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diff --git a/src/test/regress/sql/vacuum_parallel.sql b/src/test/regress/sql/vacuum_parallel.sql
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+SET max_parallel_maintenance_workers TO 4;
+SET min_parallel_index_scan_size TO '128kB';
+
+-- Bug #17245: Make sure that we don't totally fail to VACUUM individual indexes that
+-- happen to be below min_parallel_index_scan_size during parallel VACUUM:
+CREATE TABLE parallel_vacuum_table (a int) WITH (autovacuum_enabled = off);
+INSERT INTO parallel_vacuum_table SELECT i from generate_series(1, 10000) i;
+
+-- Parallel VACUUM will never be used unless there are at least two indexes
+-- that exceed min_parallel_index_scan_size.  Create two such indexes, and
+-- a third index that is smaller than min_parallel_index_scan_size.
+CREATE INDEX regular_sized_index ON parallel_vacuum_table(a);
+CREATE INDEX typically_sized_index ON parallel_vacuum_table(a);
+-- Note: vacuum_in_leader_small_index can apply deduplication, making it ~3x
+-- smaller than the other indexes
+CREATE INDEX vacuum_in_leader_small_index ON parallel_vacuum_table((1));
+
+-- Verify (as best we can) that the cost model for parallel VACUUM
+-- will make our VACUUM run in parallel, while always leaving it up to the
+-- parallel leader to handle the vacuum_in_leader_small_index index:
+SELECT EXISTS (
+SELECT 1
+FROM pg_class
+WHERE oid = 'vacuum_in_leader_small_index'::regclass AND
+  pg_relation_size(oid) <
+  pg_size_bytes(current_setting('min_parallel_index_scan_size'))
+) as leader_will_handle_small_index;
+SELECT count(*) as trigger_parallel_vacuum_nindexes
+FROM pg_class
+WHERE oid in ('regular_sized_index'::regclass, 'typically_sized_index'::regclass) AND
+  pg_relation_size(oid) >=
+  pg_size_bytes(current_setting('min_parallel_index_scan_size'));
+
+-- Parallel VACUUM with B-Tree page deletions, ambulkdelete calls:
+DELETE FROM parallel_vacuum_table;
+VACUUM (PARALLEL 4, INDEX_CLEANUP ON) parallel_vacuum_table;
+
+-- Since vacuum_in_leader_small_index uses deduplication, we expect an
+-- assertion failure with bug #17245 (in the absence of bugfix):
+INSERT INTO parallel_vacuum_table SELECT i FROM generate_series(1, 10000) i;
+
+RESET max_parallel_maintenance_workers;
+RESET min_parallel_index_scan_size;
+
+-- Deliberately don't drop table, to get further coverage from tools like
+-- pg_amcheck in some testing scenarios