# G1垃圾回收器参数配置

| 选项/默认值                               | 说明                                                                                              |
| ------------------------------------ | ----------------------------------------------------------------------------------------------- |
| -XX:+UseG1GC                         | 使用 G1 (Garbage First) 垃圾收集器                                                                     |
| -XX:MaxGCPauseMillis=n               | 设置最大GC停顿时间(GC pause time)指标(target). 这是一个软性指标(soft goal), JVM 会尽量去达成这个目标.                       |
| -XX:InitiatingHeapOccupancyPercent=n | 启动并发GC周期时的堆内存占用百分比. G1之类的垃圾收集器用它来触发并发GC周期,基于整个堆的使用率,而不只是某一代内存的使用比. 值为 0 则表示"一直执行GC循环". 默认值为 45. |
| -XX:NewRatio=n                       | 新生代与老生代(new/old generation)的大小比例(Ratio). 默认值为 2.                                                |
| -XX:SurvivorRatio=n                  | eden/survivor 空间大小的比例(Ratio). 默认值为 8.                                                           |
| -XX:MaxTenuringThreshold=n           | 提升年老代的最大临界值(tenuring threshold). 默认值为 15.                                                       |
| -XX:ParallelGCThreads=n              | 设置垃圾收集器在并行阶段使用的线程数,默认值随JVM运行的平台不同而不同.                                                           |
| -XX:ConcGCThreads=n                  | 并发垃圾收集器使用的线程数量. 默认值随JVM运行的平台不同而不同.                                                              |
| -XX:G1ReservePercent=n               | 设置堆内存保留为假天花板的总量,以降低提升失败的可能性. 默认值是 10.                                                           |
| -XX:G1HeapRegionSize=n               | 使用G1时Java堆会被分为大小统一的的区(region)。此参数可以指定每个heap区的大小. 默认值将根据 heap size 算出最优解. 最小值为 1Mb, 最大值为 32Mb.   |


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