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Overview
Comment:Performance optimization to the moveToRoot() subroutine in btree.c.
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SHA1: b5842a70f8e26456a8f0d39539bc266f097480a4
User & Date: drh 2013-12-06 23:25:27
Context
2013-12-07
16:56
At the start of each journaled write transaction, check to see if the database file has been moved, and if it has refuse to start the transaction, returning an SQLITE_READONLY_DBMOVED error code. Writing to a moved or renamed database is still allowed when journal_mode is OFF or MEMORY. check-in: 369a23e0 user: drh tags: trunk
2013-12-06
23:25
Performance optimization to the moveToRoot() subroutine in btree.c. check-in: b5842a70 user: drh tags: trunk
22:45
Use memcmp() instead of the BINARY collating function where possible, for a performance boost. check-in: c5a3a1af user: drh tags: trunk
Changes
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Changes to src/btree.c.

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** indicating a table b-tree, or if the caller did specify a KeyInfo 
** structure the flags byte is set to 0x02 or 0x0A, indicating an index
** b-tree).
*/
static int moveToRoot(BtCursor *pCur){
  MemPage *pRoot;
  int rc = SQLITE_OK;
  Btree *p = pCur->pBtree;
  BtShared *pBt = p->pBt;

  assert( cursorHoldsMutex(pCur) );
  assert( CURSOR_INVALID < CURSOR_REQUIRESEEK );
  assert( CURSOR_VALID   < CURSOR_REQUIRESEEK );
  assert( CURSOR_FAULT   > CURSOR_REQUIRESEEK );
  if( pCur->eState>=CURSOR_REQUIRESEEK ){
    if( pCur->eState==CURSOR_FAULT ){
................................................................................
      assert( pCur->skipNext!=SQLITE_OK );
      return pCur->skipNext;
    }
    sqlite3BtreeClearCursor(pCur);
  }

  if( pCur->iPage>=0 ){
    int i;
    for(i=1; i<=pCur->iPage; i++){
      releasePage(pCur->apPage[i]);
    }
    pCur->iPage = 0;
  }else if( pCur->pgnoRoot==0 ){
    pCur->eState = CURSOR_INVALID;
    return SQLITE_OK;
  }else{
    rc = getAndInitPage(pBt, pCur->pgnoRoot, &pCur->apPage[0],
                        pCur->wrFlag==0 ? PAGER_GET_READONLY : 0);
    if( rc!=SQLITE_OK ){
      pCur->eState = CURSOR_INVALID;
      return rc;
    }
    pCur->iPage = 0;

................................................................................
  assert( pRoot->isInit && (pCur->pKeyInfo==0)==pRoot->intKey );

  pCur->aiIdx[0] = 0;
  pCur->info.nSize = 0;
  pCur->atLast = 0;
  pCur->validNKey = 0;

  if( pRoot->nCell==0 && !pRoot->leaf ){


    Pgno subpage;
    if( pRoot->pgno!=1 ) return SQLITE_CORRUPT_BKPT;
    subpage = get4byte(&pRoot->aData[pRoot->hdrOffset+8]);
    pCur->eState = CURSOR_VALID;
    rc = moveToChild(pCur, subpage);
  }else{
    pCur->eState = ((pRoot->nCell>0)?CURSOR_VALID:CURSOR_INVALID);
  }
  return rc;
}

/*
** Move the cursor down to the left-most leaf entry beneath the
** entry to which it is currently pointing.







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** indicating a table b-tree, or if the caller did specify a KeyInfo 
** structure the flags byte is set to 0x02 or 0x0A, indicating an index
** b-tree).
*/
static int moveToRoot(BtCursor *pCur){
  MemPage *pRoot;
  int rc = SQLITE_OK;



  assert( cursorHoldsMutex(pCur) );
  assert( CURSOR_INVALID < CURSOR_REQUIRESEEK );
  assert( CURSOR_VALID   < CURSOR_REQUIRESEEK );
  assert( CURSOR_FAULT   > CURSOR_REQUIRESEEK );
  if( pCur->eState>=CURSOR_REQUIRESEEK ){
    if( pCur->eState==CURSOR_FAULT ){
................................................................................
      assert( pCur->skipNext!=SQLITE_OK );
      return pCur->skipNext;
    }
    sqlite3BtreeClearCursor(pCur);
  }

  if( pCur->iPage>=0 ){


    while( pCur->iPage ) releasePage(pCur->apPage[pCur->iPage--]);


  }else if( pCur->pgnoRoot==0 ){
    pCur->eState = CURSOR_INVALID;
    return SQLITE_OK;
  }else{
    rc = getAndInitPage(pCur->pBtree->pBt, pCur->pgnoRoot, &pCur->apPage[0],
                        pCur->wrFlag==0 ? PAGER_GET_READONLY : 0);
    if( rc!=SQLITE_OK ){
      pCur->eState = CURSOR_INVALID;
      return rc;
    }
    pCur->iPage = 0;

................................................................................
  assert( pRoot->isInit && (pCur->pKeyInfo==0)==pRoot->intKey );

  pCur->aiIdx[0] = 0;
  pCur->info.nSize = 0;
  pCur->atLast = 0;
  pCur->validNKey = 0;

  if( pRoot->nCell>0 ){
    pCur->eState = CURSOR_VALID;
  }else if( !pRoot->leaf ){
    Pgno subpage;
    if( pRoot->pgno!=1 ) return SQLITE_CORRUPT_BKPT;
    subpage = get4byte(&pRoot->aData[pRoot->hdrOffset+8]);
    pCur->eState = CURSOR_VALID;
    rc = moveToChild(pCur, subpage);
  }else{
    pCur->eState = CURSOR_INVALID;
  }
  return rc;
}

/*
** Move the cursor down to the left-most leaf entry beneath the
** entry to which it is currently pointing.