Consistency Management in Cloud Storage Systems - Large Scale and Big Data: Processing and Management - page 339

Upon arrival of R1 and R2, if they are consistent then 4
If they are not consistent and R1 has the most recent data then 4 and 4a
Upon arrival of R3, if it is not consistent with the most recent data then another 4.a

If (R1, R2, and R3 are consistent) then 6,
while if R3 is out of data then

4 5 6

3. Check requested data 3. Check requested data

R1 R1

1 1 4a. Issue a write to

the out-of-date
replicas

6 6

4. Response
with R1

6. Response
with R1

2.

2

R2 2.

Send direct
read request to quorum
replicas (1,2) and wait
their response

R2

2.
Send the request
to all replicas and
wait their response

Client Client

2 1. Issue

read request

2

1. Issue
read request

2

5 5

2a.
Background read
repair request

4. Issue
a write to the
out-of-date
replicas

5. Ack

3 3

4 4

R3 R3

Strong consistency in Cassandra Eventual consistency in Cassandra

FIGURE 10.2 Synchronous replication vs. Quorum replication in Cassandra [11].