Btree optimization: New field BtCursor.pPage that points to the current page,

saving a single pointer dereference on each access. FossilOrigin-Name: 373b71d19cad785922d5a80828f2fee0cbe7dff6594743e625bbdfa31b1ca131
2025-08-05 15:55:57 +03:00 · 2017-08-15 03:46:47 +00:00
parent f38dd3b68f
commit 352a35abf5
4 changed files with 103 additions and 84 deletions
--- a/14
+++ b/14
@@ -1,5 +1,5 @@
-C Minor\ssize\sand\sperformance\soptimization\sto\ssqlite3BtreeCloseCursor().
-D 2017-08-14T23:53:02.259
+C Btree\soptimization:\s\sNew\sfield\sBtCursor.pPage\sthat\spoints\sto\sthe\scurrent\spage,\nsaving\sa\ssingle\spointer\sdereference\son\seach\saccess.
+D 2017-08-15T03:46:47.011
 F Makefile.in d9873c9925917cca9990ee24be17eb9613a668012c85a343aef7e5536ae266e8
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 02b469e9dcd5b7ee63fc1fb05babc174260ee4cfa4e0ef2e48c3c6801567a016
@@ -397,9 +397,9 @@ F src/auth.c 79f96c6f33bf0e5da8d1c282cee5ebb1852bb8a6ccca3e485d7c459b035d9c3c
 F src/backup.c faf17e60b43233c214aae6a8179d24503a61e83b
 F src/bitvec.c 17ea48eff8ba979f1f5b04cc484c7bb2be632f33
 F src/btmutex.c 0e9ce2d56159b89b9bc8e197e023ee11e39ff8ca
-F src/btree.c 05781141fe24e9e24719a1d9c9b6ce38480af115f85a8a26f389a089888060d7
+F src/btree.c d2f5f347e56f8b7ed1bb798087045a3b98cd63f45fde7675fd24b9e88b61304d
 F src/btree.h 3edc5329bc59534d2d15b4f069a9f54b779a7e51289e98fa481ae3c0e526a5ca
-F src/btreeInt.h 97700795edf8a43245720414798b7b29d8e465aef46bf301ffacd431910c0da1
+F src/btreeInt.h f78671f594dafd88cf9a81253da04db81272b382d2dc074bb983d348b95d9d2d
 F src/build.c f8a85d2ad14c2201e10c2fe7185e1cb3f1db8b0c90d40d1fb99c20b135ab71bc
 F src/callback.c 930648a084a3adc741c6471adfbdc50ba47ba3542421cb80a26f259f467de65e
 F src/complete.c a3634ab1e687055cd002e11b8f43eb75c17da23e
@@ -1647,7 +1647,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 240d57143d943eaddd5f7c2d473f47a1d29417e61d28142f70f3d960bb9b30df
-R a7c4eab7d8d2ce1f319f583d46cbd640
+P 16969338841734d00ab906a94b82480c7e1e426eb0ddf7b9e6aed722aee5d91f
+R 3d6cdbe8a873abb5b839027115a07163
 U drh
-Z e48f5e9e2a338851fd6ede62f6ca96de
+Z 53459ac0c08285b40b84acbd692920bc
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-16969338841734d00ab906a94b82480c7e1e426eb0ddf7b9e6aed722aee5d91f
+373b71d19cad785922d5a80828f2fee0cbe7dff6594743e625bbdfa31b1ca131
--- a/src/btree.c
+++ b/src/btree.c
@@ -439,7 +439,8 @@ static void downgradeAllSharedCacheTableLocks(Btree *p){

 #endif /* SQLITE_OMIT_SHARED_CACHE */

-static void releasePage(MemPage *pPage);  /* Forward reference */
+static void releasePage(MemPage *pPage);
+static void releasePageNotNull(MemPage *pPage);  /* Forward reference */

 /*
 ***** This routine is used inside of assert() only ****
@@ -598,11 +599,13 @@ static void btreeClearHasContent(BtShared *pBt){
 */
 static void btreeReleaseAllCursorPages(BtCursor *pCur){
  int i;
-  for(i=0; i<=pCur->iPage; i++){
-    releasePage(pCur->apPage[i]);
-    pCur->apPage[i] = 0;
+  if( pCur->iPage>=0 ){
+    for(i=0; i<pCur->iPage; i++){
+      releasePageNotNull(pCur->apPage[i]);
    }
+    releasePageNotNull(pCur->pPage);
    pCur->iPage = -1;
+  }
 }

