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[CLJ-1084] (object-array [1]) is ~3x slower than (object-array (rseq [1])) Created: 09/Oct/12  Updated: 20/Oct/12  Resolved: 20/Oct/12

Status: Closed
Project: Clojure
Component/s: None
Affects Version/s: Release 1.4
Fix Version/s: Release 1.5

Type: Defect Priority: Minor
Reporter: Paul Stadig Assignee: Unassigned
Resolution: Completed Votes: 1
Labels: patch,

Attachments: Text File 0001-Make-PersistentVector-ChunkedSeq-implement-Counted.patch     Text File CLJ-1084-tests.patch    
Patch: Code and Test
Approval: Ok

 Description   

{{user=> (time (dotimes [_ 10000000] (object-array [1])))
"Elapsed time: 1178.116257 msecs"
nil
user=> (time (dotimes [_ 10000000] (object-array (rseq [1]))))
"Elapsed time: 422.42248 msecs"
nil}}

This appears to be because PersistentVector$ChunkedSeq does not implement Counted, so RT.count is iterating the ChunkedSeq to get its count.

 Comments   
Comment by Paul Stadig [ 09/Oct/12 2:11 PM ]

I don't believe this is Major priority, but I cannot edit the ticket after having created it.

Comment by Tassilo Horn [ 11/Oct/12 10:17 AM ]

This patch makes PersistentVector$ChunkedSeq implement Counted.

Performance before:

(let [v (vec (range 10000))
      vs (seq v)]
  (time (dotimes [_ 10000]
          (count v)))
  (time (dotimes [_ 10000]
          (count vs))))
;"Elapsed time: 0.862259 msecs"
;"Elapsed time: 7228.72486 msecs"

Performance after (with the patch):

(let [v (vec (range 10000))
      vs (seq v)]
  (time (dotimes [_ 10000]
          (count v)))
  (time (dotimes [_ 10000]
          (count vs))))
;"Elapsed time: 0.967301 msecs"
;"Elapsed time: 0.99391 msecs"

Also with Paul's test case.

Before:

(time (dotimes [_ 10000000] (object-array [1])))
;"Elapsed time: 1668.346997 msecs"
(time (dotimes [_ 10000000] (object-array (rseq [1]))))
;"Elapsed time: 662.820591 msecs"

After:

(time (dotimes [_ 10000000] (object-array [1])))
;"Elapsed time: 757.084577 msecs"
(time (dotimes [_ 10000000] (object-array (rseq [1]))))
;"Elapsed time: 680.602921 msecs"
Comment by Stuart Halloway [ 19/Oct/12 1:46 PM ]

Two patches to be applied together, the 10/19 patch adds tests and updates to latest test.generative.

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