commit 3ab03da4d103f6fdaabbb6fe740bd42586164230 Author: Michael Whittaker Date: Thu Jan 14 11:32:00 2021 -0800 Added quorum systems section to notes. diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..9090bd6 --- /dev/null +++ b/.gitignore @@ -0,0 +1,277 @@ +*.zip + +# vim ########################################################################## +# Swap +[._]*.s[a-v][a-z] +[._]*.sw[a-p] +[._]s[a-rt-v][a-z] +[._]ss[a-gi-z] +[._]sw[a-p] + +# Session +Session.vim + +# Temporary +.netrwhist +*~ +# Auto-generated tag files +tags +# Persistent undo +[._]*.un~ + +# latex ######################################################################## +## Core latex/pdflatex auxiliary files: +*.aux +*.lof +*.log +*.lot +*.fls +*.out +*.toc +*.fmt +*.fot +*.cb +*.cb2 +.*.lb + +## Intermediate documents: +*.dvi +*.xdv +*-converted-to.* +# these rules might exclude image files for figures etc. +# *.ps +# *.eps +*.pdf + +## Generated if empty string is given at "Please type another file name for output:" +.pdf + +## Bibliography auxiliary files (bibtex/biblatex/biber): +*.bbl +*.bcf +*.blg +*-blx.aux +*-blx.bib +*.run.xml + +## Build tool auxiliary files: +*.fdb_latexmk +*.synctex +*.synctex(busy) +*.synctex.gz +*.synctex.gz(busy) +*.pdfsync + +## Build tool directories for auxiliary files +# latexrun +latex.out/ + +## Auxiliary and intermediate files from other packages: +# algorithms +*.alg +*.loa + +# achemso +acs-*.bib + +# amsthm +*.thm + +# beamer +*.nav +*.pre +*.snm +*.vrb + +# changes +*.soc + +# comment +*.cut + +# cprotect +*.cpt + +# elsarticle (documentclass of Elsevier journals) +*.spl + +# endnotes +*.ent + +# fixme +*.lox + +# feynmf/feynmp +*.mf +*.mp +*.t[1-9] +*.t[1-9][0-9] +*.tfm + +#(r)(e)ledmac/(r)(e)ledpar +*.end +*.?end +*.[1-9] +*.[1-9][0-9] +*.[1-9][0-9][0-9] +*.[1-9]R +*.[1-9][0-9]R +*.[1-9][0-9][0-9]R +*.eledsec[1-9] +*.eledsec[1-9]R +*.eledsec[1-9][0-9] +*.eledsec[1-9][0-9]R +*.eledsec[1-9][0-9][0-9] +*.eledsec[1-9][0-9][0-9]R + +# glossaries +*.acn +*.acr +*.glg +*.glo +*.gls +*.glsdefs + +# gnuplottex +*-gnuplottex-* + +# gregoriotex +*.gaux +*.gtex + +# htlatex +*.4ct +*.4tc +*.idv +*.lg +*.trc +*.xref + +# hyperref +*.brf + +# knitr +*-concordance.tex +# TODO Comment the next line if you want to keep your tikz graphics files +*.tikz +*-tikzDictionary + +# listings +*.lol + +# makeidx +*.idx +*.ilg +*.ind +*.ist + +# minitoc +*.maf +*.mlf +*.mlt +*.mtc[0-9]* +*.slf[0-9]* +*.slt[0-9]* +*.stc[0-9]* + +# minted +_minted* +*.pyg + +# morewrites +*.mw + +# nomencl +*.nlg +*.nlo +*.nls + +# pax +*.pax + +# pdfpcnotes +*.pdfpc + +# sagetex +*.sagetex.sage +*.sagetex.py +*.sagetex.scmd + +# scrwfile +*.wrt + +# sympy +*.sout +*.sympy +sympy-plots-for-*.tex/ + +# pdfcomment +*.upa +*.upb + +# pythontex +*.pytxcode +pythontex-files-*/ + +# tcolorbox +*.listing + +# thmtools +*.loe + +# TikZ & PGF +*.dpth +*.md5 +*.auxlock + +# todonotes +*.tdo + +# easy-todo +*.lod + +# xcolor +*.xcp + +# xmpincl +*.xmpi + +# xindy +*.xdy + +# xypic precompiled matrices +*.xyc + +# endfloat +*.ttt +*.fff + +# Latexian +TSWLatexianTemp* + +## Editors: +# WinEdt +*.bak +*.sav + +# Texpad +.texpadtmp + +# LyX +*.lyx~ + +# Kile +*.backup + +# KBibTeX +*~[0-9]* + +# auto folder when using emacs and auctex +./auto/* +*.el + +# expex forward references with \gathertags +*-tags.tex + +# standalone packages +*.sta diff --git a/notes/notes.tex b/notes/notes.tex new file mode 100644 index 0000000..9601201 --- /dev/null +++ b/notes/notes.tex @@ -0,0 +1,16 @@ +\documentclass[12pt]{article} +\usepackage[margin=1in]{geometry} +\usepackage{pervasives} + +\begin{document} +\begin{center} + {\Large Quorum Systems} + + \today{} +\end{center} + +{\input{sections/quorum_systems.tex}} + +\bibliographystyle{plain} +\bibliography{references} +\end{document} diff --git a/notes/pervasives.sty b/notes/pervasives.sty new file mode 100644 index 0000000..c1108ce --- /dev/null +++ b/notes/pervasives.sty @@ -0,0 +1,184 @@ +\usepackage{amsfonts} +\usepackage{amsmath} +\usepackage{amssymb} +\usepackage{amsthm} +\usepackage{environ} +\usepackage{etoolbox} +\usepackage{mathrsfs} +\usepackage{mathtools} +\usepackage{tcolorbox} +\usepackage{tikz} +\usepackage{xcolor} +\tcbuselibrary{breakable} +\tcbuselibrary{skins} + +% A pretty color palette taken from https://flatuicolors.com/palette/defo. To +% see a preview of the different colors, use the \showcolors command below. +\definecolor{flatdarkgray}{HTML}{7F8C8D} +\definecolor{flatgray}{HTML}{BDC3C7} +\definecolor{flatred}{HTML}{C0392B} +\definecolor{flatorange}{HTML}{D35400} +\definecolor{flatyellow}{HTML}{F39C12} +\definecolor{flatdenim}{HTML}{2C3E50} +\definecolor{flatpurple}{HTML}{8E44AD} +\definecolor{flatblue}{HTML}{2980B9} +\definecolor{flatgreen}{HTML}{27AE60} +\definecolor{flatcyan}{HTML}{16A085} +\definecolor{flatdarkgrayalt}{HTML}{95A5A6} +\definecolor{flatgrayalt}{HTML}{ECF0F1} +\definecolor{flatredalt}{HTML}{E74C3C} +\definecolor{flatorangealt}{HTML}{E67E22} +\definecolor{flatyellowalt}{HTML}{F1C40F} +\definecolor{flatdenimalt}{HTML}{34495E} +\definecolor{flatpurplealt}{HTML}{9B59B6} +\definecolor{flatbluealt}{HTML}{3498DB} +\definecolor{flatgreenalt}{HTML}{2ECC71} +\definecolor{flatcyanalt}{HTML}{1ABC9C} +\definecolor{flatbrown}{HTML}{836953} + +\newcommand{\showcolors}{% + \begin{center} + \begin{tikzpicture} + \tikzstyle{swatch}=[minimum width=3cm, minimum height=0.5cm, y=0.5cm] + \node[swatch, fill=flatdarkgray] at (0, 9) {\texttt{flatdarkgray}}; + \node[swatch, fill=flatgray] at (0, 8) {\texttt{flatgray}}; + \node[swatch, fill=flatred] at (0, 7) {\texttt{flatred}}; + \node[swatch, fill=flatorange] at (0, 6) {\texttt{flatorange}}; + \node[swatch, fill=flatyellow] at (0, 5) {\texttt{flatyellow}}; + \node[swatch, fill=flatdenim] at (0, 4) {\texttt{flatdenim}}; + \node[swatch, fill=flatpurple] at (0, 3) {\texttt{flatpurple}}; + \node[swatch, fill=flatblue] at (0, 2) {\texttt{flatblue}}; + \node[swatch, fill=flatgreen] at (0, 1) {\texttt{flatgreen}}; + \node[swatch, fill=flatcyan] at (0, 0) {\texttt{flatcyan}}; + \node[swatch, fill=flatdarkgrayalt] at (3, 9) {\texttt{flatdarkgrayalt}}; + \node[swatch, fill=flatgrayalt] at (3, 8) {\texttt{flatgrayalt}}; + \node[swatch, fill=flatredalt] at (3, 7) {\texttt{flatredalt}}; + \node[swatch, fill=flatorangealt] at (3, 6) {\texttt{flatorangealt}}; + \node[swatch, fill=flatyellowalt] at (3, 5) {\texttt{flatyellowalt}}; + \node[swatch, fill=flatdenimalt] at (3, 4) {\texttt{flatdenimalt}}; + \node[swatch, fill=flatpurplealt] at (3, 3) {\texttt{flatpurplealt}}; + \node[swatch, fill=flatbluealt] at (3, 2) {\texttt{flatbluealt}}; + \node[swatch, fill=flatgreenalt] at (3, 