Memory overhead zh CN

MemoryBenchmark的估算基于Java Agent for Memory Measurements和Java Object Layout计算运行时大小。该大小可能受JVM确定的压缩引用、对象填充等因素影响。

通过分叉Java 5的ConcurrentHashMap，Guava凭借逐条目优化略占优势。当使用弱引用和软引用缓存时，这种优势尤为显著。由于装饰了Java 8的ConcurrentHashMap，Caffeine必须保留额外字段才能移除被回收的条目。

Caffeine可能根据使用情况延迟初始化或动态调整其内部数据结构的大小。这减少了内存占用，仅在满足使用需求（如吞吐量）时才分配额外内存。

无界

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	128 bytes	32 bytes	200 bytes	32 bytes
Guava	928 bytes	48 bytes	1,120 bytes	48 bytes

容量有界

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,296 bytes	64 bytes	1,368 bytes	64 bytes
Guava	1,280 bytes	64 bytes	1,528 bytes	64 bytes

容量有界 & 根据访问时间过期

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,328 bytes	72 bytes	1,424 bytes	72 bytes
Guava	1,280 bytes	64 bytes	1,528 bytes	64 bytes

容量有界 & 根据写入时间过期

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,360 bytes	80 bytes	1,456 bytes	80 bytes
Guava	1,440 bytes	80 bytes	1,696 bytes	80 bytes

容量有界 & 根据写入时间刷新

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,336 bytes	72 bytes	1,432 bytes	72 bytes
Guava	1,296 bytes	80 bytes	1,576 bytes	80 bytes

权重有界

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,336 bytes	72 bytes	1,336 bytes	72 bytes
Guava	1,296 bytes	64 bytes	1,520 bytes	64 bytes

根据访问时间过期

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,160 bytes	72 bytes	1,256 bytes	72 bytes
Guava	1,280 bytes	64 bytes	1,528 bytes	64 bytes

根据写入时间过期

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,128 bytes	72 bytes	1,248 bytes	72 bytes
Guava	1,088 bytes	64 bytes	1,336 bytes	64 bytes

根据访问时间 & 写入时间过期

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,208 bytes	88 bytes	1,304 bytes	88 bytes
Guava	1,440 bytes	80 bytes	1,696 bytes	80 bytes

弱引用Keys

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,144 bytes	88 bytes	1,216 bytes	88 bytes
Guava	1,136 bytes	56 bytes	1,400 bytes	56 bytes

弱引用Values

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,136 bytes	80 bytes	1,208 bytes	80 bytes
Guava	1,136 bytes	64 bytes	1,400 bytes	64 bytes

弱引用Keys & Values

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,184 bytes	112 bytes	1,256 bytes	112 bytes
Guava	1,312 bytes	72 bytes	1,504 bytes	72 bytes

弱引用 Keys & 软引用 Values

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,184 bytes	120 bytes	1,256 bytes	120 bytes
Guava	1,312 bytes	80 bytes	1,576 bytes	80 bytes

软引用Values

Cache	MemoryMeter		ObjectLayout
	Baseline	Per Entry	Baseline	Per Entry
Caffeine	1,136 bytes	88 bytes	1,208 bytes	88 bytes
Guava	1,136 bytes	72 bytes	1,400 bytes	72 bytes