From 89ee229810878e22d13e49c383e65038c054f5c6 Mon Sep 17 00:00:00 2001
From: drh <drh@noemail.net>
Date: Mon, 7 May 2018 18:41:19 +0000
Subject: [PATCH] Activate the cell-overwrite optimization for index b-trees.

FossilOrigin-Name: a68697d10ef17d452c8279181186faad7bc54e3a35858a336552f717449065ea
---
 manifest      | 14 +++++++-------
 manifest.uuid |  2 +-
 src/btree.c   | 16 ++++++++++++++++
 src/btree.h   | 21 ++++++++++++++++++---
 4 files changed, 42 insertions(+), 11 deletions(-)

diff --git a/manifest b/manifest
index 8b8e5d6d37..1db4fc0b69 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Improved\scomments\son\sthe\scell-overwrite\soptimization\scode.
-D 2018-05-07T17:27:04.995
+C Activate\sthe\scell-overwrite\soptimization\sfor\sindex\sb-trees.
+D 2018-05-07T18:41:19.103
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 5ce9343cba9c189046f1afe6d2bcc1f68079439febc05267b98aec6ecc752439
@@ -434,8 +434,8 @@ F src/auth.c 6277d63837357549fe14e723490d6dc1a38768d71c795c5eb5c0f8a99f918f73
 F src/backup.c faf17e60b43233c214aae6a8179d24503a61e83b
 F src/bitvec.c 17ea48eff8ba979f1f5b04cc484c7bb2be632f33
 F src/btmutex.c 8acc2f464ee76324bf13310df5692a262b801808984c1b79defb2503bbafadb6
-F src/btree.c 7b21976dc09778f05af0e085c40b735467ffdcea64bd07dace3f12ca0a2defce
-F src/btree.h 0866c0a08255142ea0e754aabd211c843cab32045c978a592a43152405ed0c84
+F src/btree.c abedb349c6624d3efa699b4431d5ef679838236527c694444b38ed48c494b39b
+F src/btree.h 448f15b98ea85dcf7e4eb76f731cadb89636c676ad25dfaac6de77cd66556598
 F src/btreeInt.h 620ab4c7235f43572cf3ac2ac8723cbdf68073be4d29da24897c7b77dda5fd96
 F src/build.c 0c2be5839f22aa2938f217c6c6c2120d9fc96872a546a37541a8271541cb355e
 F src/callback.c fe677cb5f5abb02f7a772a62a98c2f516426081df68856e8f2d5f950929b966a
@@ -1727,7 +1727,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 5887d8beb502ad62689d31b850f46ab50831a1e9db36adf20d55ad45619d207e
-R e6599f47435d4296a22afaa3f1649f4a
+P a4fe966da2fc479b18bf521ff596000410af3a611f7d8723d126795e595ccf22
+R 69af7d477dcc78b7b8e926f0c6facd33
 U drh
-Z 8048adc03c51022109ca997ec38e8ad8
+Z 8d5036c02e569f6033a8ae94d4ec5845
diff --git a/manifest.uuid b/manifest.uuid
index 91ceb15d7a..3d79611a88 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-a4fe966da2fc479b18bf521ff596000410af3a611f7d8723d126795e595ccf22
\ No newline at end of file
+a68697d10ef17d452c8279181186faad7bc54e3a35858a336552f717449065ea
\ No newline at end of file
diff --git a/src/btree.c b/src/btree.c
index 60635172c4..2faa40820e 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -8396,6 +8396,22 @@ int sqlite3BtreeInsert(
       }
       if( rc ) return rc;
     }
+
+    /* If the cursor is currently pointing to an entry to be overwritten
+    ** and the new content is the same as as the old, then use the
+    ** overwrite optimization.
+    */
+    if( loc==0 ){
+      getCellInfo(pCur);
+      if( pCur->info.nKey==pX->nKey ){
+        BtreePayload x2;
+        x2.pData = pX->pKey;
+        x2.nData = pX->nKey;
+        x2.nZero = 0;
+        return btreeOverwriteCell(pCur, &x2);
+      }
+    }
+
   }
   assert( pCur->eState==CURSOR_VALID || (pCur->eState==CURSOR_INVALID && loc) );
 
diff --git a/src/btree.h b/src/btree.h
index e8e114bd2a..b5bf9f7564 100644
--- a/src/btree.h
+++ b/src/btree.h
@@ -259,13 +259,28 @@ int sqlite3BtreeDelete(BtCursor*, u8 flags);
 ** entry in either an index or table btree.
 **
 ** Index btrees (used for indexes and also WITHOUT ROWID tables) contain
-** an arbitrary key and no data.  These btrees have pKey,nKey set to their
-** key and pData,nData,nZero set to zero.
+** an arbitrary key and no data.  These btrees have pKey,nKey set to the
+** key and the pData,nData,nZero fields are uninitialized.  The aMem,nMem
+** fields give an array of Mem objects that are a decomposition of the key.
+** The nMem field might be zero, indicating that no decomposition is available.
 **
 ** Table btrees (used for rowid tables) contain an integer rowid used as
 ** the key and passed in the nKey field.  The pKey field is zero.  
 ** pData,nData hold the content of the new entry.  nZero extra zero bytes
 ** are appended to the end of the content when constructing the entry.
+** The aMem,nMem fields are uninitialized for table btrees.
+**
+** Field usage summary:
+**
+**               Table BTrees                   Index Btrees
+**
+**   pKey        always NULL                    encoded key
+**   nKey        the ROWID                      length of pKey
+**   pData       data                           not used
+**   aMem        not used                       decomposed key value
+**   nMem        not used                       entries in aMem
+**   nData       length of pData                not used
+**   nZero       extra zeros after pData        not used
 **
 ** This object is used to pass information into sqlite3BtreeInsert().  The
 ** same information used to be passed as five separate parameters.  But placing
@@ -276,7 +291,7 @@ int sqlite3BtreeDelete(BtCursor*, u8 flags);
 struct BtreePayload {
   const void *pKey;       /* Key content for indexes.  NULL for tables */
   sqlite3_int64 nKey;     /* Size of pKey for indexes.  PRIMARY KEY for tabs */
-  const void *pData;      /* Data for tables.  NULL for indexes */
+  const void *pData;      /* Data for tables. */
   sqlite3_value *aMem;    /* First of nMem value in the unpacked pKey */
   u16 nMem;               /* Number of aMem[] value.  Might be zero */
   int nData;              /* Size of pData.  0 if none. */