On Sat, Dec 12, 2015 at 8:07 PM, Flavio Junqueira wrote:
Hi Kaushal,
See comments below:
ensemble of 3, then you can tolerate one crashed server, which means that
your quorums have size two. That's why two servers can elect a leader among
them.
In general, if n is the number of servers in the ensemble, then you can
tolerate f crashed servers and the relationship between n and f is n = 2f +
1.
participant in DC-2 will keep waiting for DC-1 to come back up.
This question about tolerating a DC going down using a second DC is a
classic one. If we allowed DC-2 to elect a leader in the total absence of
processes of DC-1, then we would be prone to split brain scenarios: DC-1
suspects DC-2 and vice-versa, but they are both up. If you want
availability when a DC going down, you need a third DC. Also, keep in mind
that availability here refers to both reads and writes. You can set it up
to go into read-only mode.
-Flavio
Hi Kaushal,
See comments below:
On 12 Dec 2015, at 04:07, Kaushal Shriyan wrote:
Hi,
I have couple of questions which are as below :-
1) In a 3 node single ensemble, i have 1 leader and 2 followers. when i
explicitly shutdown down the leader for testing purpose, leader election
triggers in between the remaining 2 nodes and i see that one of the node
becomes a leader and the other is a follower. I am not sure if i
completely
understood it. Since there are only 2 nodes how does leader election happen
because we need odd numbers in order to form a quorum. Please correct me if
i am understanding it wrong.
You need an odd number of total members in the ensemble. If you have anHi,
I have couple of questions which are as below :-
1) In a 3 node single ensemble, i have 1 leader and 2 followers. when i
explicitly shutdown down the leader for testing purpose, leader election
triggers in between the remaining 2 nodes and i see that one of the node
becomes a leader and the other is a follower. I am not sure if i
completely
understood it. Since there are only 2 nodes how does leader election happen
because we need odd numbers in order to form a quorum. Please correct me if
i am understanding it wrong.
ensemble of 3, then you can tolerate one crashed server, which means that
your quorums have size two. That's why two servers can elect a leader among
them.
In general, if n is the number of servers in the ensemble, then you can
tolerate f crashed servers and the relationship between n and f is n = 2f +
1.
2) Is it possible to configure 3 nodes each in DC1 and DC2?
meaning 1 ensemble consists of 6 nodes with 3 nodes in DC-1 and 3 nodes in
DC-2
DC-1 1 Leader 2 Followers
DC-2 1 Follower 2 Observers.
if DC-1 goes down, will there be a leader election between 3 nodes in DC-2?
Please advise.
No, the two observers won't participate in the election, and the remainingmeaning 1 ensemble consists of 6 nodes with 3 nodes in DC-1 and 3 nodes in
DC-2
DC-1 1 Leader 2 Followers
DC-2 1 Follower 2 Observers.
if DC-1 goes down, will there be a leader election between 3 nodes in DC-2?
Please advise.
participant in DC-2 will keep waiting for DC-1 to come back up.
This question about tolerating a DC going down using a second DC is a
classic one. If we allowed DC-2 to elect a leader in the total absence of
processes of DC-1, then we would be prone to split brain scenarios: DC-1
suspects DC-2 and vice-versa, but they are both up. If you want
availability when a DC going down, you need a third DC. Also, keep in mind
that availability here refers to both reads and writes. You can set it up
to go into read-only mode.
-Flavio
If i lets say if i set the below config
DC-1 1 Leader and 2 Followers
DC-2 2 Followers and 1 observer
Is this a good solution meaning 1 ensemble having 6 nodes. In my earlier
setup it was *1 Follower and 2 Observers in DC-2*. Now i changed it in DC-2
2 Followers and 1 observer. In this case there are 2 Followers which will
participate in the leader election to form a quorum. Please comment.
Regarding "If you want availability when a DC going down, you need a third
DC. Also, keep in mind that availability here refers to both reads and
writes. You can set it up to go into read-only mode"
you say set up the below configs for high availability.
DC-1 1 Leader and 2 Followers
DC-2 2 Followers and 1 observer
DC-3 2 Followers and 1 observer.
Please advise.
Regards,
Kaushal
