In these examples, the map/record is freshly created each time through the
loop, so caching should not be a factor.
In fact, later in the thread, AtKaaZ posted an example which demonstrated
his timing results when computing the hash repeatedly on the same object.
Oddly, the performance of hashing on maps got* worse *when repeatedly
hashing the same object (records were unaffected), implying that it was
taking more time to retrieve the cached hash than to just compute it from
scratch -- very strange.
--Mark
On Sun, Feb 3, 2013 at 4:47 PM, Paul Stadig <p...@stadig.name> wrote:
> On Sunday, February 3, 2013 1:07:41 AM UTC-5, puzzler wrote:
>>
>> I just went through the process of converting my map-based program over
>> to records, hoping it would improve speed. Much to my dismay, it actually
>> slowed my program down substantially. With some profiling, I discovered
>> that one possible explanation is that (at least in RC4) hashing of records
>> is about 60x slower than their map-based counterpart.
>>
>> (defrecord A [x y])
>> => (time (dotimes [n 10000000] (hash {:x "a" :y 3})))
>> "Elapsed time: 90.631072 msecs"
>> => (time (dotimes [n 10000000] (hash (A. "a" 3))))
>> "Elapsed time: 5549.788311 msecs"
>>
>> Any thoughts about why this is the case?
>>
>
> There was a change for 1.5 to cache hasheq for maps
> https://github.com/clojure/clojure/commit/d77489d3ce912c177fe288a6f399a5c1da6683dbbut
> the same is not done for defrecords. That is why maps are so much
> faster than records.
>
>
> Paul
>
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