nbtree: Rename _bt_search() variables.
Make some of the variable names in _bt_search() consistent with corresponding variables within _bt_getstackbuf(). This naming scheme is clearer because the variable names always express a relationship between the currently locked buffer/page and some other page.
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@ -82,9 +82,10 @@ _bt_drop_lock_and_maybe_pin(IndexScanDesc scan, BTScanPos sp)
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* The passed scankey is an insertion-type scankey (see nbtree/README),
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* but it can omit the rightmost column(s) of the index.
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*
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* Return value is a stack of parent-page pointers. *bufP is set to the
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* address of the leaf-page buffer, which is locked and pinned. No locks
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* are held on the parent pages, however!
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* Return value is a stack of parent-page pointers (i.e. there is no entry for
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* the leaf level/page). *bufP is set to the address of the leaf-page buffer,
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* which is locked and pinned. No locks are held on the parent pages,
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* however!
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*
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* If the snapshot parameter is not NULL, "old snapshot" checking will take
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* place during the descent through the tree. This is not needed when
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@ -118,21 +119,20 @@ _bt_search(Relation rel, BTScanInsert key, Buffer *bufP, int access,
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OffsetNumber offnum;
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ItemId itemid;
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IndexTuple itup;
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BlockNumber blkno;
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BlockNumber par_blkno;
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BlockNumber child;
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BTStack new_stack;
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/*
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* Race -- the page we just grabbed may have split since we read its
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* pointer in the parent (or metapage). If it has, we may need to
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* move right to its new sibling. Do that.
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* downlink in its parent page (or the metapage). If it has, we may
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* need to move right to its new sibling. Do that.
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*
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* In write-mode, allow _bt_moveright to finish any incomplete splits
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* along the way. Strictly speaking, we'd only need to finish an
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* incomplete split on the leaf page we're about to insert to, not on
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* any of the upper levels (they are taken care of in _bt_getstackbuf,
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* if the leaf page is split and we insert to the parent page). But
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* this is a good opportunity to finish splits of internal pages too.
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* any of the upper levels (internal pages with incomplete splits are
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* also taken care of in _bt_getstackbuf). But this is a good
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* opportunity to finish splits of internal pages too.
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*/
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*bufP = _bt_moveright(rel, key, *bufP, (access == BT_WRITE), stack_in,
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page_access, snapshot);
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@ -144,25 +144,23 @@ _bt_search(Relation rel, BTScanInsert key, Buffer *bufP, int access,
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break;
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/*
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* Find the appropriate item on the internal page, and get the child
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* page that it points to.
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* Find the appropriate pivot tuple on this page. Its downlink points
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* to the child page that we're about to descend to.
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*/
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offnum = _bt_binsrch(rel, key, *bufP);
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itemid = PageGetItemId(page, offnum);
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itup = (IndexTuple) PageGetItem(page, itemid);
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Assert(BTreeTupleIsPivot(itup) || !key->heapkeyspace);
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blkno = BTreeTupleGetDownLink(itup);
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par_blkno = BufferGetBlockNumber(*bufP);
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child = BTreeTupleGetDownLink(itup);
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/*
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* We need to save the location of the pivot tuple we chose in the
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* parent page on a stack. If we need to split a page, we'll use the
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* stack to work back up to its parent page. If caller ends up
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* splitting a page one level down, it usually ends up inserting a new
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* pivot tuple/downlink immediately after the location recorded here.
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* We need to save the location of the pivot tuple we chose in a new
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* stack entry for this page/level. If caller ends up splitting a
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* page one level down, it usually ends up inserting a new pivot
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* tuple/downlink immediately after the location recorded here.
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*/
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new_stack = (BTStack) palloc(sizeof(BTStackData));
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new_stack->bts_blkno = par_blkno;
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new_stack->bts_blkno = BufferGetBlockNumber(*bufP);
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new_stack->bts_offset = offnum;
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new_stack->bts_parent = stack_in;
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@ -174,8 +172,8 @@ _bt_search(Relation rel, BTScanInsert key, Buffer *bufP, int access,
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if (opaque->btpo.level == 1 && access == BT_WRITE)
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page_access = BT_WRITE;
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/* drop the read lock on the parent page, acquire one on the child */
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*bufP = _bt_relandgetbuf(rel, *bufP, blkno, page_access);
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/* drop the read lock on the page, then acquire one on its child */
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*bufP = _bt_relandgetbuf(rel, *bufP, child, page_access);
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/* okay, all set to move down a level */
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stack_in = new_stack;
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@ -196,8 +194,7 @@ _bt_search(Relation rel, BTScanInsert key, Buffer *bufP, int access,
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* If the page was split between the time that we surrendered our read
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* lock and acquired our write lock, then this page may no longer be
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* the right place for the key we want to insert. In this case, we
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* need to move right in the tree. See Lehman and Yao for an
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* excruciatingly precise description.
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* need to move right in the tree.
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*/
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*bufP = _bt_moveright(rel, key, *bufP, true, stack_in, BT_WRITE,
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snapshot);
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