1 files changed, 44 insertions, 0 deletions
diff --git a/jstests/noPassthroughWithMongod/mapreduce_intermediate_reduce.js b/jstests/noPassthroughWithMongod/mapreduce_intermediate_reduce.js
new file mode 100644
index 00000000000..fd7ec8c68e7
--- /dev/null
+++ b/jstests/noPassthroughWithMongod/mapreduce_intermediate_reduce.js
@@ -0,0 +1,44 @@
+// This test validates that map/reduce runs intermediate reduce steps in order to keep the
+// in-memory state small. See SERVER-12949 for more details.
+//
+function assertGLEOK(status) {
+    assert(status.ok && status.err === null,
+           "Expected OK status object; found " + tojson(status));
+}
+
+var db = db.getSisterDB("MapReduceTestDB");
+db.dropDatabase();
+
+var coll = db.getCollection("mrInput");
+
+// Insert 10 x 49 elements (10 i-s, 49 j-s)
+//
+var expectedOutColl = [];
+
+for (var i = 0; i < 10; i++) {
+    for (var j = 1; j < 50; j++) {
+        coll.insert({idx: i, j: j});
+    }
+    expectedOutColl.push ({ _id: i, value: j - 1 });
+}
+
+assertGLEOK(db.getLastErrorObj());
+
+function mapFn() { emit(this.idx, 1); };
+function reduceFn(key, values) { return Array.sum(values); };
+
+var out = coll.mapReduce(mapFn, reduceFn, { out: { replace: "mrOutput" } });
+
+// Check the output is as expected
+//
+var outColl = db.getCollection("mrOutput").find().toArray();
+assert.eq(outColl, expectedOutColl, "The output collection is incorrect.");
+
+assert.eq(out.counts.input, 490, "input count is wrong");
+assert.eq(out.counts.emit, 490, "emit count is wrong");
+
+// If this fails, most probably some of the configuration settings under mongo::mr::Config have
+// changed, such as reduceTriggerRatio or maxInMemSize. If not the case, then something else 
+// must have changed with when intermediate reduces occur (see mongo::mr::State::checkSize).
+//
+assert.eq(out.counts.reduce, 14, "reduce count is wrong");
+\ No newline at end of file