int rz = getRecordSize();
// data before the deletion
dataBlock.position(0);
memory bfore = new memory(dataBlock.buff);
bfore.buff.limit( startLine*rz );
bfore.position(0);
// data behind our deletion
dataBlock.position( (startLine+lenght)*rz );
memory after = new memory(dataBlock.buff);
after.position(0);
// new datablock
dataBlock = new memory( dataBlock.limit() - (lenght*rz) );
// copy data after deletion
dataBlock.put(bfore.buff);
dataBlock.put(after.buff);