ALTER SUBSCRIPTION ... ADD/DROP PUBLICATION

At present, if we want to update publications in a subscription, we
can use SET PUBLICATION.  However, it requires supplying all
publications that exists and the new publications.  If we want to add
new publications, it's inconvenient.  The new syntax only supplies the
new publications.  When the refresh is true, it only refreshes the new
publications.

Author: Japin Li <japinli@hotmail.com>
Author: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/MEYP282MB166939D0D6C480B7FBE7EFFBB6BC0@MEYP282MB1669.AUSP282.PROD.OUTLOOK.COM

doc/src/sgml/ref/alter_subscription.sgml

@@ -23,6 +23,8 @@ PostgreSQL documentation
 <synopsis>
 ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> CONNECTION '<replaceable>conninfo</replaceable>'
 ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> SET PUBLICATION <replaceable class="parameter">publication_name</replaceable> [, ...] [ WITH ( <replaceable class="parameter">set_publication_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
+ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> ADD PUBLICATION <replaceable class="parameter">publication_name</replaceable> [, ...] [ WITH ( <replaceable class="parameter">set_publication_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
+ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> DROP PUBLICATION <replaceable class="parameter">publication_name</replaceable> [, ...] [ WITH ( <replaceable class="parameter">set_publication_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
 ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> REFRESH PUBLICATION [ WITH ( <replaceable class="parameter">refresh_option</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
 ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> ENABLE
 ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> DISABLE
@@ -63,7 +65,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command> and
-   <command>ALTER SUBSCRIPTION ... SET PUBLICATION ...</command> with refresh
+   <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command> with refresh
    option as true cannot be executed inside a transaction block.
   </para>
  </refsect1>
@@ -94,12 +96,19 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
    <varlistentry>
     <term><literal>SET PUBLICATION <replaceable class="parameter">publication_name</replaceable></literal></term>
+    <term><literal>ADD PUBLICATION <replaceable class="parameter">publication_name</replaceable></literal></term>
+    <term><literal>DROP PUBLICATION <replaceable class="parameter">publication_name</replaceable></literal></term>
     <listitem>
      <para>
-      Changes list of subscribed publications. See
-      <xref linkend="sql-createsubscription"/> for more information.
-      By default this command will also act like <literal>REFRESH
-      PUBLICATION</literal>.
+      Changes the list of subscribed publications.  <literal>SET</literal>
+      replaces the entire list of publications with a new list,
+      <literal>ADD</literal> adds additional publications,
+      <literal>DROP</literal> removes publications from the list of
+      publications.  See <xref linkend="sql-createsubscription"/> for more
+      information.  By default, this command will also act like
+      <literal>REFRESH PUBLICATION</literal>, except that in case of
+      <literal>ADD</literal> or <literal>DROP</literal>, only the added or
+      dropped publications are refreshed.
      </para>
 
      <para>

src/backend/commands/subscriptioncmds.c

@@ -47,6 +47,8 @@
 #include "utils/syscache.h"
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
+static void check_duplicates_in_publist(List *publist, Datum *datums);
+static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
 
 
@@ -293,8 +295,6 @@ publicationListToArray(List *publist)
 {
 	ArrayType  *arr;
 	Datum	   *datums;
-	int			j = 0;
-	ListCell   *cell;
 	MemoryContext memcxt;
 	MemoryContext oldcxt;
 
@@ -306,28 +306,7 @@ publicationListToArray(List *publist)
 
 	datums = (Datum *) palloc(sizeof(Datum) * list_length(publist));
 
-	foreach(cell, publist)
-	{
-		char	   *name = strVal(lfirst(cell));
-		ListCell   *pcell;
-
-		/* Check for duplicates. */
-		foreach(pcell, publist)
-		{
-			char	   *pname = strVal(lfirst(pcell));
-
-			if (pcell == cell)
-				break;
-
-			if (strcmp(name, pname) == 0)
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("publication name \"%s\" used more than once",
-								pname)));
-		}
-
-		datums[j++] = CStringGetTextDatum(name);
-	}
+	check_duplicates_in_publist(publist, datums);
 
 	MemoryContextSwitchTo(oldcxt);
 
