SQLite

  /* List of nodes removed during a CondenseTree operation. List is
  ** linked together via the pointer normally used for hash chains -
  ** RtreeNode.pNext. RtreeNode.iNode stores the depth of the sub-tree 
  ** headed by the node (leaf nodes have RtreeNode.iNode==0).
  */
  RtreeNode *pDeleted;
  int iReinsertHeight;        /* Height of sub-trees Reinsert() has run on */

  /* Blob I/O on xxx_node */
  sqlite3_blob *pNodeBlob;

  /* Statements to read/write/delete a record from xxx_node */
  sqlite3_stmt *pReadNode;
  sqlite3_stmt *pWriteNode;
  sqlite3_stmt *pDeleteNode;

  /* Statements to read/write/delete a record from xxx_rowid */

    pNode->nRef = 1;
    pNode->pParent = pParent;
    pNode->isDirty = 1;
    nodeReference(pParent);
  }
  return pNode;
}

/*
** Clear the Rtree.pNodeBlob object
*/
static void nodeBlobReset(Rtree *pRtree){
  if( pRtree->pNodeBlob ){
    sqlite3_blob_close(pRtree->pNodeBlob);
    pRtree->pNodeBlob = 0;
  }
}

/*
** Obtain a reference to an r-tree node.
*/
static int nodeAcquire(
  Rtree *pRtree,             /* R-tree structure */
  i64 iNode,                 /* Node number to load */
  RtreeNode *pParent,        /* Either the parent node or NULL */
  RtreeNode **ppNode         /* OUT: Acquired node */
){
  int rc = SQLITE_OK;

  RtreeNode *pNode = 0;

  /* Check if the requested node is already in the hash table. If so,
  ** increase its reference count and return it.
  */
  if( (pNode = nodeHashLookup(pRtree, iNode)) ){
    assert( !pParent || !pNode->pParent || pNode->pParent==pParent );
    if( pParent && !pNode->pParent ){
      nodeReference(pParent);
      pNode->pParent = pParent;
    }
    pNode->nRef++;
    *ppNode = pNode;
    return SQLITE_OK;
  }

  if( pRtree->pNodeBlob ){
    sqlite3_blob *pBlob = pRtree->pNodeBlob;
    pRtree->pNodeBlob = 0;
    rc = sqlite3_blob_reopen(pBlob, iNode);
    pRtree->pNodeBlob = pBlob;
    if( rc ){
      nodeBlobReset(pRtree);
      if( rc==SQLITE_NOMEM ) return rc;
    }
  }
  if( pRtree->pNodeBlob==0 ){
    char *zTab = sqlite3_mprintf("%s_node", pRtree->zName);
    if( zTab==0 ) return SQLITE_NOMEM;
    rc = sqlite3_blob_open(pRtree->db, pRtree->zDb, zTab, "data", iNode, 0,
                           &pRtree->pNodeBlob);
    sqlite3_free(zTab);
  }
  if( rc ){
    nodeBlobReset(pRtree);
    *ppNode = 0;
  }else if( pRtree->iNodeSize==sqlite3_blob_bytes(pRtree->pNodeBlob) ){
    pNode = (RtreeNode *)sqlite3_malloc(sizeof(RtreeNode)+pRtree->iNodeSize);
    if( !pNode ){
      rc = SQLITE_NOMEM;
    }else{
      pNode->pParent = pParent;
      pNode->zData = (u8 *)&pNode[1];
      pNode->nRef = 1;
      pNode->iNode = iNode;
      pNode->isDirty = 0;
      pNode->pNext = 0;
      rc = sqlite3_blob_read(pRtree->pNodeBlob, pNode->zData,
                             pRtree->iNodeSize, 0);
      nodeReference(pParent);
    }
  }




  /* If the root node was just loaded, set pRtree->iDepth to the height
  ** of the r-tree structure. A height of zero means all data is stored on
  ** the root node. A height of one means the children of the root node
  ** are the leaves, and so on. If the depth as specified on the root node
  ** is greater than RTREE_MAX_DEPTH, the r-tree structure must be corrupt.
  */

/*
** Decrement the r-tree reference count. When the reference count reaches
** zero the structure is deleted.
*/
static void rtreeRelease(Rtree *pRtree){
  pRtree->nBusy--;
  if( pRtree->nBusy==0 ){
    nodeBlobReset(pRtree);
    sqlite3_finalize(pRtree->pReadNode);
    sqlite3_finalize(pRtree->pWriteNode);
    sqlite3_finalize(pRtree->pDeleteNode);
    sqlite3_finalize(pRtree->pReadRowid);
    sqlite3_finalize(pRtree->pWriteRowid);
    sqlite3_finalize(pRtree->pDeleteRowid);
    sqlite3_finalize(pRtree->pReadParent);

    pRtree->zDb, pRtree->zName, 
    pRtree->zDb, pRtree->zName,
    pRtree->zDb, pRtree->zName
  );
  if( !zCreate ){
    rc = SQLITE_NOMEM;
  }else{
    nodeBlobReset(pRtree);
    rc = sqlite3_exec(pRtree->db, zCreate, 0, 0, 0);
    sqlite3_free(zCreate);
  }
  if( rc==SQLITE_OK ){
    rtreeRelease(pRtree);
  }

    }
  }

constraint:
  rtreeRelease(pRtree);
  return rc;
}

/*
** Called when a transaction starts.
** This is a no-op.  But the Virtual Table mechanism needs a method
** here or else it will never call the xRollback and xCommit methods,
** and those methods are necessary for clearing the sqlite3_blob object.
*/
static int rtreeBeginTransaction(sqlite3_vtab *pVtab){
  (void)pVtab;
  return SQLITE_OK;
}

/*
** Called when a transaction completes (either by COMMIT or ROLLBACK).
** The sqlite3_blob object should be released at this point.
*/
static int rtreeEndTransaction(sqlite3_vtab *pVtab){
  Rtree *pRtree = (Rtree *)pVtab;
  nodeBlobReset(pRtree);
  return SQLITE_OK;
}

/*
** The xRename method for rtree module virtual tables.
*/
static int rtreeRename(sqlite3_vtab *pVtab, const char *zNewName){
  Rtree *pRtree = (Rtree *)pVtab;
  int rc = SQLITE_NOMEM;

  );
  if( zSql ){
    rc = sqlite3_exec(pRtree->db, zSql, 0, 0, 0);
    sqlite3_free(zSql);
  }
  return rc;
}


/*
** This function populates the pRtree->nRowEst variable with an estimate
** of the number of rows in the virtual table. If possible, this is based
** on sqlite_stat1 data. Otherwise, use RTREE_DEFAULT_ROWEST.
*/
static int rtreeQueryStat1(sqlite3 *db, Rtree *pRtree){

  rtreeClose,                 /* xClose - close a cursor */
  rtreeFilter,                /* xFilter - configure scan constraints */
  rtreeNext,                  /* xNext - advance a cursor */
  rtreeEof,                   /* xEof */
  rtreeColumn,                /* xColumn - read data */
  rtreeRowid,                 /* xRowid - read data */
  rtreeUpdate,                /* xUpdate - write data */
  rtreeBeginTransaction,      /* xBegin - begin transaction */
  0,                          /* xSync - sync transaction */
  rtreeEndTransaction,        /* xCommit - commit transaction */
  rtreeEndTransaction,        /* xRollback - rollback transaction */
  0,                          /* xFindFunction - function overloading */
  rtreeRename,                /* xRename - rename the table */
  0,                          /* xSavepoint */
  0,                          /* xRelease */
  0,                          /* xRollbackTo */
};

static int rtreeSqlInit(
  Rtree *pRtree, 
  sqlite3 *db, 
  const char *zDb, 
  const char *zPrefix, 

  }
  memset(pRtree, 0, sizeof(Rtree)+nDb+nName+2);
  pRtree->nBusy = 1;
  pRtree->base.pModule = &rtreeModule;
  pRtree->zDb = (char *)&pRtree[1];
  pRtree->zName = &pRtree->zDb[nDb+1];
  pRtree->nDim = (u8)((argc-4)/2);
  pRtree->nDim2 = pRtree->nDim*2;
  pRtree->nBytesPerCell = 8 + pRtree->nDim2*4;
  pRtree->eCoordType = (u8)eCoordType;
  memcpy(pRtree->zDb, argv[1], nDb);
  memcpy(pRtree->zName, argv[2], nName);

  /* Figure out the node size to use. */
  rc = getNodeSize(db, pRtree, isCreate, pzErr);