Clojure Leining REPL OutOfMemoryError Java heap space

Question 1

Any form evaluated at the top level of the repl is realized in full, as a result of the print step of the Read-Eval-Print-Loop. It is also stored in the heap, so that you can later access it via *1.

if you store the return value as follows:

(def parsed (xml/parse (io/reader "data/small-sample.xml")))

this returns immediately, even for a file hundreds of megabytes in size (I have verified this locally). You can then iterate across the result, which is realized in full as it is parsed from the input stream, by iterating over the clojure.data.xml.Element tree that is returned.

If you do not hold on to the elements (by binding them so they are still accessible), you can iterate over the entire structure without using more ram than it takes to hold a single node of the xml tree.

user> (time (def n (xml/parse (clojure.java.io/reader "/home/justin/clojure/ok/data.xml"))))
"Elapsed time: 0.739795 msecs"
#'user/n
user> (time (keys n))
"Elapsed time: 0.025683 msecs"
(:tag :attrs :content)
user> (time (-> n :tag))
"Elapsed time: 0.031224 msecs"
:catalog
user> (time (-> n :attrs))
"Elapsed time: 0.136522 msecs"
{}
user> (time (-> n :content first))
"Elapsed time: 0.095145 msecs"
#clojure.data.xml.Element{:tag :book, :attrs {:id "bk101"}, :content (#clojure.data.xml.Element{:tag :author, :attrs {}, :content ("Gambardella, Matthew")} #clojure.data.xml.Element{:tag :title, :attrs {}, :content ("XML Developer's Guide")} #clojure.data.xml.Element{:tag :genre, :attrs {}, :content ("Computer")} #clojure.data.xml.Element{:tag :price, :attrs {}, :content ("44.95")} #clojure.data.xml.Element{:tag :publish_date, :attrs {}, :content ("2000-10-01")} #clojure.data.xml.Element{:tag :description, :attrs {}, :content ("An in-depth look at creating applications \n      with XML.")})}
user> (time (-> n :content count))
"Elapsed time: 48178.512106 msecs"
459000
user> (time (-> n :content count))
"Elapsed time: 86.931114 msecs"
459000
;; redefining n so that we can test the performance without the pre-parsing done when we counted
user> (time (def n (xml/parse (clojure.java.io/reader "/home/justin/clojure/ok/data.xml"))))
"Elapsed time: 0.702885 msecs"
#'user/n
user> (time (doseq [el (take 100 (drop 100 (-> n :content)))] (println (:tag el))))
:book
:book
.... ;; output truncated
"Elapsed time: 26.019374 msecs"
nil
user>

Notice that it is only when I first ask for the count of the content of n (thus forcing the whole file to be parsed) that the huge time delay occurs. If I doseq across subsections of the structure, this happens very quickly.

Question 2

I don't know about lein as much but in mvn you can do the following:

mvn  -Dclojure.vmargs="-d64 -Xmx2G" clojure:nrepl

(I don't think it matters but I've always seen it with a capitol G is it case sensitive?)

Pulling 100MB of data into memory should be no problem. I routinely route GB worth of data through my projects.

I always use the server of 64bit version for large heaps too, and that seems to be what they are doing here:

JVM options using Leiningen

I think the bigger problem though, is that as you have it written this might be being evaluated at compile time. You need to wrap that call in a function, and defer it's execution. I think the compiler is trying to read that file, and that's likely not what you want. I know with mvn you get different memory settings for compile vs. run and you might be getting that too.