pgsql: Consider Incremental Sort paths at additional places

Consider Incremental Sort paths at additional places

Commit d2d8a229bc introduced Incremental Sort, but it was considered
only in create_ordered_paths() as an alternative to regular Sort. There
are many other places that require sorted input and might benefit from
considering Incremental Sort too.

This patch modifies a number of those places, but not all. The concern
is that just adding Incremental Sort to any place that already adds
Sort may increase the number of paths considered, negatively affecting
planning time, without any benefit. So we've taken a more conservative
approach, based on analysis of which places do affect a set of queries
that did seem practical. This means some less common queries may not
benefit from Incremental Sort yet.

Author: Tomas Vondra
Reviewed-by: James Coleman
Discussion: https://postgr.es/m/CAPpHfds1waRZ=NOmueYq0sx1ZSCnt+5QJvizT8ndT2=etZEeAQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ba3e76cc571eba3dea19c9465ff15ac3ac186576

Modified Files
--------------
contrib/postgres_fdw/postgres_fdw.c | 29 --
src/backend/optimizer/geqo/geqo_eval.c | 2 +-
src/backend/optimizer/path/allpaths.c | 217 ++++++++++++++-
src/backend/optimizer/path/equivclass.c | 28 ++
src/backend/optimizer/plan/planner.c | 370 ++++++++++++++++++++++++-
src/include/optimizer/paths.h | 3 +
src/test/regress/expected/incremental_sort.out | 20 +-
7 files changed, 620 insertions(+), 49 deletions(-)