SQLite

      LayerWriter *pLayer;

      pWriter->nLeafEst = ((iEnd - iStart) + 1) / FTS_MAX_APPENDABLE_HEIGHT;
      pWriter->iStart = iStart;
      pWriter->iEnd = iEnd;
      pWriter->iAbsLevel = iAbsLevel;
      pWriter->iIdx = iIdx;

      for(i=nHeight+1; i<FTS_MAX_APPENDABLE_HEIGHT; i++){
        pWriter->aLayer[i].iBlock = pWriter->iStart + i*pWriter->nLeafEst;
      }

      pLayer = &pWriter->aLayer[nHeight];
      pLayer->iBlock = pWriter->iStart;
      pLayer->iBlock += pWriter->nLeafEst*FTS_MAX_APPENDABLE_HEIGHT;
      blobGrowBuffer(&pLayer->block, MAX(nRoot, p->nNodeSize), &rc);
      if( rc==SQLITE_OK ){
        memcpy(pLayer->block.a, aRoot, nRoot);
        pLayer->block.n = nRoot;
      }

      for(i=nHeight; i>=0 && rc==SQLITE_OK; i--){
        pLayer = &pWriter->aLayer[i];
        NodeReader reader;

        rc = nodeReaderInit(&reader, pLayer->block.a, pLayer->block.n);
        while( reader.aNode && rc==SQLITE_OK ) rc = nodeReaderNext(&reader);
        blobGrowBuffer(&pLayer->key, reader.term.n, &rc);
        if( rc==SQLITE_OK ){

  /* Insert the marker in the %_segments table to make sure nobody tries
  ** to steal the space just allocated. This is also used to identify 
  ** appendable segments.  */
  if( rc==SQLITE_OK ){
    rc = fts3WriteSegment(p, pWriter->iEnd, 0, 0);
  }

  pWriter->iAbsLevel = iAbsLevel;
  pWriter->nLeafEst = nLeafEst;
  pWriter->iIdx = iIdx;

  /* Set up the array of LayerWriter objects */
  for(i=0; i<FTS_MAX_APPENDABLE_HEIGHT; i++){
    pWriter->aLayer[i].iBlock = pWriter->iStart + i*pWriter->nLeafEst;
  }




  return SQLITE_OK;
}

/*
** Remove an entry from the %_segdir table. This involves running the 
** following two statements:
**

    pNode->n = 1 + sqlite3Fts3PutVarint(&pNode->a[1], iChild);
  }else{
    assert( pNode->nAlloc>=1 );
    pNode->n = 1;
  }
}

/*
** The first two arguments are a pointer to and the size of a segment b-tree
** node. The node may be a leaf or an internal node.
**
** This function creates a new node image in blob object *pNew by copying
** all terms that are greater than or equal to zTerm/nTerm (for leaf nodes)
** or greater than zTerm/nTerm (for internal nodes) from aNode/nNode.
*/
static int fts3TruncateNode(
  const char *aNode,              /* Current node image */
  int nNode,                      /* Size of aNode in bytes */
  Blob *pNew,                     /* OUT: Write new node image here */
  const char *zTerm,              /* Omit all terms smaller than this */
  int nTerm,                      /* Size of zTerm in bytes */
  sqlite3_int64 *piBlock          /* OUT: Block number in next layer down */
){
  NodeReader reader;              /* Reader object */
  Blob prev = {0, 0, 0};
  int rc = SQLITE_OK;
  int bStarted = 0;
  int bLeaf = aNode[0]=='\0';     /* True for a leaf node */

  /* Allocate required output space */
  blobGrowBuffer(pNew, nNode, &rc);
  if( rc!=SQLITE_OK ) return rc;
  pNew->n = 0;

  /* Populate new node buffer */
  for(rc = nodeReaderInit(&reader, aNode, nNode); 
      rc==SQLITE_OK && reader.aNode; 
      rc = nodeReaderNext(&reader)
  ){
    if( bStarted==0 ){
      int res = fts3TermCmp(reader.term.a, reader.term.n, zTerm, nTerm);
      if( res<0 || (bLeaf==0 && res==0) ) continue;
      pNew->a[0] = aNode[0];
      fts3StartNode(pNew, (int)aNode[0], reader.iChild);
      *piBlock = reader.iChild;
      bStarted = 1;
    }
    rc = fts3AppendToNode(
        pNew, &prev, reader.term.a, reader.term.n,

    memset(&filter, 0, sizeof(Fts3SegFilter));
    filter.flags = FTS3_SEGMENT_REQUIRE_POS;

    rc = sqlite3Fts3SegReaderStart(p, &csr, &filter);
    assert( rc!=SQLITE_ABORT );
    if( SQLITE_ROW==(rc = sqlite3Fts3SegReaderStep(p, &csr)) ){
      rc = fts3IncrmergeWriter(p, iAbsLevel, csr.zTerm, csr.nTerm, &writer);

      if( rc==SQLITE_OK ){
        do {
          rc = fts3IncrmergeAppend(p, &writer, &csr);

          if( rc==SQLITE_OK ) rc = sqlite3Fts3SegReaderStep(p, &csr);

          if( writer.nWork>=nRem && rc==SQLITE_ROW ) rc = SQLITE_OK;
        }while( rc==SQLITE_ROW );
      }
    }
    assert( rc!=SQLITE_ABORT );
    fts3IncrmergeRelease(p, &writer, &rc);
    nRem -= (1 + writer.nWork);