Remove incorrect assertion for INSERT in logical replication's publisher

On the publisher, it was assumed that an INSERT change cannot happen for
a relation with no replica identity.  However this is true only for a
change that needs references to old rows, aka UPDATE or DELETE, so
trying to use logical replication with a relation that has no replica
identity led to an assertion failure in the publisher when issuing an
INSERT.  This commit removes the incorrect assertion, and adds more
regression tests to provide coverage for relations without replica
identity.

Reported-by: Neha Sharma
Author: Dilip Kumar, Michael Paquier
Reviewed-by: Andres Freund
Discussion: https://postgr.es/m/CANiYTQsL1Hb8_Km08qd32svrqNumXLJeoGo014O7VZymgOhZEA@mail.gmail.com
Backpatch-through: 10

Author: michaelpq

src/backend/replication/logical/proto.c

@@ -143,10 +143,6 @@ logicalrep_write_insert(StringInfo out, Relation rel, HeapTuple newtuple)
 {
 	pq_sendbyte(out, 'I');		/* action INSERT */
 
-	Assert(rel->rd_rel->relreplident == REPLICA_IDENTITY_DEFAULT ||
-		   rel->rd_rel->relreplident == REPLICA_IDENTITY_FULL ||
-		   rel->rd_rel->relreplident == REPLICA_IDENTITY_INDEX);
-
 	/* use Oid as relation identifier */
 	pq_sendint32(out, RelationGetRelid(rel));
 

src/test/subscription/t/001_rep_changes.pl

@@ -3,7 +3,7 @@
 use warnings;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 22;
+use Test::More tests => 23;
 
 # Initialize publisher node
 my $node_publisher = get_new_node('publisher');
@@ -34,6 +34,10 @@
 $node_publisher->safe_psql('postgres',
 	"CREATE TABLE tab_include (a int, b text, CONSTRAINT covering PRIMARY KEY(a) INCLUDE(b))"
 );
+# Let this table with REPLICA IDENTITY NOTHING, allowing only INSERT changes.
+$node_publisher->safe_psql('postgres', "CREATE TABLE tab_nothing (a int)");
+$node_publisher->safe_psql('postgres',
+	"ALTER TABLE tab_nothing REPLICA IDENTITY NOTHING");
 
 # Setup structure on subscriber
 $node_subscriber->safe_psql('postgres', "CREATE TABLE tab_notrep (a int)");
@@ -42,6 +46,7 @@
 $node_subscriber->safe_psql('postgres', "CREATE TABLE tab_full2 (x text)");
 $node_subscriber->safe_psql('postgres',
 	"CREATE TABLE tab_rep (a int primary key)");
+$node_subscriber->safe_psql('postgres', "CREATE TABLE tab_nothing (a int)");
 
 # different column count and order than on publisher
 $node_subscriber->safe_psql('postgres',
@@ -59,7 +64,7 @@
 $node_publisher->safe_psql('postgres',
 	"CREATE PUBLICATION tap_pub_ins_only WITH (publish = insert)");
 $node_publisher->safe_psql('postgres',
-	"ALTER PUBLICATION tap_pub ADD TABLE tab_rep, tab_full, tab_full2, tab_mixed, tab_include"
+	"ALTER PUBLICATION tap_pub ADD TABLE tab_rep, tab_full, tab_full2, tab_mixed, tab_include, tab_nothing"
 );
 $node_publisher->safe_psql('postgres',
 	"ALTER PUBLICATION tap_pub_ins_only ADD TABLE tab_ins");
@@ -97,6 +102,9 @@
 $node_publisher->safe_psql('postgres',
 	"INSERT INTO tab_mixed VALUES (2, 'bar', 2.2)");
 
+$node_publisher->safe_psql('postgres',
+	"INSERT INTO tab_nothing VALUES (generate_series(1,20))");
+
 $node_publisher->safe_psql('postgres',
 	"INSERT INTO tab_include SELECT generate_series(1,50)");
 $node_publisher->safe_psql('postgres',
@@ -117,6 +125,10 @@
 is( $result, qq(local|1.1|foo|1
 local|2.2|bar|2), 'check replicated changes with different column order');
 
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_nothing");
+is($result, qq(20), 'check replicated changes with REPLICA IDENTITY NOTHING');
+
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*), min(a), max(a) FROM tab_include");
 is($result, qq(20|-20|-1),