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Add comments to the new balance_quick() routine. (CVS 2212)

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FossilOrigin-Name: 183c42eac82b41da7905e44a43913f04acc46ade
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drh
2005-01-14 22:55:49 +00:00
parent ac245ec5af
commit f222e712a4
3 changed files with 34 additions and 9 deletions
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27
src/btree.c
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@@ -9,7 +9,7 @@
** May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.232 2005/01/14 13:50:12 danielk1977 Exp $
** $Id: btree.c,v 1.233 2005/01/14 22:55:49 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
@@ -3558,6 +3558,23 @@ static void assemblePage(
/* Forward reference */
static int balance(MemPage*, int);
/*
** This version of balance() handles the common special case where
** a new entry is being inserted on the extreme right-end of the
** tree, in other words, when the new entry will become the largest
** entry in the tree.
**
** Instead of trying balance the 3 right-most leaf pages, just add
** a new page to the right-hand side and put the one new entry in
** that page. This leaves the right side of the tree somewhat
** unbalanced. But odds are that we will be inserting new entries
** at the end soon afterwards so the nearly empty page will quickly
** fill up. On average.
**
** pPage is the leaf page which is the right-most page in the tree.
** pParent is its parent. pPage must have a single overflow entry
** which is also the right-most entry on the page.
*/
static int balance_quick(MemPage *pPage, MemPage *pParent){
int rc;
MemPage *pNew;
@@ -3681,6 +3698,14 @@ static int balance_nonroot(MemPage *pPage){
TRACE(("BALANCE: begin page %d child of %d\n", pPage->pgno, pParent->pgno));
#ifdef SQLITE_BALANCE_QUICK
/*
** A special case: If a new entry has just been inserted into a
** table (that is, a btree with integer keys and all data at the leaves)
** an the new entry is the right-most entry in the tree (it has the
** largest key) then use the special balance_quick() routine for
** balancing. balance_quick() is much faster and results in a tighter
** packing of data in the common case.
*/
if( pPage->leaf &&
pPage->intKey &&
pPage->leafData &&