lists:append performance

[Valentin Micic]

Hi all,

 

I've always been under an impression that inserting element into the list
and then reversing the list to convert it from LIFO to FIFO would generally
be faster then using lists:append/2 to create FIFO immediately. I've never
tested this assertion for a relatively small lists, thus, I've performed
some tests using a list of 240 elements, having each element as a string
like:  "The quick brown fox jumps over a lazy dog". I've written two
different functions:

 

1) insert (Count) that would always execute an insert like this:
["1"|OldList]

2) append( Count ), which would always execute a call to lists:append(
OldList, ["1"] ).

 

I cannot say that I haven't been surprised by a result:

 

50> timer:tc( benchmarks, insert, [1000000000] ).

{72152000,ok}

 

)51> timer:tc( benchmarks, append, [1000000000] ).

{72137000,ok}

 

It seems that it doesn't make much of a difference if one uses one or
another. Would this hold for a larger lists as well, and if not - how large
a list should be in order to see a notable deterioration in lists:append/2
performance?

 

Thanks in advance.

 

V.