diff --git a/manifest b/manifest
index 5ce3d3060f..6862957f3f 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fix\sharmless\scompiler\swarnings\sassociated\swith\sthe\snew\sEXPLAIN\sQUERY\sPLAN\slogic.
-D 2018-05-07T11:37:34.277
+C On\san\sUPDATE,\stry\sto\soverwrite\san\sexisting\sbtree\scell\swith\sthe\smodified\ncontent,\sif\sthe\sold\sand\snew\scell\sare\sthe\ssame\ssize.\s\sUse\smemcmp()\sfirst\nto\savoid\sdirtying\spages\sthat\sare\sunchanged.
+D 2018-05-07T11:48:22.641
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 5ce9343cba9c189046f1afe6d2bcc1f68079439febc05267b98aec6ecc752439
@@ -434,7 +434,7 @@ F src/auth.c 6277d63837357549fe14e723490d6dc1a38768d71c795c5eb5c0f8a99f918f73
 F src/backup.c faf17e60b43233c214aae6a8179d24503a61e83b
 F src/bitvec.c 17ea48eff8ba979f1f5b04cc484c7bb2be632f33
 F src/btmutex.c 8acc2f464ee76324bf13310df5692a262b801808984c1b79defb2503bbafadb6
-F src/btree.c 79982b0779c27e5ccde8c3e540f14b4e82586d6ec0394a7eb08be72d20c3e894
+F src/btree.c 6be0267a7da8ca04c466094ca9d9a8a26333e175cff794afe5138aeec0cdb7c2
 F src/btree.h 0866c0a08255142ea0e754aabd211c843cab32045c978a592a43152405ed0c84
 F src/btreeInt.h 620ab4c7235f43572cf3ac2ac8723cbdf68073be4d29da24897c7b77dda5fd96
 F src/build.c 0c2be5839f22aa2938f217c6c6c2120d9fc96872a546a37541a8271541cb355e
@@ -1131,7 +1131,7 @@ F test/oserror.test b32dc34f2363ef18532e3a0a7358e3e7e321974f
 F test/ossfuzz.c c4c4547e2c92ac52f10038b073a03248251a23c1c559728f63a18aeca0e79f03
 F test/ossshell.c f125c5bd16e537a2549aa579b328dd1c59905e7ab1338dfc210e755bb7b69f17
 F test/ovfl.test 199c482696defceacee8c8e0e0ef36da62726b2f
-F test/pager1.test f596d3bd53ce96e1d87d44d223d2ae6c8867dd782c425e5eb28b5721fa6aaa97
+F test/pager1.test a32ce299ed01ffb06e84a3af467ae1f3389786b316f40c4359f442c79144736b
 F test/pager2.test 67b8f40ae98112bcdba1f2b2d03ea83266418c71
 F test/pager3.test 4e9a83d6ca0838d7c602c9eb93d1357562d9059c1e02ffb138a8271020838370
 F test/pager4.test a122e9e6925d5b23b31e3dfef8c6a44bbf19590e
@@ -1727,7 +1727,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P b348d1193a7a3ed4d3e656b6cc95a41f87eae29222e0723850a5eb5ffabffd00
-R d09bdc73f56d4d80e2806c4c66a4e25a
+P 374d8e264487b0437a8d995ced1bc026a92d495a2d0568f65f033e9ebe11d0e2 3e11dc3183bc3e8ec49af244a8e8b3e07d12f7a2e59028b2bf64ce0ab589a91f
+R 891ce8c2c78f1f487f80460b8c248fd0
+T +closed 3e11dc3183bc3e8ec49af244a8e8b3e07d12f7a2e59028b2bf64ce0ab589a91f
 U drh
-Z 7e3b1491b97d0e22d20f39d7466da090
+Z 7955ef5d032aea210d99e8bc24e906bc
diff --git a/manifest.uuid b/manifest.uuid
index a55df92ede..3fa7a09c8a 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-374d8e264487b0437a8d995ced1bc026a92d495a2d0568f65f033e9ebe11d0e2
\ No newline at end of file
+5887d8beb502ad62689d31b850f46ab50831a1e9db36adf20d55ad45619d207e
\ No newline at end of file
diff --git a/src/btree.c b/src/btree.c
index a3794b3f2f..4d83d2e4de 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -8154,6 +8154,94 @@ static int balance(BtCursor *pCur){
   return rc;
 }
 
+/* Overwrite content from pX into pDest.  Only do the write if the
+** content is different from what is already there.
