jm + eventual-consistency   17

Don't Settle For Eventual Consistency
Quite an argument. Not sure I agree, but worth a bookmark anyway...
With an AP system, you are giving up consistency, and not really gaining anything in terms of effective availability, the type of availability you really care about.  Some might think you can regain strong consistency in an AP system by using strict quorums (where the number of nodes written + number of nodes read > number of replicas).  Cassandra calls this “tunable consistency”.  However, Kleppmann has shown that even with strict quorums, inconsistencies can result.10  So when choosing (algorithmic) availability over consistency, you are giving up consistency for not much in return, as well as gaining complexity in your clients when they have to deal with inconsistencies.
cap-theorem  databases  storage  cap  consistency  cp  ap  eventual-consistency 
11 weeks ago by jm
Existential Consistency: Measuring and Understanding Consistency at Facebook
The metric is termed φ(P)-consistency, and is actually very simple. A read for the same data is sent to all replicas in P, and φ(P)-consistency is defined as the frequency with which that read returns the same result from all replicas. φ(G)-consistency applies this metric globally, and φ(R)-consistency applies it within a region (cluster). Facebook have been tracking this metric in production since 2012.
facebook  eventual-consistency  consistency  metrics  papers  cap  distributed-computing 
october 2015 by jm
Race conditions on Facebook, DigitalOcean and others
good trick -- exploit eventual consistency and a lack of distributed transactions by launching race-condition-based attacks
attacks  exploits  race-conditions  bugs  eventual-consistency  distributed-transactions  http  facebook  digitalocean  via:aphyr 
april 2015 by jm
S3's "s3-external-1.amazonaws.com" endpoint
public documentation of how to work around the legacy S3 multi-region replication behaviour in North America
aws  s3  eventual-consistency  consistency  us-east  replication  workarounds  legacy 
april 2015 by jm
When S3's eventual consistency is REALLY eventual
a consistency outage in S3 last year, resulting in about 40 objects failing read-after-write consistency for a duration of about 23 hours
s3  eventual-consistency  aws  consistency  read-after-writes  bugs  outages  stackdriver 
april 2015 by jm
If Eventual Consistency Seems Hard, Wait Till You Try MVCC
ex-Percona MySQL wizard Baron Schwartz, noting that MVCC as implemented in common SQL databases is not all that simple or reliable compared to big bad NoSQL Eventual Consistency:
Since I am not ready to assert that there’s a distributed system I know to be better and simpler than eventually consistent datastores, and since I certainly know that InnoDB’s MVCC implementation is full of complexities, for right now I am probably in the same position most of my readers are: the two viable choices seem to be single-node MVCC and multi-node eventual consistency. And I don’t think MVCC is the simpler paradigm of the two.
nosql  concurrency  databases  mysql  riak  voldemort  eventual-consistency  reliability  storage  baron-schwartz  mvcc  innodb  postgresql 
december 2014 by jm
Mathematical Purity in Distributed Systems: CRDTs Without Fear
Via Tony Finch. Funnily enough, the example describes Swrve: mobile game analytics, backed by a CRDT-based eventually consistent data store ;)
storage  crdts  semilattice  idempotency  commutativity  data-structures  distcomp  eventual-consistency 
january 2014 by jm
Non-blocking transactional atomicity
Peter Bailis with an interesting distributed-storage atomicity algorithm for performing multi-record transactional updates
algorithms  nbta  transactions  databases  storage  distcomp  distributed  atomic  coding  eventual-consistency  crdts 
september 2013 by jm
Information on Google App Engine's recent US datacenter relocations - Google Groups
or, really, 'why we had some glitches and outages recently'. A few interesting tidbits about GAE innards though (via Bill De hOra)
gae  google  app-engine  outages  ops  paxos  eventual-consistency  replication  storage  hrd 
august 2013 by jm
"Scalable Eventually Consistent Counters over Unreliable Networks" [paper, pdf]

Counters are an important abstraction in distributed computing, and
play a central role in large scale geo-replicated systems, counting events such as web page impressions or social network "likes". Classic distributed counters, strongly consistent, cannot be made both available and partition-tolerant, due to the CAP Theorem, being unsuitable to large scale scenarios.

This paper defi nes Eventually Consistent Distributed Counters (ECDC) and presents an implementation of the concept, Hando ff Counters, that is scalable and works over unreliable networks. By giving up the sequencer aspect of classic distributed counters, ECDC implementations can be made AP in the CAP design space, while retaining the essence of counting. Handoff Counters are the first CRDT (Conflict-free Replicated Data Type) based mechanism that overcomes the identity explosion problem in naive CRDTs, such as G-Counters (where state size is linear in the number of independent actors that ever incremented the counter), by managing identities towards avoiding global propagation, and garbage collecting temporary entries. The approach used in Hando ff Counters is not restricted to counters, being more generally applicable to other data types with associative and commutative operations.
pdf  papers  eventual-consistency  counters  distributed-systems  distcomp  cap-theorem  ecdc  handoff-counters  crdts  data-structures  g-counters 
august 2013 by jm
_Bolt-On Causal Consistency_ [slides]
SIGMOD 2013 presentation from Peter Bailis, Ali Ghodsi, Joseph M. Hellerstein, Ion Stoica -- adding consistency to an eventually-consistent store by tracking dependencies
eventual-consistency  state  cap-theorem  storage  peter-bailis 
june 2013 by jm
Riak, CAP, and eventual consistency
Good (albeit draft) write-up of the implications of CAP, allow_mult, and last_write_wins conflict-resolution policies in Riak:
As Brewer's CAP theorem established, distributed systems have to make hard choices. Network partition is inevitable. Hardware failure is inevitable. When a partition occurs, a well-behaved system must choose its behavior from a spectrum of options ranging from "stop accepting any writes until the outage is resolved" (thus maintaining absolute consistency) to "allow any writes and worry about consistency later" (to maximize availability). Riak leans toward the availability end of the spectrum, but allows the operator and even the developer to tune read and write requests to better meet the business needs for any given set of data.
riak  cap  eventual-consistency  distcomp  distributed-systems  partition  last-write-wins  voldemort  allow_mult 
april 2013 by jm
Eventual Consistency Today: Limitations, Extensions, and Beyond - ACM Queue
Good overview of the current state of eventually-consistent data store research, covering CALM and CRDTs, from Peter Bailis and Ali Ghodsi
eventual-consistency  data  storage  horizontal-scaling  research  distcomp  distributed-systems  via:martin-thompson  crdts  calm  acid  cap 
april 2013 by jm
Boundary Techtalk - Large-scale OLAP with Kobayashi
Boundary on their TSD-on-Riak store.
Dietrich Featherston, Engineer at Boundary, walks through the process of designing Kobayashi, the time-series analytics database behind our network metrics. He goes through the false-starts and lessons learned in effectively using Riak as the storage layer for a large-scale OLAP database.  The system is ultimately capable of answering complex, ad-hoc queries at interactive latencies.
video  boundary  tsd  riak  eventual-consistency  storage  kobayashi  olap  time-series 
april 2013 by jm

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