Bolt-on Causal Consistency – Bailis et al. 2013
“It’ll probably be OK” seems to reflect the prevailing application developer’s attitude to working with eventually consistent stores. Thanks to the work of Bailis et al. on PBS, we can now quantify that ‘probably.’ And it looks pretty good at first glance, with 99+% probabilities achievable after a pretty short window. The greater the volume of transactions you’re processing though, the more this bites you: (a) the window between transactions is shorter, increasing the probability of staleness, and (b) you’re taking a percentage of a bigger absolute number. Let’s say 1M transactions per day, and 99.99% probability of recency under normal conditions – that’s 100 stale reads a day. Is that ok? It depends on your application semantics of course. After a year of operation you’ll have 36,500 stale reads – it’ll probably be ok?!
Presumably you’re using an eventually consistent…