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) 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-char-long String). Values are byte arrays. The target entry size is a sum of key size and value size.
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 using storeAsBinary attribute and when not.
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.