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JVM foundation - > What garbage collectors does the JVM have?

2022-06-12 22:09:00 【Ouhuang xiaodezi】

The first stage : Serial ( Serial ) The collector -> Time in JDK1.3 about

new ⽣ generation (Serial— Mark - Copy algorithm ) ⽼ years (SerialOld— Mark - Sorting algorithm ) -> The opening configuration is as follows ↓
```
-XX:+UseSerialGC
```

The second stage : Parallel ( parallel ) The collector -> JDK 6 Only then did China begin to offer ,JDK 8 By default

Parallel Collector is also called throughput collector , Use multithreading to clean up garbage
new ⽣ generation (Parallel— Mark - Copy algorithm ) ⽼ years (ParallelOld— Mark - Sorting algorithm ) -> The opening configuration is as follows ↓
```
-XX:+UseParallelGC -XX:+UseParallelOldGC
```

The third stage : CMS（ Concurrent ） The collector -> JDK 5 appear ,JDK 9 Has been abolished CMS Garbage collector

CMS The collector Minor( The younger generation ) GC Time meeting Pause all application threads , And in a multi-threaded way for garbage collection .
In the old age GC when No longer pause the application thread , Instead, several background threads are used to scan the space of the elderly on a regular basis , Recycle the objects that are no longer used in time .
new ⽣ generation (ParNew— Mark - Copy algorithm ) ⽼ years (ConcMarkSweep— Mark - Clear algorithm ) -> The opening configuration is as follows ↓
```
-XX:+UseParNewGC -XX:+UseConcMarkSweepGC
```

The fourth stage : G1（ Concurrent ） The collector -> JDK 8 Then widely used ,JDK 9 The default with G1 The collector

G1 The collector （ Or garbage priority collector ） The original intention of the design is to Try to shorten Handle Super pile （ Greater than 4GB） A pause when .
be relative to CMS In terms of the advantages of Reduce memory fragmentation .
Mark - Copy algorithm + Mark - Sorting algorithm -> The opening configuration is as follows ↓
```
-XX:+UseG1GC
```

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