SQLite

** to zero.  But it turns out that the apPage[] and aiIdx[] arrays
** do not need to be zeroed and they are large, so we can save a lot
** of run-time by skipping the initialization of those elements.
*/
void sqlite3BtreeCursorZero(BtCursor *p){
  memset(p, 0, offsetof(BtCursor, iPage));
}

/*
** Return the Btree object associated with a BtCursor.
*/
Btree *sqlite3BtreeOfCursor(BtCursor *p){
  assert( p!=0 );
  return p->pBtree;
}

/*
** Close a cursor.  The read lock on the database file is released
** when the last cursor is closed.
*/
int sqlite3BtreeCloseCursor(BtCursor *pCur){
  Btree *pBtree = pCur->pBtree;

  int wrFlag,                          /* 1 for writing.  0 for read-only */
  struct KeyInfo*,                     /* First argument to compare function */
  BtCursor *pCursor                    /* Space to write cursor structure */
);
int sqlite3BtreeCursorSize(void);
void sqlite3BtreeCursorZero(BtCursor*);
void sqlite3BtreeCursorHintFlags(BtCursor*, unsigned);
Btree *sqlite3BtreeOfCursor(BtCursor*);
#ifdef SQLITE_ENABLE_CURSOR_HINTS
void sqlite3BtreeCursorHint(BtCursor*, int, ...);
#endif

int sqlite3BtreeCloseCursor(BtCursor*);
int sqlite3BtreeMovetoUnpacked(
  BtCursor*,

** by this opcode will be used for automatically created transient
** indices in joins.
*/
case OP_OpenAutoindex: 
case OP_OpenEphemeral: {
  VdbeCursor *pCx;
  KeyInfo *pKeyInfo;
  Btree *pBt;

  static const int vfsFlags = 
      SQLITE_OPEN_READWRITE |
      SQLITE_OPEN_CREATE |
      SQLITE_OPEN_EXCLUSIVE |
      SQLITE_OPEN_DELETEONCLOSE |
      SQLITE_OPEN_TRANSIENT_DB;
  assert( pOp->p1>=0 );
  assert( pOp->p2>=0 );
  pCx = allocateCursor(p, pOp->p1, pOp->p2, -1, CURTYPE_BTREE);
  if( pCx==0 ) goto no_mem;
  pCx->nullRow = 1;

  rc = sqlite3BtreeOpen(db->pVfs, 0, db, &pBt, 
                        BTREE_OMIT_JOURNAL | BTREE_SINGLE | pOp->p5, vfsFlags);
  if( rc==SQLITE_OK ){
    rc = sqlite3BtreeBeginTrans(pBt, 1);

    if( rc==SQLITE_OK ){
      /* If a transient index is required, create it by calling
      ** sqlite3BtreeCreateTable() with the BTREE_BLOBKEY flag before
      ** opening it. If a transient table is required, just use the
      ** automatically created table with root-page 1 (an BLOB_INTKEY table).
      */
      if( (pKeyInfo = pOp->p4.pKeyInfo)!=0 ){
        int pgno;
        assert( pOp->p4type==P4_KEYINFO );
        rc = sqlite3BtreeCreateTable(pBt, &pgno, BTREE_BLOBKEY | pOp->p5); 
        if( rc==SQLITE_OK ){
          assert( pgno==MASTER_ROOT+1 );
          assert( pKeyInfo->db==db );
          assert( pKeyInfo->enc==ENC(db) );
          pCx->pKeyInfo = pKeyInfo;
          rc = sqlite3BtreeCursor(pBt, pgno, BTREE_WRCSR,
                                  pKeyInfo, pCx->uc.pCursor);
        }
        pCx->isTable = 0;
      }else{
        rc = sqlite3BtreeCursor(pBt, MASTER_ROOT, BTREE_WRCSR,
                                0, pCx->uc.pCursor);
        pCx->isTable = 1;
      }
    }
    if( rc==SQLITE_OK ){
      pCx->isEphemeral = 1;
    }else{
      sqlite3BtreeClose(pBt);
    }
  }
  pCx->isOrdered = (pOp->p5!=BTREE_UNORDERED);
  break;
}

/* Opcode: SorterOpen P1 P2 P3 P4 *

  u16 nHdrParsed;       /* Number of header fields parsed so far */
  union {
    BtCursor *pCursor;          /* CURTYPE_BTREE.  Btree cursor */
    sqlite3_vtab_cursor *pVCur; /* CURTYPE_VTAB.   Vtab cursor */
    int pseudoTableReg;         /* CURTYPE_PSEUDO. Reg holding content. */
    VdbeSorter *pSorter;        /* CURTYPE_SORTER. Sorter object */
  } uc;

  KeyInfo *pKeyInfo;    /* Info about index keys needed by index cursors */
  int seekResult;       /* Result of previous sqlite3BtreeMoveto() */
  i64 seqCount;         /* Sequence counter */
  i64 movetoTarget;     /* Argument to the deferred sqlite3BtreeMoveto() */
#ifdef SQLITE_ENABLE_COLUMN_USED_MASK
  u64 maskUsed;         /* Mask of columns used by this cursor */
#endif

** Close a VDBE cursor and release all the resources that cursor 
** happens to hold.
*/
void sqlite3VdbeFreeCursor(Vdbe *p, VdbeCursor *pCx){
  if( pCx==0 ){
    return;
  }
  assert( pCx->isEphemeral==0 || pCx->eCurType==CURTYPE_BTREE );
  switch( pCx->eCurType ){
    case CURTYPE_SORTER: {
      sqlite3VdbeSorterClose(p->db, pCx);
      break;
    }
    case CURTYPE_BTREE: {
      assert( pCx->uc.pCursor!=0 );
      if( pCx->isEphemeral ){
        sqlite3BtreeClose(sqlite3BtreeOfCursor(pCx->uc.pCursor));
        /* The pCx->pCursor will be close automatically, if it exists, by
        ** the call above. */
      }else{

        sqlite3BtreeCloseCursor(pCx->uc.pCursor);
      }
      break;
    }
#ifndef SQLITE_OMIT_VIRTUALTABLE
    case CURTYPE_VTAB: {
      sqlite3_vtab_cursor *pVCur = pCx->uc.pVCur;

  ** to exceed the maximum merge count */
#if SQLITE_MAX_WORKER_THREADS>=SORTER_MAX_MERGE_COUNT
  if( nWorker>=SORTER_MAX_MERGE_COUNT ){
    nWorker = SORTER_MAX_MERGE_COUNT-1;
  }
#endif

  assert( pCsr->pKeyInfo && !pCsr->isEphemeral );
  assert( pCsr->eCurType==CURTYPE_SORTER );
  szKeyInfo = sizeof(KeyInfo) + (pCsr->pKeyInfo->nField-1)*sizeof(CollSeq*);
  sz = sizeof(VdbeSorter) + nWorker * sizeof(SortSubtask);

  pSorter = (VdbeSorter*)sqlite3DbMallocZero(db, sz + szKeyInfo);
  pCsr->uc.pSorter = pSorter;
  if( pSorter==0 ){