Re: Support for N synchronous standby servers - take 2

On Tue, Jul 7, 2015 at 2:19 PM, Josh Berkus <josh@agliodbs.com> wrote:
> On 07/06/2015 09:56 PM, Michael Paquier wrote:
>> On Tue, Jul 7, 2015 at 12:51 PM, Josh Berkus <josh@agliodbs.com> wrote:
>>> On 07/06/2015 06:40 PM, Michael Paquier wrote:
>>>> On Tue, Jul 7, 2015 at 2:56 AM, Josh Berkus <josh@agliodbs.com> wrote:
>>>>> pro-JSON:
>>>>>
>>>>> * standard syntax which is recognizable to sysadmins and devops.
>>>>> * can use JSON/JSONB functions with ALTER SYSTEM SET to easily make
>>>>> additions/deletions from the synch rep config.
>>>>> * can add group labels (see below)
>>>>
>>>> If we go this way, I think that managing a JSON blob with a GUC
>>>> parameter is crazy, this is way longer in character size than a simple
>>>> formula because of the key names. Hence, this JSON blob should be in a
>>>> separate place than postgresql.conf not within the catalog tables,
>>>> manageable using an SQL interface, and reloaded in backends using
>>>> SIGHUP.
>>>
>>> I'm not following this at all.  What are you saying here?
>>
>> A JSON string is longer in terms of number of characters than a
>> formula because it contains key names, and those key names are usually
>> repeated several times, making it harder to read in a configuration
>> file. So what I am saying that that we do not save it as a GUC, but as
>> a separate metadata that can be accessed with a set of SQL functions
>> to manipulate it.
>
> Where, though?  Someone already pointed out the issues with storing it
> in a system catalog, and adding an additional .conf file with a
> different format is too horrible to contemplate.

Something like pg_syncinfo/ coupled with a LW lock, we already do
something similar for replication slots with pg_replslot/.