Re: auto_explain produces invalid JSON

On 02/10/2012 01:14 PM, Peter Eisentraut wrote:
> The auto_explain module appears to create invalid JSON (in all versions
> since 9.0). For example, with the settings
>
> auto_explain.log_format = 'json'
> auto_explain.log_min_duration = 0
>
> the query
>
> select * from pg_type;
>
> produces this in the log:
>
> LOG: duration: 529.808 ms plan:
> [
> "Query Text": "select * from pg_type;",
> "Plan": {
> "Node Type": "Seq Scan",
> "Relation Name": "pg_type",
> "Alias": "pg_type",
> "Startup Cost": 0.00,
> "Total Cost": 9.87,
> "Plan Rows": 287,
> "Plan Width": 611
> }
> ]
>
> Note that at the top level, it uses the array delimiters [ ] for what is
> actually an object (key/value). Running this through a JSON parser will
> fail.
>
> By contrast, EXPLAIN (FORMAT JSON) on the command line produces:
>
> QUERY PLAN
> -----------------------------------
> [
> {
> "Plan": {
> "Node Type": "Seq Scan",
> "Relation Name": "pg_type",
> "Alias": "pg_type",
> "Startup Cost": 0.00,
> "Total Cost": 9.87,
> "Plan Rows": 287,
> "Plan Width": 611
> }
> }
> ]
> (1 row)
>

Yeah, looks like this dates back to when we first got JSON output.

Auto-explain does this:

ExplainBeginOutput(&es);
ExplainQueryText(&es, queryDesc);
ExplainPrintPlan(&es, queryDesc);
ExplainEndOutput(&es);

But ExplainBeginOutput says:

case EXPLAIN_FORMAT_JSON:
/* top-level structure is an array of plans */
appendStringInfoChar(es->str, '[');

Now that's not true in the auto-explain case, which prints one query +
one plan.

Since this is an exposed API, I don't think we can just change it. We
probably need a new API that does the right thing for beginning and
ending auto_explain output. (ExplainBeginLabeledOutput?)

cheers

andrew