Re: Allow escape in application_name

On 2021/09/08 21:32, kuroda(dot)hayato(at)fujitsu(dot)com wrote:
> Dear Horiguchi-san,
>
> Thank you for reviewing! I attached the fixed version.

Thanks for updating the patch!

+ for (i = n - 1; i >= 0; i--)
+ {
+ if (strcmp(keywords[i], "application_name") == 0)
+ {
+ parse_pgfdw_appname(&buf, values[i]);
+ values[i] = buf.data;
+ break;
+ }

postgres_fdw gets out of the loop after processing appname even
when buf.data is '\0'. Is this expected behavior? Because of this,
when postgres_fdw.application_name = '%b', unprocessed appname
of the server object is used.

+CREATE FUNCTION for_escapes() RETURNS bool AS $$
+ DECLARE
+ appname text;
+ c bool;
+ BEGIN
+ SHOW application_name INTO appname;
+ EXECUTE 'SELECT COUNT(*) FROM pg_stat_activity WHERE application_name LIKE '''

Could you tell me why the statement checking
application_name should be wrapped in a function?
Instead, we can just execute something like the following?

SELECT COUNT(*) FROM pg_stat_activity WHERE application_name = current_setting('application_name') || current_user || current_database() || pg_backend_pid() || '%';

+ char *endptr = NULL;
+ padding = (int)strtol(p, &endptr, 10);

strtol() seems to work differently from process_log_prefix_padding(),
for example, when the input string is "%-p".

+ case 'a':
+ {
+ const char *appname = application_name;

When log_line_prefix() processes "%a", "%u" or "%d" characters in
log_line_prefix, it checks whether MyProcPort is NULL or not.
Likewise shouldn't parse_pgfdw_appname() do the same thing?
For now it's ok not to check that because only process having
MyProcPort can use postgres_fdw. But in the future the process
not having that may use postgres_fdw, for example, 2PC resolver
process that Sawada-san is proposing to add to support automatic
2PC among multiple remote servers.

+ You can use escape sequences for <literal>application_name</literal> even if
+ it is set as a connection or a user mapping option.
+ Please refer the later section.

I was thinking that application_name cannot be set in a user mapping.

Regards,

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