SQLite

  sqlite3VdbeJumpHere(v, addr1);
  if( memRootPage<0 ) sqlite3VdbeAddOp2(v, OP_Clear, tnum, iDb);
  sqlite3VdbeAddOp4(v, OP_OpenWrite, iIdx, tnum, iDb, 
                    (char *)pKey, P4_KEYINFO_HANDOFF);
  sqlite3VdbeChangeP5(v, OPFLAG_BULKCSR|((memRootPage>=0)?OPFLAG_P2ISREG:0));

  addr1 = sqlite3VdbeAddOp2(v, OP_SorterSort, iSorter, 0);
  assert( pKey!=0 || db->mallocFailed || pParse->nErr );
  if( pIndex->onError!=OE_None && pKey!=0 ){
    int j2 = sqlite3VdbeCurrentAddr(v) + 3;
    sqlite3VdbeAddOp2(v, OP_Goto, 0, j2);
    addr2 = sqlite3VdbeCurrentAddr(v);
    sqlite3VdbeAddOp4Int(v, OP_SorterCompare, iSorter, j2, regRecord,
                         pKey->nField - pIndex->nKeyCol);
    sqlite3HaltConstraint(pParse, SQLITE_CONSTRAINT_UNIQUE,
        OE_Abort, "indexed columns are not unique", P4_STATIC
    );
  }else{
    addr2 = sqlite3VdbeCurrentAddr(v);
  }
  sqlite3VdbeAddOp2(v, OP_SorterData, iSorter, regRecord);

*/
KeyInfo *sqlite3IndexKeyinfo(Parse *pParse, Index *pIdx){
  int i;
  int nCol = pIdx->nColumn;
  int nKey = pIdx->nKeyCol;
  KeyInfo *pKey;

  if( pIdx->uniqNotNull ){
    pKey = sqlite3KeyInfoAlloc(pParse->db, nKey, nCol-nKey);
  }else{
    pKey = sqlite3KeyInfoAlloc(pParse->db, nCol, 0);
  }
  if( pKey ){
    for(i=0; i<nCol; i++){
      char *zColl = pIdx->azColl[i];
      if( zColl==0 ) zColl = "BINARY";
      pKey->aColl[i] = sqlite3LocateCollSeq(pParse, zColl);
      pKey->aSortOrder[i] = pIdx->aSortOrder[i];
    }

    }
  }
  pCx->isOrdered = (pOp->p5!=BTREE_UNORDERED);
  pCx->isIndex = !pCx->isTable;
  break;
}

/* Opcode: SorterOpen P1 * * P4 *

**
** This opcode works like OP_OpenEphemeral except that it opens
** a transient index that is specifically designed to sort large
** tables using an external merge-sort algorithm.
*/
case OP_SorterOpen: {
  VdbeCursor *pCx;

*/
case OP_ResetCount: {
  sqlite3VdbeSetChanges(db, p->nChange);
  p->nChange = 0;
  break;
}

/* Opcode: SorterCompare P1 P2 P3 P4
** Synopsis:  if key(P1)!=rtrim(r[P3],P4) goto P2
**
** P1 is a sorter cursor. This instruction compares a prefix of the
** the record blob in register P3 against a prefix of the entry that 
** the sorter cursor currently points to.  The final P4 fields of both
** the P3 and sorter record are ignored.
**
** If either P3 or the sorter contains a NULL in one of their significant
** fields (not counting the P4 fields at the end which are ignored) then
** the comparison is assumed to be equal.
**
** Fall through to next instruction if the two records compare equal to
** each other.  Jump to P2 if they are different.
*/
case OP_SorterCompare: {
  VdbeCursor *pC;
  int res;
  int nIgnore;

  pC = p->apCsr[pOp->p1];
  assert( isSorter(pC) );
  assert( pOp->p4type==P4_INT32 );
  pIn3 = &aMem[pOp->p3];
  nIgnore = pOp->p4.i;
  rc = sqlite3VdbeSorterCompare(pC, pIn3, nIgnore, &res);
  if( res ){
    pc = pOp->p2-1;
  }
  break;
};

