Correct obsolete nbtree page deletion comment.

petergeoghegan · petergeoghegan · commit 067786cea0f1 · 2019-02-25T16:54:18.000-08:00
Commit efada2b, which made the nbtree page deletion algorithm more robust, removed _bt_getstackbuf() calls from _bt_pagedel(). It failed to update a comment that referenced the earlier approach. Update the comment to explain that the _bt_getstackbuf() page deletion call site mirrors the only other remaining _bt_getstackbuf() call site, which is reached during page splits.
diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c
@@ -1124,9 +1124,10 @@ _bt_is_page_halfdead(Relation rel, BlockNumber blk)
  *
  * "child" is the leaf page we wish to delete, and "stack" is a search stack
  * leading to it (approximately).  Note that we will update the stack
- * entry(s) to reflect current downlink positions --- this is harmless and
- * indeed saves later search effort in _bt_pagedel.  The caller should
- * initialize *target and *rightsib to the leaf page and its right sibling.
+ * entry(s) to reflect current downlink positions --- this is essentially the
+ * same as the corresponding step of splitting, and is not expected to affect
+ * caller.  The caller should initialize *target and *rightsib to the leaf
+ * page and its right sibling.
  *
  * Note: it's OK to release page locks on any internal pages between the leaf
  * and *topparent, because a safe deletion can't become unsafe due to

Original file line number	Diff line number	Diff line change
`@@ -1124,9 +1124,10 @@ _bt_is_page_halfdead(Relation rel, BlockNumber blk)`
`1124`	`1124`	`*`
`1125`	`1125`	`* "child" is the leaf page we wish to delete, and "stack" is a search stack`
`1126`	`1126`	`* leading to it (approximately). Note that we will update the stack`
`1127`		`- * entry(s) to reflect current downlink positions --- this is harmless and`
`1128`		`- * indeed saves later search effort in _bt_pagedel. The caller should`
`1129`		`- * initialize target and rightsib to the leaf page and its right sibling.`
	`1127`	`+ * entry(s) to reflect current downlink positions --- this is essentially the`
	`1128`	`+ * same as the corresponding step of splitting, and is not expected to affect`
	`1129`	`+ * caller. The caller should initialize target and rightsib to the leaf`
	`1130`	`+ * page and its right sibling.`
`1130`	`1131`	`*`
`1131`	`1132`	`* Note: it's OK to release page locks on any internal pages between the leaf`
`1132`	`1133`	`* and *topparent, because a safe deletion can't become unsafe due to`