 /*
@@ -771,7 +774,7 @@ static int btreeMoveto(
    if( pIdxKey==0 ) return SQLITE_NOMEM_BKPT;
    sqlite3VdbeRecordUnpack(pCur->pKeyInfo, (int)nKey, pKey, pIdxKey);
    if( pIdxKey->nField==0 ){
-      rc = SQLITE_CORRUPT_PGNO(pCur->apPage[pCur->iPage]->pgno);
+      rc = SQLITE_CORRUPT;
      goto moveto_done;
    }
  }else{
@@ -2049,7 +2052,7 @@ static int getAndInitPage(
  int rc;
  DbPage *pDbPage;
  assert( sqlite3_mutex_held(pBt->mutex) );
-  assert( pCur==0 || ppPage==&pCur->apPage[pCur->iPage] );
+  assert( pCur==0 || ppPage==&pCur->pPage );
  assert( pCur==0 || bReadOnly==pCur->curPagerFlags );
  assert( pCur==0 || pCur->iPage>0 );

@@ -2083,7 +2086,10 @@ static int getAndInitPage(
  return SQLITE_OK;

 getAndInitPage_error:
-  if( pCur ) pCur->iPage--;
+  if( pCur ){
+    pCur->iPage--;
+    pCur->pPage = pCur->apPage[pCur->iPage];
+  }
  testcase( pgno==0 );
  assert( pgno!=0 || rc==SQLITE_CORRUPT );
  return rc;
@@ -4293,7 +4299,6 @@ void sqlite3BtreeCursorZero(BtCursor *p){
 int sqlite3BtreeCloseCursor(BtCursor *pCur){
  Btree *pBtree = pCur->pBtree;
  if( pBtree ){
-    int i;
    BtShared *pBt = pCur->pBt;
    sqlite3BtreeEnter(pBtree);
    assert( pBt->pCursor!=0 );
@@ -4309,9 +4314,7 @@ int sqlite3BtreeCloseCursor(BtCursor *pCur){
        pPrev = pPrev->pNext;
      }while( ALWAYS(pPrev) );
    }
-    for(i=0; i<=pCur->iPage; i++){
-      releasePageNotNull(pCur->apPage[i]);
-    }
+    btreeReleaseAllCursorPages(pCur);
    unlockBtreeIfUnused(pBt);
    sqlite3_free(pCur->aOverflow);
    sqlite3_free(pCur->pKey);
@@ -4331,9 +4334,8 @@ int sqlite3BtreeCloseCursor(BtCursor *pCur){
 #ifndef NDEBUG
  static void assertCellInfo(BtCursor *pCur){
    CellInfo info;
-    int iPage = pCur->iPage;
    memset(&info, 0, sizeof(info));
-    btreeParseCell(pCur->apPage[iPage], pCur->ix, &info);
+    btreeParseCell(pCur->pPage, pCur->ix, &info);
    assert( CORRUPT_DB || memcmp(&info, &pCur->info, sizeof(info))==0 );
  }
 #else
@@ -4341,9 +4343,8 @@ int sqlite3BtreeCloseCursor(BtCursor *pCur){
 #endif
 static SQLITE_NOINLINE void getCellInfo(BtCursor *pCur){
  if( pCur->info.nSize==0 ){
-    int iPage = pCur->iPage;
    pCur->curFlags |= BTCF_ValidNKey;
-    btreeParseCell(pCur->apPage[iPage],pCur->ix,&pCur->info);
+    btreeParseCell(pCur->pPage,pCur->ix,&pCur->info);
  }else{
    assertCellInfo(pCur);
  }
@@ -4541,7 +4542,7 @@ static int accessPayload(
  unsigned char *aPayload;
  int rc = SQLITE_OK;
  int iIdx = 0;
-  MemPage *pPage = pCur->apPage[pCur->iPage]; /* Btree page of current entry */
+  MemPage *pPage = pCur->pPage;               /* Btree page of current entry */
  BtShared *pBt = pCur->pBt;                  /* Btree this cursor belongs to */
 #ifdef SQLITE_DIRECT_OVERFLOW_READ
  unsigned char * const pBufStart = pBuf;     /* Start of original out buffer */
@@ -4737,8 +4738,8 @@ static int accessPayload(
 int sqlite3BtreePayload(BtCursor *pCur, u32 offset, u32 amt, void *pBuf){
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
-  assert( pCur->iPage>=0 && pCur->apPage[pCur->iPage] );
-  assert( pCur->ix<pCur->apPage[pCur->iPage]->nCell );
+  assert( pCur->iPage>=0 && pCur->pPage );
+  assert( pCur->ix<pCur->pPage->nCell );
  return accessPayload(pCur, offset, amt, (unsigned char*)pBuf, 0);
 }

