Update comment about set_join_pathlist_hook().

Etsuro Fujita · Etsuro Fujita · commit c621467d2bc6 · 2023-09-21T19:45:00.000+09:00
The comment introduced by commit e7cb7ee was a bit too terse, which could lead to extensions doing different things within the hook function than we intend to allow. Extend the comment to explain what they can do within the hook function. Back-patch to all supported branches. In passing, I rephrased a nearby comment that I recently added to the back branches. Reviewed by David Rowley and Andrei Lepikhov. Discussion: https://postgr.es/m/CAPmGK15SBPA1nr3Aqsdm%2BYyS-ay0Ayo2BRYQ8_A2To9eLqwopQ%40mail.gmail.com
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
@@ -333,7 +333,10 @@ add_paths_to_joinrel(PlannerInfo *root,
 												 jointype, &extra);
 
 	/*
-	 * 6. Finally, give extensions a chance to manipulate the path list.
+	 * 6. Finally, give extensions a chance to manipulate the path list.  They
+	 * could add new paths (such as CustomPaths) by calling add_path(), or
+	 * add_partial_path() if parallel aware.  They could also delete or modify
+	 * paths added by the core code.
 	 */
 	if (set_join_pathlist_hook)
 		set_join_pathlist_hook(root, joinrel, outerrel, innerrel,
