Calculate memory of a Map Entry

Question

I have a Map(String, String) and I want to find the memory size of an Entry and the Map in total. I read somewhere that Instrumentation might be useful (Instrumentation). Does anyone have an idea?

Thanks in advance.

You can do plenty of things with instrumentation, but what's your main goal? A profiler can tell you how much memory a map takes. What are your Map entries? — Kayaman, Dec 08 '13 at 20:16
Both key and value are strings. The main purpose is to calculate the memory consumption of the Map object while the application is running. — STiGMa, Dec 08 '13 at 20:44
I am interested in the relative consumption per item for the various map types so I can make the speed vs memory trade off. Each map type has a different per-value overhead. ie: a hash map has a different use per value than a TreeMap, or smallest memory binary search of an array [key,value,key,value, ...] of elements. — peterk, Oct 07 '14 at 20:54

lance-java · Answer 1 · 2013-12-10T08:44:23.310

1

Use ObjectOutputStream to write the object to a ByteArrayOutputstream and check the length of the resultant byte array.

Obviously your Map.Entry will need to implement Serializable.

public int getSizeInBytes(Serializable someObject) {
    ByteArrayOutputStream byteOut = new ByteArrayOutputStream();
    ObjectOutputStream objectOut = new ObjectOutputStream(byteOut);
    objectOut.writeObject(someObject);
    objectOut.flush();
    return byteOut.toByteArray().length;
}

public int getSizeBits(Serializable someObject) {
    return getSizeInBytes(someObject) * 8;
}

edited Dec 10 '13 at 08:44

answered Dec 08 '13 at 20:46

lance-java

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Thanks for the advice. That's another possible solution. I'll give it a try to compare the answer to the solution provided above. – STiGMa Dec 09 '13 at 15:16

score 1 · Accepted Answer · answered Dec 08 '13 at 21:06

A blank instance of java.util.AbstractMap.SimpleEntry should be 24 bytes for 64-bit JVM and 12 bytes for 32-bit JVM. Here is a technique by @PeterLawrey I found useful, based on MemoryUsageExamplesTest:

System.out.printf("The average memory used by simple entry is %.1f bytes%n", new SizeofUtil() {
    @Override
    protected int create() {
        Map.Entry<String, String> e = new AbstractMap.SimpleEntry<String, String>(null, null);
        return 1;
    }
}.averageBytes());

Calculate memory of a Map Entry

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