Questions tagged [distributed-systems]

Questions about the challenges of solving problems with multiple cooperating but separate agents.

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7 views

Is AWS EC2 instance considered a cluster?

Are individual Amazon Web Service EC2 instances considered a cluster or would a cluster have to be composed of multiple EC2 instances in order to be considered a cluster?
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Resetting Vector clocks in distributed systems

I understand that vector clocks are preferred over lamport clocks because sometimes lamport clocks cannot account for the casuality and we use extra space to store the timestamps in the vector clocks. ...
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9 views

Time-slice Equalizing Algorithm

I have a requirement for which I am trying to write an algorithm and struggling a bit conceptually with. This seems like it should be a common-ish type problem so I imagine there is a name/standard ...
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Consistency CAP vs ACID

I understand that the consistency property specifies what values can be read, depending on what has been written before. For instance, if we consider a simple abstract read/write service. It enjoys ...
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Distributed Algorithm Problem

Consider a t-resilient read-write shared memory system (0 < t < N) with initial failures only: faulty processes take no steps. How could one give a consensus algorithm in this system? I don't ...
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14 views

Input distribution in FLP Impossibility

Lemma 2 in "Impossibility of Distributed Consensus with One Faulty Process" is as follows: LEMMA 2. P has a bivalent initial configuration. They prove this by showing that the opposite assumption ...
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Graph with arboricity a, all verteces are marked active

So I came across this problem that I would like help solving/explaining: We have a graph with arboricity a (can be partitioned to a min of a trees). We run the following algorithm on the graph: - All ...
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Why is there no extensive Standards Body overseeing ISAs, Bitcodes, Code Representation, etc… as there is in the case of Unicode

There exist a vast array of prominent bitcode formats, each suited for their specific task: LLVM IR: This format is build around a XML like binary streams model, designed to be used as a common ...
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Can't understand this example of convergecast addition from a book

In the book Distributed Computing: A Locality-Sensitive Approach by David Peleg, in chapter 3, Broadcast and convergecast, in section 3.4.2 Global function computation, examples are given for global ...
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50 views

Where were the ideas of vote, accept and commit phases originally introduced?

In the Stellar Consensus Protocol SCP, the voting procedure follows a 3 phase commit i.e. vote, accept and confirm i.e. see section 5. Is this a novel introduction or has this been previously been ...
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Running Time of Oral Messages Algorithm OM(m) for Byzantine Generals Fault Tolerance

Let us consider a byzantine generals problem assuming: less than 1/3 of generals are traitors Oral messages No Crypto One solution is the Oral Message algorithm OM(m), m being the maximum number ...
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Problem of making entities agree on some wavelength

I remember seeing this problem somewhere before, but don't remember what it's called and can't find it again. It was presented as two guys having $n$ phones each that don't ring when called. Each ...
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Questions while I'm making distributed key-value store

I'm CS student. I'm currently trying to make distributed key-value store. Since I'm new to distributed system concept. I'm struggling with sort of concrete implementation and methodology to apply ...
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A tree-like data structure with rights delegation for distributed computing

Every actor can create a root node and delegate a right to add a child node. Every node contains name of its’ creator or who added it, and value S. Sum of all values S at the same level of the tree ...
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How to detect a consensus is BFT or not?

Can we divide consensus algorithms into BFT (Byzantine Fault Tolerant) and non-BFT ? If so, How to detect a consensus is BFT or non-BFT ? Is there any non-BFT consensus algorithm example ?
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Data structure to know if something was calculated

There's the typical interview question about how to create a distributed and scalable URL shortener. One of the issues is to know if a URL was shortened already or not. There's a special data ...
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Distributed algorithms for finding n largest elements

It's easy to come up with a simple distributed algorithms for finding the maximum element in a set (totally ordered): Divide and conquer. There are a few publications that present algorithms for ...
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What is the relationship between Consistency Models and Consensus Algorithms?

I know that: Each replication technique should follow a consistency model. A consistency model defines a set of rules for the order of the write and read operations. In some replication techniques ...
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Construction of Omega Network

I understand that we could draw N * N Omega Network, But can we draw an Omega Network to connect 6 CPUs to 4 memories? (The number of CPUs does not equal the number of memories)
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How to make use of opponent policy on designing ours in multi-agent learning

I'm currently working on a multi-agent reinforcement learning. The setting is a cooperative multi-agent system with a stationary assumption on the opponent policy. Suppose I have the model of the ...
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Distributed selection (window) algorithm

For n records distributed amongst m processes/nodes (no shared memory) I'd like to accomplish the following for some given ranking criteria find the rth item. find the rth to r+cth items for some ...
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Why in the Map Reduce Implementation, why not stream the records to the reducer (via TCP) as they are being produced by the mappers?

In the Map-Reduce implementation, the reducers start when all mappers finish their jobs. Why don't we stream the records from mappers to reducers while they are being processed instead? I think there ...
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Distributed MST Construction in O(log log n) Rounds in a Clique

I'm reading the paper MST Construction in O(log log n) Communication Rounds in a Clique and trying to understand the correctness analysis, in page 5. It shows by induction on k (phase number), that ...
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Need a layman's example of Linearizable Consistency model

As far as I understand, Linearizable Consistency model is a Data-centric and Strong consistency model. Data-centric means: - All clients experience the consistency - All clients access the same ...
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Should I use lamport logical clock or vector clock or something else?

simplified use case: I have 3 nodes where each node sends a message to the other two always(so a message won't be sent from one to another node. It would always be sent to two other nodes) and every ...
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What is the difference between Consensus and Leader Election problems?