/* Opcode: SorterData P1 P2 * * *

int sqlite3VdbeSorterInit(sqlite3 *, VdbeCursor *);
void sqlite3VdbeSorterClose(sqlite3 *, VdbeCursor *);
int sqlite3VdbeSorterRowkey(const VdbeCursor *, Mem *);
int sqlite3VdbeSorterNext(sqlite3 *, const VdbeCursor *, int *);
int sqlite3VdbeSorterRewind(sqlite3 *, const VdbeCursor *, int *);
int sqlite3VdbeSorterWrite(sqlite3 *, const VdbeCursor *, Mem *);
int sqlite3VdbeSorterCompare(const VdbeCursor *, Mem *, int, int *);

#if !defined(SQLITE_OMIT_SHARED_CACHE) && SQLITE_THREADSAFE>0
  void sqlite3VdbeEnter(Vdbe*);
  void sqlite3VdbeLeave(Vdbe*);
#else
# define sqlite3VdbeEnter(X)
# define sqlite3VdbeLeave(X)

      int nCol = pIdx->nKeyCol+1; /* Number of index columns including rowid */
  
      nByte = sizeof(Mem) * nCol + sizeof(UnpackedRecord);
      pRec = (UnpackedRecord*)sqlite3DbMallocZero(db, nByte);
      if( pRec ){
        pRec->pKeyInfo = sqlite3IndexKeyinfo(p->pParse, pIdx);
        if( pRec->pKeyInfo ){
          assert( pRec->pKeyInfo->nField+pRec->pKeyInfo->nXField==nCol );
          pRec->pKeyInfo->enc = ENC(db);
          pRec->flags = UNPACKED_PREFIX_MATCH;
          pRec->aMem = (Mem *)&pRec[1];
          for(i=0; i<nCol; i++){
            pRec->aMem[i].flags = MEM_Null;
            pRec->aMem[i].type = SQLITE_NULL;
            pRec->aMem[i].db = db;

** Unless it is NULL, the argument must be an UnpackedRecord object returned
** by an earlier call to sqlite3Stat4ProbeSetValue(). This call deletes
** the object.
*/
void sqlite3Stat4ProbeFree(UnpackedRecord *pRec){
  if( pRec ){
    int i;
    int nCol = pRec->pKeyInfo->nField+pRec->pKeyInfo->nXField;
    Mem *aMem = pRec->aMem;
    sqlite3 *db = aMem[0].db;
    for(i=0; i<nCol; i++){
      sqlite3DbFree(db, aMem[i].zMalloc);
    }
    sqlite3DbFree(db, pRec->pKeyInfo);
    sqlite3DbFree(db, pRec);

** be less than key2. Even if key2 also contains NULL values.
**
** If pKey2 is passed a NULL pointer, then it is assumed that the pCsr->aSpace
** has been allocated and contains an unpacked record that is used as key2.
*/
static void vdbeSorterCompare(
  const VdbeCursor *pCsr,         /* Cursor object (for pKeyInfo) */
  int nIgnore,                    /* Ignore the last nIgnore fields */
  const void *pKey1, int nKey1,   /* Left side of comparison */
  const void *pKey2, int nKey2,   /* Right side of comparison */
  int *pRes                       /* OUT: Result of comparison */
){
  KeyInfo *pKeyInfo = pCsr->pKeyInfo;
  VdbeSorter *pSorter = pCsr->pSorter;
  UnpackedRecord *r2 = pSorter->pUnpacked;
  int i;

  if( pKey2 ){
    sqlite3VdbeRecordUnpack(pKeyInfo, nKey2, pKey2, r2);
  }

  if( nIgnore ){
    r2->nField = pKeyInfo->nField - nIgnore;
    assert( r2->nField>0 );
    for(i=0; i<r2->nField; i++){
      if( r2->aMem[i].flags & MEM_Null ){
        *pRes = -1;
        return;
      }
    }

** Otherwise, set *pRes to a negative, zero or positive value if the
** key in pVal is smaller than, equal to or larger than the current sorter
** key.
*/
int sqlite3VdbeSorterCompare(
  const VdbeCursor *pCsr,         /* Sorter cursor */
  Mem *pVal,                      /* Value to compare to current sorter key */
  int nIgnore,                    /* Ignore this many fields at the end */
  int *pRes                       /* OUT: Result of comparison */
){
  VdbeSorter *pSorter = pCsr->pSorter;
  void *pKey; int nKey;           /* Sorter key to compare pVal with */

  pKey = vdbeSorterRowkey(pSorter, &nKey);
  vdbeSorterCompare(pCsr, nIgnore, pVal->z, pVal->n, pKey, nKey, pRes);
  return SQLITE_OK;
}