Horton

Re: EquivalenceClasses and subqueries and PlaceHolderVars, oh my

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Greg Stark <stark@mit.edu>
Cc: Yeb Havinga <yebhavinga@gmail.com>, pgsql-hackers@postgresql.org
Date: 2012-03-17T14:46:52Z
Lists: pgsql-hackers

Commits

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  1. Fix pushing of index-expression qualifications through UNION ALL.

  2. Wrap appendrel member outputs in PlaceHolderVars in additional cases.

Greg Stark <stark@mit.edu> writes:
> On Fri, Mar 16, 2012 at 3:16 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> So I now propose reverting the earlier two patches (but not their
> regression test cases of course) and instead hacking MergeAppend plan
> building as per (2).

> As a wise man once said, "This is tricky stuff". I feel a better that
> I got stuck on this stuff when you're still trying to feel your way
> after this many go-arounds.

Well, looking back on it, I feel this was at bottom a documentation
failure.  I think that when I wrote the EquivalenceClass code, I knew
that "child" members did not have similar semantics to regular members.
But I had forgotten that when Teodor reported the MergeAppend bug,
and so misdiagnosed what I was seeing happen as being corruption of
the EC contents, when it wasn't really.  I added some documentation
around this point in the patch I committed yesterday...

			regards, tom lane