The following documentation comment has been logged on the website: Page: https://www.postgresql.org/docs/14/git.html Description:
We've spent days investigating a performance issue related to "explicit join order"/"from_collapse_limit", where we would have expected a query using "explicit join clauses" (we didn't know were named this way obviously, and we are only using for ease-of-query-building purposes) to use the same plan as a flat query. During this time, we have naturally read the documentation at https://www.postgresql.org/docs/current/planner-optimizer.html to see if it would mention anything that would explain why these would behave differently. However, this documentation currently only says: "If the query uses fewer than geqo_threshold relations, a near-exhaustive search is conducted to find the best join sequence" (which we checked for), but does not mention the explicit join behavior (https://www.postgresql.org/docs/current/explicit-joins.html) nor the from_collapse_limit or join_collapse_limit parameters. (https://www.postgresql.org/docs/current/runtime-config-query.html#GUC-FROM-COLLAPSE-LIMIT). Mentioning these in a similar way as we explain geqo_threshold's possible impact on query planning would be a huge improvement, and would have saved us a lot of time. Thanks,
