G1MixedGCLIveThresholdPercent实时数据的旧区域。默认值为8个混合垃圾收集|246352|-XX:G1OldCSetRegionThresholdPercent=10|246353|设置在混合垃圾回收周期中要收集的旧区域数的上限。缺省值为Java堆的10%25|246354|-XX:G1ReservePercent=10|246355|设置保留内存以保持可用的百分比，以降低to-space溢出的风险。默认值为10%25。当您增加或减少百分比时，请确保将总Java堆调整为相同的量。|246356|您已经重新配置了许多G1GC参数，如果您按照上面的文档页面操作，这些参数是不需要的。请交叉检查上面的建议，特别是基于您的CPU内核的ParallelGCThreads和ConcGCThreads，。删除不必要参数的重新配置。|246357|来自oracle的Recommendations：|246358|在评估和微调G1+GC时，请牢记以下建议：|246359|246360|Young生成大小：避免使用-Xmn选项或任何或其他相关选项(如-XX:NewRatio+)显式设置年轻生成大小。修复年轻一代的大小会覆盖目标暂停时间goal.|246361|Pause时间目标：当您评估或调优任何垃圾收集时，总是存在延迟与吞吐量之间的权衡。G1+GC是一个增量垃圾收集器，具有统一的暂停，但也会增加应用程序线程的开销。|246362|的G1+GC的吞吐量目标是90+%25的应用程序时间和10+%25的垃圾收集时间。|246363|246364|246365|246366|246367|在Java7中对其他收集器如cms或并行收集器有什么改变吗？|246368|246369|Java7有一些变化。看一下这个article|246370|246371|246372|246373|246374|在哪里可以找到关于Java7中垃圾回收的好文档？|246375|246376|有关gc和相关SE问题，请参阅oracle文档页面：|246377|Java+G1+garbage+collection+in+production|246378|entityMap|0|LINK|mutability|MUTABLE|url|http://www.oracle.com/technetwork/articles/java/g1gc-1984535.html|1|2|http://www.oracle.com/technetwork/java/javase/jdk7-relnotes-418459.html|3|http://www.oracle.com/webfolder/technetwork/tutorials/obe/java/gc01/index.html|4|https://stackoverflow.com/questions/2254041/java-g1-garbage-collection-in-production/34254401#34254401^0|0|0|0|0|0|0|H|C|0|0|0|0|0|0|0|H|6|0|0|0|0|0|0|0|E|0|0|0|F|0|0|0|6|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|1U|H|2C|D|0|9|F|1|0|0|0|0|9|E|4|W|C|0|0|A|0|0|0|0|0|0|0|0|G|7|2|0|0|0|0|0|0|0|2|2|3|0|0|14|4|0^^$0|@$1|2|3|-4|4|5|6|46|7|@]|8|@]|9|$]]|$1|A|3|-4|4|B|6|47|7|@]|8|@]|9|$]]|$1|C|3|-4|4|5|6|48|7|@]|8|@]|9|$]]|$1|D|3|-4|4|5|6|49|7|@]|8|@]|9|$]]|$1|E|3|F|4|G|6|4A|7|@]|8|@]|9|$]]|$1|H|3|-4|4|5|6|4B|7|@]|8|@]|9|$]]|$1|I|3|J|4|5|6|4C|7|@$K|4D|L|4E|M|N]]|8|@]|9|$]]|$1|O|3|-4|4|5|6|4F|7|@]|8|@]|9|$]]|$1|P|3|-4|4|B|6|4G|7|@]|8|@]|9|$]]|$1|Q|3|-4|4|5|6|4H|7|@]|8|@]|9|$]]|$1|R|3|-4|4|5|6|4I|7|@]|8|@]|9|$]]|$1|S|3|T|4|G|6|4J|7|@]|8|@]|9|$]]|$1|U|3|-4|4|5|6|4K|7|@]|8|@]|9|$]]|$1|V|3|W|4|5|6|4L|7|@]|8|@$K|4M|L|4N|1|4O]]|9|$]]|$1|X|3|-4|4|5|6|4P|7|@]|8|@]|9|$]]|$1|Y|3|Z|4|B|6|4Q|7|@]|8|@]|9|$]]|$1|10|3|-4|4|5|6|4R|7|@]|8|@]|9|$]]|$1|11|3|-4|4|5|6|4S|7|@]|8|@]|9|$]]|$1|12|3|13|4|5|6|4T|7|@$K|4U|L|4V|M|14]]|8|@]|9|$]]|$1|15|3|16|4|17|6|4W|7|@]|8|@]|9|$18|19]]|$1|1A|3|1B|4|5|6|4X|7|@$K|4Y|L|4Z|M|14]]|8|@]|9|$]]|$1|1C|3|1D|4|5|6|50|7|@]|8|@]|9|$]]|$1|1E|3|1F|4|5|6|51|7|@$K|52|L|53|M|14]]|8|@]|9|$]]|$1|1G|3|1H|4|17|6|54|7|@]|8|@]|9|$18|19]]|$1|1I|3|1J|4|5|6|55|7|@]|8|@]|9|$]]|$1|1K|3|1L|4|17|6|56|7|@]|8|@]|9|$18|19]]|$1|1M|3|1N|4|5|6|57|7|@]|8|@]|9|$]]|$1|1O|3|1P|4|17|6|58|7|@]|8|@]|9|$18|19]]|$1|1Q|3|1R|4|5|6|59|7|@]|8|@]|9|$]]|$1|1S|3|1T|4|17|6|5A|7|@]|8|@]|9|$18|19]]|$1|1U|3|1V|4|5|6|5B|7|@]|8|@]|9|$]]|$1|1W|3|1X|4|17|6|5C|7|@]|8|@]|9|$18|19]]|$1|1Y|3|1Z|4|5|6|5D|7|@]|8|@]|9|$]]|$1|20|3|21|4|5|6|5E|7|@]|8|@]|9|$]]|$1|22|3|23|4|17|6|5F|7|@]|8|@]|9|$18|19]]|$1|24|3|25|4|5|6|5G|7|@]|8|@]|9|$]]|$1|26|3|27|4|17|6|5H|7|@]|8|@]|9|$18|19]]|$1|28|3|29|4|5|6|5I|7|@]|8|@]|9|$]]|$1|2A|3|2B|4|17|6|5J|7|@]|8|@]|9|$18|19]]|$1|2C|3|2D|4|5|6|5K|7|@]|8|@]|9|$]]|$1|2E|3|2F|4|17|6|5L|7|@]|8|@]|9|$18|19]]|$1|2G|3|2H|4|5|6|5M|7|@]|8|@]|9|$]]|$1|2I|3|2J|4|17|6|5N|7|@]|8|@]|9|$18|19]]|$1|2K|3|2L|4|5|6|5O|7|@]|8|@]|9|$]]|$1|2M|3|2N|4|17|6|5P|7|@]|8|@]|9|$18|19]]|$1|2O|3|2P|4|5|6|5Q|7|@]|8|@]|9|$]]|$1|2Q|3|2R|4|17|6|5R|7|@]|8|@]|9|$18|19]]|$1|2S|3|2T|4|5|6|5S|7|@]|8|@]|9|$]]|$1|2U|3|2V|4|5|6|5T|7|@$K|5U|L|5V|M|14]|$K|5W|L|5X|M|14]]|8|@]|9|$]]|$1|2W|3|2X|4|5|6|5Y|7|@]|8|@$K|5Z|L|60|1|61]]|9|$]]|$1|2Y|3|2Z|4|5|6|62|7|@]|8|@]|9|$]]|$1|30|3|-4|4|5|6|63|7|@]|8|@]|9|$]]|$1|31|3|32|4|G|6|64|7|@$K|65|L|66|M|14]|$K|67|L|68|M|N]|$K|69|L|6A|M|N]]|8|@]|9|$]]|$1|33|3|34|4|G|6|6B|7|@$K|6C|L|6D|M|14]]|8|@]|9|$]]|$1|35|3|36|4|5|6|6E|7|@]|8|@]|9|$]]|$1|37|3|-4|4|5|6|6F|7|@]|8|@]|9|$]]|$1|38|3|-4|4|B|6|6G|7|@]|8|@]|9|$]]|$1|39|3|-4|4|5|6|6H|7|@]|8|@]|9|$]]|$1|3A|3|-4|4|5|6|6I|7|@]|8|@]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<blockquote>
 <ol>
 <li>Is G1 the default collector in Java 7 and if not how do I activate G1?</li>
 </ol>
</blockquote>

