SERVER-23496 adding ShardLocal class, child class of Shard

12 files changed, 523 insertions, 49 deletions

diff --git a/src/mongo/db/repl/storage_interface_impl_test.cpp b/src/mongo/db/repl/storage_interface_impl_test.cpp
index 087780f8afa..9b8cdabd32a 100644
--- a/src/mongo/db/repl/storage_interface_impl_test.cpp
+++ b/src/mongo/db/repl/storage_interface_impl_test.cpp
@@ -190,4 +190,10 @@ TEST_F(StorageInterfaceImplTest, MinValid) {
     ASSERT_TRUE(recoveryUnit->waitUntilDurableCalled);
 }
 
+TEST_F(StorageInterfaceImplTest, SnapshotNotSupported) {
+    auto txn = getClient()->makeOperationContext();
+    Status status = txn->recoveryUnit()->setReadFromMajorityCommittedSnapshot();
+    ASSERT_EQUALS(status, ErrorCodes::CommandNotSupported);
+}
+
 }  // namespace
diff --git a/src/mongo/db/storage/ephemeral_for_test/SConscript b/src/mongo/db/storage/ephemeral_for_test/SConscript
index 88e38cdcfbb..02e848fa9c2 100644
--- a/src/mongo/db/storage/ephemeral_for_test/SConscript
+++ b/src/mongo/db/storage/ephemeral_for_test/SConscript
@@ -25,6 +25,7 @@ env.Library(
         '$BUILD_DIR/mongo/db/namespace_string',
         '$BUILD_DIR/mongo/db/catalog/collection_options',
         '$BUILD_DIR/mongo/db/index/index_descriptor',
+        '$BUILD_DIR/mongo/db/repl/repl_coordinator_global',
         '$BUILD_DIR/mongo/db/storage/index_entry_comparison',
         '$BUILD_DIR/mongo/db/storage/journal_listener',
         '$BUILD_DIR/mongo/util/foundation',
diff --git a/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_recovery_unit.cpp b/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_recovery_unit.cpp
index ef80739cd31..c94d659ac53 100644
--- a/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_recovery_unit.cpp
+++ b/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_recovery_unit.cpp
@@ -32,6 +32,7 @@
 
 #include "mongo/db/storage/ephemeral_for_test/ephemeral_for_test_recovery_unit.h"
 
+#include "mongo/db/repl/replication_coordinator_global.h"
 #include "mongo/db/storage/sorted_data_interface.h"
 #include "mongo/util/log.h"
 
@@ -66,4 +67,13 @@ void EphemeralForTestRecoveryUnit::abortUnitOfWork() {
         std::terminate();
     }
 }
+
+Status EphemeralForTestRecoveryUnit::setReadFromMajorityCommittedSnapshot() {
+    if (!repl::getGlobalReplicationCoordinator()->isReplEnabled()) {
+        return Status::OK();
+    } else {
+        return {ErrorCodes::CommandNotSupported,
+                "Current storage engine does not support majority readConcerns"};
+    }
+}
 }
diff --git a/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_recovery_unit.h b/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_recovery_unit.h
index 4b7925248e4..7de00846992 100644
--- a/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_recovery_unit.h
+++ b/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_recovery_unit.h
@@ -58,6 +58,8 @@ public:
 
     virtual void abandonSnapshot() {}
 
+    Status setReadFromMajorityCommittedSnapshot() final;
+
     virtual void registerChange(Change* change) {
         _changes.push_back(ChangePtr(change));
     }
diff --git a/src/mongo/db/storage/kv/kv_engine_test_snapshots.cpp b/src/mongo/db/storage/kv/kv_engine_test_snapshots.cpp
index 874c94c8cde..0af84c354de 100644
--- a/src/mongo/db/storage/kv/kv_engine_test_snapshots.cpp
+++ b/src/mongo/db/storage/kv/kv_engine_test_snapshots.cpp
@@ -204,7 +204,6 @@ TEST_F(SnapshotManagerTests, ConsistentIfNotSupported) {
     auto ru = op->recoveryUnit();
     ASSERT(!ru->isReadingFromMajorityCommittedSnapshot());
     ASSERT(!ru->getMajorityCommittedSnapshot());
-    ASSERT_EQ(ru->setReadFromMajorityCommittedSnapshot(), ErrorCodes::CommandNotSupported);
 }
 
