JVM调优:CardTable简介 | EZLippi-浮生志



JVM调优:CardTable简介 | EZLippi-浮生志

网上关于JVM调优的文章很多,这篇文章主要介绍JVM里Card Table的作用。我们知道JVM GC可以分为MinorGC、MajorGC和FullGC,对于Mirnor GC来讲它的耗时主要由两个因素决定:

  1. 复制活跃对象的时间
  2. 扫描card table(老年代对象引用新生代对象)的时间

Java虚拟机用了一个叫做CardTable(卡表)的数据结构来标记老年代的某一块内存区域中的对象是否持有新生代对象的引用,卡表的数量取决于老年代的大小和每张卡对应的内存大小，每张卡在卡表中对应一个比特位,当老年代中的某个对象持有了新生代对象的引用时,JVM就把这个对象对应的Card所在的位置标记为dirty(bit位设置为1)，这样在Minor GC时就不用扫描整个老年代，而是扫描Card为Dirty对应的那些内存区域。


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