Re: [BUGS] Invalid YAML output from EXPLAIN

* Greg Smith:

> Florian Weimer wrote:
>> It has been claimed before that YAML is a superset of JSON, so why
>> can't the YAML folks use the existing JSON output instead?
>>   
>
> Because JSON just crosses the line where it feels like there's so much
> markup that people expect a tool is necessary to read it, which has
> always been the issue with XML too--bad human readability.

But YAML is not human-readable.  There are human-readable subsets of
it, but the general serializers do not produce them, and specific
serializers are difficult to get right (as we've seen).

> EXPLAIN (FORMAT YAML) SELECT * FROM customers WHERE customerid>1000
> ORDER BY zip;
>             QUERY PLAN
> -------------------------------------
> - Plan:                            +
>     Node Type: Sort                +
>     Startup Cost: 4449.30          +
>     Total Cost: 4496.80            +
>     Plan Rows: 19000               +
>     Plan Width: 268                +
>     Sort Key:                      +
>       - zip                        +
>     Plans:                         +
>       - Node Type: Seq Scan        +
>         Parent Relationship: Outer +
>         Relation Name: customers   +
>         Alias: customers           +
>         Startup Cost: 0.00         +
>         Total Cost: 726.00         +
>         Plan Rows: 19000           +
>         Plan Width: 268            +
>         Filter: (customerid > 1000)

What does your parser do with this (equivalent but shorter) YAML
output?

- Plan: !!map   &0 Node Type: Sort   &1 Startup Cost: 4449.30   &2 Total Cost: 4496.80   &3 Plan Rows: &5 19000   &4 Plan Width: &6 268   Sort Key: ["zip"]   Plans: !!seq     - *0: Seq Scan       Parent Relationship: Outer       Relation Name: &7 customers       Alias: *7       *1: 0.00       *2: 726.00       *3: *5       *4: *6       Filter: (customerid > 1000)

Looking at the spec, it's rather difficult to come up with a readable
subset which can parsed easily and is general in the sense that it can
express empty strings, strings with embedded newlines, and so on.
YAML's rules for dealing with whitespace are fairly complex, but are
probably needed to get a more compact notation than JSON.

-- 
Florian Weimer                
BFK edv-consulting GmbH       http://www.bfk.de/
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