Memory overhead

MemoryBenchmark estimates are performed using Java Agent for Memory Measurements and Java Object Layout to calculate the runtime size. The size may be affected by compressed references, object padding, etc. as determined by the JVM.

By forking Java 5's ConcurrentHashMap, Guava has a slight advantage with per-entry optimizations. This is especially evident when weak and soft reference caching is used. Caffeine must retain additional fields to remove a collected entry due to decorating a Java 8 ConcurrentHashMap.

Caffeine may lazily initialize or dynamically resize its internal data structures based on usage. This reduces the footprint in favor of using additional memory only as required to meet usage demands (e.g. throughput).

Unbounded

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

Maximum Size

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

Maximum Size & Expire after Access

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

Maximum Size & Expire after Write

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

Maximum Size & Refresh after Write

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

Maximum Weight

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

Expire after Access

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

Expire after Write

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

Expire after Access & after Write

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

Weak Keys

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

Weak Values

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

Weak Keys & Weak Values

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

Weak Keys & Soft Values

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

Soft Values

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