export FUNC_MAX_ARGS as a read-only GUC variable (was: [GENERAL] SELECT Question)

[Joe Conway <mail(at)joeconway(dot)com>]

Tom Lane wrote:
> I was thinking of proposing that we provide something just about like
> that as a standard function (written in C, not in plpgsql, so that it
> would be available whether or not you'd installed plpgsql).  There are
> some places in the information_schema that desperately need it ---
> right now, the value of FUNC_MAX_ARGS is effectively hard-wired into
> some of the information_schema views, which means they are broken if
> one changes that #define.  We could fix this if we had a function like
> the above and exported FUNC_MAX_ARGS as a read-only GUC variable.

First installment. The attached exports FUNC_MAX_ARGS as a read-only GUC 
variable -- func_max_args. Comments?

While I was in guc.c, I also added short_desc to the definition of the 
pg_settings view. I wasn't sure if I ought to add the long_desc too, and 
if so, should it be it's own column in the view, or be concatenated with 
short_desc -- any thoughts on that?

Current output looks like this:

regression=# \x
Expanded display is on.
regression=# select * from pg_settings where name = 'func_max_args';
-[ RECORD 1 ]-----------------------------------------------------------
name       | func_max_args
setting    | 32
short_desc | Shows the compiled-in maximum number of function arguments.
context    | internal
vartype    | integer
source     | default
min_val    | 32
max_val    | 32

This will require a catalog version bump when I apply it (not done in 
the attached patch).

Joe

Index: src/backend/catalog/system_views.sql
===================================================================
RCS file: /cvsroot/pgsql-server/src/backend/catalog/system_views.sql,v
retrieving revision 1.3
diff -c -r1.3 system_views.sql
*** src/backend/catalog/system_views.sql	29 Nov 2003 22:39:40 -0000	1.3
--- src/backend/catalog/system_views.sql	30 Nov 2003 04:58:51 -0000
***************
*** 260,266 ****
  CREATE VIEW pg_settings AS 
      SELECT * 
      FROM pg_show_all_settings() AS A 
!     (name text, setting text, context text, vartype text, 
       source text, min_val text, max_val text);
  
  CREATE RULE pg_settings_u AS 
--- 260,266 ----
  CREATE VIEW pg_settings AS 
      SELECT * 
      FROM pg_show_all_settings() AS A 
!     (name text, setting text, short_desc text, context text, vartype text, 
       source text, min_val text, max_val text);
  
  CREATE RULE pg_settings_u AS 
Index: src/backend/utils/misc/guc.c
===================================================================
RCS file: /cvsroot/pgsql-server/src/backend/utils/misc/guc.c,v
retrieving revision 1.172
diff -c -r1.172 guc.c
*** src/backend/utils/misc/guc.c	29 Nov 2003 19:52:03 -0000	1.172
--- src/backend/utils/misc/guc.c	30 Nov 2003 04:58:52 -0000
***************
*** 156,161 ****
--- 156,162 ----
  static char *session_authorization_string;
  static char *timezone_string;
  static char *XactIsoLevel_string;
+ static int	func_max_args;
  
  
  /* Macros for freeing malloc'd pointers only if appropriate to do so */
***************
*** 862,867 ****
--- 863,878 ----
  		8, 1, INT_MAX, NULL, NULL
  	},
  	{
+ 		/* Can't be set in postgresql.conf */
+ 		{"func_max_args", PGC_INTERNAL, UNGROUPED,
+ 			gettext_noop("Shows the compiled-in maximum number of function "
+ 						 "arguments."),
+ 			NULL
+ 		},
+ 		&func_max_args,
+ 		FUNC_MAX_ARGS, FUNC_MAX_ARGS, FUNC_MAX_ARGS, NULL, NULL
+ 	},
+ 	{
  		{"join_collapse_limit", PGC_USERSET, QUERY_TUNING_OTHER,
  			gettext_noop("Sets the FROM-list size beyond which JOIN constructs are not "
  						 "flattened."),
***************
*** 3468,3481 ****
  	/* setting : use _ShowOption in order to avoid duplicating the logic */
  	values[1] = _ShowOption(conf);
  
