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Commit7b37f4b

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Correct more obsolete nbtree page split comments.
Commit3f34283 corrected obsolete comments about buffer locks at themain _bt_insert_parent() call site, but missed similar obsolete commentsabove _bt_insert_parent() itself. Both sets of comments were renderedobsolete by commit40dae7e, which made the nbtree page splitalgorithm more robust. Fix the comments that were missed the first timearound now.In passing, refine a related _bt_insert_parent() comment aboutre-finding the parent page to insert new downlink.
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‎src/backend/access/nbtree/nbtinsert.c

Lines changed: 13 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -1687,13 +1687,15 @@ _bt_split(Relation rel, BTScanInsert itup_key, Buffer buf, Buffer cbuf,
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}
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/*
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* _bt_insert_parent() -- Insert downlink into parent after a page split.
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* _bt_insert_parent() -- Insert downlink into parent, completing split.
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*
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* On entry, buf and rbuf are the left and right split pages, which we
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* still hold write locks on per the L&Y algorithm. We release the
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* write locks once we have write lock on the parent page. (Any sooner,
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* and it'd be possible for some other process to try to split or delete
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* one of these pages, and get confused because it cannot find the downlink.)
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* still hold write locks on. Both locks will be released here. We
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* release the rbuf lock once we have a write lock on the page that we
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* intend to insert a downlink to rbuf on (i.e. buf's current parent page).
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* The lock on buf is released at the same point as the lock on the parent
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* page, since buf's INCOMPLETE_SPLIT flag must be cleared by the same
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* atomic operation that completes the split by inserting a new downlink.
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*
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* stack - stack showing how we got here. Will be NULL when splitting true
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*root, or during concurrent root split, where we can be inefficient
@@ -1771,11 +1773,13 @@ _bt_insert_parent(Relation rel,
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BTreeInnerTupleSetDownLink(new_item,rbknum);
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/*
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*Find the parent bufferandgetthe parentpage.
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*Re-findandwrite lockthe parentof buf.
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*
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* Oops - if we were moved right then we need to change stack item! We
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* want to find parent pointing to where we are, right ?- vadim
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* 05/27/97
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* It's possible that the location of buf's downlink has changed
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* since our initial _bt_search() descent. _bt_getstackbuf() will
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* detect and recover from this, updating the stack, which ensures
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* that the new downlink will be inserted at the correct offset.
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* Even buf's parent may have changed.
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*/
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stack->bts_btentry=bknum;
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pbuf=_bt_getstackbuf(rel,stack);

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