Re: Sync Rep v17

On 02.03.2011 17:07, Robert Haas wrote:
> On Wed, Mar 2, 2011 at 9:53 AM, Heikki Linnakangas
> <heikki.linnakangas@enterprisedb.com>  wrote:
>> On 02.03.2011 12:40, Simon Riggs wrote:
>>>
>>> allow_standalone_primary seems to need to be better through than it is
>>> now, yet neither of us think its worth having.
>>>
>>> If the people that want it can think it through a little better then it
>>> might make this release, but I propose to remove it from this current
>>> patch to allow us to commit with greater certainty and fewer bugs.
>>
>> If you leave it out, then let's rename the feature to "semi-synchronous
>> replication" or such. The point of synchronous replication is
>> zero-data-loss, and you don't achieve that with allow_standalone_primary=on.
>
> I think that'd just be adding confusion.  Replication will still be
> synchronous; it'll just be more likely to be not happening when you
> think it is.

The defining property of synchronous replication is that when a 
transaction is acknowledged as committed to the client, it has also been 
replicated to the standby. You don't achieve that with 
allow_standalone_primary=on, plain and simple. That's fine for a lot of 
people, most people don't actually want synchronous replication because 
they're not willing to pay the availability penalty. But IMHO it would 
be disingenuous to call it synchronous replication if you can't achieve 
zero data loss with it.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com