1) {\texttt{flatgreenalt}}; + \node[swatch, fill=flatcyanalt] at (3, 0) {\texttt{flatcyanalt}}; + \end{tikzpicture} + \end{center} +} + +% New theorem environments. +\newtheorem{theorem}{Theorem} +\theoremstyle{definition} +\newtheorem{definition}{Definition} +\newtheorem{benchmark}{Benchmark} +\newtheorem{example}{Example} +\newtheorem{invariant}{Invariant} + +% Toggleable TODOs. +\newtoggle{showtodos} +\toggletrue{showtodos} +% \togglefalse{showtodos} +\newcommand{\TODO}[2][]{% + \iftoggle{showtodos}{{\textcolor{blue}{\textbf{TODO(#1): #2}}}}{}% +} + +% Toggleable notes. +\newtoggle{shownotes} +\toggletrue{shownotes} +% \togglefalse{shownotes} +\newcommand{\NOTE}[2][]{% + \iftoggle{shownotes}{{\textcolor{red}{NOTE(#1): #2}}}{}% +} + +% Labels and references. To label a figure use the \figlabel command, to label +% a lemma, use the \lemlabel command, etc. Similarly, use the \figref, lemref, +% etc. commands to reference these labels. For example: +% +% \begin{figure} +% % ... +% \caption{A nice figure}\figlabel{MyNiceFigure} +% \end{figure} +% +% Refer to \figref{MyNiceFigure} for a nice figure. +% +% Toggle showlabels to show or hide all labels. +\newtoggle{showlabels} +% \toggletrue{showlabels} +\togglefalse{showlabels} +\newcommand{\genericlabel}[2]{% + \label{#1:#2}% + \iftoggle{showlabels}{\textcolor{flatdarkgray}{\texttt{[#2]}}}{}% +} +\newcommand{\algolabel}[1]{\genericlabel{alg}{#1}} +\newcommand{\algoref}[1]{Algorithm~\ref{alg:#1}} +\newcommand{\applabel}[1]{\genericlabel{app}{#1}} +\newcommand{\appref}[1]{Appendix~\ref{app:#1}} +\newcommand{\benchlabel}[1]{\genericlabel{bench}{#1}} +\newcommand{\benchref}[1]{Benchmark~\ref{bench:#1}} +\newcommand{\clmlabel}[1]{\genericlabel{clm}{#1}} +\newcommand{\clmref}[1]{Claim~\ref{clm:#1}} +\newcommand{\eqnlabel}[1]{\genericlabel{eqn}{#1}} +\newcommand{\eqnref}[1]{\eqref{eqn:#1}} +\newcommand{\invlabel}[1]{\genericlabel{inv}{#1}} +\newcommand{\invref}[1]{Invariant~\ref{inv:#1}} +\newcommand{\examplelabel}[1]{\genericlabel{exa}{#1}} +\newcommand{\exampleref}[1]{Example~\ref{exa:#1}} +\newcommand{\figlabel}[1]{\genericlabel{fig}{#1}} +\newcommand{\figref}[1]{Figure~\ref{fig:#1}} +\newcommand{\lemlabel}[1]{\genericlabel{lem}{#1}} +\newcommand{\lemref}[1]{Lemma~\ref{lem:#1}} +\newcommand{\linelabel}[1]{\genericlabel{line}{#1}} +\newcommand{\lineref}[1]{line~\ref{line:#1}} +\newcommand{\Lineref}[1]{Line~\ref{line:#1}} +\newcommand{\lstlabel}[1]{\genericlabel{lst}{#1}} +\newcommand{\lstref}[1]{Listing~\ref{lst:#1}} +\newcommand{\seclabel}[1]{\genericlabel{sec}{#1}} +\newcommand{\secref}[1]{Section~\ref{sec:#1}} +\newcommand{\appendixlabel}[1]{\genericlabel{appendix}{#1}} +\newcommand{\appendixref}[1]{Appendix~\ref{appendix:#1}} +\newcommand{\tablabel}[1]{\genericlabel{tab}{#1}} +\newcommand{\tabref}[1]{Table~\ref{tab:#1}} +\newcommand{\thmlabel}[1]{\genericlabel{thm}{#1}} +\newcommand{\thmref}[1]{Theorem~\ref{thm:#1}} + +% Surrounding symbols. +\DeclarePairedDelimiter{\parens}{(}{)} +\DeclarePairedDelimiter{\set}{\{}{\}} +\DeclarePairedDelimiterX{\setst}[2]{\{}{\}}{#1 \,\delimsize|\, #2} +\DeclarePairedDelimiter{\brackets}{[}{]} +\DeclarePairedDelimiterX{\pfrac}[2]{(}{)}{\frac{#1}{#2}} +\DeclarePairedDelimiter{\ceil}{\lceil}{\rceil} +\DeclarePairedDelimiter{\floor}{\lfloor}{\rfloor} + +% Symbols and