Re: making the backend's json parser work in frontend code

On 1/15/20 4:40 PM, Andres Freund wrote:
>
> I'm not sure where I come down between using json and a simple ad-hoc
> format, when the dependency for the former is making the existing json
> parser work in the frontend. But if the alternative is to add a second
> json parser, it very clearly shifts towards using an ad-hoc
> format. Having to maintain a simple ad-hoc parser is a lot less
> technical debt than having a second full blown json parser.

Maybe at first, but it will grow and become more complex as new features
are added. This has been our experience with pgBackRest, at least.

> Imo even
> when an external project or three also has to have that simple parser.

I don't agree here. Especially if we outgrow the format and they need
two parsers, depending on the version of PostgreSQL.

To do page-level incrementals (which this feature is intended to enable)
the user will need to be able to associate full and incremental backups
and the only way I see to do that (currently) is to read the manifests,
since the prior backup should be stored there. I think this means that
parsing the manifest is not really optional -- it will be required to do
any kind of automation with incrementals.

It's easy enough for a tool like pgBackRest to do something like that,
much harder for a user hacking together a tool in bash based on
pg_basebackup.

> If the alternative were to use that newly proposed json parser to
> *replace* the backend one too, the story would again be different.

That was certainly not my intention.

Regards,
--
-David
david(at)pgmasters(dot)net