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Bob Foster wrote:
>K. Ari Krupnikov wrote:
> > David Megginson <dmeggin@attglobal.net> writes:
> >
> >>Java objects have an awful lot of built-in
> >>memory overhead just for the java.lang.Object base class
> >
> > Do you know how much memory you actually use for a "new Object()"?
>
>Yes, a pinch of actual fact would make a nice spice for this latest
>round of the "objects cost too much" permathread.
>
>
>
In older JVMs (1.1.8) even a simple Object would take about 32 bytes.
Now that's down to 8 bytes, for the Sun JVM 1.4.2 on Linux:
Base Object starting memory usage 884792, ending usage 2484792
Base Object size in bytes: 8
Base Object construction time in ms. for 200000 instances: 59
String (4 characters) starting memory usage 884952, ending usage 10484952
String (4 characters) size in bytes: 48
String (4 characters) construction time in ms. for 200000 instances: 851
Integer starting memory usage 884952, ending usage 4084952
Integer size in bytes: 16
Integer construction time in ms. for 200000 instances: 135
byte Array (0 length) starting memory usage 884952, ending usage 4084952
byte Array (0 length) size in bytes: 16
byte Array (0 length) construction time in ms. for 200000 instances: 128
byte Array (8 length) starting memory usage 884952, ending usage 5684952
byte Array (8 length) size in bytes: 24
byte Array (8 length) construction time in ms. for 200000 instances: 211
Reference Array (8 length) starting memory usage 884952, ending usage
10484952
Reference Array (8 length) size in bytes: 48
Reference Array (8 length) construction time in ms. for 200000
instances: 628
This is from a modified version of the code I used for a JavaWorld
article a few years back (the article now mostly obsolete, so I won't
link it). Don't know why Strings are so slow and so large (figure 24
bytes for the char[4], but that still leaves another 24 bytes just for
the String data), but it would certainly account for a lot of the bloat
in document models. In general, document models take about 4-8X the
document size in bytes (with the low end for documents that are mostly
text): http://www.sosnoski.com/opensrc/xmlbench/results.html#size These
results are a couple of years old (and from a 1.3.X JVM), but still
fairly accurate from what I've seen.
- Dennis
--
Dennis M. Sosnoski
Enterprise Java, XML, and Web Services
Training and Consulting
http://www.sosnoski.com
Redmond, WA 425.885.7197
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