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postgres_fdw: Allow application_name of remote connection to be set via GUC.

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This commit adds postgres_fdw.application_name GUC which specifies
a value for application_name configuration parameter used
when postgres_fdw establishes a connection to a foreign server.
This GUC setting always overrides application_name option of
the foreign server object. This GUC is useful when we want to
specify our own application_name per remote connection.

Previously application_name of a remote connection could be set
basically only via options of a server object. But which meant that
every session connecting to the same foreign server basically
should use the same application_name. Also if we want to change
the setting, we had to execute "ALTER SERVER ... OPTIONS ..." command.
It was inconvenient.

Author: Hayato Kuroda
Reviewed-by: Masahiro Ikeda, Fujii Masao
Discussion: https://postgr.es/m/TYCPR01MB5870D1E8B949DAF6D3B84E02F5F29@TYCPR01MB5870.jpnprd01.prod.outlook.com
This commit is contained in:
Fujii Masao
2021-09-07 12:27:30 +09:00
parent 4c3478859b
commit 449ab63505
6 changed files with 199 additions and 5 deletions
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25
contrib/postgres_fdw/connection.c
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@ -353,10 +353,11 @@ connect_pg_server(ForeignServer *server, UserMapping *user)
/*
* Construct connection params from generic options of ForeignServer
* and UserMapping. (Some of them might not be libpq options, in
* which case we'll just waste a few array slots.) Add 3 extra slots
* for fallback_application_name, client_encoding, end marker.
* which case we'll just waste a few array slots.) Add 4 extra slots
* for application_name, fallback_application_name, client_encoding,
* end marker.
*/
n = list_length(server->options) + list_length(user->options) + 3;
n = list_length(server->options) + list_length(user->options) + 4;
keywords = (const char **) palloc(n * sizeof(char *));
values = (const char **) palloc(n * sizeof(char *));
@ -366,7 +367,23 @@ connect_pg_server(ForeignServer *server, UserMapping *user)
n += ExtractConnectionOptions(user->options,
keywords + n, values + n);
/* Use "postgres_fdw" as fallback_application_name. */
/*
* Use pgfdw_application_name as application_name if set.
*
* PQconnectdbParams() processes the parameter arrays from start to
* end. If any key word is repeated, the last value is used. Therefore
* note that pgfdw_application_name must be added to the arrays after
* options of ForeignServer are, so that it can override
* application_name set in ForeignServer.
*/
if (pgfdw_application_name && *pgfdw_application_name != '\0')
{
keywords[n] = "application_name";
values[n] = pgfdw_application_name;
n++;
}
/* Use "postgres_fdw" as fallback_application_name */
keywords[n] = "fallback_application_name";
values[n] = "postgres_fdw";
n++;