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Comment:Another performance tweak: Split the sqlite3BtreeCursorHasMoved() routine into two with the second routine named sqlite3BtreeCursorRestore(). The first now only reports whether or not the cursor has moved and the second tries to restore the cursor. This allows the sqlite3VdbeCursorMoveto() routine to be refactored to avoid stack pointer movements, for a noticable performance gain.
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SHA1:ce123b5c592556a8cd38b01fcc91ba76231d3098
User & Date: drh 2014-08-22 23:33:03
Context
2014-08-23
17:21
Performance optimization in the applyAffinity() logic inside the VDBE. check-in: 25f2246b user: drh tags: trunk
2014-08-22
23:33
Another performance tweak: Split the sqlite3BtreeCursorHasMoved() routine into two with the second routine named sqlite3BtreeCursorRestore(). The first now only reports whether or not the cursor has moved and the second tries to restore the cursor. This allows the sqlite3VdbeCursorMoveto() routine to be refactored to avoid stack pointer movements, for a noticable performance gain. check-in: ce123b5c user: drh tags: trunk
22:26
Factor the saveAllCursors() routine of btree.c into two separate routines, for a noticable performance improvement. check-in: 3eb08439 user: drh tags: trunk
Changes
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Changes to src/btree.c.

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#define restoreCursorPosition(p) \
  (p->eState>=CURSOR_REQUIRESEEK ? \
         btreeRestoreCursorPosition(p) : \
         SQLITE_OK)

/*
** Determine whether or not a cursor has moved from the position it

** was last placed at.  Cursors can move when the row they are pointing
** at is deleted out from under them.


**
** This routine returns an error code if something goes wrong.  The
** integer *pHasMoved is set as follows:

**
**    0:   The cursor is unchanged
**    1:   The cursor is still pointing at the same row, but the pointers
**         returned by sqlite3BtreeKeyFetch() or sqlite3BtreeDataFetch()
**         might now be invalid because of a balance() or other change to the
**         b-tree.
**    2:   The cursor is no longer pointing to the row.  The row might have





**         been deleted out from under the cursor.
*/






int sqlite3BtreeCursorHasMoved(BtCursor *pCur, int *pHasMoved){


  int rc;


  if( pCur->eState==CURSOR_VALID ){
    *pHasMoved = 0;
    return SQLITE_OK;
  }
  rc = restoreCursorPosition(pCur);
  if( rc ){
    *pHasMoved = 2;

    return rc;
  }
  if( pCur->eState!=CURSOR_VALID || NEVER(pCur->skipNext!=0) ){
    *pHasMoved = 2;
  }else{
    *pHasMoved = 1;
  }
  return SQLITE_OK;
}

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** Given a page number of a regular database page, return the page







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#define restoreCursorPosition(p) \
  (p->eState>=CURSOR_REQUIRESEEK ? \
         btreeRestoreCursorPosition(p) : \
         SQLITE_OK)

/*
** Determine whether or not a cursor has moved from the position where
** it was last placed, or has been invalidated for any other reason.
** Cursors can move when the row they are pointing at is deleted out

** from under them, for example.  Cursor might also move if a btree
** is rebalanced.
**


** Calling this routine with a NULL cursor pointer returns false.
**

** Use the separate sqlite3BtreeCursorRestore() routine to restore a cursor
** back to where it ought to be if this routine returns true.
*/
int sqlite3BtreeCursorHasMoved(BtCursor *pCur){
  return pCur && pCur->eState!=CURSOR_VALID;
}

/*
** This routine restores a cursor back to its original position after it
** has been moved by some outside activity (such as a btree rebalance or
** a row having been deleted out from under the cursor).  
**
** On success, the *pDifferentRow parameter is false if the cursor is left
** pointing at exactly the same row.  *pDifferntRow is the row the cursor
** was pointing to has been deleted, forcing the cursor to point to some
** nearby row.
**
** This routine should only be called for a cursor that just returned
** TRUE from sqlite3BtreeCursorHasMoved().
*/
int sqlite3BtreeCursorRestore(BtCursor *pCur, int *pDifferentRow){
  int rc;

  assert( pCur!=0 );
  assert( pCur->eState!=CURSOR_VALID );



  rc = restoreCursorPosition(pCur);
  if( rc ){

    *pDifferentRow = 1;
    return rc;
  }
  if( pCur->eState!=CURSOR_VALID || NEVER(pCur->skipNext!=0) ){
    *pDifferentRow = 1;
  }else{
    *pDifferentRow = 0;
  }
  return SQLITE_OK;
}

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** Given a page number of a regular database page, return the page

Changes to src/btree.h.