G1 is not default collector in Java 7. <code>-XX:+UseG1GC</code> will enable G1GC 

<blockquote>
 <ol start="2">
 <li>What optional settings does g1 have in Java7?</li>
 </ol>
</blockquote>

There are many. Have a look at this <a href="http://www.oracle.com/technetwork/articles/java/g1gc-1984535.html" rel="noreferrer">oracle</a> article for complete information.

<blockquote>
 The G1 GC is an adaptive garbage collector with defaults that enable it to work efficiently without modification. 
</blockquote>

Due to this reason, customize critical parameters

<pre><code>-XX:MaxGCPauseMillis
-XX:G1HeapRegionSize
-XX:ParallelGCThreads
-XX:ConcGCThreads
</code></pre>

and leave all other parameters to default value.

Here is a list of important options and their default values. This list applies to the latest Java HotSpot VM, build 24. You can adapt and tune the G1 GC settings on the JVM command line.

Important Defaults:

<pre><code>-XX:G1HeapRegionSize=n
</code></pre>

Sets the size of a G1 region. The value will be a power of two and can range from 1MB to 32MB. The goal is to have around 2048 regions based on the minimum Java heap size.

<pre><code>-XX:MaxGCPauseMillis=200
</code></pre>

Sets a target value for desired maximum pause time. The default value is 200 milliseconds. The specified value does not adapt to your heap size.

<pre><code>-XX:G1NewSizePercent=5
</code></pre>

Sets the percentage of the heap to use as the minimum for the young generation size. The default value is 5 percent of your Java heap. 

