Re: Standalone synchronous master

From: "Andres Freund" <andres@2ndquadrant.com>
> On 2014-01-08 14:42:37 -0800, Joshua D. Drake wrote:
>> If we have the following:
>>
>> db0->db1:down
>>
>> Using the model (as I understand it) that is being discussed we have
>> increased our failure rate because the moment db1:down we also lose db0. 
>> The
>> node db0 may be up but if it isn't going to process transactions it is
>> useless. I can tell you that I have exactly 0 customers that would want 
>> that
>> model because a single node failure would cause a double node failure.
>
> That's why you should configure a second standby as another (candidate)
> synchronous replica, also listed in synchronous_standby_names.

Let me ask a (probably) stupid question.  How is the sync rep different from 
RAID-1?

When I first saw sync rep, I expected that it would provide the same 
guarantees as RAID-1 in terms of durability (data is always mirrored on two 
servers) and availability (if one server goes down, another server continues 
full service).

The cost is reasonable with RAID-1.  The sync rep requires high cost to get 
both durability and availability --- three servers.

Am I expecting too much?


Regards
MauMau