SQLite

  u8 nAux;                    /* # of auxiliary columns in %_rowid */
  int iDepth;                 /* Current depth of the r-tree structure */
  char *zDb;                  /* Name of database containing r-tree table */
  char *zName;                /* Name of r-tree table */ 
  u32 nBusy;                  /* Current number of users of this structure */
  i64 nRowEst;                /* Estimated number of rows in this table */
  u32 nCursor;                /* Number of open cursors */
  u32 nNodeRef;               /* Number RtreeNodes with positive nRef */
  char *zReadAuxSql;          /* SQL for statement to read aux data */

  /* 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).
  */

}

/*
** Increment the reference count of node p.
*/
static void nodeReference(RtreeNode *p){
  if( p ){
    assert( p->nRef>0 );
    p->nRef++;
  }
}

/*
** Clear the content of node p (set all bytes to 0x00).
*/

static RtreeNode *nodeNew(Rtree *pRtree, RtreeNode *pParent){
  RtreeNode *pNode;
  pNode = (RtreeNode *)sqlite3_malloc(sizeof(RtreeNode) + pRtree->iNodeSize);
  if( pNode ){
    memset(pNode, 0, sizeof(RtreeNode) + pRtree->iNodeSize);
    pNode->zData = (u8 *)&pNode[1];
    pNode->nRef = 1;
    pRtree->nNodeRef++;
    pNode->pParent = pParent;
    pNode->isDirty = 1;
    nodeReference(pParent);
  }
  return pNode;
}

){
  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))!=0 ){
    assert( !pParent || !pNode->pParent || pNode->pParent==pParent );
    if( pParent && !pNode->pParent ){
      pParent->nRef++;
      pNode->pParent = pParent;
    }
    pNode->nRef++;
    *ppNode = pNode;
    return SQLITE_OK;
  }

    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;
      pRtree->nNodeRef++;
      pNode->iNode = iNode;
      pNode->isDirty = 0;
      pNode->pNext = 0;
      rc = sqlite3_blob_read(pRtree->pNodeBlob, pNode->zData,
                             pRtree->iNodeSize, 0);
      nodeReference(pParent);
    }

    if( pNode!=0 ){
      nodeHashInsert(pRtree, pNode);
    }else{
      rc = SQLITE_CORRUPT_VTAB;
    }
    *ppNode = pNode;
  }else{
    if( pNode ){
      pRtree->nNodeRef--;
      sqlite3_free(pNode);
    }
    *ppNode = 0;
  }

  return rc;
}

/*

** Release a reference to a node. If the node is dirty and the reference
** count drops to zero, the node data is written to the database.
*/
static int nodeRelease(Rtree *pRtree, RtreeNode *pNode){
  int rc = SQLITE_OK;
  if( pNode ){
    assert( pNode->nRef>0 );
    assert( pRtree->nNodeRef>0 );
    pNode->nRef--;
    if( pNode->nRef==0 ){
      pRtree->nNodeRef--;
      if( pNode->iNode==1 ){
        pRtree->iDepth = -1;
      }
      if( pNode->pParent ){
        rc = nodeRelease(pRtree, pNode->pParent);
      }
      if( rc==SQLITE_OK ){

** 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 ){
    pRtree->inWrTrans = 0;
    assert( pRtree->nCursor==0 );
    nodeBlobReset(pRtree);
    assert( pRtree->nNodeRef==0 );
    sqlite3_finalize(pRtree->pWriteNode);
    sqlite3_finalize(pRtree->pDeleteNode);
    sqlite3_finalize(pRtree->pReadRowid);
    sqlite3_finalize(pRtree->pWriteRowid);
    sqlite3_finalize(pRtree->pDeleteRowid);
    sqlite3_finalize(pRtree->pReadParent);
    sqlite3_finalize(pRtree->pWriteParent);

      int ii;
      pNew = rtreeEnqueue(pCur, rScore, iLevel);
      if( pNew==0 ) return 0;
      ii = (int)(pNew - pCur->aPoint) + 1;
      if( ii<RTREE_CACHE_SZ ){
        assert( pCur->aNode[ii]==0 );
        pCur->aNode[ii] = pCur->aNode[0];
      }else{
        nodeRelease(RTREE_OF_CURSOR(pCur), pCur->aNode[0]);
      }
      pCur->aNode[0] = 0;
      *pNew = pCur->sPoint;
    }
    pCur->sPoint.rScore = rScore;
    pCur->sPoint.iLevel = iLevel;