According to this paper written by Lamport, `selecting a unique leader is equivalent to solving the consensus problem'. Based on the above quote, my question is: What is the difference between ...
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How is consensus impossible under FLP even when no fault exists at that moment?

Could some give an illustration of the following sentence? In fact, for every purported consensus protocol that guarantees agreement and validity, there is some execution in which there are no ...
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What does asynchronous communication in FLP impossibility comprise of?

Conditions: (i) Is it just async networks, that is, messages might be arbitrarily delayed? (ii) Does it also require that the processors should be running at different speeds? (iii) Is the absence ...
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43 views

How is the literal meaning of “rendezvous” related to its usage in distributed computing?

I am trying to figure out the difference between RPC and Rendezvous. Is it correct that they differ only on their implementation on server side: RPC will involve creating a new process/thread to ...
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24 views

Optimal scalability of a distributed algorithm

What's the optimal scalability of some algorithm when I implement it in a distributed manner? Intuitively, it seems to me that any algorithm can scale at most linearly with number of computing nodes....
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45 views

How does paxos algorithm handle partial failures of accept messages?

I've been reading the basic paxos algorithm from the "Paxos Made Simple" paper. I can't understand how paxos algorithm maintains the safety properties under partial failures of the accept messages, ...
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Distributed maximal matching from vertex coloring

How to use a $\Delta +1$ vertex coloring to find a maximal matching in a distributed graph.
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How do distributed algorithms for shortest path finding handle negative cycles?

I am searching the web for an answer to this question, but I have only found answers for non-distributed algorithms. I am interested in this for its application to Distance Vector routing.
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What is a counterexample for Lamport's distributed mutual exclusion algorithm with non-FIFO message queues?

Lamport's distributed mutual exclusion algorithm (also described here) solves mutual exclusion problem for $N$ processes with $3(N-1)$ messages per request ("take and release lock" cycle). It ...
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Why don't RDBMS use a quorum based solution to do failover

For RDBMS viz. MySql, PostgreSql a common solution for scalability and high availability is to run a primary instance as master that is a read-write instance and one or more read replicas. If the ...
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What is a genuine atomic multicast?

What is a genuine atomic multicast? What is the difference between a genuine and non-genuine atomic multicast?
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Does the Paxos algorithm use failure detectors?

Does the Paxos algorithm use failure detectors? If not, how can it solve consensus, given the impossibility result?
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38 views

Is There An Established Way To Send Code Over a Network?

Let's say I have two computers on a network. I want to write code in some language on machine A, send the code in an efficient way over a network, and run the code on machine B. It seems to me that ...
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In the FLP Impossibility paper, why did the authors claim that e is applicable to every E in proof of lemma 3?

The paper is available here: https://groups.csail.mit.edu/tds/papers/Lynch/jacm85.pdf The 1st paragraph of lemma 3's proof says In other words,if event e is applicable to config C,and E is any ...
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Under which conditions is it possible to scale a distributed log with checksums?

This question is related to Amazon's QLDB, but my question is about the generic architecture of such a software system. The question arises from the fact that Amazon advertises the service as "highly ...
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353 views

Difference between Lamport timestamps and Vector clocks

Lamport timestamps and vector clocks sound like almost the same thing. Both are used to determine the order of events in a distributed system. What are their key differences?
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Proof of impossibility result for distributed consensus

I am reading the classic paper by Fisher, Lynch, Merritt "Easy impossibility proofs for distributed consensus problems", and cannot understand the model they are using. It seems it was already ...
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Event-based architecture (in the context of Distributed Systems)

Our course lecture slides divide architectures of distributed systems into: object based architectures (e.g. typical distributed web application) resource-centered architectures (e.g. torrents and ...
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Start with highest ID in bully algorithm?

I try to implement the bully algorithm for leader election in a distributed system. The pseudo code says to send an election message to all nodes with a higher ID then the own node and to wait for ...
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What's the difference between strong consistency and sequential consistency?

How to Make a Multiprocessor Computer That Correctly Executes Multiprocess Programs ... the result of any execution is the same as if the operations of all the processors were executed in some ...
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Distributed Computing: Persistent Data Structures in Functional Programming versus Wait-Free Data Structures

Persistent (aka immutable) data structures in functional programming sidestep issues of shared memory mutual exclusion, and thus also issues such as data races that arise and which may be difficult to ...
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Lamport logical clock: why event occurs in a process with smaller pid is treated earlier?

In lamport's paper1, he define global local timestamp, which is composed of process id and local lamport timestamp. This timestamp is used to order all the events in a distributed system. The rule ...
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146 views

Lamport logical clock: what does partial mean in the concept of `Partial ordering`?

In lamport's paper[1], he define two concept The partial ordering and The totally ordering. What does partial mean in ...
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Algorithms / heuristics for a distributed sorting problem

The setting: There's a cluster of $k$ computers (= nodes). For simplicity, assume their hardware is identical. The network topology can be complicated, but let's simplify and assume it's a clique ...
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Can a distributed algorithm be serial?

Can a distributed algorithm be serial? For example if I have 3 distinct agents in a network would an algorithm that looks like this be considered a distributed algorithm? ...