Re: Standalone synchronous master

On 01/10/2014 01:49 PM, Andres Freund wrote:
>>
>> I know I am the one that instigated all of this so I want to be very clear
>> on what I and what I am confident that my customers would expect.
>>
>> If a synchronous slave goes down, the master continues to operate. That is
>> all. I don't care if it is configurable (I would be fine with that). I don't
>> care if it is not automatic (e.g; slave goes down and we have to tell the
>> master to continue).
>
> Would you please explain, as precise as possible, what the advantages of
> using a synchronous standby would be in such a scenario?

Current behavior:

db01->sync->db02

Transactions are happening. Everything is happy. Website is up. Orders 
are being made.

db02 goes down. It doesn't matter why. It is down. Because it is down, 
db01 for all intents and purposes is also down because we are using sync 
replication. We have just lost continuity of service, we can no longer 
accept orders, we can no longer allow people to log into the website, we 
can no longer service accounts.

In short, we are out of business.

Proposed behavior:

db01->sync->db02

Transactions are happening. Everything is happy. Website is up. Orders 
are being made.

db02 goes down. It doesn't matter why. It is down. db01 continues to 
accept orders, allow people to log into the website and we can still 
service accounts. The continuity of service continues.

Yes, there are all kinds of things that need to be considered when that 
happens, that isn't the point. The point is, PostgreSQL continues its 
uptime guarantee and allows the business to continue to function as (if) 
nothing has happened.

For many and I dare say the majority of businesses, this is enough. They 
know that if the slave goes down they can continue to operate. They know 
if the master goes down they can fail over. They know that while both 
are up they are using sync rep (with various caveats). They are happy. 
They like that it is simple and just works. They continue to use PostgreSQL.


Sincerely,

JD

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