Ketih,
I think what you have done, at least at the JVM level, is create 100,000
lists, with basically each list containing an element and a pointer to the
next element. Because one list points to the next, none of them can be
garbage collected. It seems to me that this would be roughly equivalent to
one list with 100,000 elements, in terms of memory usage. In your map
example, the memory usage is 52 * 100,000 bytes, so that's about 5MB. How
much memory is used by the equivalent Java code?
List l = new ArrayList();
for(int i = 0; i < 100000; i++) {
l.add("x");
}
On Mon, Feb 2, 2009 at 1:06 PM, Keith Bennett <keithrbenn...@gmail.com>wrote:
>
> All -
>
> I'm curious to know how to minimize memory consumption in Clojure for
> large lists. I did the following test in repl:
>
> (def d ())
> (dotimes [_ 100000] (def d (cons "x" d)))
>
> Then, I used VisualVM, an awesome free profiling tool (https://
> visualvm.dev.java.net/) to examine the results. It indicated that the
> number of clojure.lang.PersistentList instances increased by 100,000.
> Each instance appeared to consume 48 bytes (not including the actual
> value, but only its reference, I presume). I don't think any were
> eligible for garbage collection, because I initiated gc several times,
> and they were not removed. (I know that gc() is not deterministic,
> but am pretty sure that they would have been removed. Feel free to
> correct me.)
>
> Thinking that maybe the special functions like map did some magic to
> save memory, I tried this:
>
> (def a (map #(* 2 %) (range 100000)))
>
> The result was 100,000 clojure.lang.LazyCons objects, each of which
> consuming 52 bytes.
>
> Are there alternate strategies for building a large sequence that
> would consume less memory per element?
>
> Thanks,
> Keith
>
> >
>
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