Preserve pg_index.indisreplident across REINDEX CONCURRENTLY

If the flag value is lost, logical decoding would work the same way as
REPLICA IDENTITY NOTHING, meaning that no old tuple values would be
included in the changes anymore produced by logical decoding.

Author: Michael Paquier
Reviewed-by: Euler Taveira
Discussion: https://postgr.es/m/20200603065340.GK89559@paquier.xyz
Backpatch-through: 12

src/backend/catalog/index.c

@@ -1538,6 +1538,10 @@ index_concurrently_swap(Oid newIndexId, Oid oldIndexId, const char *oldName)
 	newIndexForm->indimmediate = oldIndexForm->indimmediate;
 	oldIndexForm->indimmediate = true;
 
+	/* Preserve indisreplident in the new index */
+	newIndexForm->indisreplident = oldIndexForm->indisreplident;
+	oldIndexForm->indisreplident = false;
+
 	/* Preserve indisclustered in the new index */
 	newIndexForm->indisclustered = oldIndexForm->indisclustered;
 

src/test/regress/expected/create_index.out

@@ -2141,6 +2141,27 @@ SELECT indexrelid::regclass, indisclustered FROM pg_index
 (1 row)
 
 DROP TABLE concur_clustered;
+-- Check that indisreplident updates are preserved.
+CREATE TABLE concur_replident(i int NOT NULL);
+CREATE UNIQUE INDEX concur_replident_i_idx ON concur_replident(i);
+ALTER TABLE concur_replident REPLICA IDENTITY
+  USING INDEX concur_replident_i_idx;
+SELECT indexrelid::regclass, indisreplident FROM pg_index
+  WHERE indrelid = 'concur_replident'::regclass;
+       indexrelid       | indisreplident 
+------------------------+----------------
+ concur_replident_i_idx | t
+(1 row)
+
+REINDEX TABLE CONCURRENTLY concur_replident;
+SELECT indexrelid::regclass, indisreplident FROM pg_index
+  WHERE indrelid = 'concur_replident'::regclass;
+       indexrelid       | indisreplident 
+------------------------+----------------
+ concur_replident_i_idx | t
+(1 row)
+
+DROP TABLE concur_replident;
 -- Partitions
 -- Create some partitioned tables
 CREATE TABLE concur_reindex_part (c1 int, c2 int) PARTITION BY RANGE (c1);

src/test/regress/sql/create_index.sql

@@ -866,6 +866,17 @@ REINDEX TABLE CONCURRENTLY concur_clustered;
 SELECT indexrelid::regclass, indisclustered FROM pg_index
   WHERE indrelid = 'concur_clustered'::regclass;
 DROP TABLE concur_clustered;
+-- Check that indisreplident updates are preserved.
+CREATE TABLE concur_replident(i int NOT NULL);
+CREATE UNIQUE INDEX concur_replident_i_idx ON concur_replident(i);
+ALTER TABLE concur_replident REPLICA IDENTITY
+  USING INDEX concur_replident_i_idx;
+SELECT indexrelid::regclass, indisreplident FROM pg_index
+  WHERE indrelid = 'concur_replident'::regclass;
+REINDEX TABLE CONCURRENTLY concur_replident;
+SELECT indexrelid::regclass, indisreplident FROM pg_index
+  WHERE indrelid = 'concur_replident'::regclass;
+DROP TABLE concur_replident;
 
 -- Partitions
 -- Create some partitioned tables