 TEST_F(SnapshotManagerTests, FailsWithNoCommittedSnapshot) {
diff --git a/src/mongo/s/client/SConscript b/src/mongo/s/client/SConscript
index 6754a18de16..64d064b3e4b 100644
--- a/src/mongo/s/client/SConscript
+++ b/src/mongo/s/client/SConscript
@@ -6,7 +6,6 @@ env.Library(
     target='sharding_client',
     source=[
         'dbclient_multi_command.cpp',
-        'shard.cpp',
         'shard_connection.cpp',
         'shard_factory.cpp',
         'shard_registry.cpp',
@@ -21,6 +20,7 @@ env.Library(
         '$BUILD_DIR/mongo/executor/connection_pool_stats',
         '$BUILD_DIR/mongo/executor/task_executor_pool',
         '$BUILD_DIR/mongo/rpc/metadata',
+        'shard_interface',
     ],
     LIBDEPS_TAGS=[
         # Circular with both coreshard and coredb! Also relies on some
@@ -58,3 +58,35 @@ env.CppUnitTest(
         '$BUILD_DIR/mongo/util/net/network',
     ]
 )
+
+env.Library(
+    target='shard_interface',
+    source=[
+        'shard.cpp',
+    ],
+)
+
+env.Library(
+    target='shard_local',
+    source=[
+        'shard_local.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/client/clientdriver',
+        'shard_interface'
+    ],
+)
+
+env.CppUnitTest(
+    target='shard_local_test',
+    source=[
+        'shard_local_test.cpp',
+    ],
+    LIBDEPS=[
+        'shard_local',
+        '$BUILD_DIR/mongo/db/repl/replmocks',
+        '$BUILD_DIR/mongo/db/serveronly',
+        '$BUILD_DIR/mongo/db/service_context_d_test_fixture',
+    ],
+    NO_CRUTCH = True,
+)
diff --git a/src/mongo/s/client/shard.cpp b/src/mongo/s/client/shard.cpp
index 963e746e8a8..06908cb4dd7 100644
--- a/src/mongo/s/client/shard.cpp
+++ b/src/mongo/s/client/shard.cpp
@@ -1,29 +1,29 @@
 /**
- *    Copyright (C) 2008-2015 MongoDB Inc.
+ * Copyright (C) 2016 MongoDB Inc.
  *
- *    This program is free software: you can redistribute it and/or  modify
- *    it under the terms of the GNU Affero General Public License, version 3,
- *    as published by the Free Software Foundation.
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
  *
- *    This program is distributed in the hope that it will be useful,
- *    but WITHOUT ANY WARRANTY; without even the implied warranty of
- *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *    GNU Affero General Public License for more details.
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
  *
- *    You should have received a copy of the GNU Affero General Public License
- *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
- *    As a special exception, the copyright holders give permission to link the
- *    code of portions of this program with the OpenSSL library under certain
- *    conditions as described in each individual source file and distribute
- *    linked combinations including the program with the OpenSSL library. You
- *    must comply with the GNU Affero General Public License in all respects
- *    for all of the code used other than as permitted herein. If you modify
- *    file(s) with this exception, you may extend this exception to your
- *    version of the file(s), but you are not obligated to do so. If you do not
- *    wish to do so, delete this exception statement from your version. If you
- *    delete this exception statement from all source files in the program,
- *    then also delete it in the license file.
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects
+ * for all of the code used other than as permitted herein. If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so. If you do not
+ * wish to do so, delete this exception statement from your version. If you
+ * delete this exception statement from all source files in the program,
+ * then also delete it in the license file.
  */
 
