chore: import upstream snapshot with attribution

testing/go/regression/tests/mvcc.sql

@@ -0,0 +1,44 @@
+--
+-- Verify that index scans encountering dead rows produced by an
+-- aborted subtransaction of the current transaction can utilize the
+-- kill_prio_tuple optimization
+--
+-- NB: The table size is currently *not* expected to stay the same, we
+-- don't have logic to trigger opportunistic pruning in cases like
+-- this.
+BEGIN;
+
+SET LOCAL enable_seqscan = false;
+SET LOCAL enable_indexonlyscan = false;
+SET LOCAL enable_bitmapscan = false;
+
+-- Can't easily use a unique index, since dead tuples can be found
+-- independent of the kill_prior_tuples optimization.
+CREATE TABLE clean_aborted_self(key int, data text);
+CREATE INDEX clean_aborted_self_key ON clean_aborted_self(key);
+INSERT INTO clean_aborted_self (key, data) VALUES (-1, 'just to allocate metapage');
+
+-- save index size from before the changes, for comparison
+SELECT pg_relation_size('clean_aborted_self_key') AS clean_aborted_self_key_before \gset
+
+DO $$
+BEGIN
+    -- iterate often enough to see index growth even on larger-than-default page sizes
+    FOR i IN 1..100 LOOP
+        BEGIN
+	    -- perform index scan over all the inserted keys to get them to be seen as dead
+            IF EXISTS(SELECT * FROM clean_aborted_self WHERE key > 0 AND key < 100) THEN
+	        RAISE data_corrupted USING MESSAGE = 'these rows should not exist';
+            END IF;
+            INSERT INTO clean_aborted_self SELECT g.i, 'rolling back in a sec' FROM generate_series(1, 100) g(i);
+	    -- just some error that's not normally thrown
+	    RAISE reading_sql_data_not_permitted USING MESSAGE = 'round and round again';
+	EXCEPTION WHEN reading_sql_data_not_permitted THEN END;
+    END LOOP;
+END;$$;
+
+-- show sizes only if they differ
+SELECT :clean_aborted_self_key_before AS size_before, pg_relation_size('clean_aborted_self_key') size_after
+WHERE :clean_aborted_self_key_before != pg_relation_size('clean_aborted_self_key');
+
+ROLLBACK;