@@ -4796,15 +4797,15 @@ static const void *fetchPayload(
  u32 *pAmt            /* Write the number of available bytes here */
 ){
  u32 amt;
-  assert( pCur!=0 && pCur->iPage>=0 && pCur->apPage[pCur->iPage]);
+  assert( pCur!=0 && pCur->iPage>=0 && pCur->pPage);
  assert( pCur->eState==CURSOR_VALID );
  assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
  assert( cursorOwnsBtShared(pCur) );
-  assert( pCur->ix<pCur->apPage[pCur->iPage]->nCell );
+  assert( pCur->ix<pCur->pPage->nCell );
  assert( pCur->info.nSize>0 );
-  assert( pCur->info.pPayload>pCur->apPage[pCur->iPage]->aData || CORRUPT_DB );
-  assert( pCur->info.pPayload<pCur->apPage[pCur->iPage]->aDataEnd ||CORRUPT_DB);
-  amt = (int)(pCur->apPage[pCur->iPage]->aDataEnd - pCur->info.pPayload);
+  assert( pCur->info.pPayload>pCur->pPage->aData || CORRUPT_DB );
+  assert( pCur->info.pPayload<pCur->pPage->aDataEnd ||CORRUPT_DB);
+  amt = (int)(pCur->pPage->aDataEnd - pCur->info.pPayload);
  if( pCur->info.nLocal<amt ) amt = pCur->info.nLocal;
  *pAmt = amt;
  return (void*)pCur->info.pPayload;
@@ -4851,10 +4852,11 @@ static int moveToChild(BtCursor *pCur, u32 newPgno){
  }
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl);
-  pCur->aiIdx[pCur->iPage++] = pCur->ix;
+  pCur->aiIdx[pCur->iPage] = pCur->ix;
+  pCur->apPage[pCur->iPage] = pCur->pPage;
  pCur->ix = 0;
-  return getAndInitPage(pBt, newPgno, &pCur->apPage[pCur->iPage],
-                        pCur, pCur->curPagerFlags);
+  pCur->iPage++;
+  return getAndInitPage(pBt, newPgno, &pCur->pPage, pCur, pCur->curPagerFlags);
 }

 #ifdef SQLITE_DEBUG
@@ -4888,20 +4890,23 @@ static void assertParentIndex(MemPage *pParent, int iIdx, Pgno iChild){
 ** the largest cell index.
 */
 static void moveToParent(BtCursor *pCur){
+  MemPage *pLeaf;
  assert( cursorOwnsBtShared(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  assert( pCur->iPage>0 );
-  assert( pCur->apPage[pCur->iPage] );
+  assert( pCur->pPage );
  assertParentIndex(
    pCur->apPage[pCur->iPage-1], 
    pCur->aiIdx[pCur->iPage-1], 
-    pCur->apPage[pCur->iPage]->pgno
+    pCur->pPage->pgno
  );
  testcase( pCur->aiIdx[pCur->iPage-1] > pCur->apPage[pCur->iPage-1]->nCell );
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl);
  pCur->ix = pCur->aiIdx[pCur->iPage-1];
-  releasePageNotNull(pCur->apPage[pCur->iPage--]);
+  pLeaf = pCur->pPage;
+  pCur->pPage = pCur->apPage[--pCur->iPage];
+  releasePageNotNull(pLeaf);
 }