 #define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kSharding
diff --git a/src/mongo/s/client/shard.h b/src/mongo/s/client/shard.h
index 11efad1d348..db71e1b944b 100644
--- a/src/mongo/s/client/shard.h
+++ b/src/mongo/s/client/shard.h
@@ -1,29 +1,29 @@
 /**
- *    Copyright (C) 2008-2015 MongoDB Inc.
+ * Copyright (C) 2016 MongoDB Inc.
  *
- *    This program is free software: you can redistribute it and/or  modify
- *    it under the terms of the GNU Affero General Public License, version 3,
- *    as published by the Free Software Foundation.
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
  *
- *    This program is distributed in the hope that it will be useful,
- *    but WITHOUT ANY WARRANTY; without even the implied warranty of
- *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *    GNU Affero General Public License for more details.
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
  *
- *    You should have received a copy of the GNU Affero General Public License
- *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
- *    As a special exception, the copyright holders give permission to link the
- *    code of portions of this program with the OpenSSL library under certain
- *    conditions as described in each individual source file and distribute
- *    linked combinations including the program with the OpenSSL library. You
- *    must comply with the GNU Affero General Public License in all respects
- *    for all of the code used other than as permitted herein. If you modify
- *    file(s) with this exception, you may extend this exception to your
- *    version of the file(s), but you are not obligated to do so. If you do not
- *    wish to do so, delete this exception statement from your version. If you
- *    delete this exception statement from all source files in the program,
- *    then also delete it in the license file.
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects
+ * for all of the code used other than as permitted herein. If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so. If you do not
+ * wish to do so, delete this exception statement from your version. If you
+ * delete this exception statement from all source files in the program,
+ * then also delete it in the license file.
  */
 
 #pragma once
@@ -31,12 +31,14 @@
 #include "mongo/bson/bsonobj.h"
 #include "mongo/client/connection_string.h"
 #include "mongo/client/read_preference.h"
-#include "mongo/client/remote_command_targeter.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/repl/optime.h"
 
 namespace mongo {
 
+class OperationContext;
+class RemoteCommandTargeter;
+
 using ShardId = std::string;
 
 /**
@@ -84,7 +86,7 @@ public:
      *
      * This is only valid to call on ShardRemote instances.
      */
-    virtual std::shared_ptr<RemoteCommandTargeter> getTargeter() = 0;
+    virtual std::shared_ptr<RemoteCommandTargeter> getTargeter() const = 0;
 
