/* SEGDIR_SELECT */
  "select start_block, leaves_end_block, root from %_segdir "
  " where level = ? order by idx",
  /* SEGDIR_SPAN */
  "select min(start_block), max(end_block) from %_segdir "
  " where level = ? and start_block <> 0",
  /* SEGDIR_DELETE */ "delete from %_segdir where level = ?",

  /* SEGDIR_SELECT_ALL */ "select root from %_segdir order by level desc, idx",
};

/*
** A connection to a fulltext index is an instance of the following
** structure.  The xCreate and xConnect methods create an instance
** of this structure and xDestroy and xDisconnect free that instance.
** All other methods receive a pointer to the structure as one of their
................................................................................
  assert( !pReader->eof );
  return leafReaderData(&pReader->leafReader);
}

static int leavesReaderAtEnd(LeavesReader *pReader){
  return pReader->eof;
}


















static void leavesReaderDestroy(LeavesReader *pReader){
  leafReaderDestroy(&pReader->leafReader);
  dataBufferDestroy(&pReader->rootData);
  SCRAMBLE(pReader);
}

................................................................................

  assert( nData>1 );
  assert( *pData=='\0' );
  rc = leavesReaderInit(v, 0, 0, 0, pData, nData, &reader);
  if( rc!=SQLITE_OK ) return rc;

  rc = loadSegmentLeavesInt(v, &reader, pTerm, nTerm, out);



















  leavesReaderDestroy(&reader);
  return rc;
}

/* Taking pData/nData as an interior node, find the child node which
** could include pTerm/nTerm.  Note that the interior node terms
** logically come between the blocks, so there is one more blockid
** than there are terms (that block contains terms >= the last
** interior-node term).
*/
static void getNextChild(const char *pData, int nData,
                         const char *pTerm, int nTerm,
                         sqlite_int64 *piBlockid){
  InteriorReader reader;

  assert( nData>1 );
  assert( *pData!='\0' );
  interiorReaderInit(pData, nData, &reader);

  while( !interiorReaderAtEnd(&reader) ){
................................................................................
    if( interiorReaderTermCmp(&reader, pTerm, nTerm)>0 ) break;
    interiorReaderStep(&reader);
  }
  *piBlockid = interiorReaderCurrentBlockid(&reader);

  interiorReaderDestroy(&reader);
}






































/* Traverse the tree represented by pData[nData] looking for
** pTerm[nTerm], merging its doclist over *out if found (any duplicate
** doclists read from the segment rooted at pData will overwrite those
** in *out).
*/
static int loadSegment(fulltext_vtab *v, const char *pData, int nData,

                       const char *pTerm, int nTerm, DataBuffer *out){
  int rc;
  sqlite3_stmt *s = NULL;

  assert( nData>1 );

  /* This code should never be called with buffered updates. */
  assert( v->nPendingData<0 );

  /* Process data as an interior node until we reach a leaf. */
  while( *pData!='\0' ){



    sqlite_int64 iBlockid;
    getNextChild(pData, nData, pTerm, nTerm, &iBlockid);

    rc = sql_get_statement(v, BLOCK_SELECT_STMT, &s);
    if( rc!=SQLITE_OK ) return rc;


    rc = sqlite3_bind_int64(s, 1, iBlockid);




    if( rc!=SQLITE_OK ) return rc;

    rc = sql_step_statement(v, BLOCK_SELECT_STMT, &s);
    if( rc==SQLITE_DONE ) return SQLITE_ERROR;
    if( rc!=SQLITE_ROW ) return rc;

    pData = sqlite3_column_blob(s, 0);
    nData = sqlite3_column_bytes(s, 0);
  }

  rc = loadSegmentLeaf(v, pData, nData, pTerm, nTerm, out);
  if( rc!=SQLITE_OK ) return rc;

  /* If we selected a child node, we need to finish that select. */
  if( s!=NULL ){
    /* We expect only one row.  We must execute another sqlite3_step()
     * to complete the iteration; otherwise the table will remain
     * locked. */
    rc = sqlite3_step(s);
    if( rc==SQLITE_ROW ) return SQLITE_ERROR;
    if( rc!=SQLITE_DONE ) return rc;
  }
  return SQLITE_OK;
}

