Re: [HACKERS] Built-in plugin for logical decoding output

It seems test_decoding.c could be easily changed to support JSON by using the built in PostgreSQL functions (json.c composite_to_json) to convert a Datum into SQL. It's use of OidOutputFunctionCall could be modified to emit arrays and composite types as JSON. This might be enough to enable downstream frameworks to parse (without having to code to the terse and positional composite structure format).

It could be a minimal change to have in core using the built in JSON support with no additional libraries. I have not made changes to this code but it seems like it should work.

Thank you,

Henry

On Tue, Sep 26, 2017 at 9:37 AM Alvaro Hernandez <aht@ongres.com> wrote:

On 26/09/17 17:50, Craig Ringer wrote:

On 26 September 2017 at 22:14, Magnus Hagander <magnus@hagander.net> wrote:

On Tue, Sep 26, 2017 at 2:16 PM, Alvaro Hernandez <aht@ongres.com> wrote:

    But what about earlier versions? Any chance it could be backported down to 9.4? If that would be acceptable, I could probably help/do that...

The likelihood is zero if you mean backported into core of earlier versions.

Right. We don't add features to back branches.

    Yeah, I know the policy. But asking is free ;) and in my opinion this would be a very good reason to have an exception, if there would be a clear desire to have a single, unified, production quality output plugin across all PostgreSQL versions. At least I tried ;)

 

If you mean backported as a standalone extension that could be installed on a previous version, probably. I'm not sure if it relies on any internals not present before that would make it harder, but it would probably at least be possible. 

All the pub/sub stuff is new and hooked into syscache etc. So you'd be doing a bunch of emulation/shims using user catalogs. Not impossible, but probably irritating and verbose. And you'd have none of the DDL required to manage it, so you'd need SQL-function equivalents.

I suspect you'd be better off tweaking pglogical to speak the same protocol as pg10, since the pgoutput protocol is an evolution of pglogical's protocol. Then using pglogical on older versions.

    Given all this, if I would be doing an app based on logical decoding, I think I will stick to test_decoding for <10....


    Thanks,

    Álvaro

-- 

Alvaro Hernandez


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