Memory overhead

The cache and entry objects only require certain fields depending on the configuration options specified when creating the cache. To minimize memory, code generation is used to avoid retaining unnecessary fields.

Estimates were performed using Java Agent for Memory Measurements to calculate the runtime size. The size may be affected by compressed references, object padding, etc. applied by the JVM. This benchmark may be run using gradle memoryOverhead which executes MemoryBenchmark.

By forking Java 5's ConcurrentHashMap, Guava has a slight advantage with per-entry optimizations. This is 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.

Guava uses an unbounded ConcurrentLinkedQueue per segment. This reduces the baseline footprint at the cost of unpredictable growth, GC pauses, and slower execution. Caffeine pre-allocates a segmented ring buffer resulting in a higher, but fixed, initial footprint.

Pending optimizations

Caffeine's ring buffers are fixed to a size optimal for high concurrency. Instead, the buffers should grow dynamically based upon contention so that footprint is minimized.

Unbounded

Cache	Baseline	Entry
Caffeine	656 bytes	42 bytes
Guava	1,136 bytes	58 bytes

Maximum Size

Cache	Baseline	Entry
Caffeine	23,552 bytes	74 bytes
Guava	1,560 bytes	74 bytes

Maximum Size & Expire after Access

Cache	Baseline	Entry
Caffeine	23,640 bytes	82 bytes
Guava	1,560 bytes	74 bytes

Maximum Size & Expire after Write

Cache	Baseline	Entry
Caffeine	23,672 bytes	90 bytes
Guava	1,728 bytes	90 bytes

Maximum Size & Refresh after Write

Cache	Baseline	Entry
Caffeine	23,664 bytes	82 bytes
Guava	27,480 bytes	90 bytes

Maximum Weight

Cache	Baseline	Entry
Caffeine	23,584 bytes	74 bytes
Guava	1,552 bytes	74 bytes

Expire after Access

Cache	Baseline	Entry
Caffeine	23,616 bytes	82 bytes
Guava	1,560 bytes	74 bytes

Expire after Write

Cache	Baseline	Entry
Caffeine	504 bytes	82 bytes
Guava	1,360 bytes	74 bytes

Expire after Access & after Write

Cache	Baseline	Entry
Caffeine	23,664 bytes	98 bytes
Guava	1,728 bytes	90 bytes

Weak Keys

Cache	Baseline	Entry
Caffeine	384 bytes	98 bytes
Guava	1,416 bytes	66 bytes

Weak Values

Cache	Baseline	Entry
Caffeine	384 bytes	98 bytes
Guava	1,416 bytes	74 bytes

Weak Keys & Weak Values

Cache	Baseline	Entry
Caffeine	440 bytes	130 bytes
Guava	1,512 bytes	82 bytes

Weak Keys & Soft Values

Cache	Baseline	Entry
Caffeine	440 bytes	146 bytes
Guava	1,584 bytes	90 bytes

Soft Values

Cache	Baseline	Entry
Caffeine	384 bytes	114 bytes
Guava	1,416 bytes	90 bytes