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int sqlite3BtreeMovetoUnpacked(
  BtCursor*,
  UnpackedRecord *pUnKey,
  i64 intKey,
  int bias,
  int *pRes
);
int sqlite3BtreeCursorHasMoved(BtCursor*, int*);

int sqlite3BtreeDelete(BtCursor*);
int sqlite3BtreeInsert(BtCursor*, const void *pKey, i64 nKey,
                                  const void *pData, int nData,
                                  int nZero, int bias, int seekResult);
int sqlite3BtreeFirst(BtCursor*, int *pRes);
int sqlite3BtreeLast(BtCursor*, int *pRes);
int sqlite3BtreeNext(BtCursor*, int *pRes);







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int sqlite3BtreeMovetoUnpacked(
  BtCursor*,
  UnpackedRecord *pUnKey,
  i64 intKey,
  int bias,
  int *pRes
);
int sqlite3BtreeCursorHasMoved(BtCursor*);
int sqlite3BtreeCursorRestore(BtCursor*, int*);
int sqlite3BtreeDelete(BtCursor*);
int sqlite3BtreeInsert(BtCursor*, const void *pKey, i64 nKey,
                                  const void *pData, int nData,
                                  int nZero, int bias, int seekResult);
int sqlite3BtreeFirst(BtCursor*, int *pRes);
int sqlite3BtreeLast(BtCursor*, int *pRes);
int sqlite3BtreeNext(BtCursor*, int *pRes);

Changes to src/vdbeaux.c.

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  if( p->pNext ){
    p->pNext->pPrev = p->pPrev;
  }
  p->magic = VDBE_MAGIC_DEAD;
  p->db = 0;
  sqlite3DbFree(db, p);
}











































/*
** Make sure the cursor p is ready to read or write the row to which it
** was last positioned.  Return an error code if an OOM fault or I/O error
** prevents us from positioning the cursor to its correct position.
**
** If a MoveTo operation is pending on the given cursor, then do that
................................................................................
** a NULL row.
**
** If the cursor is already pointing to the correct row and that row has
** not been deleted out from under the cursor, then this routine is a no-op.
*/
int sqlite3VdbeCursorMoveto(VdbeCursor *p){
  if( p->deferredMoveto ){
    int res, rc;
#ifdef SQLITE_TEST
    extern int sqlite3_search_count;
#endif
    assert( p->isTable );
    rc = sqlite3BtreeMovetoUnpacked(p->pCursor, 0, p->movetoTarget, 0, &res);
    if( rc ) return rc;
    p->lastRowid = p->movetoTarget;
    if( res!=0 ) return SQLITE_CORRUPT_BKPT;
    p->rowidIsValid = 1;
#ifdef SQLITE_TEST
    sqlite3_search_count++;
#endif
    p->deferredMoveto = 0;
    p->cacheStatus = CACHE_STALE;
  }else if( p->pCursor ){
    int hasMoved;
    int rc = sqlite3BtreeCursorHasMoved(p->pCursor, &hasMoved);
    if( rc ) return rc;
    if( hasMoved ){
      p->cacheStatus = CACHE_STALE;
      if( hasMoved==2 ) p->nullRow = 1;
    }


  }
  return SQLITE_OK;
}

/*
** The following functions:
**







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  if( p->pNext ){
    p->pNext->pPrev = p->pPrev;
  }
  p->magic = VDBE_MAGIC_DEAD;
  p->db = 0;
  sqlite3DbFree(db, p);
}

/*
** The cursor "p" has a pending seek operation that has not yet been
** carried out.  Seek the cursor now.  If an error occurs, return
** the appropriate error code.
*/
static int SQLITE_NOINLINE handleDeferredMoveto(VdbeCursor *p){
  int res, rc;
#ifdef SQLITE_TEST
  extern int sqlite3_search_count;
#endif
  assert( p->deferredMoveto );
  assert( p->isTable );
  rc = sqlite3BtreeMovetoUnpacked(p->pCursor, 0, p->movetoTarget, 0, &res);
  if( rc ) return rc;
  p->lastRowid = p->movetoTarget;
  if( res!=0 ) return SQLITE_CORRUPT_BKPT;
  p->rowidIsValid = 1;
#ifdef SQLITE_TEST
  sqlite3_search_count++;
#endif
  p->deferredMoveto = 0;
  p->cacheStatus = CACHE_STALE;
  return SQLITE_OK;
}

/*
** Something has moved cursor "p" out of place.  Maybe the row it was
** pointed to was deleted out from under it.  Or maybe the btree was
** rebalanced.  Whatever the cause, try to restore "p" to the place it
** is suppose to be pointing.  If the row was deleted out from under the
** cursor, set the cursor to point to a NULL row.
*/
static int SQLITE_NOINLINE handleMovedCursor(VdbeCursor *p){
  int isDifferentRow, rc;
  assert( p->pCursor!=0 );
  assert( sqlite3BtreeCursorHasMoved(p->pCursor) );
  rc = sqlite3BtreeCursorRestore(p->pCursor, &isDifferentRow);
  p->cacheStatus = CACHE_STALE;
  if( isDifferentRow ) p->nullRow = 1;
  return rc;
}

/*
** Make sure the cursor p is ready to read or write the row to which it
** was last positioned.  Return an error code if an OOM fault or I/O error
** prevents us from positioning the cursor to its correct position.
**
** If a MoveTo operation is pending on the given cursor, then do that
................................................................................
** a NULL row.
**
** If the cursor is already pointing to the correct row and that row has
** not been deleted out from under the cursor, then this routine is a no-op.
*/
int sqlite3VdbeCursorMoveto(VdbeCursor *p){
  if( p->deferredMoveto ){













    return handleDeferredMoveto(p);








  }
  if( sqlite3BtreeCursorHasMoved(p->pCursor) ){
    return handleMovedCursor(p);
  }
  return SQLITE_OK;
}

/*
** The following functions:
**