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David Rowley 1349d2790b Improve performance of ORDER BY / DISTINCT aggregates ... ORDER BY / DISTINCT aggreagtes have, since implemented in Postgres, been executed by always performing a sort in nodeAgg.c to sort the tuples in the current group into the correct order before calling the transition function on the sorted tuples. This was not great as often there might be an index that could have provided pre-sorted input and allowed the transition functions to be called as the rows come in, rather than having to store them in a tuplestore in order to sort them once all the tuples for the group have arrived. Here we change the planner so it requests a path with a sort order which supports the most amount of ORDER BY / DISTINCT aggregate functions and add new code to the executor to allow it to support the processing of ORDER BY / DISTINCT aggregates where the tuples are already sorted in the correct order. Since there can be many ORDER BY / DISTINCT aggregates in any given query level, it's very possible that we can't find an order that suits all of these aggregates. The sort order that the planner chooses is simply the one that suits the most aggregate functions. We take the most strictly sorted variation of each order and see how many aggregate functions can use that, then we try again with the order of the remaining aggregates to see if another order would suit more aggregate functions. For example: SELECT agg(a ORDER BY a),agg2(a ORDER BY a,b) ... would request the sort order to be {a, b} because {a} is a subset of the sort order of {a,b}, but; SELECT agg(a ORDER BY a),agg2(a ORDER BY c) ... would just pick a plan ordered by {a} (we give precedence to aggregates which are earlier in the targetlist). SELECT agg(a ORDER BY a),agg2(a ORDER BY b),agg3(a ORDER BY b) ... would choose to order by {b} since two aggregates suit that vs just one that requires input ordered by {a}. Author: David Rowley Reviewed-by: Ronan Dunklau, James Coleman, Ranier Vilela, Richard Guo, Tom Lane Discussion: https://postgr.es/m/CAApHDvpHzfo92%3DR4W0%2BxVua3BUYCKMckWAmo-2t_KiXN-wYH%3Dw%40mail.gmail.com		3 years ago
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expected	Improve performance of ORDER BY / DISTINCT aggregates	3 years ago
sql	Improve performance of ORDER BY / DISTINCT aggregates	3 years ago
.gitignore	…
Makefile	postgres_fdw: Add function to list cached connections to foreign servers.	5 years ago
connection.c	Replace many MemSet calls with struct initialization	3 years ago
deparse.c	postgres_fdw: be more wary about shippability of reg* constants.	3 years ago
option.c	Tweak detail and hint messages to be consistent with project policy	3 years ago
postgres_fdw--1.0--1.1.sql	postgres_fdw: Add functions to discard cached connections.	4 years ago
postgres_fdw--1.0.sql	…
postgres_fdw.c	postgres_fdw: Fix bug in checking of return value of PQsendQuery().	3 years ago
postgres_fdw.control	postgres_fdw: Add function to list cached connections to foreign servers.	5 years ago
postgres_fdw.h	Fix postgres_fdw to check shippability of sort clauses properly.	3 years ago
shippable.c	Update copyright for 2022	4 years ago