/* Scan the database and merge together the posting lists for the term
** into *out.
*/
static int termSelect(fulltext_vtab *v, int iColumn,
                      const char *pTerm, int nTerm,
................................................................................

  dataBufferInit(&doclist, 0);

  /* Traverse the segments from oldest to newest so that newer doclist
  ** elements for given docids overwrite older elements.
  */
  while( (rc=sql_step_statement(v, SEGDIR_SELECT_ALL_STMT, &s))==SQLITE_ROW ){

    rc = loadSegment(v, sqlite3_column_blob(s, 0), sqlite3_column_bytes(s, 0),

                     pTerm, nTerm, &doclist);
    if( rc!=SQLITE_OK ) goto err;
  }
  if( rc==SQLITE_DONE ){
    if( doclist.nData!=0 ){
      /* TODO(shess) The old term_select_all() code applied the column
      ** restrict as we merged segments, leading to smaller buffers.
      ** This is probably worthwhile to bring back, once the new storage

  /* SEGDIR_SELECT */
  "select start_block, leaves_end_block, root from %_segdir "
  " where level = ? order by idx",
  /* SEGDIR_SPAN */
  "select min(start_block), max(end_block) from %_segdir "
  " where level = ? and start_block <> 0",
  /* SEGDIR_DELETE */ "delete from %_segdir where level = ?",
  /* SEGDIR_SELECT_ALL */
  "select root, leaves_end_block from %_segdir order by level desc, idx",
};

/*
** A connection to a fulltext index is an instance of the following
** structure.  The xCreate and xConnect methods create an instance
** of this structure and xDestroy and xDisconnect free that instance.
** All other methods receive a pointer to the structure as one of their
................................................................................
  assert( !pReader->eof );
  return leafReaderData(&pReader->leafReader);
}

static int leavesReaderAtEnd(LeavesReader *pReader){
  return pReader->eof;
}

/* loadSegmentLeaves() may not read all the way to SQLITE_DONE, thus
** leaving the statement handle open, which locks the table.
*/
/* TODO(shess) This "solution" is not satisfactory.  Really, there
** should be check-in function for all statement handles which
** arranges to call sqlite3_reset().  This most likely will require
** modification to control flow all over the place, though, so for now
** just punt.
**
** Note the the current system assumes that segment merges will run to
** completion, which is why this particular probably hasn't arisen in
** this case.  Probably a brittle assumption.
*/
static int leavesReaderReset(LeavesReader *pReader){
  return sqlite3_reset(pReader->pStmt);
}

static void leavesReaderDestroy(LeavesReader *pReader){
  leafReaderDestroy(&pReader->leafReader);
  dataBufferDestroy(&pReader->rootData);
  SCRAMBLE(pReader);
}

................................................................................

  assert( nData>1 );
  assert( *pData=='\0' );
  rc = leavesReaderInit(v, 0, 0, 0, pData, nData, &reader);
  if( rc!=SQLITE_OK ) return rc;

  rc = loadSegmentLeavesInt(v, &reader, pTerm, nTerm, out);
  leavesReaderReset(&reader);
  leavesReaderDestroy(&reader);
  return rc;
}

/* Call loadSegmentLeavesInt() with the leaf nodes from iStartLeaf to
** iEndLeaf (inclusive) as input, and merge the resulting doclist into
** out.
*/
static int loadSegmentLeaves(fulltext_vtab *v,
                             sqlite_int64 iStartLeaf, sqlite_int64 iEndLeaf,
                             const char *pTerm, int nTerm,
                             DataBuffer *out){
  LeavesReader reader;
  int rc = leavesReaderInit(v, 0, iStartLeaf, iEndLeaf, NULL, 0, &reader);
  if( rc!=SQLITE_OK ) return rc;

  rc = loadSegmentLeavesInt(v, &reader, pTerm, nTerm, out);
  leavesReaderReset(&reader);
  leavesReaderDestroy(&reader);
  return rc;
}

