From 0d8f4ae1d0966fc42086ce1d5236fd99ea548d90 Mon Sep 17 00:00:00 2001
From: Alex Kasko <alex@staticlibs.net>
Date: Mon, 10 Aug 2026 09:07:39 +0100
Subject: [PATCH] Add a test to cover parallel scans safety

This PR adds a test that has uncovered a concurrency problem in MySQL
scanner:

 - duckdb/duckdb-mysql#225
 - duckdb/duckdb-mysql#254

Note that Postgres scanner is not affected by the same problem due to
`INITIALIZE_ON_SCHEDULE` changes added in #252. The test is still
necessary to cover possible modifications to this logic in future.
---
 test/sql/storage/multi_scan_aggregate.test | 55 ++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 test/sql/storage/multi_scan_aggregate.test

diff --git a/test/sql/storage/multi_scan_aggregate.test b/test/sql/storage/multi_scan_aggregate.test
new file mode 100644
index 000000000..9ae996a94
--- /dev/null
+++ b/test/sql/storage/multi_scan_aggregate.test
@@ -0,0 +1,55 @@
+# name: test/sql/storage/multi_scan_aggregate.test
+# description: Test multiple simultaneous scans that are aggregated on DuckDB side
+# group: [storage]
+
+require postgres_scanner
+
+require-env POSTGRES_TEST_DATABASE_AVAILABLE
+
+statement ok
+ATTACH 'dbname=postgresscanner' AS s (TYPE POSTGRES)
+
+statement ok
+CREATE OR REPLACE TABLE s.aggr_union_test_a AS
+SELECT '2020-01-01' insert_date, unnest(range(1<<14)) amount
+
+statement ok
+CREATE OR REPLACE TABLE s.aggr_union_test_b AS
+SELECT '2021-01-01' insert_date, unnest(range(1<<14)) amount
+
+# Note, 'divide()' is necessary to prevent remote-execute pushdown
+
+query II
+SELECT date(t.insert_date) AS d, divide(sum(t.amount), 1) AS s
+FROM s.aggr_union_test_a t
+GROUP BY 1
+----
+2020-01-01	134209536
+
+query II
+SELECT date(t.insert_date) AS d, divide(sum(t.amount), 1) AS s
+FROM s.aggr_union_test_b t
+GROUP BY 1
+----
+2021-01-01	134209536
+
+query II
+SELECT date(t.insert_date) AS d, divide(sum(t.amount), 1) AS s
+FROM s.aggr_union_test_a t
+GROUP BY 1
+UNION ALL
+SELECT date(t.insert_date) AS d, divide(sum(t.amount), 1) AS s
+FROM s.aggr_union_test_b t
+GROUP BY 1   
+----
+2020-01-01	134209536
+2021-01-01	134209536
+
+statement ok
+DROP TABLE s.aggr_union_test_a
+
+statement ok
+DROP TABLE s.aggr_union_test_b
+
+statement ok
+DETACH s;