SERVER-61750: Use DISTINCT_SCAN when a regex is a prefix of an index

1 files changed, 27 insertions, 0 deletions

diff --git a/jstests/core/regex_distinct.js b/jstests/core/regex_distinct.js
new file mode 100644
index 00000000000..7852950853c
--- /dev/null
+++ b/jstests/core/regex_distinct.js
@@ -0,0 +1,27 @@
+/**
+ * Verify the usage of DISTINCT_SCAN when a regex ending with .* is a prefix of an index.
+ *
+ * @tags: [
+ *  requires_fcv_53,
+ *  assumes_read_concern_local,
+ * ]
+ */
+
+(function() {
+"use strict";
+load("jstests/libs/analyze_plan.js");     // For getPlanStages.
+load("jstests/libs/fixture_helpers.js");  // For numberOfShardsForCollection.
+
+const coll = db.regex_distinct;
+coll.drop();
+
+assert.commandWorked(coll.insertMany(
+    [{a: "abc", b: "foo"}, {a: "abc", b: "bar"}, {a: "abd", b: "far"}, {a: "aeb", b: "car"}]));
+
+assert.commandWorked(coll.createIndex({a: 1}));
+assert.eq(2, coll.distinct("a", {a: {"$regex": "^ab.*"}}).length);
+const distinctScanStages =
+    getPlanStages(coll.explain().distinct("a", {a: {"$regex": "^ab.*"}}), "DISTINCT_SCAN");
+
+assert.eq(distinctScanStages.length, FixtureHelpers.numberOfShardsForCollection(coll));
+})();