Tinker10:02. R 1, W 1: today 2 stale reads, 0 refused.North 6/1, East 7/1, West 7/1 · 1 stale
Chapter 4 of 7
Quorums
Stay open or stay right is too blunt. The team wants a dial: how many copies must agree before a read or a sale counts.
This chapter: How many copies must a read and a write reach to never miss the latest sale?
About this chapter
You will learn
- N, R and W: copies, reads and writes
- Why R + W > N makes every read see the latest write
- What a bigger W costs when the line is down
Words you’ll meet
- N
- How many replicas each count has: here, 3.
- R
- How many replicas a read must hear from.
- W
- How many replicas must take a write before the receipt prints.
- Quorum
- A set of replicas big enough that any read set and any write set share at least one.
Step 1 of 4
Each count has = 3 replicas. A read asks of them; a write reaches before its receipt.
Predict.