 /*
@@ -4938,10 +4943,11 @@ static int moveToRoot(BtCursor *pCur){

  if( pCur->iPage>=0 ){
    if( pCur->iPage ){
-      do{
-        assert( pCur->apPage[pCur->iPage]!=0 );
-        releasePageNotNull(pCur->apPage[pCur->iPage--]);
-      }while( pCur->iPage);
+      releasePageNotNull(pCur->pPage);
+      while( --pCur->iPage ){
+        releasePageNotNull(pCur->apPage[pCur->iPage]);
+      }
+      pCur->pPage = pCur->apPage[0];
      goto skip_init;
    }
  }else if( pCur->pgnoRoot==0 ){
@@ -4956,16 +4962,16 @@ static int moveToRoot(BtCursor *pCur){
      }
      sqlite3BtreeClearCursor(pCur);
    }
-    rc = getAndInitPage(pCur->pBtree->pBt, pCur->pgnoRoot, &pCur->apPage[0],
+    rc = getAndInitPage(pCur->pBtree->pBt, pCur->pgnoRoot, &pCur->pPage,
                        0, pCur->curPagerFlags);
    if( rc!=SQLITE_OK ){
      pCur->eState = CURSOR_INVALID;
      return rc;
    }
    pCur->iPage = 0;
-    pCur->curIntKey = pCur->apPage[0]->intKey;
+    pCur->curIntKey = pCur->pPage->intKey;
  }
-  pRoot = pCur->apPage[0];
+  pRoot = pCur->pPage;
  assert( pRoot->pgno==pCur->pgnoRoot );

  /* If pCur->pKeyInfo is not NULL, then the caller that opened this cursor
@@ -4980,7 +4986,7 @@ static int moveToRoot(BtCursor *pCur){
  ** (or the freelist).  */
  assert( pRoot->intKey==1 || pRoot->intKey==0 );
  if( pRoot->isInit==0 || (pCur->pKeyInfo==0)!=pRoot->intKey ){
-    return SQLITE_CORRUPT_PGNO(pCur->apPage[pCur->iPage]->pgno);
+    return SQLITE_CORRUPT_PGNO(pCur->pPage->pgno);
  }

 skip_init:  
@@ -4988,7 +4994,7 @@ skip_init:
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_AtLast|BTCF_ValidNKey|BTCF_ValidOvfl);

-  pRoot = pCur->apPage[0];
+  pRoot = pCur->pPage;
  if( pRoot->nCell>0 ){
    pCur->eState = CURSOR_VALID;
  }else if( !pRoot->leaf ){
@@ -5018,7 +5024,7 @@ static int moveToLeftmost(BtCursor *pCur){

  assert( cursorOwnsBtShared(pCur) );
  assert( pCur->eState==CURSOR_VALID );
-  while( rc==SQLITE_OK && !(pPage = pCur->apPage[pCur->iPage])->leaf ){
+  while( rc==SQLITE_OK && !(pPage = pCur->pPage)->leaf ){
    assert( pCur->ix<pPage->nCell );
    pgno = get4byte(findCell(pPage, pCur->ix));
    rc = moveToChild(pCur, pgno);
@@ -5043,7 +5049,7 @@ static int moveToRightmost(BtCursor *pCur){

  assert( cursorOwnsBtShared(pCur) );
  assert( pCur->eState==CURSOR_VALID );
-  while( !(pPage = pCur->apPage[pCur->iPage])->leaf ){
+  while( !(pPage = pCur->pPage)->leaf ){
    pgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    pCur->ix = pPage->nCell;
    rc = moveToChild(pCur, pgno);
@@ -5066,11 +5072,11 @@ int sqlite3BtreeFirst(BtCursor *pCur, int *pRes){
  assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
  rc = moveToRoot(pCur);
  if( rc==SQLITE_OK ){
-    assert( pCur->apPage[pCur->iPage]->nCell>0 );
+    assert( pCur->pPage->nCell>0 );
    *pRes = 0;
    rc = moveToLeftmost(pCur);
  }else if( rc==SQLITE_EMPTY ){
-    assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
+    assert( pCur->pgnoRoot==0 || pCur->pPage->nCell==0 );
    *pRes = 1;
    rc = SQLITE_OK;
  }
@@ -5096,8 +5102,8 @@ int sqlite3BtreeLast(BtCursor *pCur, int *pRes){
    for(ii=0; ii<pCur->iPage; ii++){
      assert( pCur->aiIdx[ii]==pCur->apPage[ii]->nCell );
    }
-    assert( pCur->ix==pCur->apPage[pCur->iPage]->nCell-1 );
-    assert( pCur->apPage[pCur->iPage]->leaf );
+    assert( pCur->ix==pCur->pPage->nCell-1 );
+    assert( pCur->pPage->leaf );
 #endif
    return SQLITE_OK;
  }
@@ -5113,7 +5119,7 @@ int sqlite3BtreeLast(BtCursor *pCur, int *pRes){
      pCur->curFlags &= ~BTCF_AtLast;
    }
  }else if( rc==SQLITE_EMPTY ){
-    assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
+    assert( pCur->pgnoRoot==0 || pCur->pPage->nCell==0 );
    *pRes = 1;
    rc = SQLITE_OK;
  }
@@ -5215,22 +5221,22 @@ int sqlite3BtreeMovetoUnpacked(
  rc = moveToRoot(pCur);
  if( rc ){
    if( rc==SQLITE_EMPTY ){
-      assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
+      assert( pCur->pgnoRoot==0 || pCur->pPage->nCell==0 );
      *pRes = -1;
      return SQLITE_OK;
    }
    return rc;
  }
-  assert( pCur->apPage[pCur->iPage] );
-  assert( pCur->apPage[pCur->iPage]->isInit );
+  assert( pCur->pPage );
+  assert( pCur->pPage->isInit );
  assert( pCur->eState==CURSOR_VALID );
-  assert( pCur->apPage[pCur->iPage]->nCell > 0 );
-  assert( pCur->apPage[0]->intKey==pCur->curIntKey );
+  assert( pCur->pPage->nCell > 0 );
+  assert( pCur->iPage==0 || pCur->apPage[0]->intKey==pCur->curIntKey );
  assert( pCur->curIntKey || pIdxKey );
  for(;;){
    int lwr, upr, idx, c;
    Pgno chldPg;
-    MemPage *pPage = pCur->apPage[pCur->iPage];
+    MemPage *pPage = pCur->pPage;
    u8 *pCell;                          /* Pointer to current cell in pPage */

