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().
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@ -2230,10 +2230,10 @@ _bt_newroot(Relation rel, Buffer lbuf, Buffer rbuf)
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*
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* The main difference between this routine and a bare PageAddItem call
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* is that this code knows that the leftmost index tuple on a non-leaf
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* btree page doesn't need to have a key. Therefore, it strips such
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* tuples down to just the tuple header. CAUTION: this works ONLY if
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* we insert the tuples in order, so that the given itup_off does
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* represent the final position of the tuple!
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* btree page has a key that must be treated as minus infinity.
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* Therefore, it truncates away all attributes. CAUTION: this works
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* ONLY if we insert the tuples in order, so that the given itup_off
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* does represent the final position of the tuple!
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*/
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static bool
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_bt_pgaddtup(Page page,
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@ -2248,7 +2248,6 @@ _bt_pgaddtup(Page page,
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{
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trunctuple = *itup;
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trunctuple.t_info = sizeof(IndexTupleData);
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/* Deliberately zero INDEX_ALT_TID_MASK bits */
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BTreeTupleSetNAtts(&trunctuple, 0);
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itup = &trunctuple;
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itemsize = sizeof(IndexTupleData);
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@ -756,9 +756,9 @@ _bt_slideleft(Page page)
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* Add an item to a page being built.
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*
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* The main difference between this routine and a bare PageAddItem call
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* is that this code knows that the leftmost data item on a non-leaf
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* btree page doesn't need to have a key. Therefore, it strips such
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* items down to just the item header.
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* is that this code knows that the leftmost data item on a non-leaf btree
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* page has a key that must be treated as minus infinity. Therefore, it
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* truncates away all attributes.
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*
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* This is almost like nbtinsert.c's _bt_pgaddtup(), but we can't use
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* that because it assumes that P_RIGHTMOST() will return the correct
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@ -778,7 +778,6 @@ _bt_sortaddtup(Page page,
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{
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trunctuple = *itup;
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trunctuple.t_info = sizeof(IndexTupleData);
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/* Deliberately zero INDEX_ALT_TID_MASK bits */
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BTreeTupleSetNAtts(&trunctuple, 0);
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itup = &trunctuple;
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itemsize = sizeof(IndexTupleData);
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