abbreviations. +\newcommand{\nats}{\mathbb{N}} +\newcommand{\ints}{\mathbb{Z}} +\newcommand{\rats}{\mathbb{Q}} +\newcommand{\reals}{\mathbb{R}} +\newcommand{\complexes}{\mathbb{C}} +\newcommand{\partialto}{\rightharpoonup} +% https://tex.stackexchange.com/a/74132 +\newcommand{\defeq}{\stackrel{\mathclap{\mbox{\normalfont \tiny def}}}{=}} + + +% Misc. +\newcommand{\defword}[1]{\textbf{\textcolor{flatdenim}{#1}}} + +% Tech report environment. +% +% If you're writing a paper and there's too much content, you might want to +% move some content out of the paper and into the technical report version of +% the paper. To do this, you can put the content in the techreport environment +% like this: +% +% This text will appear in the paper and tech report. +% \begin{techreport} +% This text will only appear in the tech report. +% \end{techreport} +% +% When the techreportenabled toggle is enabled, the tech report content will be +% shown. When the toggle is disabled, the tech report content will be hidden. +% Moreover, when the toggle is enabled, the tech report content will be shown +% with a red bar on its left margin to make it easier for readers to figure out +% what is new in the tech report. +\newtoggle{techreportenabled} +\toggletrue{techreportenabled} +\togglefalse{techreportenabled} diff --git a/notes/references.bib b/notes/references.bib new file mode 100644 index 0000000..40b71e3 --- /dev/null +++ b/notes/references.bib @@ -0,0 +1,19 @@ +@article{naor1998load, + title={The load, capacity, and availability of quorum systems}, + author={Naor, Moni and Wool, Avishai}, + journal={SIAM Journal on Computing}, + volume={27}, + number={2}, + pages={423--447}, + year={1998}, + publisher={SIAM} +} + +@article{vukolic2013origin, + title={The origin of quorum systems}, + author={Vukoli{\'c}, Marko and others}, + journal={Bulletin of EATCS}, + volume={2}, + number={101}, + year={2013} +} diff --git a/notes/sections/quorum_systems.tex b/notes/sections/quorum_systems.tex new file mode 100644 index 0000000..0e08f49 --- /dev/null +++ b/notes/sections/quorum_systems.tex @@ -0,0 +1,85 @@ +\section{Quorum Systems} +These definitions are taken from \cite{naor1998load} and +\cite{vukolic2013origin}. +% +Given a set $X = \set{x_1, \ldots, x_n}$, a \defword{quorum system} over $X$ is +a set $Q = \set{q_1, \ldots, q_m}$ of subsets of $X$, called \defword{quorums}, +such that every pair of quorums intersect. That is, for every $q_1, q_2 \in +Q$, $q_1 \cap q_2 \neq \emptyset$. + +A quorum system $Q$ is a \defword{coterie} if there does not exist quorums +$q_1, q_2 \in Q$ such that $q_1 \subset q_2$. In other words, a coterie is a +quorum system that does not contain some quorum $q_1$ that is a strict subset +of some other quorum $q_2$. + +Let $P, Q$ be two coteries over the same set $X$. $P$ \defword{dominates} $Q$, +denoted $P > Q$, if $P \neq Q$ and for every $q \in Q$, there exists some $p +\in P$ such that $p \subseteq q$. A coterie $Q$ is \defword{dominated} if there +exists some coterie $P$ that dominates it. + +\begin{example} + Let $P$ be the majority quorum system over the set $X = \set{a, b, c}$. That + is, $P = \set{\set{a, b}, \set{a, c}, \set{b, c}}$. Let $Q = \set{\set{a, b, + c}}$. Note that both quorum systems are coteries. $P$ dominates $Q$. To see + this, we first confirm that $P \neq Q$. Next, we