Bruce Momjian <br...@momjian.us> writes:
> On Sat, May 11, 2024 at 01:27:25PM +0800, Andy Fan wrote: >> >> Hello Bruce, >> >> > I have committed the first draft of the PG 17 release notes; you can >> > see the results here: >> > >> > https://momjian.us/pgsql_docs/release-17.html >> >> Thank you for working on this! >> >> > I welcome feedback. For some reason it was an easier job than usual. >> >> Do you think we need to add the following 2 items? >> >> - 9f133763961e280d8ba692bcad0b061b861e9138 this is an optimizer >> transform improvement. > > It was unclear from the commit message exactly what user-visible > optimization this allowed. Do you have details? Yes, It allows the query like "SELECT * FROM t1 WHERE t1.a in (SELECT a FROM t2 WHERE t2.b = t1.b)" be pulled up a semi join, hence more join methods / join orders are possible. > >> - a8a968a8212ee3ef7f22795c834b33d871fac262 this is an optimizer costing >> improvement. > > Does this allow faster UNION ALL with LIMIT, perhaps? Yes, for example: (subquery-1) UNION ALL (subquery-2) LIMIT n; When planning the subquery-1 or subquery-2, limit N should be considered. As a consequence, maybe hash join should be replaced with Nested Loop. Before this commits, it is ignored if it is flatten into appendrel, and the "flatten" happens very often. David provided a summary for the both commits in [1]. [1] https://www.postgresql.org/message-id/CAApHDvqAQgq27LgYmJ85VVGTR0%3DhRW6HHq2oZgK0ZiYC_a%2BEww%40mail.gmail.com -- Best Regards Andy Fan
