Preserve pg_index.indisclustered across REINDEX CONCURRENTLY

If the flag value is lost, a CLUSTER query following REINDEX
CONCURRENTLY could fail.  Non-concurrent REINDEX is already handling
this case consistently.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20200229024202.GH29456@telsasoft.com
Backpatch-through: 12

2 files changed, 22 insertions, 0 deletions

diff --git a/src/test/regress/expected/create_index.out b/src/test/regress/expected/create_index.out
index 6ddf3a63c3a..ae95bb38a64 100644
--- a/src/test/regress/expected/create_index.out
+++ b/src/test/regress/expected/create_index.out
@@ -2128,6 +2128,19 @@ SELECT obj_description('testcomment_idx1'::regclass, 'pg_class');
 (1 row)
 
 DROP TABLE testcomment;
+-- Check that indisclustered updates are preserved
+CREATE TABLE concur_clustered(i int);
+CREATE INDEX concur_clustered_i_idx ON concur_clustered(i);
+ALTER TABLE concur_clustered CLUSTER ON concur_clustered_i_idx;
+REINDEX TABLE CONCURRENTLY concur_clustered;
+SELECT indexrelid::regclass, indisclustered FROM pg_index
+  WHERE indrelid = 'concur_clustered'::regclass;
+       indexrelid       | indisclustered 
+------------------------+----------------
+ concur_clustered_i_idx | t
+(1 row)
+
+DROP TABLE concur_clustered;
 -- Partitions
 -- Create some partitioned tables
 CREATE TABLE concur_reindex_part (c1 int, c2 int) PARTITION BY RANGE (c1);
diff --git a/src/test/regress/sql/create_index.sql b/src/test/regress/sql/create_index.sql
index f7fd756189b..c3246cb296f 100644
--- a/src/test/regress/sql/create_index.sql
+++ b/src/test/regress/sql/create_index.sql
@@ -858,6 +858,15 @@ SELECT obj_description('testcomment_idx1'::regclass, 'pg_class');
 REINDEX TABLE CONCURRENTLY testcomment ;
 SELECT obj_description('testcomment_idx1'::regclass, 'pg_class');
 DROP TABLE testcomment;
+-- Check that indisclustered updates are preserved
+CREATE TABLE concur_clustered(i int);
+CREATE INDEX concur_clustered_i_idx ON concur_clustered(i);
+ALTER TABLE concur_clustered CLUSTER ON concur_clustered_i_idx;
+REINDEX TABLE CONCURRENTLY concur_clustered;
+SELECT indexrelid::regclass, indisclustered FROM pg_index
+  WHERE indrelid = 'concur_clustered'::regclass;
+DROP TABLE concur_clustered;
+
 -- Partitions
 -- Create some partitioned tables
 CREATE TABLE concur_reindex_part (c1 int, c2 int) PARTITION BY RANGE (c1);