fts3.c

最新的sqlite3.6.2源代码

** readers when there is a duplicate docid.  pReaders is assumed to be
** ordered by age, oldest first.
*/
/* TODO(shess) nReaders must be <= MERGE_COUNT.  This should probably
** be fixed.
*/
static void docListMerge(DataBuffer *out,
                         DLReader *pReaders, int nReaders){
  OrderedDLReader readers[MERGE_COUNT];
  DLWriter writer;
  int i, n;
  const char *pStart = 0;
  int nStart = 0;
  sqlite_int64 iFirstDocid = 0, iLastDocid = 0;

  assert( nReaders>0 );
  if( nReaders==1 ){
    dataBufferAppend(out, dlrDocData(pReaders), dlrAllDataBytes(pReaders));
    return;
  }

  assert( nReaders<=MERGE_COUNT );
  n = 0;
  for(i=0; i<nReaders; i++){
    assert( pReaders[i].iType==pReaders[0].iType );
    readers[i].pReader = pReaders+i;
    readers[i].idx = i;
    n += dlrAllDataBytes(&pReaders[i]);
  }
  /* Conservatively size output to sum of inputs.  Output should end
  ** up strictly smaller than input.
  */
  dataBufferExpand(out, n);

  /* Get the readers into sorted order. */
  while( i-->0 ){
    orderedDLReaderReorder(readers+i, nReaders-i);
  }

  dlwInit(&writer, pReaders[0].iType, out);
  while( !dlrAtEnd(readers[0].pReader) ){
    sqlite_int64 iDocid = dlrDocid(readers[0].pReader);

    /* If this is a continuation of the current buffer to copy, extend
    ** that buffer.  memcpy() seems to be more efficient if it has a
    ** lots of data to copy.
    */
    if( dlrDocData(readers[0].pReader)==pStart+nStart ){
      nStart += dlrDocDataBytes(readers[0].pReader);
    }else{
      if( pStart!=0 ){
        dlwAppend(&writer, pStart, nStart, iFirstDocid, iLastDocid);
      }
      pStart = dlrDocData(readers[0].pReader);
      nStart = dlrDocDataBytes(readers[0].pReader);
      iFirstDocid = iDocid;
    }
    iLastDocid = iDocid;
    dlrStep(readers[0].pReader);

    /* Drop all of the older elements with the same docid. */
    for(i=1; i<nReaders &&
             !dlrAtEnd(readers[i].pReader) &&
             dlrDocid(readers[i].pReader)==iDocid; i++){
      dlrStep(readers[i].pReader);
    }

    /* Get the readers back into order. */
    while( i-->0 ){
      orderedDLReaderReorder(readers+i, nReaders-i);
    }
  }

  /* Copy over any remaining elements. */
  if( nStart>0 ) dlwAppend(&writer, pStart, nStart, iFirstDocid, iLastDocid);
  dlwDestroy(&writer);
}

/* Helper function for posListUnion().  Compares the current position
** between left and right, returning as standard C idiom of <0 if
** left<right, >0 if left>right, and 0 if left==right.  "End" always
** compares greater.
*/
static int posListCmp(PLReader *pLeft, PLReader *pRight){
  assert( pLeft->iType==pRight->iType );
  if( pLeft->iType==DL_DOCIDS ) return 0;

  if( plrAtEnd(pLeft) ) return plrAtEnd(pRight) ? 0 : 1;
  if( plrAtEnd(pRight) ) return -1;

  if( plrColumn(pLeft)<plrColumn(pRight) ) return -1;
  if( plrColumn(pLeft)>plrColumn(pRight) ) return 1;

  if( plrPosition(pLeft)<plrPosition(pRight) ) return -1;
  if( plrPosition(pLeft)>plrPosition(pRight) ) return 1;
  if( pLeft->iType==DL_POSITIONS ) return 0;

  if( plrStartOffset(pLeft)<plrStartOffset(pRight) ) return -1;
  if( plrStartOffset(pLeft)>plrStartOffset(pRight) ) return 1;

  if( plrEndOffset(pLeft)<plrEndOffset(pRight) ) return -1;
  if( plrEndOffset(pLeft)>plrEndOffset(pRight) ) return 1;

  return 0;
}

/* Write the union of position lists in pLeft and pRight to pOut.
** "Union" in this case meaning "All unique position tuples".  Should
** work with any doclist type, though both inputs and the output
** should be the same type.
*/
static void posListUnion(DLReader *pLeft, DLReader *pRight, DLWriter *pOut){
  PLReader left, right;
  PLWriter writer;

  assert( dlrDocid(pLeft)==dlrDocid(pRight) );
  assert( pLeft->iType==pRight->iType );
  assert( pLeft->iType==pOut->iType );

  plrInit(&left, pLeft);
  plrInit(&right, pRight);
  plwInit(&writer, pOut, dlrDocid(pLeft));

  while( !plrAtEnd(&left) || !plrAtEnd(&right) ){
    int c = posListCmp(&left, &right);
    if( c<0 ){
      plwCopy(&writer, &left);
      plrStep(&left);
    }else if( c>0 ){
      plwCopy(&writer, &right);
      plrStep(&right);
    }else{
      plwCopy(&writer, &left);
      plrStep(&left);
      plrStep(&right);
    }
  }

  plwTerminate(&writer);
  plwDestroy(&writer);
  plrDestroy(&left);
  plrDestroy(&right);
}