     /**
      * Notifies the RemoteCommandTargeter owned by the shard of a particular mode of failure for
diff --git a/src/mongo/s/client/shard_local.cpp b/src/mongo/s/client/shard_local.cpp
new file mode 100644
index 00000000000..337089aa76c
--- /dev/null
+++ b/src/mongo/s/client/shard_local.cpp
@@ -0,0 +1,143 @@
+/**
+ * Copyright (C) 2016 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects
+ * for all of the code used other than as permitted herein. If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so. If you do not
+ * wish to do so, delete this exception statement from your version. If you
+ * delete this exception statement from all source files in the program,
+ * then also delete it in the license file.
+ */
+
+#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kSharding
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/s/client/shard_local.h"
+
+#include "mongo/base/status.h"
+#include "mongo/base/status_with.h"
+#include "mongo/client/remote_command_targeter.h"
+#include "mongo/db/curop.h"
+#include "mongo/db/dbdirectclient.h"
+#include "mongo/db/repl/repl_client_info.h"
+#include "mongo/db/repl/replication_coordinator_global.h"
+#include "mongo/rpc/get_status_from_command_result.h"
+#include "mongo/rpc/unique_message.h"
+#include "mongo/util/log.h"
+
+namespace mongo {
+
+const ConnectionString ShardLocal::getConnString() const {
+    MONGO_UNREACHABLE;
+}
+
+std::shared_ptr<RemoteCommandTargeter> ShardLocal::getTargeter() const {
+    MONGO_UNREACHABLE;
+};
+
+const ConnectionString ShardLocal::originalConnString() const {
+    MONGO_UNREACHABLE;
+}
+
+void ShardLocal::updateReplSetMonitor(const HostAndPort& remoteHost,
+                                      const Status& remoteCommandStatus) {
+    MONGO_UNREACHABLE;
+}
+
+std::string ShardLocal::toString() const {
+    return getId() + ":<local>";
+}
+
+StatusWith<Shard::CommandResponse> ShardLocal::_runCommand(OperationContext* txn,
+                                                           const ReadPreferenceSetting& unused,
+                                                           const std::string& dbName,
+                                                           const BSONObj& cmdObj,
+                                                           const BSONObj& metadata) {
+    try {
+        DBDirectClient client(txn);
+        rpc::UniqueReply commandResponse =
+            client.runCommandWithMetadata(dbName, cmdObj.firstElementFieldName(), metadata, cmdObj);
+        BSONObj responseReply = commandResponse->getCommandReply().getOwned();
+        BSONObj responseMetadata = commandResponse->getMetadata().getOwned();
+        return Shard::CommandResponse{responseReply, responseMetadata};
+    } catch (const DBException& ex) {
+        return ex.toStatus();
+    }
+}
+
+StatusWith<Shard::QueryResponse> ShardLocal::_exhaustiveFindOnConfig(
+    OperationContext* txn,
+    const ReadPreferenceSetting& readPref,
+    const NamespaceString& nss,
+    const BSONObj& query,
+    const BSONObj& sort,
+    boost::optional<long long> limit) {
+    // Set up operation context with majority read snapshot so correct optime can be retrieved.
+    Status status = txn->recoveryUnit()->setReadFromMajorityCommittedSnapshot();
+    auto replCoord = repl::ReplicationCoordinator::get(txn);
+
+    // Ensure timeout is set on the txn so we don't wait forever for the snapshot.
+    // TODO (SERVER-18277): Remove this
+    CurOp::get(txn)->ensureStarted();
+
+    // Wait until a snapshot is available.
+    while (status == ErrorCodes::ReadConcernMajorityNotAvailableYet) {
+        LOG(1) << "Waiting for ReadFromMajorityCommittedSnapshot to become available";
+        replCoord->waitUntilSnapshotCommitted(txn, SnapshotName::min());
+        status = txn->recoveryUnit()->setReadFromMajorityCommittedSnapshot();
+    }
+
+    if (!status.isOK()) {
+        return status;
+    }
+
+    DBDirectClient client(txn);
+    Query fullQuery(query);
+    if (!sort.isEmpty()) {
+        fullQuery.sort(sort);
+    }
+    fullQuery.readPref(readPref.pref, BSONArray());
