> On Nov 2, 2020, at 10:17 PM, Tomas Vondra <tomas.vondra@xxxxxxxxxxxxxxx> wrote: > > On Mon, Nov 02, 2020 at 03:08:12PM -0500, Tom Lane wrote: >> Philip Semanchuk <philip@xxxxxxxxxxxxxxxxxxxxx> writes: >>> The query I asked about in the original post of this thread has 13 relations in it. IIUC, that's 13! or > 6 billion possible plans. How did the planner pick one plan out of 6 billion? I'm curious, both for practical purposes (I want my query to run well) and also because it's fascinating. >> >> The twenty-thousand-foot overview is >> >> https://www.postgresql.org/docs/devel/planner-optimizer.html >> >> and then ten-thousand-foot level is the planner README file, >> >> https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob_plain;f=src/backend/optimizer/README;hb=HEAD >> >> and then you pretty much gotta start reading code. You could also dig >> into various planner expository talks that people have given at PG >> conferences. I don't have links at hand, but there have been several. >> > > Yeah. The jump from high-level overviews to reading source code is a bit > brutal, though ... > > > FWIW a short list of relevant talks I'm aware of & would recommend: > > * Explaining the Postgres Query Optimizer [Bruce Momjian] > https://www.postgresql.org/files/developer/tour.pdf > > * Intro to Postgres Planner Hacking [Melanie Plageman] > https://www.pgcon.org/2019/schedule/events/1379.en.html > > * Learning to Hack on Postgres Planner [Melanie Plageman] > https://www.pgcon.org/2019/schedule/attachments/540_debugging_planner_pgcon2019_v4.pdf > > * What’s in a Plan? [Robert Haas] > https://www.postgresql.eu/events/pgconfeu2019/schedule/session/2741-whats-in-a-plan/ > * A Tour of PostgreSQL Internals [Tom Lane] > https://www.postgresql.org/files/developer/tour.pdf > > * Inside thePostgreSQL Query Optimizer [Neil Conway] > http://www.neilconway.org/talks/optimizer/optimizer.pdf > > Some are a bit dated, but the overall principles don't change much. Thank you so much to Tomas V, Tom L, Guillaume, Justin, and Michael for all the suggestions and direction. I really appreciate your time & wisdom (not to mention your contributions to Postgres!) Cheers Philip
