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Overview
Comment:Performance optimization in moveToRoot(). Avoid repeated validity checking of the root page on each call. Once is enough.
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SHA1:98795c2dd9a6d8fa8d49a9f5c36cdf824cae7246
User & Date: drh 2016-10-24 01:01:09
Context
2016-10-25
15:06
Add test case to demonstrate a "BEGIN EXCLUSIVE" command returning SQLITE_BUSY_SNAPSHOT. check-in: b1158564 user: dan tags: trunk
2016-10-24
01:01
Performance optimization in moveToRoot(). Avoid repeated validity checking of the root page on each call. Once is enough. check-in: 98795c2d user: drh tags: trunk
2016-10-22
01:22
In the sessions module, avoid recording a change if an UPDATE statement overwrites a column with REAL affinity containing an integer value with the same value. check-in: 5f3e6028 user: drh tags: trunk
Changes
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Changes to src/btree.c.

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      assert( pCur->skipNext!=SQLITE_OK );
      return pCur->skipNext;
    }
    sqlite3BtreeClearCursor(pCur);
  }

  if( pCur->iPage>=0 ){
    while( pCur->iPage ){

      assert( pCur->apPage[pCur->iPage]!=0 );
      releasePageNotNull(pCur->apPage[pCur->iPage--]);


    }
  }else if( pCur->pgnoRoot==0 ){
    pCur->eState = CURSOR_INVALID;
    return SQLITE_OK;
  }else{
    assert( pCur->iPage==(-1) );
    rc = getAndInitPage(pCur->pBtree->pBt, pCur->pgnoRoot, &pCur->apPage[0],
                        0, pCur->curPagerFlags);
    if( rc!=SQLITE_OK ){
      pCur->eState = CURSOR_INVALID;
      return rc;
    }
    pCur->iPage = 0;
    pCur->curIntKey = pCur->apPage[0]->intKey;
  }
  pRoot = pCur->apPage[0];
  assert( pRoot->pgno==pCur->pgnoRoot );

................................................................................
  ** in such a way that page pRoot is linked into a second b-tree table 
  ** (or the freelist).  */
  assert( pRoot->intKey==1 || pRoot->intKey==0 );
  if( pRoot->isInit==0 || (pCur->pKeyInfo==0)!=pRoot->intKey ){
    return SQLITE_CORRUPT_BKPT;
  }


  pCur->aiIdx[0] = 0;
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_AtLast|BTCF_ValidNKey|BTCF_ValidOvfl);


  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;







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      assert( pCur->skipNext!=SQLITE_OK );
      return pCur->skipNext;
    }
    sqlite3BtreeClearCursor(pCur);
  }

  if( pCur->iPage>=0 ){
    if( pCur->iPage ){
      do{
        assert( pCur->apPage[pCur->iPage]!=0 );
        releasePageNotNull(pCur->apPage[pCur->iPage--]);
      }while( pCur->iPage);
      goto skip_init;
    }
  }else if( pCur->pgnoRoot==0 ){
    pCur->eState = CURSOR_INVALID;
    return SQLITE_OK;
  }else{
    assert( pCur->iPage==(-1) );
    rc = getAndInitPage(pCur->pBtree->pBt, pCur->pgnoRoot, &pCur->apPage[0],
                        0, pCur->curPagerFlags);
    if( rc!=SQLITE_OK ){
      pCur->eState = CURSOR_INVALID;
       return rc;
    }
    pCur->iPage = 0;
    pCur->curIntKey = pCur->apPage[0]->intKey;
  }
  pRoot = pCur->apPage[0];
  assert( pRoot->pgno==pCur->pgnoRoot );

................................................................................
  ** in such a way that page pRoot is linked into a second b-tree table 
  ** (or the freelist).  */
  assert( pRoot->intKey==1 || pRoot->intKey==0 );
  if( pRoot->isInit==0 || (pCur->pKeyInfo==0)!=pRoot->intKey ){
    return SQLITE_CORRUPT_BKPT;
  }

skip_init:  
  pCur->aiIdx[0] = 0;
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_AtLast|BTCF_ValidNKey|BTCF_ValidOvfl);

  pRoot = pCur->apPage[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;