Re: Invalid YAML output from EXPLAIN

On Mon, Jun 7, 2010 at 4:14 AM, Dean Rasheed <dean.a.rasheed@gmail.com> wro=
te:
> Testing 9.0 beta, I found that EXPLAINing certain queries in YAML
> format will produce invalid YAML, for example:
>
> explain (format yaml) select * from foo where str_val =3D 'a: b';
>
> The problem in this case is that a colon followed by whitespace is not
> allowed in an unquoted plain YAML string because a parser would
> interpret it as the start of a map.
>
> So the current code in escape_yaml() is inadequate for producing valid
> YAML. I think it would have to also consider at least the following
> characters as special "-" =A0":" =A0"[" =A0"]" =A0"{" =A0"}" =A0"," =A0"\=
"" =A0"'"
> "|" =A0"*" =A0"&". Technically, it would also need to trap empty strings,
> and strings with leading or trailing whitespace.
>
> Making escape_yaml() completely bulletproof with this approach would
> be quite difficult, and (IMO) not worth the effort, especially given
> that an important requirement is that the output be machine readable,
> and in my experience YAML parsers are often far from perfect.
>
> I would therefore argue for simply calling escape_json() to produce
> double quoted output for all string values, and only have numeric
> values unquoted. This is not really any less human readable, and is
> far more machine readable.
>
> Patch attached.

I've committed a patch which I think will address this issue without
uglifying the output quite so much.  Also, I didn't like the idea of
not applying escaping to both the keys and values, even though we
think we'll never have a key that requires escaping.  With this
approach, that change isn't needed.

--=20
Robert Haas
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