/* Taking pData/nData as an interior node, find the child node which
** could include pTerm/nTerm.  Note that the interior node terms
** logically come between the blocks, so there is one more blockid
** than there are terms (that block contains terms >= the last
** interior-node term).
*/
static void getChildContaining(const char *pData, int nData,
                               const char *pTerm, int nTerm,
                               sqlite_int64 *piBlockid){
  InteriorReader reader;

  assert( nData>1 );
  assert( *pData!='\0' );
  interiorReaderInit(pData, nData, &reader);

  while( !interiorReaderAtEnd(&reader) ){
................................................................................
    if( interiorReaderTermCmp(&reader, pTerm, nTerm)>0 ) break;
    interiorReaderStep(&reader);
  }
  *piBlockid = interiorReaderCurrentBlockid(&reader);

  interiorReaderDestroy(&reader);
}

/* Read block at iBlockid and pass it with other params to
** getChildContaining().
*/
static int loadAndGetChildContaining(fulltext_vtab *v, sqlite_int64 iBlockid,
                                     const char *pTerm, int nTerm,
                                     sqlite_int64 *piBlockid){
  sqlite3_stmt *s = NULL;
  int rc;

  assert( iBlockid!=0 );
  assert( pTerm!=NULL );
  assert( nTerm!=0 );        /* TODO(shess) Why not allow this? */
  assert( piBlockid!=NULL );

  rc = sql_get_statement(v, BLOCK_SELECT_STMT, &s);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3_bind_int64(s, 1, iBlockid);
  if( rc!=SQLITE_OK ) return rc;

  rc = sql_step_statement(v, BLOCK_SELECT_STMT, &s);
  if( rc==SQLITE_DONE ) return SQLITE_ERROR;
  if( rc!=SQLITE_ROW ) return rc;

  getChildContaining(sqlite3_column_blob(s, 0), sqlite3_column_bytes(s, 0),
                     pTerm, nTerm, piBlockid);

  /* We expect only one row.  We must execute another sqlite3_step()
   * to complete the iteration; otherwise the table will remain
   * locked. */
  rc = sqlite3_step(s);
  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
  if( rc!=SQLITE_DONE ) return rc;

  return SQLITE_OK;
}

/* Traverse the tree represented by pData[nData] looking for
** pTerm[nTerm], merging its doclist over *out if found (any duplicate
** doclists read from the segment rooted at pData will overwrite those
** in *out).
*/
static int loadSegment(fulltext_vtab *v, const char *pData, int nData,
                       sqlite_int64 iLeavesEnd,
                       const char *pTerm, int nTerm, DataBuffer *out){



  assert( nData>1 );

  /* This code should never be called with buffered updates. */
  assert( v->nPendingData<0 );

  /* Special case where root is a leaf. */
  if( *pData=='\0' ){
    return loadSegmentLeaf(v, pData, nData, pTerm, nTerm, out);
  }else{
    int rc;
    sqlite_int64 iBlockid;





    /* Process pData as an interior node, then loop down the tree
    ** until we find a leaf node to scan for the term.
    */
    getChildContaining(pData, nData, pTerm, nTerm, &iBlockid);
    while( iBlockid>iLeavesEnd ){
      rc = loadAndGetChildContaining(v, iBlockid, pTerm, nTerm, &iBlockid);
      if( rc!=SQLITE_OK ) return rc;
    }





    return loadSegmentLeaves(v, iBlockid, iBlockid, pTerm, nTerm, out);
  }














}

/* Scan the database and merge together the posting lists for the term
** into *out.
*/
static int termSelect(fulltext_vtab *v, int iColumn,
                      const char *pTerm, int nTerm,
................................................................................

  dataBufferInit(&doclist, 0);

  /* Traverse the segments from oldest to newest so that newer doclist
  ** elements for given docids overwrite older elements.
  */
  while( (rc=sql_step_statement(v, SEGDIR_SELECT_ALL_STMT, &s))==SQLITE_ROW ){
    const char *pData = sqlite3_column_blob(s, 0);
    const int nData = sqlite3_column_bytes(s, 0);
    const sqlite_int64 iLeavesEnd = sqlite3_column_int64(s, 1);
    rc = loadSegment(v, pData, nData, iLeavesEnd, pTerm, nTerm, &doclist);
    if( rc!=SQLITE_OK ) goto err;
  }
  if( rc==SQLITE_DONE ){
    if( doclist.nData!=0 ){
      /* TODO(shess) The old term_select_all() code applied the column
      ** restrict as we merged segments, leading to smaller buffers.
      ** This is probably worthwhile to bring back, once the new storage