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1 files changed, 62 insertions, 12 deletions
diff --git a/doc/talks/2023-01-18-tocatta/talk.tex b/doc/talks/2023-01-18-tocatta/talk.tex index 09250cf1..1a5b18a8 100644 --- a/doc/talks/2023-01-18-tocatta/talk.tex +++ b/doc/talks/2023-01-18-tocatta/talk.tex @@ -780,18 +780,74 @@ \begin{frame} \frametitle{K2V Design} \begin{itemize} - \item A new, custom, minimal API + \item A new, custom, minimal API\\ + \vspace{.5em} + \begin{itemize} + \item Single-item operations + \item Operations on ranges and batches of items + \item Polling operations to help implement a PubSub pattern + \end{itemize} \vspace{1em} \item<2-> Exposes the partitoning mechanism of Garage\\ K2V = partition key / sort key / value (like Dynamo) \vspace{1em} - \item<3-> Coordination-free, CRDT-friendly (inspired by Riak)\\ + \item<3-> Weakly consistent, CRDT-friendly\\ + $\to$ no support for transactions (not ACID) \vspace{1em} \item<4-> Cryptography-friendly: values are binary blobs \end{itemize} \end{frame} \begin{frame} + \frametitle{Handling concurrent values} + \textbf{How to handle concurrency?} Example: + \vspace{1em} + \begin{enumerate} + \item Client $A$ reads the initial value of a key, $x_0$ + \vspace{1em} + \item<2-> Client $B$ also reads the initial value $x_0$ of that key + \vspace{1em} + \item<3-> Client $A$ modifies $x_0$, and writes a new value $x_1$ + \vspace{1em} + \item<4-> Client $B$ also modifies $x_0$, and writes a new value $x'_1$,\\ + without having a chance to first read $x_1$\\ + \vspace{1em} + $\to$ what should the final state be? + \end{enumerate} +\end{frame} + +\begin{frame} + \frametitle{Handling concurrent values} + \begin{itemize} + \item If we keep only $x_1$ or $x'_1$, we risk \textbf{loosing application data} + \vspace{1.5em} + \item Values are opaque binary blobs, \textbf{K2V cannot resolve conflicts} by itself\\ + (e.g. by implementing a CRDT) + \vspace{1.5em} + \item Solution: \textbf{we keep both!}\\ + $\to$ the value of the key is now $\{x_1, x'_1\}$\\ + $\to$ the client application can decide how to resolve conflicts on the next read + \end{itemize} +\end{frame} + +\begin{frame} + \frametitle{Keeping track of causality} + How does K2V know that $x_1$ and $x'_1$ are concurrent? + \vspace{1em} + \begin{itemize} + \item $read()$ returns \textbf{a set of values} and an associated \textbf{causality token}\\ + \vspace{1.5em} + \item When calling $write()$, the client sends \textbf{the causality token from its last read} + \vspace{1.5em} + \item The causality token represents the set of values \textbf{already seen by the client}\\ + $\to$ those values are the \textbf{causal past} of the write operation\\ + $\to$ K2V can keep concurrent values and overwrite all ones in the causal past + \vspace{1.5em} + \item Internally, the causality token is \textbf{a vector clock} + \end{itemize} +\end{frame} + +\begin{frame} \frametitle{Application: an e-mail storage server} \begin{center} \only<1>{\includegraphics[width=.9\linewidth]{assets/aerogramme.png}}% @@ -800,7 +856,7 @@ \begin{frame} \frametitle{A new model for building resilient software} - \begin{itemize} + \begin{enumerate} \item Design a data model suited to K2V\\ {\footnotesize (see Cassandra docs on porting SQL data models to Cassandra)} \vspace{1em} @@ -810,22 +866,16 @@ \item Store opaque binary blobs to provide End-to-End Encryption\\ \end{itemize} \vspace{1em} - \item Store big blobs (files) in S3 + \item Store big blobs (files) using the S3 API \vspace{1em} \item Let Garage manage sharding, replication, failover, etc. - \end{itemize} + \end{enumerate} \end{frame} \begin{frame} \frametitle{Research perspectives} \begin{itemize} - \item Write about Garage's global architecture \emph{(paper in progress)} - \vspace{1em} - \item Measure and improve Garage's performances - \vspace{1em} - \item Discuss the optimal layout algorithm, provide proofs - \vspace{1em} - \item Write about our proposed architecture for (E2EE) apps over K2V+S3 + \item TODO \end{itemize} \end{frame} |