@@ -923,7 +902,7 @@ AlterSubscription(AlterSubscriptionStmt *stmt, bool isTopLevel)
 			update_tuple = true;
 			break;
 
-		case ALTER_SUBSCRIPTION_PUBLICATION:
+		case ALTER_SUBSCRIPTION_SET_PUBLICATION:
 			{
 				bool		copy_data;
 				bool		refresh;
@@ -964,6 +943,54 @@ AlterSubscription(AlterSubscriptionStmt *stmt, bool isTopLevel)
 				break;
 			}
 
+		case ALTER_SUBSCRIPTION_ADD_PUBLICATION:
+		case ALTER_SUBSCRIPTION_DROP_PUBLICATION:
+			{
+				bool		isadd = stmt->kind == ALTER_SUBSCRIPTION_ADD_PUBLICATION;
+				bool		copy_data;
+				bool		refresh;
+				List	   *publist;
+
+				publist = merge_publications(sub->publications, stmt->publication, isadd, stmt->subname);
+
+				parse_subscription_options(stmt->options,
+										   NULL,	/* no "connect" */
+										   NULL, NULL,	/* no "enabled" */
+										   NULL,	/* no "create_slot" */
+										   NULL, NULL,	/* no "slot_name" */
+										   isadd ? &copy_data : NULL,	/* for drop, no
+																		 * "copy_data" */
+										   NULL,	/* no "synchronous_commit" */
+										   &refresh,
+										   NULL, NULL,	/* no "binary" */
+										   NULL, NULL); /* no "streaming" */
+
+				values[Anum_pg_subscription_subpublications - 1] =
+					publicationListToArray(publist);
+				replaces[Anum_pg_subscription_subpublications - 1] = true;
+
+				update_tuple = true;
+
+				/* Refresh if user asked us to. */
+				if (refresh)
+				{
+					if (!sub->enabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_SYNTAX_ERROR),
+								 errmsg("ALTER SUBSCRIPTION with refresh is not allowed for disabled subscriptions"),
+								 errhint("Use ALTER SUBSCRIPTION ... SET PUBLICATION ... WITH (refresh = false).")));
+
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION with refresh");
+
+					/* Only refresh the added/dropped list of publications. */
+					sub->publications = stmt->publication;
+
+					AlterSubscription_refresh(sub, copy_data);
+				}
+
+				break;
+			}
+
 		case ALTER_SUBSCRIPTION_REFRESH:
 			{
 				bool		copy_data;
@@ -1548,3 +1575,103 @@ ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err)
 			 errhint("Use %s to disassociate the subscription from the slot.",
 					 "ALTER SUBSCRIPTION ... SET (slot_name = NONE)")));
 }
+
+/*
+ * Check for duplicates in the given list of publications and error out if
+ * found one.  Add publications to datums as text datums, if datums is not
+ * NULL.
+ */
+static void
+check_duplicates_in_publist(List *publist, Datum *datums)
+{
+	ListCell   *cell;
+	int			j = 0;
+
+	foreach(cell, publist)
+	{
+		char	   *name = strVal(lfirst(cell));
+		ListCell   *pcell;
+
+		foreach(pcell, publist)
+		{
+			char	   *pname = strVal(lfirst(pcell));
+
+			if (pcell == cell)
+				break;
+
+			if (strcmp(name, pname) == 0)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("publication name \"%s\" used more than once",
+								pname)));
+		}
+
+		if (datums)
+			datums[j++] = CStringGetTextDatum(name);
+	}
+}
+
+/*
+ * Merge current subscription's publications and user-specified publications
+ * from ADD/DROP PUBLICATIONS.
+ *
+ * If addpub is true, we will add the list of publications into oldpublist.
+ * Otherwise, we will delete the list of publications from oldpublist.  The
+ * returned list is a copy, oldpublist itself is not changed.
+ *
+ * subname is the subscription name, for error messages.
+ */
+static List *
+merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname)
+{
+	ListCell   *lc;
+
+	oldpublist = list_copy(oldpublist);
+
+	check_duplicates_in_publist(newpublist, NULL);
+
+	foreach(lc, newpublist)
+	{
+		char	   *name = strVal(lfirst(lc));
+		ListCell   *lc2;
+		bool		found = false;
+
+		foreach(lc2, oldpublist)
+		{
+			char	   *pubname = strVal(lfirst(lc2));
+
+			if (strcmp(name, pubname) == 0)
+			{
+				found = true;
+				if (addpub)
+					ereport(ERROR,
+							(errcode(ERRCODE_DUPLICATE_OBJECT),
+							 errmsg("publication \"%s\" is already in subscription \"%s\"",
+									name, subname)));
+				else
+					oldpublist = foreach_delete_current(oldpublist, lc2);
+
+				break;
+			}
+		}
+
+		if (addpub && !found)
+			oldpublist = lappend(oldpublist, makeString(name));
+		else if (!addpub && !found)
+			ereport(ERROR,
+					(errcode(ERRCODE_SYNTAX_ERROR),
+					 errmsg("publication \"%s\" is not in subscription \"%s\"",
+							name, subname)));
+	}
+
+	/*
+	 * XXX Probably no strong reason for this, but for now it's to make ALTER
+	 * SUBSCRIPTION ... DROP PUBLICATION consistent with SET PUBLICATION.
+	 */
+	if (!oldpublist)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("subscription must contain at least one publication")));
+
+	return oldpublist;
+}