<pre><code>-XX:G1MaxNewSizePercent=60
</code></pre>

Sets the percentage of the heap size to use as the maximum for young generation size. The default value is 60 percent of your Java heap.

<pre><code>-XX:ParallelGCThreads=n
</code></pre>

Sets the value of the STW worker threads. Sets the value of n to the number of logical processors. The value of n is the same as the number of logical processors up to a value of 8.

If there are more than eight logical processors, sets the value of n to approximately 5/8 of the logical processors. This works in most cases except for larger SPARC systems where the value of n can be approximately 5/16 of the logical processors.

<pre><code>-XX:ConcGCThreads=n
</code></pre>

Sets the number of parallel marking threads. Sets n to approximately 1/4 of the number of parallel garbage collection threads (ParallelGCThreads).

<pre><code>-XX:InitiatingHeapOccupancyPercent=45
</code></pre>

Sets the Java heap occupancy threshold that triggers a marking cycle. The default occupancy is 45 percent of the entire Java heap.

<pre><code>-XX:G1MixedGCLiveThresholdPercent=65
</code></pre>

Sets the occupancy threshold for an old region to be included in a mixed garbage collection cycle. The default occupancy is 65 percent

<pre><code>-XX:G1HeapWastePercent=10
</code></pre>

Sets the percentage of heap that you are willing to waste. The Java HotSpot VM does not initiate the mixed garbage collection cycle when the reclaimable percentage is less than the heap waste percentage

<pre><code>-XX:G1MixedGCCountTarget=8
</code></pre>

Sets the target number of mixed garbage collections after a marking cycle to collect old regions with at most G1MixedGCLIveThresholdPercent live data. The default is 8 mixed garbage collections

<pre><code>-XX:G1OldCSetRegionThresholdPercent=10
</code></pre>

Sets an upper limit on the number of old regions to be collected during a mixed garbage collection cycle. The default is 10 percent of the Java heap

<pre><code>-XX:G1ReservePercent=10
</code></pre>

Sets the percentage of reserve memory to keep free so as to reduce the risk of to-space overflows. The default is 10 percent. When you increase or decrease the percentage, make sure to adjust the total Java heap by the same amount.

You have re-configured many G1GC parameters, which are not required if you follow above documentation page. Please cross check with above recommendations especially on ParallelGCThreads and ConcGCThreads, which are to be based on your CPU cores. Remove re-configuration of un-necessary parameters. 

<a href="http://www.oracle.com/technetwork/articles/java/g1gc-1984535.html" rel="noreferrer">Recommendations</a> from oracle:

When you evaluate and fine-tune G1 GC, keep the following recommendations in mind:

<ol>
<li>Young Generation Size: Avoid explicitly setting young generation size with the <code>-Xmn</code> option or any or other related option such as <code>-XX:NewRatio</code>. Fixing the size of the young generation overrides the target pause-time goal.</li>
<li>Pause Time Goals: When you evaluate or tune any garbage collection, there is always a latency versus throughput trade-off. The G1 GC is an incremental garbage collector with uniform pauses, but also more overhead on the application threads. The throughput goal for the G1 GC is 90 percent application time and 10 percent garbage collection time.</li>
</ol>

<blockquote>
 <ol start="3">
 <li>Were there any changes made to other collectors like cms or the parallel collector in Java 7?</li>
 </ol>
</blockquote>

There are some changes with Java 7. Have a look at this <a href="http://www.oracle.com/technetwork/java/javase/jdk7-relnotes-418459.html" rel="noreferrer">article</a>

<blockquote>
 <ol start="4">
 <li>Where can I find good documentation on garbage collection in Java 7?</li>
 </ol>
</blockquote>

Refer to oracle documentation page about <a href="http://www.oracle.com/webfolder/technetwork/tutorials/obe/java/gc01/index.html" rel="noreferrer">gc</a> and related SE question:

<a href="https://stackoverflow.com/questions/2254041/java-g1-garbage-collection-in-production/34254401#34254401">Java G1 garbage collection in production</a>

Java 7 has been out for a while now, but I cannot find any good resources on the configuration of the garbage collectors, specifically the new G1 collector.

My questions:

<ol>
<li>Is G1 the default collector in Java 7 and if not how do I activate G1?</li>
<li>What optional settings does g1 have in Java7?</li>
<li>Were there any changes made to other collectors like cms or the parallel collector in Java 7?</li>
<li>Where can I find good documentation on garbage collection in Java 7? </li>
</ol>

Java 7 (JDK 7) garbage collection and documentation on G1

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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Java7已经发布了一段时间，但是我找不到任何关于垃圾收集器配置的好资源，特别是新的G1收集器。我的问题：是G1是Java7中的默认收集器，如果不是，如何激活g1？g1在Java7中有哪些可选设置？在Java7中对其他收集器(如cms或并行收集器)进行了任何更改吗？在哪里可以找到有关Java7中垃圾收集的好文档？

问G1上的Java7(JDK7)垃圾收集和文档
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