Saturday, 12 January 2013

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:

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.


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.


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