src/backend/parser/gram.y

@@ -9687,11 +9687,31 @@ AlterSubscriptionStmt:
 					n->options = $6;
 					$$ = (Node *)n;
 				}
+			| ALTER SUBSCRIPTION name ADD_P PUBLICATION name_list opt_definition
+				{
+					AlterSubscriptionStmt *n =
+						makeNode(AlterSubscriptionStmt);
+					n->kind = ALTER_SUBSCRIPTION_ADD_PUBLICATION;
+					n->subname = $3;
+					n->publication = $6;
+					n->options = $7;
+					$$ = (Node *)n;
+				}
+			| ALTER SUBSCRIPTION name DROP PUBLICATION name_list opt_definition
+				{
+					AlterSubscriptionStmt *n =
+						makeNode(AlterSubscriptionStmt);
+					n->kind = ALTER_SUBSCRIPTION_DROP_PUBLICATION;
+					n->subname = $3;
+					n->publication = $6;
+					n->options = $7;
+					$$ = (Node *)n;
+				}
 			| ALTER SUBSCRIPTION name SET PUBLICATION name_list opt_definition
 				{
 					AlterSubscriptionStmt *n =
 						makeNode(AlterSubscriptionStmt);
-					n->kind = ALTER_SUBSCRIPTION_PUBLICATION;
+					n->kind = ALTER_SUBSCRIPTION_SET_PUBLICATION;
 					n->subname = $3;
 					n->publication = $6;
 					n->options = $7;

src/bin/psql/tab-complete.c

@@ -1652,7 +1652,8 @@ psql_completion(const char *text, int start, int end)
 	/* ALTER SUBSCRIPTION <name> */
 	else if (Matches("ALTER", "SUBSCRIPTION", MatchAny))
 		COMPLETE_WITH("CONNECTION", "ENABLE", "DISABLE", "OWNER TO",
-					  "RENAME TO", "REFRESH PUBLICATION", "SET");
+					  "RENAME TO", "REFRESH PUBLICATION", "SET",
+					  "ADD PUBLICATION", "DROP PUBLICATION");
 	/* ALTER SUBSCRIPTION <name> REFRESH PUBLICATION */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) &&
 			 TailMatches("REFRESH", "PUBLICATION"))
@@ -1672,14 +1673,15 @@ psql_completion(const char *text, int start, int end)
 	{
 		/* complete with nothing here as this refers to remote publications */
 	}
-	/* ALTER SUBSCRIPTION <name> SET PUBLICATION <name> */
+	/* ALTER SUBSCRIPTION <name> ADD|DROP|SET PUBLICATION <name> */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) &&
-			 TailMatches("SET", "PUBLICATION", MatchAny))
+			 TailMatches("ADD|DROP|SET", "PUBLICATION", MatchAny))
 		COMPLETE_WITH("WITH (");
-	/* ALTER SUBSCRIPTION <name> SET PUBLICATION <name> WITH ( */
+	/* ALTER SUBSCRIPTION <name> ADD|DROP|SET PUBLICATION <name> WITH ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) &&
-			 TailMatches("SET", "PUBLICATION", MatchAny, "WITH", "("))
+			 TailMatches("ADD|DROP|SET", "PUBLICATION", MatchAny, "WITH", "("))
 		COMPLETE_WITH("copy_data", "refresh");
+
 	/* ALTER SCHEMA <name> */
 	else if (Matches("ALTER", "SCHEMA", MatchAny))
 		COMPLETE_WITH("OWNER TO", "RENAME TO");

