SERVER-26334 fix mongos handling of ntoreturn:1

5 files changed, 31 insertions, 31 deletions

diff --git a/jstests/core/tailable_skip_limit.js b/jstests/core/tailable_skip_limit.js
index f771621ad83..7e09d1bfbfa 100644
--- a/jstests/core/tailable_skip_limit.js
+++ b/jstests/core/tailable_skip_limit.js
@@ -58,6 +58,20 @@
     assert.throws(function() {
         t.find().addOption(2).limit(-100).next();
     });
+    assert.throws(function() {
+        t.find().addOption(2).limit(-1).itcount();
+    });
+
+    // When using read commands, a limit of 1 with the tailable option is allowed. In legacy
+    // readMode, an ntoreturn of 1 means the same thing as ntoreturn -1 and is disallowed with
+    // tailable.
+    if (db.getMongo().useReadCommands()) {
+        assert.eq(1, t.find().addOption(2).limit(1).itcount());
+    } else {
+        assert.throws(function() {
+            t.find().addOption(2).limit(1).itcount();
+        });
+    }
 
     // Tests that a tailable cursor over an empty capped collection produces a dead cursor, intended
     // to be run on both mongod and mongos. For SERVER-20720.
diff --git a/jstests/sharding/sharded_limit_batchsize.js b/jstests/sharding/sharded_limit_batchsize.js
index cd636b56cdc..a3fe4f5906f 100644
--- a/jstests/sharding/sharded_limit_batchsize.js
+++ b/jstests/sharding/sharded_limit_batchsize.js
@@ -41,6 +41,17 @@
         assert.eq(2, cursor.next()["_id"]);
         assert.eq(3, cursor.next()["_id"]);
         assert(!cursor.hasNext());
+
+        // Ensure that in the limit 1 case, which is special when in legacy readMode, the server
+        // does not leave a cursor open.
+        var openCursorsBefore =
+            assert.commandWorked(coll.getDB().serverStatus()).metrics.cursor.open.total;
+        cursor = coll.find().sort({x: 1}).limit(1);
+        assert(cursor.hasNext());
+        assert.eq(-10, cursor.next()["_id"]);
+        var openCursorsAfter =
+            assert.commandWorked(coll.getDB().serverStatus()).metrics.cursor.open.total;
+        assert.eq(openCursorsBefore, openCursorsAfter);
     }
 
     //
diff --git a/src/mongo/db/query/find.cpp b/src/mongo/db/query/find.cpp
index 14645bd55e1..bbce97fc50b 100644
--- a/src/mongo/db/query/find.cpp
+++ b/src/mongo/db/query/find.cpp
@@ -89,11 +89,7 @@ bool shouldSaveCursor(OperationContext* txn,
     }
 
     const QueryRequest& qr = exec->getCanonicalQuery()->getQueryRequest();
-    if (!qr.wantMore() && !qr.isTailable()) {
-        return false;
-    }
-
-    if (qr.getNToReturn().value_or(0) == 1) {
+    if (!qr.wantMore()) {
         return false;
     }
 
diff --git a/src/mongo/db/query/query_request.cpp b/src/mongo/db/query/query_request.cpp
index b0aa759e853..af2c46b550c 100644
--- a/src/mongo/db/query/query_request.cpp
+++ b/src/mongo/db/query/query_request.cpp
@@ -734,6 +734,11 @@ Status QueryRequest::init(int ntoskip,
         }
     }
 
+    // An ntoreturn of 1 is special because it also means to return at most one batch.
+    if (_ntoreturn.value_or(0) == 1) {
+        _wantMore = false;
+    }
+
     // Initialize flags passed as 'queryOptions' bit vector.
     initFromInt(queryOptions);
 
diff --git a/src/mongo/dbtests/querytests.cpp b/src/mongo/dbtests/querytests.cpp
index de55f54f45d..cd2f902372a 100644
--- a/src/mongo/dbtests/querytests.cpp
+++ b/src/mongo/dbtests/querytests.cpp
@@ -416,31 +416,6 @@ public:
     }
 };
 
-class ReturnOneOfManyAndTail : public ClientBase {
-public:
-    ~ReturnOneOfManyAndTail() {
-        _client.dropCollection("unittests.querytests.ReturnOneOfManyAndTail");
-    }
-    void run() {
-        const char* ns = "unittests.querytests.ReturnOneOfManyAndTail";
-        _client.createCollection(ns, 1024, true);
-        insert(ns, BSON("a" << 0));
-        insert(ns, BSON("a" << 1));
-        insert(ns, BSON("a" << 2));
-        unique_ptr<DBClientCursor> c =
-            _client.query(ns,
-                          QUERY("a" << GT << 0).hint(BSON("$natural" << 1)),
-                          1,
-                          0,
-                          0,
-                          QueryOption_CursorTailable);
-        // If only one result requested, a cursor is not saved.
-        ASSERT_EQUALS(0, c->getCursorId());
-        ASSERT(c->more());
-        ASSERT_EQUALS(1, c->next().getIntField("a"));
-    }
-};
-
 class TailNotAtEnd : public ClientBase {
 public:
     ~TailNotAtEnd() {
@@ -1783,7 +1758,6 @@ public:
         add<GetMoreKillOp>();
         add<GetMoreInvalidRequest>();
         add<PositiveLimit>();
-        add<ReturnOneOfManyAndTail>();
         add<TailNotAtEnd>();
         add<EmptyTail>();
         add<TailableDelete>();