Re: Query plan degradation 8.2 --> 8.3

[Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>]

Josh Berkus <josh(at)agliodbs(dot)com> writes:
> I now have a simple test case which shows significant performance 
> degradation on 8.3devel for a specific query, apparenly due to an 
> unnecessary call to Top-N sort.

It does the right thing if t_s_symb is declared as text instead of
varchar.  When it's varchar, even setting enable_sort off won't make
it pick the right plan, which suggests that it fails to recognize that
the index can match the query's ORDER BY.  I'm guessing I overlooked
a binary-compatibility case when I rejiggered the handling of PathKeys
in connection with the NULLS FIRST/LAST stuff.  No time to look deeper
right now.

			regards, tom lane