consider every $q \in Q$ and + find a corresponding $p \in P$ where $p \subseteq q$. Here, we only have one + choice for $q$ (i.e. $q = \set{a, b, c}$), and for every $p \in P$, $p + \subseteq q$. +\end{example} + +There is an intuitive way to think about non-dominated coteries. A coterie $Q$ +is non-dominated if (1) removing any element from any quorum would make $Q$ no +longer a coterie and (2) there are no other quorums that we can add to $Q$ +while preserving the fact that $Q$ is a coterie. Here's why. (1) Assume for +contradiction that we remove some element from some quorum in $Q$ to +form a new coterie $P$. $P$ dominates $Q$ in the obvious way, but $Q$ is +non-dominated. (2) Assume for contradiction that we add some quorum to $Q$ to +form a new coterie $P$. Again, $P$ dominates $Q$ in the obvious way, but $Q$ is +non-dominated. Intuitively, a non-dominated coterie is a maximal coterie (we +cannot add any more quorums) with minimal quorums (we cannot remove any +elements from any quorums). + +\NOTE[michael]{% + I think domination will be an important property for recursive quorum + systems. I think there are some quorum systems that we cannot form as a + recursive quorum system, but we can form a recursive quorum system that + dominates it. The definition of domination that I found is only defined on + coteries. Can we define this without coteries? I think so, but we have to + double check. +} + +Let $\sigma: Q \to [0, 1]$ be a discrete probability distribution over the +quorums of $Q$ (i.e., $\sum_{q \in Q} \sigma(q) = 1$). We call $\sigma$ a +\defword{strategy}. Intuitively, $\sigma$ is a strategy to pick quorums at +random. We have the following definitions. +\begin{align*} + l_\sigma(x) &\defeq \sum_{\setst{q \in Q}{x \in q}} \sigma(q) \\ + L_\sigma(Q) &\defeq \max_{x \in X} l_\sigma(x) \\ + L(Q) &\defeq \min_\sigma L_\sigma(Q) +\end{align*} +$l_\sigma(x)$ is the load on $x$ given some strategy $\sigma$. $L_\sigma(Q)$ is +the load on most loaded element $x$. $L(Q)$ is the \defword{load} of the best +possible strategy. Intuitively, the lower the load of a quorum system, the +higher the throughput it can support. + +\begin{example} + Consider the majority quorum system $Q = \set{\set{a, b}, \set{a, c}, \set{b, + c}}$ on elements $X = \set{a, b, c}$. Let $\sigma(\set{a, b}) = + \sigma(\set{a, c}) = 0.5$ and $\sigma(\set{b, c}) = 0$. + \begin{align*} + l_\sigma(a) &= \sigma(\set{a, b}) + \sigma(\set{a, c}) = 0.5 + 0.5 = 1 \\ + l_\sigma(b) &= \sigma(\set{a, b}) + \sigma(\set{b, c}) = 0.5 + 0 = 0.5 \\ + l_\sigma(c) &= \sigma(\set{a, c}) + \sigma(\set{b, c}) = 0.5 + 0 = 0.5 \\ + L_\sigma(Q) &= \max(1, 0.5, 0.5) = 1 + \end{align*} + The load of $Q$ with respect to $\sigma$ is 1, but the load $L(Q)$ is not 1 + because $\sigma$ is not an optimal strategy. If we instead choose + $\sigma_{\text{opt}}(-) = \frac{1}{3}$, the load is reduced to $\frac{2}{3}$ + which is optimal. +\end{example} + +The \defword{resilience} or \defword{fault tolerance} of a quorum system $Q$ is +the largest number $f$ such that for every subset $F \subseteq X$ with $|F| = +f$, there still exists some quorum $q \in Q$ such that $q \cap F = \emptyset$. +Intuitively, a quorum system has fault tolerance $f$ if we can fail an +arbitrary set of $f$ elements and still have some quorum left.