    /* pPage->nCell must be greater than zero. If this is the root-page
@@ -5369,7 +5375,7 @@ int sqlite3BtreeMovetoUnpacked(
    assert( lwr==upr+1 || (pPage->intKey && !pPage->leaf) );
    assert( pPage->isInit );
    if( pPage->leaf ){
-      assert( pCur->ix<pCur->apPage[pCur->iPage]->nCell );
+      assert( pCur->ix<pCur->pPage->nCell );
      pCur->ix = (u16)idx;
      *pRes = c;
      rc = SQLITE_OK;
@@ -5423,9 +5429,10 @@ i64 sqlite3BtreeRowCountEst(BtCursor *pCur){
  ** opcode, and it that case the cursor will always be valid and
  ** will always point to a leaf node. */
  if( NEVER(pCur->eState!=CURSOR_VALID) ) return -1;
-  if( NEVER(pCur->apPage[pCur->iPage]->leaf==0) ) return -1;
+  if( NEVER(pCur->pPage->leaf==0) ) return -1;

-  for(n=1, i=0; i<=pCur->iPage; i++){
+  n = pCur->pPage->nCell;
+  for(i=0; i<pCur->iPage; i++){
    n *= pCur->apPage[i]->nCell;
  }
  return n;
@@ -5478,7 +5485,7 @@ static SQLITE_NOINLINE int btreeNext(BtCursor *pCur){
    }
  }

-  pPage = pCur->apPage[pCur->iPage];
+  pPage = pCur->pPage;
  idx = ++pCur->ix;
  assert( pPage->isInit );

@@ -5501,7 +5508,7 @@ static SQLITE_NOINLINE int btreeNext(BtCursor *pCur){
        return SQLITE_DONE;
      }
      moveToParent(pCur);
-      pPage = pCur->apPage[pCur->iPage];
+      pPage = pCur->pPage;
    }while( pCur->ix>=pPage->nCell );
    if( pPage->intKey ){
      return sqlite3BtreeNext(pCur, 0);
@@ -5524,7 +5531,7 @@ int sqlite3BtreeNext(BtCursor *pCur, int flags){
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl);
  if( pCur->eState!=CURSOR_VALID ) return btreeNext(pCur);
-  pPage = pCur->apPage[pCur->iPage];
+  pPage = pCur->pPage;
  if( (++pCur->ix)>=pPage->nCell ){
    pCur->ix--;
    return btreeNext(pCur);
@@ -5583,7 +5590,7 @@ static SQLITE_NOINLINE int btreePrevious(BtCursor *pCur){
    }
  }

