Revert idea of zer-padding padding session id in log_line_prefix

Removal of doc adjustment and release note mention as well.

doc/src/sgml/config.sgml

@@ -4089,14 +4089,14 @@ local0.*    /var/log/postgresql
          </informaltable>
 
          The <literal>%c</> escape prints a quasi-unique session identifier,
-         consisting of two 4-byte hexadecimal numbers separated by a dot.
-         The numbers are the process start time and the
+         consisting of two 4-byte hexadecimal numbers (without leading zeros)
+         separated by a dot.  The numbers are the process start time and the
          process ID, so <literal>%c</> can also be used as a space saving way
          of printing those items.  For example, to generate the session
          identifier from <literal>pg_stat_activity</>, use this query:
 <programlisting>
 SELECT to_hex(EXTRACT(EPOCH FROM backend_start)::integer) || '.' ||
-       regexp_replace('0000' || '0133e3', '^0*(.{4,})$', '\1')
+       to_hex(pid)
 FROM pg_stat_activity;
 </programlisting>
 

doc/src/sgml/release-9.3.sgml

@@ -78,14 +78,6 @@
        </para>
       </listitem>
 
-      <listitem>
-       <para>
-        Have <quote>session id</> (<literal>%c</>) in <link
-        linkend="guc-log-line-prefix"><varname>log_line_prefix</></link>
-        always output at least four hex digits after the period (Bruce Momjian)
-       </para>
-      </listitem>
-
      </itemizedlist>
 
    </sect3>

src/backend/utils/error/elog.c

@@ -2087,7 +2087,7 @@ log_line_prefix(StringInfo buf, ErrorData *edata)
 				}
 				break;
 			case 'c':
-				appendStringInfo(buf, "%lx.%04x", (long) (MyStartTime), MyProcPid);
+				appendStringInfo(buf, "%lx.%x", (long) (MyStartTime), MyProcPid);
 				break;
 			case 'p':
 				appendStringInfo(buf, "%d", MyProcPid);
@@ -2266,7 +2266,7 @@ write_csvlog(ErrorData *edata)
 	appendStringInfoChar(&buf, ',');
 
 	/* session id */
-	appendStringInfo(&buf, "%lx.%04x", (long) MyStartTime, MyProcPid);
+	appendStringInfo(&buf, "%lx.%x", (long) MyStartTime, MyProcPid);
 	appendStringInfoChar(&buf, ',');
 
 	/* Line number */