src/include/nodes/parsenodes.h

@@ -3618,7 +3618,9 @@ typedef enum AlterSubscriptionType
 {
 	ALTER_SUBSCRIPTION_OPTIONS,
 	ALTER_SUBSCRIPTION_CONNECTION,
-	ALTER_SUBSCRIPTION_PUBLICATION,
+	ALTER_SUBSCRIPTION_SET_PUBLICATION,
+	ALTER_SUBSCRIPTION_ADD_PUBLICATION,
+	ALTER_SUBSCRIPTION_DROP_PUBLICATION,
 	ALTER_SUBSCRIPTION_REFRESH,
 	ALTER_SUBSCRIPTION_ENABLED
 } AlterSubscriptionType;

src/test/regress/expected/subscription.out

@@ -200,6 +200,45 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | f         | off                | dbname=regress_doesnotexist
 (1 row)
 
+-- fail - publication already exists
+ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub WITH (refresh = false);
+ERROR:  publication "testpub" is already in subscription "regress_testsub"
+-- fail - publication used more than once
+ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub1 WITH (refresh = false);
+ERROR:  publication name "testpub1" used more than once
+-- ok - add two publications into subscription
+ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
+-- fail - publications already exist
+ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
+ERROR:  publication "testpub1" is already in subscription "regress_testsub"
+\dRs+
+                                                                    List of subscriptions
+      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Synchronous commit |          Conninfo           
+-----------------+---------------------------+---------+-----------------------------+--------+-----------+--------------------+-----------------------------
+ regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | f         | off                | dbname=regress_doesnotexist
+(1 row)
+
+-- fail - publication used more then once
+ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub1 WITH (refresh = false);
+ERROR:  publication name "testpub1" used more than once
+-- fail - all publications are deleted
+ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub, testpub1, testpub2 WITH (refresh = false);
+ERROR:  subscription must contain at least one publication
+-- fail - publication does not exist in subscription
+ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub3 WITH (refresh = false);
+ERROR:  publication "testpub3" is not in subscription "regress_testsub"
+-- fail - do not support copy_data option
+ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1 WITH (refresh = false, copy_data = true);
+ERROR:  unrecognized subscription parameter: "copy_data"
+-- ok - delete publications
+ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (refresh = false);
+\dRs+
+                                                            List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Synchronous commit |          Conninfo           
+-----------------+---------------------------+---------+-------------+--------+-----------+--------------------+-----------------------------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | f         | off                | dbname=regress_doesnotexist
+(1 row)
+
 DROP SUBSCRIPTION regress_testsub;
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION mypub
        WITH (connect = false, create_slot = false, copy_data = false);

src/test/regress/sql/subscription.sql

@@ -145,6 +145,37 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 
 \dRs+
 
+-- fail - publication already exists
+ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub WITH (refresh = false);
+
+-- fail - publication used more than once
+ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub1 WITH (refresh = false);
+
+-- ok - add two publications into subscription
+ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
+
+-- fail - publications already exist
+ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
+
+\dRs+
+
+-- fail - publication used more then once
+ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub1 WITH (refresh = false);
+
+-- fail - all publications are deleted
+ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub, testpub1, testpub2 WITH (refresh = false);
+
+-- fail - publication does not exist in subscription
+ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub3 WITH (refresh = false);
+
+-- fail - do not support copy_data option
+ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1 WITH (refresh = false, copy_data = true);
+
+-- ok - delete publications
+ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (refresh = false);
+
+\dRs+
+
 DROP SUBSCRIPTION regress_testsub;
 
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION mypub