Tweak the default behavior of psql's \dconfig.

\dconfig without an argument originally printed all parameters, but it seems more useful to print only those parameters with non-default settings. You can easily get the show-everything behavior with "\dconfig *", but that output is unwieldy and seems unlikely to be wanted very often. Per suggestion from Christoph Berg. Discussion: https://postgr.es/m/YlFQLzlPi4QD0wSi@msg.df7cb.de

Author: tglsfdc

doc/src/sgml/ref/psql-ref.sgml

@@ -129,7 +129,7 @@ echo '\x \\ SELECT * FROM foo;' | psql
  for more details about how the server handles multi-query strings.)
  </para>
  <para>
- If having several commands executed in one transaction is not desired, 
+ If having several commands executed in one transaction is not desired,
  use repeated <option>-c</option> commands or feed multiple commands to
  <application>psql</application>'s standard input,
  either using <application>echo</application> as illustrated above, or
@@ -1385,9 +1385,11 @@ testdb=&gt;
  <listitem>
  <para>
  Lists server configuration parameters and their values.
- If <replaceable class="parameter">pattern</replaceable>
- is specified, only parameters whose names match the pattern are
- listed.
+ If <replaceable class="parameter">pattern</replaceable> is specified,
+ only parameters whose names match the pattern are listed. Without
+ a <replaceable class="parameter">pattern</replaceable>, only
+ parameters that are set to non-default values are listed.
+ (Use <literal>\dconfig *</literal> to see all parameters.)
  If <literal>+</literal> is appended to the command name, each
  parameter is listed with its data type, context in which the
  parameter can be set, and access privileges (if non-default access

src/bin/psql/describe.c

@@ -4404,10 +4404,13 @@ describeConfigurationParameters(const char *pattern, bool verbose,
  " LEFT JOIN pg_catalog.pg_parameter_acl p\n"
  " ON pg_catalog.lower(s.name) = p.parname\n");
 
-processSQLNamePattern(pset.db, &buf, pattern,
- false, false,
- NULL, "pg_catalog.lower(s.name)", NULL,
- NULL);
+if (pattern)
+processSQLNamePattern(pset.db, &buf, pattern,
+ false, false,
+ NULL, "pg_catalog.lower(s.name)", NULL,
+ NULL);
+else
+appendPQExpBufferStr(&buf, "WHERE s.source <> 'default'\n");
 
 appendPQExpBufferStr(&buf, "ORDER BY 1;");
 
@@ -4417,7 +4420,10 @@ describeConfigurationParameters(const char *pattern, bool verbose,
 return false;
 
 myopt.nullPrint = NULL;
-myopt.title = _("List of configuration parameters");
+if (pattern)
+myopt.title = _("List of configuration parameters");
+else
+myopt.title = _("List of non-default configuration parameters");
 myopt.translate_header = true;
 
 printQuery(res, &myopt, pset.queryFout, false, pset.logfile);