VACUUM VERBOSE pg_constraint;
INFO:  vacuuming "pg_catalog.pg_constraint"
INFO:  scanned index "pg_constraint_conname_nsp_index" to remove 84 row versions
DETAIL:  CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  scanned index "pg_constraint_conrelid_index" to remove 84 row versions
DETAIL:  CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  scanned index "pg_constraint_contypid_index" to remove 84 row versions
DETAIL:  CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  scanned index "pg_constraint_oid_index" to remove 84 row versions
DETAIL:  CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "pg_constraint": removed 84 row versions in 3 pages
DETAIL:  CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "pg_constraint_conname_nsp_index" now contains 16 row versions in 2 pages
DETAIL:  84 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "pg_constraint_conrelid_index" now contains 16 row versions in 2 pages
DETAIL:  84 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "pg_constraint_contypid_index" now contains 16 row versions in 2 pages
DETAIL:  84 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "pg_constraint_oid_index" now contains 16 row versions in 2 pages
DETAIL:  84 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "pg_constraint": found 84 removable, 16 nonremovable row versions in 3 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
3 pages contain useful free space.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  vacuuming "pg_toast.pg_toast_2606"
INFO:  index "pg_toast_2606_index" now contains 0 row versions in 1 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "pg_toast_2606": found 0 removable, 0 nonremovable row versions in 0 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
0 pages contain useful free space.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
EXPLAIN SELECT conname FROM pg_constraint WHERE conrelid = 'clstr_tst'::regclass;
                                            QUERY PLAN                                             
---------------------------------------------------------------------------------------------------
 Index Scan using pg_constraint_conrelid_index on pg_constraint  (cost=0.00..8.27 rows=1 width=64)
   Index Cond: (conrelid = 28867::oid)
(2 rows)

SELECT conname FROM pg_constraint WHERE conrelid = 'clstr_tst'::regclass;
    conname     
----------------
 clstr_tst_con
 clstr_tst_pkey
(2 rows)

SET enable_indexscan = 0;
EXPLAIN SELECT conname FROM pg_constraint WHERE conrelid = 'clstr_tst'::regclass;
                                        QUERY PLAN                                         
-------------------------------------------------------------------------------------------
 Bitmap Heap Scan on pg_constraint  (cost=4.26..8.27 rows=1 width=64)
   Recheck Cond: (conrelid = 28867::oid)
   ->  Bitmap Index Scan on pg_constraint_conrelid_index  (cost=0.00..4.26 rows=1 width=0)
         Index Cond: (conrelid = 28867::oid)
(4 rows)

SELECT conname FROM pg_constraint WHERE conrelid = 'clstr_tst'::regclass;
    conname     
----------------
 clstr_tst_pkey
 clstr_tst_con
(2 rows)

SET enable_bitmapscan = 0;
EXPLAIN SELECT conname FROM pg_constraint WHERE conrelid = 'clstr_tst'::regclass;
                          QUERY PLAN                           
---------------------------------------------------------------
 Seq Scan on pg_constraint  (cost=0.00..27.20 rows=1 width=64)
   Filter: (conrelid = 28867::oid)
(2 rows)

SELECT conname FROM pg_constraint WHERE conrelid = 'clstr_tst'::regclass;
    conname     
----------------
 clstr_tst_pkey
 clstr_tst_con
(2 rows)

SET enable_indexscan = 1;
SET enable_bitmapscan = 1;
SELECT count(*) FROM pg_constraint;
 count 
-------
    16
(1 row)