\begin{frame}
  \frametitle{Phantom Row Problem}

  \begin{exampleblock}{}
    \begin{tcenter}
    \begin{tabular}{|l|l|l|}
    \hline
    \emph{Transaction 1} & \emph{Transaction 2}  & \emph{Effect} \\
    \hline
    & & \\[-1ex]
    \emph{scan} relation R & & $T_1$ locks all rows\\
    & \emph{insert} new row into R & $T_2$ locks new row\\
    & commit & $T_2$'s lock released\\
    \emph{scan} relation R & & reads \emph{new} row too!\\
    \hline
    \end{tabular}
    \end{tcenter}
  \end{exampleblock}
  \pause
  
  \begin{alertblock}{}
  Both transactions properly follow the 2 PL protocol!
  \\[1ex]
  Nevertheless, $T_1$ observed an effect caused by $T_2$. 
  \begin{itemize}
    \item Isolation violated!
    \item Cause of the problem: \emph{$T_1$ can only lock existing rows}.
  \end{itemize}
  \end{alertblock}
  
  \pause
  \begin{goal}{Solutions}
    \begin{enumerate}
      \item \emph{multi-granularity locking} (locking the table)
      \item \emph{declarative locking}: key-range or predicate locking
    \end{enumerate}
  \end{goal}
\end{frame}