repl_show_cmd_with_docs.patch

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 9ba147c..111f3b8 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1392,6 +1392,28 @@ The commands accepted in walsender mode are:
      </para>
     </listitem>
   </varlistentry>
+  <varlistentry>
+    <term><literal>SHOW</literal> <replaceable class="parameter">name</replaceable>
+     <indexterm><primary>SHOW</primary></indexterm>
+    </term>
+    <listitem>
+     <para>
+      Requests the server to send the current setting of a run-time parameter. If the passed argument is a valid configuration name, server will return its value. This is similar to the SQL command <xref linkend="sql-show">.
+     </para>
+
+     <variablelist>
+      <varlistentry>
+       <term><replaceable class="parameter">name</></term>
+       <listitem>
+         <para>
+          The name of a run-time parameter. Available parameters are documented
+          in <xref linkend="runtime-config">.
+         </para>
+       </listitem>
+      </varlistentry>
+     </variablelist>
+    </listitem>
+  </varlistentry>
 
   <varlistentry>
     <term><literal>TIMELINE_HISTORY</literal> <replaceable class="parameter">tli</replaceable>
diff --git a/src/backend/replication/repl_gram.y b/src/backend/replication/repl_gram.y
index d962c76..2348195 100644
--- a/src/backend/replication/repl_gram.y
+++ b/src/backend/replication/repl_gram.y
@@ -61,6 +61,7 @@ Node *replication_parse_result;
 /* Keyword tokens. */
 %token K_BASE_BACKUP
 %token K_IDENTIFY_SYSTEM
+%token K_SHOW
 %token K_START_REPLICATION
 %token K_CREATE_REPLICATION_SLOT
 %token K_DROP_REPLICATION_SLOT
@@ -82,7 +83,7 @@ Node *replication_parse_result;
 %type <node>	command
 %type <node>	base_backup start_replication start_logical_replication
 				create_replication_slot drop_replication_slot identify_system
-				timeline_history
+				timeline_history show
 %type <list>	base_backup_opt_list
 %type <defelt>	base_backup_opt
 %type <uintval>	opt_timeline
@@ -112,6 +113,7 @@ command:
 			| create_replication_slot
 			| drop_replication_slot
 			| timeline_history
+			| show
 			;
 
 /*
@@ -125,6 +127,18 @@ identify_system:
 			;
 
 /*
+ * SHOW setting
+ */
+show:
+			K_SHOW IDENT
+				{
+					ShowCmd *cmd = makeNode(ShowCmd);
+					cmd->arg = $2;
+					$$ = (Node *) cmd;
+				}
+			;
+
+/*
  * BASE_BACKUP [LABEL '<label>'] [PROGRESS] [FAST] [WAL] [NOWAIT]
  * [MAX_RATE %d] [TABLESPACE_MAP]
  */
diff --git a/src/backend/replication/repl_scanner.l b/src/backend/replication/repl_scanner.l
index a3b5f92..37f8579 100644
--- a/src/backend/replication/repl_scanner.l
+++ b/src/backend/replication/repl_scanner.l
@@ -83,6 +83,7 @@ identifier		{ident_start}{ident_cont}*
 BASE_BACKUP			{ return K_BASE_BACKUP; }
 FAST			{ return K_FAST; }
 IDENTIFY_SYSTEM		{ return K_IDENTIFY_SYSTEM; }
+SHOW		{ return K_SHOW; }
 LABEL			{ return K_LABEL; }
 NOWAIT			{ return K_NOWAIT; }
 PROGRESS			{ return K_PROGRESS; }
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index f3082c3..1d60d68 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -294,6 +294,46 @@ WalSndShutdown(void)
 }
 
 /*
+ * Handle SHOW command
+ */
+static void
+GetConfig(ShowCmd *cmd)
+{
+	StringInfoData buf;
+	const char *varname;
+	char	   *value;
+	Size		len;
+
+	/* Get the value and canonical spelling of arg */
+	value = GetConfigOptionByName(cmd->arg, &varname, false);
+
+	/* Send a RowDescription message */
+	pq_beginmessage(&buf, 'T');
+	pq_sendint(&buf, 1, 2);		/* 1 field */
+
+	/* first field */
+	pq_sendstring(&buf, varname);		/* col name */
+	pq_sendint(&buf, 0, 4);		/* table oid */
+	pq_sendint(&buf, 0, 2);		/* attnum */
+	pq_sendint(&buf, TEXTOID, 4);		/* type oid */
+	pq_sendint(&buf, -1, 2);	/* typlen */
+	pq_sendint(&buf, 0, 4);		/* typmod */
+	pq_sendint(&buf, 0, 2);		/* format code */
+	pq_endmessage(&buf);
+
+	/* Send a DataRow message */
+	pq_beginmessage(&buf, 'D');
+	pq_sendint(&buf, 1, 2);		/* # of columns */
+
+	/* column 1: Wal segment size */
+	len = strlen(value);
+	pq_sendint(&buf, len, 4);
+	pq_sendbytes(&buf, value, len);
+
+	pq_endmessage(&buf);
+}
+
+/*
  * Handle the IDENTIFY_SYSTEM command.
  */
 static void
@@ -1338,6 +1378,10 @@ exec_replication_command(const char *cmd_string)
 			IdentifySystem();
 			break;
 
+		case T_ShowCmd:
+			GetConfig((ShowCmd *) cmd_node);
+			break;
+
 		case T_BaseBackupCmd:
 			SendBaseBackup((BaseBackupCmd *) cmd_node);
 			break;
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index a1bb0ac..9709cff 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -464,6 +464,7 @@ typedef enum NodeTag
 	 * TAGS FOR REPLICATION GRAMMAR PARSE NODES (replnodes.h)
 	 */
 	T_IdentifySystemCmd,
+	T_ShowCmd,
 	T_BaseBackupCmd,
 	T_CreateReplicationSlotCmd,
 	T_DropReplicationSlotCmd,
diff --git a/src/include/nodes/replnodes.h b/src/include/nodes/replnodes.h
index f27354f..0e5646a 100644
--- a/src/include/nodes/replnodes.h
+++ b/src/include/nodes/replnodes.h
@@ -33,6 +33,16 @@ typedef struct IdentifySystemCmd
 	NodeTag		type;
 } IdentifySystemCmd;
 
+/* ---------------------------
+ *		SHOW command
+ * ---------------------------
+ */
+typedef struct ShowCmd
+{
+	NodeTag		type;
+	char	   *arg;
+}	ShowCmd;
+
 
 /* ----------------------
  *		BASE_BACKUP command