Re: Sync Rep Design

On 31.12.2010 09:50, Hannu Krosing wrote:
> On 30.12.2010 22:27, Robert Haas wrote:
>> On Thu, Dec 30, 2010 at 2:04 PM, Simon Riggs<simon(at)2ndquadrant(dot)com>
>> wrote:
>>> synchronous_replication (boolean)
>>> Specifies whether transaction commit will wait for WAL records
>>> to be replicated before the command returns a "success"
>>> indication to the client.
>> The word "replicated" here could be taken to mean different things,
>> most obviously:
>>
>> - slave has received the WAL
>> - slave has fsync'd the WAL
>> - slave has applied the WAL
> Perhaps the level of "replication guarantee" should be decided on the
> slave side, by
> having a configuration parameter there
>
> report_as_replicated = received|written_to_disk|fsynced|applied
>
> for different types of hosts may have wildly different guarantees and
> performance
> parameters for these. One could envision a WAL-archive type "standby"
> which is
> there for data persistence only will and never "apply" WAL.

Agreed, it feels natural to specify when a piece of WAL is acknowledged
in the standby.

Regarding the rest of the proposal, I would still prefer the UI
discussed here:

http://archives.postgresql.org/message-id/4CAE030A.2060701@enterprisedb.com

It ought to be the same amount of work to implement, and provides the
same feature set, but makes administration a bit easier by being able to
name the standbys. Also, I dislike the idea of having the standby
specify that it's a synchronous standby that the master has to wait for.
Behavior on the master should be configured on the master.

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