+
+    try {
+        std::unique_ptr<DBClientCursor> cursor =
+            client.query(nss.ns().c_str(), fullQuery, limit.get_value_or(0));
+
+        if (!cursor) {
+            return {ErrorCodes::OperationFailed,
+                    str::stream() << "Failed to establish a cursor for reading " << nss.ns()
+                                  << " from local storage"};
+        }
+
+        std::vector<BSONObj> documentVector;
+        while (cursor->more()) {
+            BSONObj document = cursor->nextSafe().getOwned();
+            documentVector.push_back(std::move(document));
+        }
+
+        return Shard::QueryResponse{std::move(documentVector),
+                                    replCoord->getCurrentCommittedSnapshotOpTime()};
+    } catch (const DBException& ex) {
+        return ex.toStatus();
+    }
+}
+
+
+}  // namespace mongo
diff --git a/src/mongo/s/client/shard_local.h b/src/mongo/s/client/shard_local.h
new file mode 100644
index 00000000000..e2330a059b4
--- /dev/null
+++ b/src/mongo/s/client/shard_local.h
@@ -0,0 +1,73 @@
+/**
+ * Copyright (C) 2016 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects
+ * for all of the code used other than as permitted herein. If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so. If you do not
+ * wish to do so, delete this exception statement from your version. If you
+ * delete this exception statement from all source files in the program,
+ * then also delete it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/client/dbclientinterface.h"
+#include "mongo/s/client/shard.h"
+
+namespace mongo {
+
+class ShardLocal : public Shard {
+    MONGO_DISALLOW_COPYING(ShardLocal);
+
+public:
+    explicit ShardLocal(const ShardId& id) : Shard(id) {}
+
+    ~ShardLocal() = default;
+
+    /**
+     * These functions are implemented for the Shard interface's sake. They should not be called on
+     * ShardLocal because doing so triggers invariants.
+     */
+    const ConnectionString getConnString() const override;
+    const ConnectionString originalConnString() const override;
+    std::shared_ptr<RemoteCommandTargeter> getTargeter() const override;
+    void updateReplSetMonitor(const HostAndPort& remoteHost,
+                              const Status& remoteCommandStatus) override;
+
+    std::string toString() const override;
+
+private:
+    StatusWith<Shard::CommandResponse> _runCommand(OperationContext* txn,
+                                                   const ReadPreferenceSetting& unused,
+                                                   const std::string& dbName,
+                                                   const BSONObj& cmdObj,
+                                                   const BSONObj& metadata) override;
+
+    StatusWith<Shard::QueryResponse> _exhaustiveFindOnConfig(
+        OperationContext* txn,
+        const ReadPreferenceSetting& readPref,
+        const NamespaceString& nss,
+        const BSONObj& query,
+        const BSONObj& sort,
+        boost::optional<long long> limit) override;
+};
+
+}  // namespace mongo
diff --git a/src/mongo/s/client/shard_local_test.cpp b/src/mongo/s/client/shard_local_test.cpp
new file mode 100644
index 00000000000..ac0dc929ee4
--- /dev/null
+++ b/src/mongo/s/client/shard_local_test.cpp
@@ -0,0 +1,208 @@
+/**
+ * Copyright (C) 2016 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects
+ * for all of the code used other than as permitted herein. If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so. If you do not
+ * wish to do so, delete this exception statement from your version. If you
+ * delete this exception statement from all source files in the program,
+ * then also delete it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/s/client/shard_local.h"
+
+#include "mongo/client/read_preference.h"
+#include "mongo/db/client.h"
+#include "mongo/db/catalog/database_holder.h"
+#include "mongo/db/db_raii.h"
+#include "mongo/db/query/find_and_modify_request.h"
+#include "mongo/db/repl/replication_coordinator_global.h"
