replication and sharding in mongodb

Question 1

replica set

Answer 1

has one primary and multiple secondary and all write operations must go to the primary which maintains a log; “oplog”
secondaries periodically read and apply the log from the primary site

Question 2

what are some benefits of replica sets

Answer 2

allows flexibility availability and load balancing and fault tolerance

Question 3

what are replica sets based on

Answer 3

based on master slave architecture

Question 4

how does writing and reading work in replica sets

Answer 4

all writes go to the primary
writes are accepted once the primary accepts the operation in memory
the secondaries are not updated yet
all reads go to the primary ensuring strict consitency

Question 5

how does persistent writing (journaling/logging) work in replica sets

Answer 5

a write is only accepted after being written to a log on disk
still on the primary site
accepted data becomes persistent