/* Write the union of doclists in pLeft and pRight to pOut.  For
** docids in common between the inputs, the union of the position
** lists is written.  Inputs and outputs are always type DL_DEFAULT.
*/
static void docListUnion(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 ){
    if( nRight!=0) dataBufferAppend(pOut, pRight, nRight);
    return;
  }
  if( nRight==0 ){
    dataBufferAppend(pOut, pLeft, nLeft);
    return;
  }

  dlrInit(&left, DL_DEFAULT, pLeft, nLeft);
  dlrInit(&right, DL_DEFAULT, pRight, nRight);
  dlwInit(&writer, DL_DEFAULT, pOut);

  while( !dlrAtEnd(&left) || !dlrAtEnd(&right) ){
    if( dlrAtEnd(&right) ){
      dlwCopy(&writer, &left);
      dlrStep(&left);
    }else if( dlrAtEnd(&left) ){
      dlwCopy(&writer, &right);
      dlrStep(&right);
    }else if( dlrDocid(&left)<dlrDocid(&right) ){
      dlwCopy(&writer, &left);
      dlrStep(&left);
    }else if( dlrDocid(&left)>dlrDocid(&right) ){
      dlwCopy(&writer, &right);
      dlrStep(&right);
    }else{
      posListUnion(&left, &right, &writer);
      dlrStep(&left);
      dlrStep(&right);
    }
  }

  dlrDestroy(&left);
  dlrDestroy(&right);
  dlwDestroy(&writer);
}

/* 
** This function is used as part of the implementation of phrase and
** NEAR matching.
**
** pLeft and pRight are DLReaders positioned to the same docid in
** lists of type DL_POSITION. This function writes an entry to the
** DLWriter pOut for each position in pRight that is less than
** (nNear+1) greater (but not equal to or smaller) than a position 
** in pLeft. For example, if nNear is 0, and the positions contained
** by pLeft and pRight are:
**
**    pLeft:  5 10 15 20
**    pRight: 6  9 17 21
**
** then the docid is added to pOut. If pOut is of type DL_POSITIONS,
** then a positionids "6" and "21" are also added to pOut.
**
** If boolean argument isSaveLeft is true, then positionids are copied
** from pLeft instead of pRight. In the example above, the positions "5"
** and "20" would be added instead of "6" and "21".
*/
static void posListPhraseMerge(
  DLReader *pLeft, 
  DLReader *pRight,
  int nNear,
  int isSaveLeft,
  DLWriter *pOut
){
  PLReader left, right;
  PLWriter writer;
  int match = 0;

  assert( dlrDocid(pLeft)==dlrDocid(pRight) );
  assert( pOut->iType!=DL_POSITIONS_OFFSETS );

  plrInit(&left, pLeft);
  plrInit(&right, pRight);

  while( !plrAtEnd(&left) && !plrAtEnd(&right) ){
    if( plrColumn(&left)<plrColumn(&right) ){
      plrStep(&left);
    }else if( plrColumn(&left)>plrColumn(&right) ){
      plrStep(&right);
    }else if( plrPosition(&left)>=plrPosition(&right) ){
      plrStep(&right);
    }else{
      if( (plrPosition(&right)-plrPosition(&left))<=(nNear+1) ){
        if( !match ){
          plwInit(&writer, pOut, dlrDocid(pLeft));
          match = 1;
        }
        if( !isSaveLeft ){
          plwAdd(&writer, plrColumn(&right), plrPosition(&right), 0, 0);
        }else{
          plwAdd(&writer, plrColumn(&left), plrPosition(&left), 0, 0);
        }
        plrStep(&right);
      }else{
        plrStep(&left);
      }
    }
  }

  if( match ){
    plwTerminate(&writer);
    plwDestroy(&writer);
  }

  plrDestroy(&left);
  plrDestroy(&right);
}

/*
** Compare the values pointed to by the PLReaders passed as arguments. 
** Return -1 if the value pointed to by pLeft is considered less than
** the value pointed to by pRight, +1 if it is considered greater
** than it, or 0 if it is equal. i.e.
**
**     (*pLeft - *pRight)
**
** A PLReader that is in the EOF condition is considered greater than
** any other. If neither argument is in EOF state, the return value of
** plrColumn() is used. If the plrColumn() values are equal, the
** comparison is on the basis of plrPosition().
*/
static int plrCompare(PLReader *pLeft, PLReader *pRight){
  assert(!plrAtEnd(pLeft) || !plrAtEnd(pRight));

