Woops. I sent the wrong patch. My apologies. Attached is the real
patch. Sorry, also forgot this is made against 9.0 alpha 4 tag.
Thanks,
Mike
--
Michael Lewis
lolrus.org
mikelikespie@gmail.com
On Wed, Mar 31, 2010 at 12:39 AM, Mike Lewis <mikelikespie@gmail.com> wrote:
> I noticed while doing work with very large arrays that several
> functions such as array_length detoast the entire array instead of
> only what is required.
>
> I found the solution to be just unpacking the header portion of the
> array and ignoring the rest. Since the header (including the
> dimensions) is variable length, I just unpack the size of what the
> header would be if it had MAXDIM dimensions. (Patch is attached)
>
> I made a test case to demonstrate performance gains (watch out, it
> creates a big table):
>
> create temporary table foo as
> select array_agg(i) as a
> from (
> select generate_series(1,10000000) as i) as bar;
> \timing
> select array_length(a, 1) from foo; -- Run a few times. First time will be cold
>
> Results (after warming up)
>
> Before patch:
> Time: 6.251 ms
> Time: 6.078 ms
> Time: 5.983 ms
>
> After patch:
> Time: 0.401 ms
> Time: 0.397 ms
> Time: 0.441 ms
> ...
>
> --
> Michael Lewis
> lolrus.org
> mikelikespie@gmail.com
>