Acknowledge Write – 1 – DB Setting – False – Fast Response – Small error of missing write
Acknowledge Write – 1 – DB Setting – True – Slow Response – No Error
Unacknowledge Write-0 – Not waiting for server to respond.
In replicated environment, there are many more variables.
use case 1: Write to DB, Due to network error, system didn’t responded. Data was written to disk
Option 1: Based on case, due to failure, try to write one more time.
Option 2: In sensitive case, read data to make sure that data was written and act acordingly.
To select Primary, we need to have odd number of servers.
Types of Replica Set Nodes
1. Regular Node – Primary or Secondary
2. Arbiter Node – Only for voting purposes. No Data on it.
3. Delayed Node – It can’t become primary node. This is one hour late on updates with compare to other nodes.
4. Hidden Node – It can’t become primary node. Used for Analytics
All nodes can participate in election
Always writes/reads goes to Primary
Application can read from secondary
During the time when failover is occurring, can writes successfully complete?
mongos is router..takes care of distribution…
Sharding is used for horizontal scalability