Re: Support for N synchronous standby servers - take 2

Hello,

Tue, Jul 7, 2015 at 02:56 AM, Josh Berkus 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)

Adding group labels do have a lot of values but as Amit has pointed out,
with little modification, they can be included in GUC as well. It will not
make it any more complex.

On Tue, Jul 7, 2015 at 2:19 PM, Michael Paquier wrote:

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

I was trying to figure out how the JSON metadata can be used.
It would have to be set using a given set of functions. Right?
I am sorry this question is very basic.

The functions could be something like:
1. pg_add_synch_set(set_name NAME, quorum INT, is_priority bool, set_members
VARIADIC)

This will be used to add a sync set. The set_members can be individual
elements of another set name. The parameter is_priority is used to decide
whether the set is priority (true) set or quorum (false). This function call
will create a folder pg_syncinfo/groups/$NAME and store the json blob?

The root group would be automatically sset by finding the group which is not
included in other groups? or can be set by another function?

2. pg_modify_sync_set(set_name NAME, quorum INT, is_priority bool,
set_members VARIADIC)

This will update the pg_syncinfo/groups/$NAME to store the new values.

3. pg_drop_synch_set(set_name NAME)

This will update the pg_syncinfo/groups/$NAME folder. Also all the groups
which included this would be updated?

4. pg_show_synch_set()

this will display the current sync setting in json format.

Am I missing something?

Is JSON being preferred because it would be ALTER SYSTEM friendly and in a
format already known to users?

In a real-life scenario, at most how many groups and nesting would be
expected?

-----
Beena Emerson

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