Re: documenting the backup manifest file format

On 4/14/20 12:56 PM, Robert Haas wrote:
> On Mon, Apr 13, 2020 at 5:43 PM Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:
>> Yeah, I guess I'm just saying that it feels brittle to have a file
>> format that's supposed to be good for data exchange and then make it
>> itself depend on representation details such as the order that fields
>> appear in, the letter case, or the format of newlines. Maybe this isn't
>> really of concern, but it seemed strange.
>
> I didn't want to use JSON for this at all, but I got outvoted. When I
> raised this issue, it was suggested that I deal with it in this way,
> so I did. I can't really defend it too far beyond that, although I do
> think that one nice thing about this is that you can verify the
> checksum using shell commands if you want. Just figure out the number
> of lines in the file, minus one, and do head -n$LINES backup_manifest
> | shasum -a256 and boom. If there were some whitespace-skipping thing
> figuring out how to reproduce the checksum calculation would be hard.
>
>> I think strict ISO 8601 might be preferable (with the T in the middle
>> and ending in Z instead of " GMT").
>
> Hmm, did David suggest that before? I don't recall for sure. I think
> he had some suggestion, but I'm not sure if it was the same one.

"I'm also partial to using epoch time in the manifest because it is
generally easier for programs to work with. But, human-readable doesn't
suck, either."

Also you don't need to worry about time-zone conversion errors -- even
if the source time is UTC this can easily happen if you are not careful.
It also saves a parsing step.

The downside is it is not human-readable but this is intended to be a
machine-readable format so I don't think it's a big deal (encoded
filenames will be just as opaque). If a user really needs to know what
time some file is (rare, I think) they can paste it with a web tool to
find out.

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