+*/
+static int btreeOverwriteContent(
+  MemPage *pPage,           /* MemPage on which writing will occur */
+  u8 *pDest,                /* Pointer to the place to start writing */
+  const BtreePayload *pX,   /* Source of data to write */
+  int iOffset,              /* Offset of first byte to write */
+  int iAmt                  /* Number of bytes to be written */
+){
+  int nData = pX->nData - iOffset;
+  if( nData<=0 ){
+    /* Overwritting with zeros */
+    int i;
+    for(i=0; i<iAmt && pDest[i]==0; i++){}
+    if( i<iAmt ){
+      int rc = sqlite3PagerWrite(pPage->pDbPage);
+      if( rc ) return rc;
+      memset(pDest + i, 0, iAmt - i);
+    }
+  }else{
+    if( nData<iAmt ){
+      /* Mixed read data and zeros at the end.  Make a recursive call
+      ** to write the zeros then fall through to write the real data */
+      int rc = btreeOverwriteContent(pPage, pDest+nData, pX, iOffset+nData,
+                                 iAmt-nData);
+      if( rc ) return rc;
+      iAmt = nData;
+    }
+    if( memcmp(pDest, ((u8*)pX->pData) + iOffset, iAmt)!=0 ){
+      int rc = sqlite3PagerWrite(pPage->pDbPage);
+      if( rc ) return rc;
+      memcpy(pDest, ((u8*)pX->pData) + iOffset, iAmt);
+    }
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Overwrite the cell that cursor pCur is pointing to with fresh content
+** contained in pX.
+*/
+static int btreeOverwriteCell(BtCursor *pCur, const BtreePayload *pX){
+  int iOffset;                        /* Next byte of pX->pData to write */
+  int nTotal = pX->nData + pX->nZero; /* Total bytes of to write */
+  int rc;                             /* Return code */
+  MemPage *pPage = pCur->pPage;       /* Page being written */
+  BtShared *pBt;                      /* Btree */
+  Pgno ovflPgno;                      /* Next overflow page to write */
+  u32 ovflPageSize;                   /* Size to write on overflow page */
+
+  if( pCur->info.pPayload + pCur->info.nLocal > pPage->aDataEnd ){
+    return SQLITE_CORRUPT_BKPT;
+  }
+  /* Overwrite the local portion first */
+  rc = btreeOverwriteContent(pPage, pCur->info.pPayload, pX,
+                             0, pCur->info.nLocal);
+  if( rc ) return rc;
+  if( pCur->info.nLocal==nTotal ) return SQLITE_OK;
+
+  /* Now overwrite the overflow pages */
+  iOffset = pCur->info.nLocal;
+  assert( nTotal>=0 );
+  assert( iOffset>=0 );
+  ovflPgno = get4byte(pCur->info.pPayload + iOffset);
+  pBt = pPage->pBt;
+  ovflPageSize = pBt->usableSize - 4;
+  do{
+    rc = btreeGetPage(pBt, ovflPgno, &pPage, 0);
+    if( rc ) return rc;
+    if( sqlite3PagerPageRefcount(pPage->pDbPage)!=1 ){
+      rc = SQLITE_CORRUPT_BKPT;
+    }else{
+      if( iOffset+ovflPageSize<(u32)nTotal ){
+        ovflPgno = get4byte(pPage->aData);
+      }else{
+        ovflPageSize = nTotal - iOffset;
+      }
+      rc = btreeOverwriteContent(pPage, pPage->aData+4, pX,
+                                 iOffset, ovflPageSize);
+    }
+    sqlite3PagerUnref(pPage->pDbPage);
+    if( rc ) return rc;
+    iOffset += ovflPageSize;
+  }while( iOffset<nTotal );
+  return SQLITE_OK;    
+}
+
 
 /*
 ** Insert a new record into the BTree.  The content of the new record
@@ -8252,6 +8340,14 @@ int sqlite3BtreeInsert(
     ** new row onto the end, set the "loc" to avoid an unnecessary
     ** btreeMoveto() call */
     if( (pCur->curFlags&BTCF_ValidNKey)!=0 && pX->nKey==pCur->info.nKey ){
+      /* The current is currently pointing to the entry that is to be
+      ** overwritten */
+      assert( pX->nData>=0 && pX->nZero>=0 );
+      if( pCur->info.nSize!=0
+       && pCur->info.nPayload==(u32)pX->nData+pX->nZero
+      ){
+        return btreeOverwriteCell(pCur, pX);
+      }
       loc = 0;
     }else if( loc==0 ){
       rc = sqlite3BtreeMovetoUnpacked(pCur, 0, pX->nKey, flags!=0, &loc);
diff --git a/test/pager1.test b/test/pager1.test
index 42edc3d16b..1d56fad30b 100644
--- a/test/pager1.test
+++ b/test/pager1.test
@@ -1149,7 +1149,7 @@ do_test pager1-5.5.1 {
     PRAGMA journal_mode = PERSIST;
     CREATE TABLE t3(a, b);
     INSERT INTO t3 SELECT randomblob(1500), randomblob(1500) FROM t1;
-    UPDATE t3 SET b = randomblob(1500);
+    UPDATE t3 SET b = randomblob(1501);
   }
   expr [file size test.db-journal] > 15000
 } {1}