Infinispan memory overhead

Have you ever wondered how much Java heap memory is actually consumed when data is stored in Infinispan cache? Let's look at some numbers obtained through real measurement.

The strategy was the following:

1) Start Infinispan server in local mode (only one server instance, eviction disabled)
2) Keep calling full garbage collection (via JMX or directly via System.gc() when Infinispan is deployed as a library) until the difference in consumed memory by the running server gets under 100kB between two consecutive runs of GC
3) Load the cache with 100MB of data via respective client (or directly store in the cache when Infinispan is deployed as a library)
4) Keep calling the GC until the used memory is stabilised
5) Measure the difference between the final values of consumed memory after the first and second cycle of GC runs
6) Repeat steps 3, 4 and 5 four times to get an average value (first iteration ignored)

The amount of consumed memory was obtained from a verbose GC log (related JVM options: -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -Xloggc:/tmp/gc.log)

The test output looks like this: https://gist.github.com/4512589

The operating system (Ubuntu) as well as JVM (Oracle JDK 1.6) were 64-bit. Infinispan 5.2.0.Beta6. Keys were kept intentionally small (10 character Strings) with byte arrays as values. The target entry size is a sum of key size and value size.

Memory overhead of Infinispan accessed through clients

HotRod client

entry size -> overall memory

512B       -> 137144kB

1kB        -> 120184kB

10kB       -> 104145kB

1MB        -> 102424kB

So how much additional memory is consumed on top of each entry?

entry size/actual memory per entry -> overhead per entry

512B/686B                -> ~174B

1kB(1024B)/1202B         -> ~178B

10kB(10240B)/10414B      -> ~176B

1MB(1048576B)/1048821B   -> ~245B

MemCached client (text protocol, SpyMemcached client) 

entry size -> overall memory

512B       -> 139197kB

1kB        -> 120517kB

10kB       -> 104226kB

1MB        -> N/A (SpyMemcached allows max. 20kB per entry)

entry size/actual memory per entry -> overhead per entry

512B/696B               -> ~184B

1kB(1024B)/1205B        -> ~181B

10kB(10240B)/10422B     -> ~182B

REST client (Content-Type: application/octet-stream)

entry size -> overall memory

512B       -> 143998kB

1kB        -> 122909kB

10kB       -> 104466kB

1MB        -> 102412kB

entry size/actual memory per entry -> overhead per entry

512B/720B               -> ~208B

1kB(1024B)/1229B        -> ~205B

10kB(10240B)/10446B     -> ~206B

1MB(1048576B)/1048698B  -> ~123B

The memory overhead for individual entries seems to be more or less constant
across different cache entry sizes.

Memory overhead of Infinispan deployed as a library

Infinispan was deployed to JBoss Application Server 7 using Arquillian.

entry size -> overall memory/overall with storeAsBinary

512B       -> 132736kB / 132733kB

1kB        -> 117568kB / 117568kB

10kB       -> 103953kB / 103950kB

1MB        -> 102414kB / 102415kB

There was almost no difference in overall consumed memory when enabling or disabling storeAsBinary.

entry size/actual memory per entry-> overhead per entry (w/o storeAsBinary)

512B/663B               -> ~151B

1kB(1024B)/1175B        -> ~151B

10kB(10240B)/10395B     -> ~155B

1MB(1048576B)/1048719B  -> ~143B

As you can see, the overhead per entry is constant across different entry sizes and is ~151 bytes.

Conclusion

The memory overhead is slightly more than 150 bytes per entry when storing data into the cache locally. When accessing the cache via remote clients, the memory overhead is a little bit higher and ranges from ~170 to ~250 bytes, depending on remote client type and cache entry size. If we ignored the statistics for 1MB entries, which could be affected by a small number of entries (100) stored in the cache, the range would have been even narrower.


Cheers,
Martin