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Category: Trex

Pre-voting in distributed consensus

Another top notch Paxos post from the inventor of UPaxos covers leader election in Paxos. The outlined approach is similar to that used in TRex which is based on a sloppy timeout mechanism. This post will get into why this is a must read for consensus fans. Read the rest of this entry »

Observability in Paxos clusters

David Turner the inventor of UPaxos has posted a great blog post about monitoring Paxos clusters. It’s a must read for consensus aficionados.

TRex UPaxos Experimental Code

There is now a sketch (hack!) demoing the happy path flow of a UPaxos reconfiguration written up on the TRex wiki.

Paxos Voting Weights

The last UPaxos post took a run through the reconfiguration stall avoiding aspects of the UPaxos paper. In this post, we will take a quick look at how the paper describes hot swapping of nodes using voting weights. Read the rest of this entry »

UPaxos: Unbounded Paxos Reconfigurations

The year 2016 turned out to be a bumper year for pragmatic Paxos discoveries. Hot on the heels of the FPaxos discovery of more flexible quorums comes Unbounded Pipelining in Dynamically Reconfigurable Paxos Clusters or “UPaxos”. This uses overlapping quorums between consecutive cluster configurations, and a leader “casting vote”, to enable cluster reconfigurations in a non-stop manner even when reconfiguration messages are lost. Read the rest of this entry »

Paxos Reconfiguration Stalls

In a previous post I covered using the Paxos engine itself to do cluster reconfiguration as per the 2001 Paxos Made Simple paper. In this post I will cover a problem with that technique know as pipeline stalls. This post is to set the scene for a new technical report published 2016 which fixes the problem with a state-of-the-art Paxos implementation called UPaxos which we will discuss in the next post. Read the rest of this entry »

Just say NO to custom hardware for Paxos 

Today’s Morning Paper on “Just say NO to Paxos overhead: replacing consensus with network ordering” was a thrilling disappointment. It’s always with both excitement and trepidation I read about new developments in distributed consensus; is today the day that I learn that Paxos is obsolete? The NOPaxos paper (“network ordered Paxos”) reviewed at the link above has a title which suggests a breakthrough. Unfortunately, it has far less general applicability, and far higher economic cost to implement, than “vanilla” Paxos.

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Failures In Distributed Databases

The “Morning Paper” blog has some fascinating insights into critical production failures in distributed data-intensive databases such as Cassandra and HBase. This reveals that simple testing can prevent most critical failures. In this blog post we take a quick look to see what an embeddable Paxos algorithm project such as Trex can learn from this study.  Read the rest of this entry »

The FPaxos “Even Nodes” Optimisation 

Up until 2016, it was well understood that the optimal size for typical Paxos clusters is three or five nodes. With typical replication workloads, it was known that four or six nodes clusters are no better, and in fact worse, than having one less node. The FPaxos “Flexible Paxos” paper changes the rules of the consensus game with the “even nodes” optimisation.  Read the rest of this entry »

Trex now supports Flexible Paxos (FPaxos) Strategies

2016 has turned out to be a great year for Paxos with the discovery of a more flexible Paxos known as FPaxos. Only a simple change was required to the TRex paxos JVM library to support this new discovery. You can now supply a pluggable QuorumStraregy which can do things like “grid consensus”. The code on the master branch now has a default strategy which does the  “even nodes” optimisation. Enjoy!