  	/* context */
! 	values[2] = GucContext_Names[conf->context];
  
  	/* vartype */
! 	values[3] = config_type_names[conf->vartype];
  
  	/* source */
! 	values[4] = GucSource_Names[conf->source];
  
  	/* now get the type specifc attributes */
  	switch (conf->vartype)
--- 3479,3495 ----
  	/* setting : use _ShowOption in order to avoid duplicating the logic */
  	values[1] = _ShowOption(conf);
  
+ 	/* short_desc */
+ 	values[2] = conf->short_desc;
+ 
  	/* context */
! 	values[3] = GucContext_Names[conf->context];
  
  	/* vartype */
! 	values[4] = config_type_names[conf->vartype];
  
  	/* source */
! 	values[5] = GucSource_Names[conf->source];
  
  	/* now get the type specifc attributes */
  	switch (conf->vartype)
***************
*** 3483,3492 ****
  		case PGC_BOOL:
  			{
  				/* min_val */
! 				values[5] = NULL;
  
  				/* max_val */
! 				values[6] = NULL;
  			}
  			break;
  
--- 3497,3506 ----
  		case PGC_BOOL:
  			{
  				/* min_val */
! 				values[6] = NULL;
  
  				/* max_val */
! 				values[7] = NULL;
  			}
  			break;
  
***************
*** 3496,3506 ****
  
  				/* min_val */
  				snprintf(buffer, sizeof(buffer), "%d", lconf->min);
! 				values[5] = pstrdup(buffer);
  
  				/* max_val */
  				snprintf(buffer, sizeof(buffer), "%d", lconf->max);
! 				values[6] = pstrdup(buffer);
  			}
  			break;
  
--- 3510,3520 ----
  
  				/* min_val */
  				snprintf(buffer, sizeof(buffer), "%d", lconf->min);
! 				values[6] = pstrdup(buffer);
  
  				/* max_val */
  				snprintf(buffer, sizeof(buffer), "%d", lconf->max);
! 				values[7] = pstrdup(buffer);
  			}
  			break;
  
***************
*** 3510,3530 ****
  
  				/* min_val */
  				snprintf(buffer, sizeof(buffer), "%g", lconf->min);
! 				values[5] = pstrdup(buffer);
  
  				/* max_val */
  				snprintf(buffer, sizeof(buffer), "%g", lconf->max);
! 				values[6] = pstrdup(buffer);
  			}
  			break;
  
  		case PGC_STRING:
  			{
  				/* min_val */
! 				values[5] = NULL;
  
  				/* max_val */
! 				values[6] = NULL;
  			}
  			break;
  
--- 3524,3544 ----
  
  				/* min_val */
  				snprintf(buffer, sizeof(buffer), "%g", lconf->min);
! 				values[6] = pstrdup(buffer);
  
  				/* max_val */
  				snprintf(buffer, sizeof(buffer), "%g", lconf->max);
! 				values[7] = pstrdup(buffer);
  			}
  			break;
  
  		case PGC_STRING:
  			{
  				/* min_val */
! 				values[6] = NULL;
  
  				/* max_val */
! 				values[7] = NULL;
  			}
  			break;
  
***************
*** 3536,3545 ****
  				 */
  
  				/* min_val */
! 				values[5] = NULL;
  
  				/* max_val */
! 				values[6] = NULL;
  			}
  			break;
  	}
--- 3550,3559 ----
  				 */
  
  				/* min_val */
! 				values[6] = NULL;
  
  				/* max_val */
! 				values[7] = NULL;
  			}
  			break;
  	}
***************
*** 3582,3588 ****
   * show_all_settings - equiv to SHOW ALL command but implemented as
   * a Table Function.
   */
! #define NUM_PG_SETTINGS_ATTS	7
  
  Datum
  show_all_settings(PG_FUNCTION_ARGS)
--- 3596,3602 ----
   * show_all_settings - equiv to SHOW ALL command but implemented as
   * a Table Function.
   */
! #define NUM_PG_SETTINGS_ATTS	8
  