+#include "mongo/db/repl/replication_coordinator_mock.h"
+#include "mongo/db/service_context_d_test_fixture.h"
+#include "mongo/db/write_concern_options.h"
+
+namespace mongo {
+namespace {
+
+class ShardLocalTest : public ServiceContextMongoDTest {
+protected:
+    ServiceContext::UniqueOperationContext _txn;
+    ShardLocal* _shardLocal;
+
+    /**
+     * Sets up and runs a FindAndModify command with ShardLocal's runCommand. Finds a document in
+     * namespace "nss" that matches "find" and updates the document with "set". Upsert and new are
+     * set to true in the FindAndModify request.
+     */
+    StatusWith<Shard::CommandResponse> runFindAndModifyRunCommand(NamespaceString nss,
+                                                                  BSONObj find,
+                                                                  BSONObj set);
+    /**
+     * Facilitates running a find query by supplying the redundant parameters. Finds documents in
+     * namespace "nss" that match "query" and returns "limit" (if there are that many) number of
+     * documents in "sort" order.
+     */
+    StatusWith<Shard::QueryResponse> runFindQuery(NamespaceString nss,
+                                                  BSONObj query,
+                                                  BSONObj sort,
+                                                  boost::optional<long long> limit);
+
+private:
+    void setUp() override;
+    void tearDown() override;
+};
+
+void ShardLocalTest::setUp() {
+    ServiceContextMongoDTest::setUp();
+    Client::initThreadIfNotAlready();
+    _txn = getGlobalServiceContext()->makeOperationContext(&cc());
+    _shardLocal = new ShardLocal("shardOrConfig");
+    const repl::ReplSettings replSettings = {};
+    repl::setGlobalReplicationCoordinator(new repl::ReplicationCoordinatorMock(replSettings));
+}
+
+void ShardLocalTest::tearDown() {
+    _txn.reset();
+    ServiceContextMongoDTest::tearDown();
+    repl::setGlobalReplicationCoordinator(nullptr);
+}
+
+StatusWith<Shard::CommandResponse> ShardLocalTest::runFindAndModifyRunCommand(NamespaceString nss,
+                                                                              BSONObj find,
+                                                                              BSONObj set) {
+    FindAndModifyRequest findAndModifyRequest = FindAndModifyRequest::makeUpdate(nss, find, set);
+    findAndModifyRequest.setUpsert(true);
+    findAndModifyRequest.setShouldReturnNew(true);
+    findAndModifyRequest.setWriteConcern(WriteConcernOptions(
+        WriteConcernOptions::kMajority, WriteConcernOptions::SyncMode::UNSET, Seconds(15)));
+
+    return _shardLocal->runCommand(_txn.get(),
+                                   ReadPreferenceSetting{ReadPreference::PrimaryOnly},
+                                   nss.db().toString(),
+                                   findAndModifyRequest.toBSON(),
+                                   BSONObj());
+}
+
+/**
+ * Takes a FindAndModify command's BSON response and parses it for the returned "value" field.
+ */
+BSONObj extractFindAndModifyNewObj(const BSONObj& responseObj) {
+    const auto& newDocElem = responseObj["value"];
+    ASSERT(!newDocElem.eoo());
+    ASSERT(newDocElem.isABSONObj());
+    return newDocElem.Obj();
+}
+
+StatusWith<Shard::QueryResponse> ShardLocalTest::runFindQuery(NamespaceString nss,
+                                                              BSONObj query,
+                                                              BSONObj sort,
+                                                              boost::optional<long long> limit) {
+    return _shardLocal->exhaustiveFindOnConfig(
+        _txn.get(), ReadPreferenceSetting{ReadPreference::PrimaryOnly}, nss, query, sort, limit);
+}
+
+TEST_F(ShardLocalTest, RunCommand) {
+    NamespaceString nss("foo.bar");
+    StatusWith<Shard::CommandResponse> findAndModifyResponse = runFindAndModifyRunCommand(
+        nss, BSON("fooItem" << 1), BSON("$set" << BSON("fooRandom" << 254)));
+
+    Shard::CommandResponse commandResponse = unittest::assertGet(findAndModifyResponse);
