From f222e712a40ed76ac421427b7ae7aa3ca3ce1edb Mon Sep 17 00:00:00 2001
From: drh <drh@noemail.net>
Date: Fri, 14 Jan 2005 22:55:49 +0000
Subject: [PATCH] Add comments to the new balance_quick() routine. (CVS 2212)

FossilOrigin-Name: 183c42eac82b41da7905e44a43913f04acc46ade
---
 manifest      | 14 +++++++-------
 manifest.uuid |  2 +-
 src/btree.c   | 27 ++++++++++++++++++++++++++-
 3 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/manifest b/manifest
index 76222c9340..e6cb2882c3 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Experimental\spatch\sto\sbalance()\s(use\s-DSQLITE_BALANCE_QUICK).\s(CVS\s2211)
-D 2005-01-14T13:50:12
+C Add\scomments\sto\sthe\snew\sbalance_quick()\sroutine.\s(CVS\s2212)
+D 2005-01-14T22:55:49
 F Makefile.in 6ce51dde6a8fe82fc12f20dec750572f6a19f56a
 F Makefile.linux-gcc a9e5a0d309fa7c38e7c14d3ecf7690879d3a5457
 F README a01693e454a00cc117967e3f9fdab2d4d52e9bc1
@@ -29,7 +29,7 @@ F sqlite3.def dbaeb20c153e1d366e8f421b55a573f5dfc00863
 F sqlite3.pc.in 985b9bf34192a549d7d370e0f0b6b34a4f61369a
 F src/attach.c e49d09dad9f5f9fb10b4b0c1be5a70ae4c45e689
 F src/auth.c 3b81f2a42f48a62c2c9c9b0eda31a157c681edea
-F src/btree.c 1a351402dbbf5cc5f8ecf1b338f8da20c073c46e
+F src/btree.c 01027e3c1b9f53f17eec964da2a3e45d253b2b87
 F src/btree.h 74d19cf40ab49fd69abe9e4e12a6c321ad86c497
 F src/build.c af1296e8a21a406b4f4c4f1e1365e075071219f3
 F src/cursor.c f883813759742068890b1f699335872bfa8fdf41
@@ -269,7 +269,7 @@ F www/tclsqlite.tcl e73f8f8e5f20e8277619433f7970060ab01088fc
 F www/vdbe.tcl 095f106d93875c94b47367384ebc870517431618
 F www/version3.tcl 092a01f5ef430d2c4acc0ae558d74c4bb89638a0
 F www/whentouse.tcl c3b50d3ac31c54be2a1af9b488a89d22f1e6e746
-P c772f75166d55192132e732e8a0ddda5926f00f2
-R a2176157e002acaa6ba57b3b04bf35d8
-U danielk1977
-Z be978985848951cc4077641a9406e5b8
+P c550d80c25ec88fceb20acabd00c21faa2d552f5
+R 11aa1732839148efceafec181a4aacf2
+U drh
+Z 125f4f4e919590f6f1ede4bc594f0cdf
diff --git a/manifest.uuid b/manifest.uuid
index 0a9619bf96..3580b5d9aa 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-c550d80c25ec88fceb20acabd00c21faa2d552f5
\ No newline at end of file
+183c42eac82b41da7905e44a43913f04acc46ade
\ No newline at end of file
diff --git a/src/btree.c b/src/btree.c
index c21e2e1909..b80189304a 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -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 &&