nbtree: Tweak _bt_pgaddtup() comments.

Make it clear that _bt_pgaddtup() truncates the first data item on an
internal page because its key is supposed to be treated as minus
infinity within _bt_compare().

diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index b84bf1c3dfac9a5574ab0a8833b77813f0fd2f0e..b93b2a0ffd6f3f3014cef4bedd5728f002f72f5d 100644 (file)
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -2230,10 +2230,10 @@ _bt_newroot(Relation rel, Buffer lbuf, Buffer rbuf)
  *
  *     The main difference between this routine and a bare PageAddItem call
  *     is that this code knows that the leftmost index tuple on a non-leaf
- *     btree page doesn't need to have a key.  Therefore, it strips such
- *     tuples down to just the tuple header.  CAUTION: this works ONLY if
- *     we insert the tuples in order, so that the given itup_off does
- *     represent the final position of the tuple!
+ *     btree page has a key that must be treated as minus infinity.
+ *     Therefore, it truncates away all attributes.  CAUTION: this works
+ *     ONLY if we insert the tuples in order, so that the given itup_off
+ *     does represent the final position of the tuple!
  */
 static bool
 _bt_pgaddtup(Page page,
@@ -2248,7 +2248,6 @@ _bt_pgaddtup(Page page,
    {
        trunctuple = *itup;
        trunctuple.t_info = sizeof(IndexTupleData);
-       /* Deliberately zero INDEX_ALT_TID_MASK bits */
        BTreeTupleSetNAtts(&trunctuple, 0);
        itup = &trunctuple;
        itemsize = sizeof(IndexTupleData);

diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c
index c11a3fb570d4d9a8ba5b03d66ee59fd69ddf367a..fc7d43a0f310660fcc920abba1eb936bef71e1e0 100644 (file)
--- a/src/backend/access/nbtree/nbtsort.c
+++ b/src/backend/access/nbtree/nbtsort.c
@@ -756,9 +756,9 @@ _bt_slideleft(Page page)
  * Add an item to a page being built.
  *
  * The main difference between this routine and a bare PageAddItem call
- * is that this code knows that the leftmost data item on a non-leaf
- * btree page doesn't need to have a key.  Therefore, it strips such
- * items down to just the item header.
+ * is that this code knows that the leftmost data item on a non-leaf btree
+ * page has a key that must be treated as minus infinity.  Therefore, it
+ * truncates away all attributes.
  *
  * This is almost like nbtinsert.c's _bt_pgaddtup(), but we can't use
  * that because it assumes that P_RIGHTMOST() will return the correct
@@ -778,7 +778,6 @@ _bt_sortaddtup(Page page,
    {
        trunctuple = *itup;
        trunctuple.t_info = sizeof(IndexTupleData);
-       /* Deliberately zero INDEX_ALT_TID_MASK bits */
        BTreeTupleSetNAtts(&trunctuple, 0);
        itup = &trunctuple;
        itemsize = sizeof(IndexTupleData);