Minimizing application data memory overhead in java processes

Question

I need to store lots of data (Objects) in memory (for computations).
Since computations are done based on this data it is critical that all data will reside in the same JVM process memory.
Most data will be built from Strings, Integers and other sub-objects (Collections, HashSet, etc...).
Since Java's objects memory overhead is significant (Strings are UTF-16, each object has 8 bytes overhead) I'm looking for libraries which enable storing such data in memory with lower overhead.
I've read interesting articles about reducing memory:
* http://www.cs.virginia.edu/kim/publicity/pldi09tutorials/memory-efficient-java-tutorial.pdf * http://blog.griddynamics.com/2010/01/java-tricks-reducing-memory-consumption.html

I was just wondering if there is some library for such scenarios out there or I'll need to start from scratch.
To understand better my requirement imagine a server which process high volume of records and need to analyze them based on millions of other records which are stored in memory (for high processing rate).

radai · Accepted Answer · 2013-01-05T17:32:14.133

5

for collection overhead have a look at trove - their memory overhead is lower than the built-in Collections classes (especially for maps and sets which, in the JDK are based on maps).
if you have large objects it might be worthwhile to save them "serialized" as some compact binary representation (not java serialization) and deserialize back to a full-blown object when needed)
you could also use a cache library that can page out to disk? take a look at infinispan or ehcache. also, some of those libraries (ehcache among them, if memory serves) provide "off-heap storage" as part of your jvm process - a chunk of memory not subject to GC managed by the (native) library. if you have an efficient binary representation you could store it there (wont lower your footpring but might make GC behave better)

edited Jan 05 '13 at 17:32

answered Jan 05 '13 at 17:15

radai

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Thanks! the trove library looks great. Are you familiar with some library to reduce the Strings overhead? – Avner Levy Jan 05 '13 at 17:31
not really. except for storing ascii strings as binary and "deserializing" them back there's nothing much i know of that you can do - java only has one internal string representation and thats unicode. – radai Jan 05 '13 at 17:33
well, now that i think about it some more, if those strings repeat themselves you could intern() them to get a unique instance, but the flip side is that the pool of those unique instances resides in the permgen (at least in java 6) and isnt cleaned up, so you might leak. if they really repeat maybe you could add your own unique string pool – radai Jan 05 '13 at 18:01

score 1 · Answer 2 · answered Jan 05 '13 at 17:45

For the String bit you can store the byte[] you get from String.getBytes("UTF8"). If you require a String object again you can then create it again from the ByteArray. It will ofcourse incur some more CPU for creating the String objects over and over again, so it will be a tradeoff between size<->speed.

score 0 · Answer 3 · edited May 23 '17 at 10:24

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Regarding strings, also look into -XX:+UseCompressedStrings jvm option, but looks like is has been dropped from latest jvm updates, see this other question

edited May 23 '17 at 10:24

Community

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answered Jan 05 '13 at 17:41

Persimmonium

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Minimizing application data memory overhead in java processes

3 Answers3