  if( plrAtEnd(pRight) || plrAtEnd(pLeft) ){
    return (plrAtEnd(pRight) ? -1 : 1);
  }
  if( plrColumn(pLeft)!=plrColumn(pRight) ){
    return ((plrColumn(pLeft)<plrColumn(pRight)) ? -1 : 1);
  }
  if( plrPosition(pLeft)!=plrPosition(pRight) ){
    return ((plrPosition(pLeft)<plrPosition(pRight)) ? -1 : 1);
  }
  return 0;
}

/* We have two doclists with positions:  pLeft and pRight. Depending
** on the value of the nNear parameter, perform either a phrase
** intersection (if nNear==0) or a NEAR intersection (if nNear>0)
** and write the results into pOut.
**
** A phrase intersection means that two documents only match
** if pLeft.iPos+1==pRight.iPos.
**
** A NEAR intersection means that two documents only match if 
** (abs(pLeft.iPos-pRight.iPos)<nNear).
**
** If a NEAR intersection is requested, then the nPhrase argument should
** be passed the number of tokens in the two operands to the NEAR operator
** combined. For example:
**
**       Query syntax               nPhrase
**      ------------------------------------
**       "A B C" NEAR "D E"         5
**       A NEAR B                   2
**
** iType controls the type of data written to pOut.  If iType is
** DL_POSITIONS, the positions are those from pRight.
*/
static void docListPhraseMerge(
  const char *pLeft, int nLeft,
  const char *pRight, int nRight,
  int nNear,            /* 0 for a phrase merge, non-zero for a NEAR merge */
  int nPhrase,          /* Number of tokens in left+right operands to NEAR */
  DocListType iType,    /* Type of doclist to write to pOut */
  DataBuffer *pOut      /* Write the combined doclist here */
){
  DLReader left, right;
  DLWriter writer;

  if( nLeft==0 || nRight==0 ) return;

  assert( iType!=DL_POSITIONS_OFFSETS );

  dlrInit(&left, DL_POSITIONS, pLeft, nLeft);
  dlrInit(&right, DL_POSITIONS, pRight, nRight);
  dlwInit(&writer, iType, pOut);

  while( !dlrAtEnd(&left) && !dlrAtEnd(&right) ){
    if( dlrDocid(&left)<dlrDocid(&right) ){
      dlrStep(&left);
    }else if( dlrDocid(&right)<dlrDocid(&left) ){
      dlrStep(&right);
    }else{
      if( nNear==0 ){
        posListPhraseMerge(&left, &right, 0, 0, &writer);
      }else{
        /* This case occurs when two terms (simple terms or phrases) are
         * connected by a NEAR operator, span (nNear+1). i.e.
         *
         *     '"terrible company" NEAR widget'
         */
        DataBuffer one = {0, 0, 0};
        DataBuffer two = {0, 0, 0};

        DLWriter dlwriter2;
        DLReader dr1 = {0, 0, 0, 0, 0}; 
        DLReader dr2 = {0, 0, 0, 0, 0};

        dlwInit(&dlwriter2, iType, &one);
        posListPhraseMerge(&right, &left, nNear-3+nPhrase, 1, &dlwriter2);
        dlwInit(&dlwriter2, iType, &two);
        posListPhraseMerge(&left, &right, nNear-1, 0, &dlwriter2);

        if( one.nData) dlrInit(&dr1, iType, one.pData, one.nData);
        if( two.nData) dlrInit(&dr2, iType, two.pData, two.nData);

        if( !dlrAtEnd(&dr1) || !dlrAtEnd(&dr2) ){
          PLReader pr1 = {0};
          PLReader pr2 = {0};

          PLWriter plwriter;
          plwInit(&plwriter, &writer, dlrDocid(dlrAtEnd(&dr1)?&dr2:&dr1));

          if( one.nData ) plrInit(&pr1, &dr1);
          if( two.nData ) plrInit(&pr2, &dr2);
          while( !plrAtEnd(&pr1) || !plrAtEnd(&pr2) ){
            int iCompare = plrCompare(&pr1, &pr2);
            switch( iCompare ){
              case -1:
                plwCopy(&plwriter, &pr1);
                plrStep(&pr1);
                break;
              case 1:
                plwCopy(&plwriter, &pr2);
                plrStep(&pr2);
                break;
              case 0:
                plwCopy(&plwriter, &pr1);
                plrStep(&pr1);
                plrStep(&pr2);
                break;
            }
          }
          plwTerminate(&plwriter);
        }
        dataBufferDestroy(&one);