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deep hash code for byte[] and other array in tuple #746

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deep hash code for byte[] and other array in tuple #746

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7870b26
use java.util.Arrays.deepHashCode() instead of List.hashCode() for tuple
xiaokang Jan 7, 2013
03c130a
Merge branch 'master' of https://github.com/nathanmarz/storm into sto…
xiaokang Nov 14, 2013
b846ea1
implement deep-hash-code in clojure
xiaokang Nov 14, 2013
92e30be
fix according to review comments
xiaokang Nov 16, 2013
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30 changes: 29 additions & 1 deletion storm-core/src/clj/backtype/storm/tuple.clj
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Expand Up @@ -4,5 +4,33 @@

(bootstrap)

(def ARRAY-TYPES-MAP
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This should be a set. The syntax is #{}

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Yes. It should be a set instead of map. It's due to my mis-understanding that contains? only work with map.

{
(type (to-array [])) nil
(type (byte-array 0)) nil
(type (char-array 0)) nil
(type (short-array 0)) nil
(type (int-array 0)) nil
(type (long-array 0)) nil
(type (float-array 0)) nil
(type (double-array 0)) nil
(type (boolean-array 0)) nil
})

(defn deep-hash-code [alist]
"deep hash code based on array/list content.
it's the same as java.util.Arrays.deepHashCode(),
but without convert a list to array to avoid copy."
(reduce
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We can make this code much faster by not doing the reduce (which is constantly boxing and unboxing the numbers) and instead iterating through the list. It's doable in Clojure, though I'm ok with writing this code in Java and then calling it from here.

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Do you mean ".intValue" and "+" cause constantly boxing and unboxing the numbers? Can we use unchecked-add-int and unchecked-multiply-int to avoid boxing and unboxing?
I tested with unchecked-* and it's 10% faster than ".intValue" and "+" on 100KB and 1000KB byte array.

#(.intValue (+ (.intValue (* 31 %1)) (hash-code %2)))
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How does this even compile? hash-code isn't declared anywhere

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I am really sorry that the code cause compiling error and I have not tested it carefully. I just tested it in Clojure REPL using load-file. I'll fix it and test it on cluster.

1 alist))

(defn hash-code [obj]
(let [t (type obj)]
(if (contains? ARRAY-TYPES-MAP t)
(deep-hash-code obj)
(.hashCode obj))))

(defn list-hash-code [^List alist]
(.hashCode alist))
(deep-hash-code alist))