Re: type cache for concat functions

Hi Pavel,

I tried applying your patch, it applies and compiles fine, check and
checkworld pass.

I ran a simple performance test, select
concat(generate_series(1,100000), ... [x5 total]) vs select
generate_series(1,100000)::text || ... .
Operator || runs in 60 ms, while unpatched concat takes 90 and patched
-- 55 ms.

About the code:
* There seems to be an extra tab here:
FmgrInfo *typcache;
It's not aligned with the previous declaration with tab size 4.

* You could allocate the cache and store it into the context inside
rebuildConcatCache. It would return return the cache pointer, and the
calling code would look cleaner -- just one line. This is a matter of
taste though.

* The nearby functions use snake_case, so it should be
rebuild_concat_cache too.

Overall the patch looks good to me.

--
Alexander Kuzmenkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company