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().
This commit is contained in:
Peter Geoghegan 2019-11-18 13:04:53 -08:00
parent bf2efc55da
commit 2110f71696
2 changed files with 7 additions and 9 deletions

View File

@ -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);

View File

@ -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);