Omit the check for cell-pointer consistency in sqlite3BtreeInitPage()

for a 2.5% performance gain. (CVS 5433)

FossilOrigin-Name: b88087e69dffb743c5b552703e14a030349cf65b

manifest

@@ -1,5 +1,5 @@
-C Optimization\sto\ssqltie3BtreeParseCellPtr.\s\s0.3%\sperformance\sincrease.\s(CVS\s5432)
+C Omit\sthe\scheck\sfor\scell-pointer\sconsistency\sin\ssqlite3BtreeInitPage()\nfor\sa\s2.5%\sperformance\sgain.\s(CVS\s5433)
-D 2008-07-18T00:57:33
+D 2008-07-18T02:44:18
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in a03f7cb4f7ad50bc53a788c6c544430e81f95de4
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -96,9 +96,9 @@ F src/attach.c b18ba42c77f7d3941f5d23d2ca20fa1d841a4e91
 F src/auth.c c8b2ab5c8bad4bd90ed7c294694f48269162c627
 F src/bitvec.c 95c86bd18d8fedf0533f5af196192546e10a7e7d
 F src/btmutex.c 709cad2cdca0afd013f0f612363810e53f59ec53
-F src/btree.c 5299a702966d3c32618340cae49cebafc5e93870
+F src/btree.c 134d2f76fb9144e81b6ca9e426922ac3626d1d77
 F src/btree.h 03256ed7ee42b5ecacbe887070b0f8249e7d069d
-F src/btreeInt.h 2aa6dc53b1801bb22815a5be22e03be121f3bd8f
+F src/btreeInt.h e5b952467935fc29033da138c3d74673329d9770
 F src/build.c bac7233d984be3805aaa41cf500f7ee12dc97249
 F src/callback.c aa492a0ad8c2d454edff9fb8a57fae13743cf71d
 F src/complete.c cb14e06dbe79dee031031f0d9e686ff306afe07c
@@ -608,7 +608,7 @@ F tool/speedtest16.c c8a9c793df96db7e4933f0852abb7a03d48f2e81
 F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 1dbced29de5f59ba2ebf877edcadf171540374d1
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
-P 29d3bfd7c9a68078385354394052612bf812859b
+P 77e099ad7de84fe07dfeb4c045c769653dd13b93
-R 52c1e00d28149edaa06e0b96ba148399
+R c5135664a56b05b1461fc48c1c5e4a98
 U drh
-Z ba442f29937e797f8880a62ff02e96e8
+Z 1e2af38c22a126d0243f54deb66a7f3a

manifest.uuid

@@ -1 +1 @@
-77e099ad7de84fe07dfeb4c045c769653dd13b93
+b88087e69dffb743c5b552703e14a030349cf65b

src/btree.c

@@ -9,7 +9,7 @@
 **    May you share freely, never taking more than you give.
 **
 *************************************************************************
-** $Id: btree.c,v 1.485 2008/07/18 00:57:33 drh Exp $
+** $Id: btree.c,v 1.486 2008/07/18 02:44:18 drh Exp $
 **
 ** This file implements a external (disk-based) database using BTrees.
 ** See the header comment on "btreeInt.h" for additional information.
@@ -516,8 +516,8 @@ static int ptrmapGet(BtShared *pBt, Pgno key, u8 *pEType, Pgno *pPgno){
 **
 ** This routine works only for pages that do not contain overflow cells.
 */
-#define findCell(pPage, iCell) \
+#define findCell(P,I) \
-  ((pPage)->aData + get2byte(&(pPage)->aData[(pPage)->cellOffset+2*(iCell)]))
+  ((P)->aData + ((P)->maskPage & get2byte(&(P)->aData[(P)->cellOffset+2*(I)])))
 
 /*
 ** This a more complex version of findCell() that works for
@@ -929,9 +929,6 @@ int sqlite3BtreeInitPage(
   int cellOffset;    /* Offset from start of page to first cell pointer */
   int nFree;         /* Number of unused bytes on the page */
   int top;           /* First byte of the cell content area */
-  u8 *pOff;          /* Iterator used to check all cell offsets are in range */
-  u8 *pEnd;          /* Pointer to end of cell offset array */
-  u8 mask;           /* Mask of bits that must be zero in MSB of cell offsets */
 
   pBt = pPage->pBt;
   assert( pBt!=0 );
@@ -952,6 +949,8 @@ int sqlite3BtreeInitPage(
   hdr = pPage->hdrOffset;
   data = pPage->aData;
   if( decodeFlags(pPage, data[hdr]) ) return SQLITE_CORRUPT_BKPT;
+  assert( pBt->pageSize>=512 && pBt->pageSize<=32768 );
+  pPage->maskPage = pBt->pageSize - 1;
   pPage->nOverflow = 0;
   pPage->idxShift = 0;
   usableSize = pBt->usableSize;
@@ -991,13 +990,25 @@ int sqlite3BtreeInitPage(
     return SQLITE_CORRUPT_BKPT; 
   }
 
-  /* Check that all the offsets in the cell offset array are within range. */
+#if 0
+  /* Check that all the offsets in the cell offset array are within range. 
+  ** 
+  ** Omitting this consistency check and using the pPage->maskPage mask
+  ** to prevent overrunning the page buffer in findCell() results in a
+  ** 2.5% performance gain.
+  */
+  {
+    u8 *pOff;        /* Iterator used to check all cell offsets are in range */
+    u8 *pEnd;        /* Pointer to end of cell offset array */
+    u8 mask;         /* Mask of bits that must be zero in MSB of cell offsets */
     mask = ~(((u8)(pBt->pageSize>>8))-1);
     pEnd = &data[cellOffset + pPage->nCell*2];
     for(pOff=&data[cellOffset]; pOff!=pEnd && !((*pOff)&mask); pOff+=2);
     if( pOff!=pEnd ){
       return SQLITE_CORRUPT_BKPT;
     }
+  }
+#endif
 
   pPage->isInit = 1;
   return SQLITE_OK;
@@ -1029,6 +1040,8 @@ static void zeroPage(MemPage *pPage, int flags){
   pPage->hdrOffset = hdr;
   pPage->cellOffset = first;
   pPage->nOverflow = 0;
+  assert( pBt->pageSize>=512 && pBt->pageSize<=32768 );
+  pPage->maskPage = pBt->pageSize - 1;
   pPage->idxShift = 0;
   pPage->nCell = 0;
   pPage->isInit = 1;

src/btreeInt.h

@@ -9,7 +9,7 @@
 **    May you share freely, never taking more than you give.
 **
 *************************************************************************
-** $Id: btreeInt.h,v 1.27 2008/07/17 18:39:58 drh Exp $
+** $Id: btreeInt.h,v 1.28 2008/07/18 02:44:18 drh Exp $
 **
 ** This file implements a external (disk-based) database using BTrees.
 ** For a detailed discussion of BTrees, refer to
@@ -284,6 +284,7 @@ struct MemPage {
   u16 idxParent;       /* Index in parent of this node */
   u16 nFree;           /* Number of free bytes on the page */
   u16 nCell;           /* Number of cells on this page, local and ovfl */
+  u16 maskPage;        /* Mask for page offset */
   struct _OvflCell {   /* Cells that will not fit on aData[] */
     u8 *pCell;          /* Pointers to the body of the overflow cell */
     u16 idx;            /* Insert this cell before idx-th non-overflow cell */