Remove block number field from nbtree stack.

The initial value of the nbtree stack downlink block number field
recorded during an initial descent of the tree wasn't actually used.
Both _bt_getstackbuf() callers overwrote the value with their own value.

Remove the block number field from the stack struct, and add a child
block number argument to _bt_getstackbuf() in its place.  This makes the
overall design of _bt_getstackbuf() clearer.

Author: Peter Geoghegan
Reviewed-By: Anastasia Lubennikova
Discussion: https://postgr.es/m/CAH2-Wzmx+UbXt2YNOUCZ-a04VdXU=S=OHuAuD7Z8uQq-PXTYUg@mail.gmail.com

1 files changed, 6 insertions, 10 deletions

diff --git a/src/include/access/nbtree.h b/src/include/access/nbtree.h
index 83e0e6c28e0..7e54c456f7d 100644
--- a/src/include/access/nbtree.h
+++ b/src/include/access/nbtree.h
@@ -403,20 +403,16 @@ typedef struct BTMetaPageData
 #define BT_WRITE		BUFFER_LOCK_EXCLUSIVE
 
 /*
- *	BTStackData -- As we descend a tree, we push the (location, downlink)
- *	pairs from internal pages onto a private stack.  If we split a
- *	leaf, we use this stack to walk back up the tree and insert data
- *	into parent pages (and possibly to split them, too).  Lehman and
- *	Yao's update algorithm guarantees that under no circumstances can
- *	our private stack give us an irredeemably bad picture up the tree.
- *	Again, see the paper for details.
+ * BTStackData -- As we descend a tree, we push the location of pivot
+ * tuples whose downlink we are about to follow onto a private stack.  If
+ * we split a leaf, we use this stack to walk back up the tree and insert
+ * data into its parent page at the correct location.  We may also have to
+ * recursively split a grandparent of the leaf page (and so on).
  */
-
 typedef struct BTStackData
 {
 	BlockNumber bts_blkno;
 	OffsetNumber bts_offset;
-	BlockNumber bts_btentry;
 	struct BTStackData *bts_parent;
 } BTStackData;
 
@@ -731,7 +727,7 @@ extern void _bt_parallel_advance_array_keys(IndexScanDesc scan);
  */
 extern bool _bt_doinsert(Relation rel, IndexTuple itup,
 						 IndexUniqueCheck checkUnique, Relation heapRel);
-extern Buffer _bt_getstackbuf(Relation rel, BTStack stack);
+extern Buffer _bt_getstackbuf(Relation rel, BTStack stack, BlockNumber child);
 extern void _bt_finish_split(Relation rel, Buffer bbuf, BTStack stack);
 
 /*