Add explanations about quorums

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Alex 2023-01-12 17:39:12 +01:00
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6 changed files with 66 additions and 27 deletions

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@ -683,6 +683,61 @@
\end{figure} \end{figure}
\end{frame} \end{frame}
\begin{frame}
\frametitle{Read-after-write consistency:}
\textbf{Property:} If node $A$ did an operation $write(x)$ and received an OK response,\\
\hspace{2cm} and node $B$ starts an operation $read()$ after $A$ received OK,\\
\hspace{2cm} then $B$ will read a value $x' \sqsupseteq x$.
\vspace{1em}
\hspace{1em}
\begin{minipage}{6.8cm}
\textbf{Algorithm $write(x)$:}
\begin{enumerate}
\item Broadcast $write(x)$ to all nodes
\item Wait for $k > n/2$ nodes to reply OK
\item Return OK
\end{enumerate}
\end{minipage}
\hfill
\begin{minipage}{6.8cm}
\vspace{1em}
\textbf{Algorithm $read()$:}
\begin{enumerate}
\item Broadcast $read()$ to all nodes
\item Wait for $k > n/2$ nodes to reply\\
with values $x_1, \dots, x_k$
\item Return $x_1 \sqcup \dots \sqcup x_k$
\end{enumerate}
\end{minipage}
\hspace{1em}
\vspace{2em}
\textbf{Why does it work?} There is at least one node at the intersection between the two sets of nodes that replied to each request, that ``saw'' $x$ before the $read()$ started ($x_i \sqsupseteq x$).
\end{frame}
\begin{frame}
\frametitle{Monotonical read consistency:}
\textbf{Property:} If node $A$ did an operation $read()$ and received $x$ as a response,\\
\hspace{2cm} and node $B$ starts an operation $read()$ after $A$ received $x$,\\
\hspace{2cm} then $B$ will read a value $x' \sqsupseteq x$.
\vspace{1em}
\textbf{Algorithm $read()$:}
\begin{enumerate}
\item Broadcast $read()$ to all nodes
\item Wait for $k > n/2$ nodes to reply with values $x_1, \dots, x_k$
\item If $x_i \ne x_j$ for some nodes $i$ and $j$,\\
\hspace{1cm}then call $write(x_1 \sqcup \dots \sqcup x_k)$ and wait for OK from $k' > n/2$ nodes
\item Return $x_1 \sqcup \dots \sqcup x_k$
\end{enumerate}
\vspace{1em}
This makes reads slower in some cases, and is \textbf{not implemented in Garage}.
\end{frame}
\begin{frame} \begin{frame}
\frametitle{Performance gains in practice} \frametitle{Performance gains in practice}
\begin{center} \begin{center}
@ -690,14 +745,16 @@
\end{center} \end{center}
\end{frame} \end{frame}
\begin{frame} \begin{frame}
\frametitle{An ever-increasing compatibility list} \frametitle{The hard parts we don't address (yet!)}
\begin{center} \begin{itemize}
\includegraphics[width=.7\linewidth]{assets/compatibility.png} \item Maintain consistency changes when nodes assigned to a partition change:\\
\end{center} \item TODO
\end{itemize}
\end{frame} \end{frame}
\section{Going further than the S3 API}
\begin{frame} \begin{frame}
\frametitle{Further plans for Garage} \frametitle{Further plans for Garage}
\begin{center} \begin{center}
@ -728,24 +785,6 @@
\end{center} \end{center}
\end{frame} \end{frame}
\begin{frame}
\frametitle{Aerogramme data model}
\begin{center}
\only<1>{\includegraphics[width=.4\linewidth]{assets/aerogramme_datatype.drawio.pdf}}%
\only<2->{\includegraphics[width=.9\linewidth]{assets/aerogramme_keys.drawio.pdf}\vspace{1em}}%
\end{center}
\visible<3->{Aerogramme encrypts all stored values for privacy\\
(Garage server administrators can't read your mail)}
\end{frame}
\begin{frame}
\frametitle{Different deployment scenarios}
\begin{center}
\only<1>{\includegraphics[width=.9\linewidth]{assets/aerogramme_components1.drawio.pdf}}%
\only<2>{\includegraphics[width=.9\linewidth]{assets/aerogramme_components2.drawio.pdf}}%
\end{center}
\end{frame}
\begin{frame} \begin{frame}
\frametitle{A new model for building resilient software} \frametitle{A new model for building resilient software}
\begin{itemize} \begin{itemize}