-  pPage = pCur->apPage[pCur->iPage];
+  pPage = pCur->pPage;
  assert( pPage->isInit );
  if( !pPage->leaf ){
    int idx = pCur->ix;
@@ -5602,7 +5609,7 @@ static SQLITE_NOINLINE int btreePrevious(BtCursor *pCur){
    assert( (pCur->curFlags & (BTCF_ValidOvfl))==0 );

    pCur->ix--;
-    pPage = pCur->apPage[pCur->iPage];
+    pPage = pCur->pPage;
    if( pPage->intKey && !pPage->leaf ){
      rc = sqlite3BtreePrevious(pCur, 0);
    }else{
@@ -5620,7 +5627,7 @@ int sqlite3BtreePrevious(BtCursor *pCur, int flags){
  pCur->info.nSize = 0;
  if( pCur->eState!=CURSOR_VALID
   || pCur->ix==0
-   || pCur->apPage[pCur->iPage]->leaf==0
+   || pCur->pPage->leaf==0
  ){
    return btreePrevious(pCur);
  }
@@ -7934,7 +7941,7 @@ static int balance(BtCursor *pCur){

  do {
    int iPage = pCur->iPage;
-    MemPage *pPage = pCur->apPage[iPage];
+    MemPage *pPage = pCur->pPage;

    if( iPage==0 ){
      if( pPage->nOverflow ){
@@ -7950,7 +7957,9 @@ static int balance(BtCursor *pCur){
          pCur->iPage = 1;
          pCur->ix = 0;
          pCur->aiIdx[0] = 0;
-          assert( pCur->apPage[1]->nOverflow );
+          pCur->apPage[0] = pPage;
+          pCur->pPage = pCur->apPage[1];
+          assert( pCur->pPage->nOverflow );
        }
      }else{
        break;
@@ -8030,6 +8039,7 @@ static int balance(BtCursor *pCur){
      releasePage(pPage);
      pCur->iPage--;
      assert( pCur->iPage>=0 );
+      pCur->pPage = pCur->apPage[pCur->iPage];
    }
  }while( rc==SQLITE_OK );

@@ -8161,7 +8171,7 @@ int sqlite3BtreeInsert(
  }
  assert( pCur->eState==CURSOR_VALID || (pCur->eState==CURSOR_INVALID && loc) );

-  pPage = pCur->apPage[pCur->iPage];
+  pPage = pCur->pPage;
  assert( pPage->intKey || pX->nKey>=0 );
  assert( pPage->leaf || !pPage->intKey );

@@ -8248,7 +8258,7 @@ int sqlite3BtreeInsert(
    ** fails. Internal data structure corruption will result otherwise. 
    ** Also, set the cursor state to invalid. This stops saveCursorPosition()
    ** from trying to save the current position of the cursor.  */
-    pCur->apPage[pCur->iPage]->nOverflow = 0;
+    pCur->pPage->nOverflow = 0;
    pCur->eState = CURSOR_INVALID;
    if( (flags & BTREE_SAVEPOSITION) && rc==SQLITE_OK ){
      btreeReleaseAllCursorPages(pCur);
@@ -8265,7 +8275,7 @@ int sqlite3BtreeInsert(
      pCur->nKey = pX->nKey;
    }
  }
-  assert( pCur->iPage<0 || pCur->apPage[pCur->iPage]->nOverflow==0 );
+  assert( pCur->iPage<0 || pCur->pPage->nOverflow==0 );

 end_insert:
  return rc;
@@ -8306,13 +8316,13 @@ int sqlite3BtreeDelete(BtCursor *pCur, u8 flags){
  assert( pCur->curFlags & BTCF_WriteFlag );
  assert( hasSharedCacheTableLock(p, pCur->pgnoRoot, pCur->pKeyInfo!=0, 2) );
  assert( !hasReadConflicts(p, pCur->pgnoRoot) );
-  assert( pCur->ix<pCur->apPage[pCur->iPage]->nCell );
+  assert( pCur->ix<pCur->pPage->nCell );
  assert( pCur->eState==CURSOR_VALID );
  assert( (flags & ~(BTREE_SAVEPOSITION | BTREE_AUXDELETE))==0 );

  iCellDepth = pCur->iPage;
  iCellIdx = pCur->ix;
-  pPage = pCur->apPage[iCellDepth];
+  pPage = pCur->pPage;
  pCell = findCell(pPage, iCellIdx);

