On Fri, Sep 25, 2009 at 1:05 AM, Andrew Gierth
<andrew@tao11.riddles.org.uk> wrote:
>>>>>> "Euler" == Euler Taveira de Oliveira <euler@timbira.com> writes:
>
> Euler> Ops... forgot to remove it from other test. It seems much
> Euler> better but far from the ideal. :( I've never taken a look at
> Euler> the pl/pgsql code but it could be nice if there would be two
> Euler> path codes: access-data and non-access-data paths. I have no
> Euler> idea if it will be possible (is path type too complex to
> Euler> detect?) but it will certainly improve the non-access-data
> Euler> functions.
>
> Like Tom said, this benchmark is silly. Some comparisons (note that in
> all these cases I've replaced the power(10,8) with a constant, because
> you weren't comparing like with like there):
>
> plpgsql 13.3 sec
> tcl85 29.9 sec
> perl5.8 7.7 sec
> python2.6 11.5 sec
> C 0.242 sec
>
> What this suggests to me is that plpgsql isn't so far off the norm for
> interpreted scripting languages; sure it's slower than perl, but then
> most things are; comparing it with C code is just silly.
>
> There is, though, one genuine case that's come up a few times in IRC
> regarding slowness of procedural code in pg, and that's any time
> someone tries to implement some array-based algorithm in plpgsql. The
> fact that a[i] is O(i) not O(1) (unless the array type is fixed length)
> comes as a nasty shock since iterating over an array becomes O(n^2).
>
> This is obviously a consequence of the array storage format; is there
> any potential for changing that to some format which has, say, an array
> of element offsets at the start, rather than relying on stepping over
> length fields?
Couple points:
*) Surely, it's better to encourage use of 'unnest' style approaches
for array iteration
*) If an array has fixed length elements and doesn't have null
elements (a fairly common case), maybe it's worthwhile not
generating/storing the lengths vector?
*) Wouldn't it be possible to store offsets always, not lengths, since
you can calculate the length from the next offset?
merlin