    pLeft = nodeNew(pRtree, pNode);
    pRtree->iDepth++;
    pNode->isDirty = 1;
    writeInt16(pNode->zData, pRtree->iDepth);
  }else{
    pLeft = pNode;
    pRight = nodeNew(pRtree, pLeft->pParent);
    pLeft->nRef++;
  }

  if( !pLeft || !pRight ){
    rc = SQLITE_NOMEM;
    goto splitnode_out;
  }

  /* Re-insert the contents of any underfull nodes removed from the tree. */
  for(pLeaf=pRtree->pDeleted; pLeaf; pLeaf=pRtree->pDeleted){
    if( rc==SQLITE_OK ){
      rc = reinsertNodeContent(pRtree, pLeaf);
    }
    pRtree->pDeleted = pLeaf->pNext;
    pRtree->nNodeRef--;
    sqlite3_free(pLeaf);
  }

  /* Release the reference to the root node. */
  if( rc==SQLITE_OK ){
    rc = nodeRelease(pRtree, pRoot);
  }else{

  sqlite_int64 *pRowid
){
  Rtree *pRtree = (Rtree *)pVtab;
  int rc = SQLITE_OK;
  RtreeCell cell;                 /* New cell to insert if nData>1 */
  int bHaveRowid = 0;             /* Set to 1 after new rowid is determined */

  if( pRtree->nNodeRef ){
    /* Unable to write to the btree while another cursor is reading from it,
    ** since the write might do a rebalance which would disrupt the read
    ** cursor. */
    return SQLITE_LOCKED_VTAB;
  }
  rtreeReference(pRtree);
  assert(nData>=1);

  cell.iRowid = 0;  /* Used only to suppress a compiler warning */

  /* Constraint handling. A write operation on an r-tree table may return
  ** SQLITE_CONSTRAINT for two reasons:

do_test rtree8-1.1.1 {
  execsql { PRAGMA page_size = 512 }
  execsql { CREATE VIRTUAL TABLE t1 USING rtree_i32(id, x1, x2) }
  populate_t1 5
} {}
do_test rtree8-1.1.2 {
  set res [list]
  set rc [catch {
    db eval { SELECT * FROM t1 } { 
      lappend res $x1 $x2
      if {$id==3} { db eval { DELETE FROM t1 WHERE id>3 } }
    }
  } msg];
  lappend rc $msg
  set rc
} {1 {database table is locked}}
do_test rtree8-1.1.2b {
  db eval { SELECT * FROM t1 ORDER BY +id } { 
    if {$id==3} { db eval { DELETE FROM t1 WHERE id>3 } }
  }
  db eval {SELECT x1, x2 FROM t1}
} {1 3 2 4 3 5}
do_test rtree8-1.1.3 {
  execsql { SELECT * FROM t1 }
} {1 1 3 2 2 4 3 3 5}

# Many SELECTs on the same small table.
#

#define SQLITE_IOERR_CONVPATH          (SQLITE_IOERR | (26<<8))
#define SQLITE_IOERR_VNODE             (SQLITE_IOERR | (27<<8))
#define SQLITE_IOERR_AUTH              (SQLITE_IOERR | (28<<8))
#define SQLITE_IOERR_BEGIN_ATOMIC      (SQLITE_IOERR | (29<<8))
#define SQLITE_IOERR_COMMIT_ATOMIC     (SQLITE_IOERR | (30<<8))
#define SQLITE_IOERR_ROLLBACK_ATOMIC   (SQLITE_IOERR | (31<<8))
#define SQLITE_LOCKED_SHAREDCACHE      (SQLITE_LOCKED |  (1<<8))
#define SQLITE_LOCKED_VTAB             (SQLITE_LOCKED |  (2<<8))
#define SQLITE_BUSY_RECOVERY           (SQLITE_BUSY   |  (1<<8))
#define SQLITE_BUSY_SNAPSHOT           (SQLITE_BUSY   |  (2<<8))
#define SQLITE_CANTOPEN_NOTEMPDIR      (SQLITE_CANTOPEN | (1<<8))
#define SQLITE_CANTOPEN_ISDIR          (SQLITE_CANTOPEN | (2<<8))
#define SQLITE_CANTOPEN_FULLPATH       (SQLITE_CANTOPEN | (3<<8))
#define SQLITE_CANTOPEN_CONVPATH       (SQLITE_CANTOPEN | (4<<8))
#define SQLITE_CORRUPT_VTAB            (SQLITE_CORRUPT | (1<<8))