  Datum
  show_all_settings(PG_FUNCTION_ARGS)
***************
*** 3616,3630 ****
  						   TEXTOID, -1, 0, false);
  		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "setting",
  						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 3, "context",
  						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 4, "vartype",
  						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 5, "source",
  						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 6, "min_val",
  						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 7, "max_val",
  						   TEXTOID, -1, 0, false);
  
  		/* allocate a slot for a tuple with this tupdesc */
--- 3630,3646 ----
  						   TEXTOID, -1, 0, false);
  		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "setting",
  						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 3, "short_desc",
! 						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 4, "context",
  						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 5, "vartype",
  						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 6, "source",
  						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 7, "min_val",
  						   TEXTOID, -1, 0, false);
! 		TupleDescInitEntry(tupdesc, (AttrNumber) 8, "max_val",
  						   TEXTOID, -1, 0, false);
  
  		/* allocate a slot for a tuple with this tupdesc */
Index: src/test/regress/expected/rules.out
===================================================================
RCS file: /cvsroot/pgsql-server/src/test/regress/expected/rules.out,v
retrieving revision 1.82
diff -c -r1.82 rules.out
*** src/test/regress/expected/rules.out	21 Nov 2003 22:32:49 -0000	1.82
--- src/test/regress/expected/rules.out	30 Nov 2003 04:58:53 -0000
***************
*** 1278,1284 ****
   pg_indexes               | SELECT n.nspname AS schemaname, c.relname AS tablename, i.relname AS indexname, pg_get_indexdef(i.oid) AS indexdef FROM (((pg_index x JOIN pg_class c ON ((c.oid = x.indrelid))) JOIN pg_class i ON ((i.oid = x.indexrelid))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE ((c.relkind = 'r'::"char") AND (i.relkind = 'i'::"char"));
   pg_locks                 | SELECT l.relation, l."database", l."transaction", l.pid, l."mode", l.granted FROM pg_lock_status() l(relation oid, "database" oid, "transaction" xid, pid integer, "mode" text, granted boolean);
   pg_rules                 | SELECT n.nspname AS schemaname, c.relname AS tablename, r.rulename, pg_get_ruledef(r.oid) AS definition FROM ((pg_rewrite r JOIN pg_class c ON ((c.oid = r.ev_class))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE (r.rulename <> '_RETURN'::name);
!  pg_settings              | SELECT a.name, a.setting, a.context, a.vartype, a.source, a.min_val, a.max_val FROM pg_show_all_settings() a(name text, setting text, context text, vartype text, source text, min_val text, max_val text);
   pg_stat_activity         | SELECT d.oid AS datid, d.datname, pg_stat_get_backend_pid(s.backendid) AS procpid, pg_stat_get_backend_userid(s.backendid) AS usesysid, u.usename, pg_stat_get_backend_activity(s.backendid) AS current_query, pg_stat_get_backend_activity_start(s.backendid) AS query_start FROM pg_database d, (SELECT pg_stat_get_backend_idset() AS backendid) s, pg_shadow u WHERE ((pg_stat_get_backend_dbid(s.backendid) = d.oid) AND (pg_stat_get_backend_userid(s.backendid) = u.usesysid));
   pg_stat_all_indexes      | SELECT c.oid AS relid, i.oid AS indexrelid, n.nspname AS schemaname, c.relname, i.relname AS indexrelname, pg_stat_get_numscans(i.oid) AS idx_scan, pg_stat_get_tuples_returned(i.oid) AS idx_tup_read, pg_stat_get_tuples_fetched(i.oid) AS idx_tup_fetch FROM (((pg_class c JOIN pg_index x ON ((c.oid = x.indrelid))) JOIN pg_class i ON ((i.oid = x.indexrelid))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE (c.relkind = 'r'::"char");
