Re: [NOVICE] WHERE clause not used when index is used

On Tue, Mar 1, 2016 at 7:40 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Tobias Florek <postgres@ibotty.net> writes:
>> When creating an index to use for an ORDER BY clause, a simple query
>> starts to return more results than expected.  See the following detailed
>> log.
>
> Ugh.  That is *badly* broken.  I thought maybe it had something to do with
> the "abbreviated keys" work, but the same thing happens if you change the
> numeric column to integer, so I'm not very sure where to look.  Who's
> touched btree key comparison logic lately?
>
> (Problem is reproducible in 9.5 and HEAD, but not 9.4.)


Bisects down to:

606c0123d627b37d5ac3f7c2c97cd715dde7842f is the first bad commit
commit 606c0123d627b37d5ac3f7c2c97cd715dde7842f
Author: Simon Riggs <simon@2ndQuadrant.com>
Date:   Tue Nov 18 10:24:55 2014 +0000

    Reduce btree scan overhead for < and > strategies

    For <, <=, > and >= strategies, mark the first scan key
    as already matched if scanning in an appropriate direction.
    If index tuple contains no nulls we can skip the first
    re-check for each tuple.

    Author: Rajeev Rastogi
    Reviewer: Haribabu Kommi
    Rework of the code and comments by Simon Riggs