Class meta-data class Metadata

Source: Internet
Author: User

Tag: Specify a different application for the map point class res

Java classes is represented as a class metadata inside a Java hotspot VM. In the previous Java Hotspot VM version, the class metadata was allocated in the persistence generation. In JDK8, persistent generations are removed, and the class metadata is allocated in local memory. By default, local memory can be used for class metadata. can useThe maxmetaspacesize option sets the maximum class metadata that is allowed to be set in local memory. The management metadata space displayed by the Java hotspot VM. The OS requests space, then divides into shards, the ClassLoader allocates metadata space from the Shard, and when the class is not loaded by the loader, its shard intersection is recycled for the OS to reuse.The metadata uses the space allocated by the mmap, not by malloc. IfThe usecompressedoops and usecompressedclassespointers options are used at the same time, so the two logical different local memory regions handle the class metadata. When the class is unloaded, the class metadata is freed. Garbage collection unloads and releases the class metadata because of the Java classes that were unloaded because of garbage collection. garbage collection can occur when the class metadata reaches a certain level. After garbage collection, you can determine whether to raise high-water mark or lower High-water mark based on the amount of space freed by the class metadata. If you raise high-water mark may cause garbage collection. High-water Mark was initially set to the value of the metaspacesize option. depending on the maxmetaspacefreeratio and minmetaspacefreeratio two options, the increase or decrease of high-water mark is determined. if the allocated class metadata space is greater than the value of Maxmetaspacefreeratio, then high-water mark will be lowered. if the allocated class metadata space is less than the minmetaspacefreeratio value, High-water mark will ascend. you can choose to specify a higher value for the metaspacesize to avoid premature garbage collection of class metadata. The amount of class metadata space allocated to an application depends on the application and does not have a common standard. Heap Psyounggen Total 10752K, used 4419K [0xffffffff6ac00000, 0xffffffff6b800000, 0xffffffff6b800000) Eden Space 9216 K, 47% used [0xffffffff6ac00000,0xffffffff6b050d68,0xffffffff6b500000) from Space 1536K, 0% used [0xffffffff6b680000, 0xffffffff6b680000,0xffffffff6b800000) to space 1536K, 0% used [0xffffffff6b500000,0xffffffff6b500000, 0xffffffff6b680000) Paroldgen total 20480K, used 20011K [0xffffffff69800000, 0xffffffff6ac00000, 0xffffffff6ac00000) Object Space 20480K, 97% used [0xffffffff69800000,0xffffffff6ab8add8,0xffffffff6ac00000) Metaspace used 2425K, capacity 4498K, committed 4864K, reserved 1056768K class space used 262K, capacity 386K, committed 512K, reserved 1048576Kused the space used for the load classcapacity as a metadata space available in the current Shardcommitted the number of shards availablereserved amount of space reserved for metadata

Class meta-data class Metadata

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