+    BSONObj newDocument = extractFindAndModifyNewObj(commandResponse.response);
+
+    ASSERT_EQUALS(1, newDocument["fooItem"].numberInt());
+    ASSERT_EQUALS(254, newDocument["fooRandom"].numberInt());
+}
+
+TEST_F(ShardLocalTest, FindOneWithoutLimit) {
+    NamespaceString nss("foo.bar");
+
+    // Set up documents to be queried.
+    StatusWith<Shard::CommandResponse> findAndModifyResponse = runFindAndModifyRunCommand(
+        nss, BSON("fooItem" << 1), BSON("$set" << BSON("fooRandom" << 254)));
+    ASSERT_OK(findAndModifyResponse.getStatus());
+    findAndModifyResponse = runFindAndModifyRunCommand(
+        nss, BSON("fooItem" << 3), BSON("$set" << BSON("fooRandom" << 452)));
+    ASSERT_OK(findAndModifyResponse.getStatus());
+
+    // Find a single document.
+    StatusWith<Shard::QueryResponse> response =
+        runFindQuery(nss, BSON("fooItem" << 3), BSONObj(), boost::none);
+    Shard::QueryResponse queryResponse = unittest::assertGet(response);
+
+    std::vector<BSONObj> docs = queryResponse.docs;
+    const unsigned long size = 1;
+    ASSERT_EQUALS(size, docs.size());
+    BSONObj foundDoc = docs[0];
+    ASSERT_EQUALS(3, foundDoc["fooItem"].numberInt());
+    ASSERT_EQUALS(452, foundDoc["fooRandom"].numberInt());
+}
+
+TEST_F(ShardLocalTest, FindManyWithLimit) {
+    NamespaceString nss("foo.bar");
+
+    // Set up documents to be queried.
+    StatusWith<Shard::CommandResponse> findAndModifyResponse = runFindAndModifyRunCommand(
+        nss, BSON("fooItem" << 1), BSON("$set" << BSON("fooRandom" << 254)));
+    ASSERT_OK(findAndModifyResponse.getStatus());
+    findAndModifyResponse = runFindAndModifyRunCommand(
+        nss, BSON("fooItem" << 2), BSON("$set" << BSON("fooRandom" << 444)));
+    ASSERT_OK(findAndModifyResponse.getStatus());
+    findAndModifyResponse = runFindAndModifyRunCommand(
+        nss, BSON("fooItem" << 3), BSON("$set" << BSON("fooRandom" << 452)));
+    ASSERT_OK(findAndModifyResponse.getStatus());
+
+    // Find 2 of 3 documents.
+    StatusWith<Shard::QueryResponse> response =
+        runFindQuery(nss, BSONObj(), BSON("fooItem" << 1), 2LL);
+    Shard::QueryResponse queryResponse = unittest::assertGet(response);
+
+    std::vector<BSONObj> docs = queryResponse.docs;
+    const unsigned long size = 2;
+    ASSERT_EQUALS(size, docs.size());
+    BSONObj firstDoc = docs[0];
+    ASSERT_EQUALS(1, firstDoc["fooItem"].numberInt());
+    ASSERT_EQUALS(254, firstDoc["fooRandom"].numberInt());
+    BSONObj secondDoc = docs[1];
+    ASSERT_EQUALS(2, secondDoc["fooItem"].numberInt());
+    ASSERT_EQUALS(444, secondDoc["fooRandom"].numberInt());
+}
+
+TEST_F(ShardLocalTest, FindNoMatchingDocumentsEmpty) {
+    NamespaceString nss("foo.bar");
+
+    // Set up a document.
+    StatusWith<Shard::CommandResponse> findAndModifyResponse = runFindAndModifyRunCommand(
+        nss, BSON("fooItem" << 1), BSON("$set" << BSON("fooRandom" << 254)));
+    ASSERT_OK(findAndModifyResponse.getStatus());
+
+    // Run a query that won't find any results.
+    StatusWith<Shard::QueryResponse> response =
+        runFindQuery(nss, BSON("fooItem" << 3), BSONObj(), boost::none);
+    Shard::QueryResponse queryResponse = unittest::assertGet(response);
+
+    std::vector<BSONObj> docs = queryResponse.docs;
+    const unsigned long size = 0;
+    ASSERT_EQUALS(size, docs.size());
+}
+
+}  // namespace
+}  // namespace mongo
diff --git a/src/mongo/s/client/shard_remote.h b/src/mongo/s/client/shard_remote.h
index 3c943f81b9b..35befdf8417 100644
--- a/src/mongo/s/client/shard_remote.h
+++ b/src/mongo/s/client/shard_remote.h
@@ -36,8 +36,6 @@
 
 namespace mongo {
 
-using ShardId = std::string;
-
 /*
  * Maintains the targeting and command execution logic for a single shard. Performs polling of
  * the shard (if replica set).
@@ -61,7 +59,7 @@ public:
         return _originalConnString;
     }
 
-    std::shared_ptr<RemoteCommandTargeter> getTargeter() override {
+    std::shared_ptr<RemoteCommandTargeter> getTargeter() const override {
         return _targeter;
     }