  /* If the bPreserve flag is set to true, then the cursor position must
@@ -8378,11 +8388,16 @@ int sqlite3BtreeDelete(BtCursor *pCur, u8 flags){
  ** node. The cell from the leaf node needs to be moved to the internal
  ** node to replace the deleted cell.  */
  if( !pPage->leaf ){
-    MemPage *pLeaf = pCur->apPage[pCur->iPage];
+    MemPage *pLeaf = pCur->pPage;
    int nCell;
-    Pgno n = pCur->apPage[iCellDepth+1]->pgno;
+    Pgno n;
    unsigned char *pTmp;

+    if( iCellDepth<pCur->iPage-1 ){
+      n = pCur->apPage[iCellDepth+1]->pgno;
+    }else{
+      n = pCur->pPage->pgno;
+    }
    pCell = findCell(pLeaf, pLeaf->nCell-1);
    if( pCell<&pLeaf->aData[4] ) return SQLITE_CORRUPT_BKPT;
    nCell = pLeaf->xCellSize(pLeaf, pCell);
@@ -8414,16 +8429,19 @@ int sqlite3BtreeDelete(BtCursor *pCur, u8 flags){
  ** well.  */
  rc = balance(pCur);
  if( rc==SQLITE_OK && pCur->iPage>iCellDepth ){
+    releasePageNotNull(pCur->pPage);
+    pCur->iPage--;
    while( pCur->iPage>iCellDepth ){
      releasePage(pCur->apPage[pCur->iPage--]);
    }
+    pCur->pPage = pCur->apPage[pCur->iPage];
    rc = balance(pCur);
  }

  if( rc==SQLITE_OK ){
    if( bSkipnext ){
      assert( bPreserve && (pCur->iPage==iCellDepth || CORRUPT_DB) );
-      assert( pPage==pCur->apPage[pCur->iPage] || CORRUPT_DB );
+      assert( pPage==pCur->pPage || CORRUPT_DB );
      assert( (pPage->nCell>0 || CORRUPT_DB) && iCellIdx<=pPage->nCell );
      pCur->eState = CURSOR_SKIPNEXT;
      if( iCellIdx>=pPage->nCell ){
@@ -8920,7 +8938,7 @@ int sqlite3BtreeCount(BtCursor *pCur, i64 *pnEntry){
    ** this page contains countable entries. Increment the entry counter
    ** accordingly.
    */
-    pPage = pCur->apPage[pCur->iPage];
+    pPage = pCur->pPage;
    if( pPage->leaf || !pPage->intKey ){
      nEntry += pPage->nCell;
    }
@@ -8943,10 +8961,10 @@ int sqlite3BtreeCount(BtCursor *pCur, i64 *pnEntry){
          return moveToRoot(pCur);
        }
        moveToParent(pCur);
-      }while ( pCur->ix>=pCur->apPage[pCur->iPage]->nCell );
+      }while ( pCur->ix>=pCur->pPage->nCell );

      pCur->ix++;
-      pPage = pCur->apPage[pCur->iPage];
+      pPage = pCur->pPage;
    }

    /* Descend to the child node of the cell that the cursor currently 
@@ -9787,7 +9805,7 @@ int sqlite3BtreePutData(BtCursor *pCsr, u32 offset, u32 amt, void *z){
              && pCsr->pBt->inTransaction==TRANS_WRITE );
  assert( hasSharedCacheTableLock(pCsr->pBtree, pCsr->pgnoRoot, 0, 2) );
  assert( !hasReadConflicts(pCsr->pBtree, pCsr->pgnoRoot) );
-  assert( pCsr->apPage[pCsr->iPage]->intKey );
+  assert( pCsr->pPage->intKey );

  return accessPayload(pCsr, offset, amt, (unsigned char *)z, 1);
 }
--- a/src/btreeInt.h
+++ b/src/btreeInt.h
@@ -522,7 +522,8 @@ struct BtCursor {
  u16 ix;                   /* Current index for apPage[iPage] */
  u16 aiIdx[BTCURSOR_MAX_DEPTH-1];     /* Current index in apPage[i] */
  struct KeyInfo *pKeyInfo;            /* Arg passed to comparison function */
-  MemPage *apPage[BTCURSOR_MAX_DEPTH]; /* Pages from root to current page */
+  MemPage *pPage;                        /* Current page */
+  MemPage *apPage[BTCURSOR_MAX_DEPTH-1]; /* Stack of parents of current page */
 };

 /*