   pg_stat_all_tables       | SELECT c.oid AS relid, n.nspname AS schemaname, c.relname, pg_stat_get_numscans(c.oid) AS seq_scan, pg_stat_get_tuples_returned(c.oid) AS seq_tup_read, sum(pg_stat_get_numscans(i.indexrelid)) AS idx_scan, sum(pg_stat_get_tuples_fetched(i.indexrelid)) AS idx_tup_fetch, pg_stat_get_tuples_inserted(c.oid) AS n_tup_ins, pg_stat_get_tuples_updated(c.oid) AS n_tup_upd, pg_stat_get_tuples_deleted(c.oid) AS n_tup_del FROM ((pg_class c LEFT JOIN pg_index i ON ((c.oid = i.indrelid))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE (c.relkind = 'r'::"char") GROUP BY c.oid, n.nspname, c.relname;
--- 1278,1284 ----
   pg_indexes               | SELECT n.nspname AS schemaname, c.relname AS tablename, i.relname AS indexname, pg_get_indexdef(i.oid) AS indexdef FROM (((pg_index x JOIN pg_class c ON ((c.oid = x.indrelid))) JOIN pg_class i ON ((i.oid = x.indexrelid))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE ((c.relkind = 'r'::"char") AND (i.relkind = 'i'::"char"));
   pg_locks                 | SELECT l.relation, l."database", l."transaction", l.pid, l."mode", l.granted FROM pg_lock_status() l(relation oid, "database" oid, "transaction" xid, pid integer, "mode" text, granted boolean);
   pg_rules                 | SELECT n.nspname AS schemaname, c.relname AS tablename, r.rulename, pg_get_ruledef(r.oid) AS definition FROM ((pg_rewrite r JOIN pg_class c ON ((c.oid = r.ev_class))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE (r.rulename <> '_RETURN'::name);
!  pg_settings              | SELECT a.name, a.setting, a.short_desc, a.context, a.vartype, a.source, a.min_val, a.max_val FROM pg_show_all_settings() a(name text, setting text, short_desc text, context text, vartype text, source text, min_val text, max_val text);
   pg_stat_activity         | SELECT d.oid AS datid, d.datname, pg_stat_get_backend_pid(s.backendid) AS procpid, pg_stat_get_backend_userid(s.backendid) AS usesysid, u.usename, pg_stat_get_backend_activity(s.backendid) AS current_query, pg_stat_get_backend_activity_start(s.backendid) AS query_start FROM pg_database d, (SELECT pg_stat_get_backend_idset() AS backendid) s, pg_shadow u WHERE ((pg_stat_get_backend_dbid(s.backendid) = d.oid) AND (pg_stat_get_backend_userid(s.backendid) = u.usesysid));
   pg_stat_all_indexes      | SELECT c.oid AS relid, i.oid AS indexrelid, n.nspname AS schemaname, c.relname, i.relname AS indexrelname, pg_stat_get_numscans(i.oid) AS idx_scan, pg_stat_get_tuples_returned(i.oid) AS idx_tup_read, pg_stat_get_tuples_fetched(i.oid) AS idx_tup_fetch FROM (((pg_class c JOIN pg_index x ON ((c.oid = x.indrelid))) JOIN pg_class i ON ((i.oid = x.indexrelid))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE (c.relkind = 'r'::"char");
   pg_stat_all_tables       | SELECT c.oid AS relid, n.nspname AS schemaname, c.relname, pg_stat_get_numscans(c.oid) AS seq_scan, pg_stat_get_tuples_returned(c.oid) AS seq_tup_read, sum(pg_stat_get_numscans(i.indexrelid)) AS idx_scan, sum(pg_stat_get_tuples_fetched(i.indexrelid)) AS idx_tup_fetch, pg_stat_get_tuples_inserted(c.oid) AS n_tup_ins, pg_stat_get_tuples_updated(c.oid) AS n_tup_upd, pg_stat_get_tuples_deleted(c.oid) AS n_tup_del FROM ((pg_class c LEFT JOIN pg_index i ON ((c.oid = i.indrelid))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE (c.relkind = 'r'::"char") GROUP BY c.oid, n.nspname, c.relname;