Subject: Re: Allow escape in application_name (was: [postgres_fdw] add local
 pid to fallback_application_name)
To: "kuroda.hayato@fujitsu.com" <kuroda.hayato@fujitsu.com>
Cc: "'pgsql-hackers@lists.postgresql.org'"
 <pgsql-hackers@lists.postgresql.org>, 'Tom Lane' <tgl@sss.pgh.pa.us>
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From: Fujii Masao <masao.fujii@oss.nttdata.com>
Message-ID: <0d5df322-c9ad-308e-982b-a3d3275bcdc0@oss.nttdata.com>
Date: Thu, 2 Sep 2021 00:40:48 +0900
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On 2021/09/01 19:04, kuroda.hayato@fujitsu.com wrote:
> OK, I split and attached like that. 0001 adds new GUC, and
> 0002 allows to accept escapes.

Thanks for splitting and updating the patches!

Here are the comments for 0001 patch.

-		/* Use "postgres_fdw" as fallback_application_name. */
+		/* Use GUC paramter if set */
+		if (pgfdw_application_name && *pgfdw_application_name != '\0')

This GUC parameter should be set after the options of foreign server
are set so that its setting can override the server-level ones.
Isn't it better to comment this?


+static bool
+check_pgfdw_application_name(char **newval, void **extra, GucSource source)
+{
+	/* Only allow clean ASCII chars in the application name */
+	if (*newval)
+		pg_clean_ascii(*newval);
+	return true;

Do we really need this check hook? Even without that, any non-ASCII characters
in application_name would be replaced with "?" in the foreign PostgreSQL server
when it's passed to that.

On the other hand, if it's really necessary, application_name set in foreign
server object also needs to be processed in the same way.


+							   NULL,
+							   PGC_USERSET,
+							   GUC_IS_NAME,

Why is GUC_IS_NAME flag necessary?


postgres_fdw.application_name overrides application_name set in foreign server object.
Shouldn't this information be documented?


Isn't it better to have the regression test for this feature?

Regards,


-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION