Re: Invalid YAML output from EXPLAIN

On Mon, Jun 7, 2010 at 4:14 AM, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> wrote:
> 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 = '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 "-"  ":"  "["  "]"  "{"  "}"  ","  "\""  "'"
> "|"  "*"  "&". 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.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company