SERVER-39672: default to local if no read concern specified for a multi-statment transaction

jstests/core/txns/speculative_snapshot_includes_all_writes.js

@@ -22,15 +22,21 @@
     assert.commandWorked(testDB.createCollection(collName2, {writeConcern: {w: "majority"}}));
 
     const sessionOptions = {causalConsistency: false};
-    const session = db.getMongo().startSession(sessionOptions);
-    const sessionDb = session.getDatabase(dbName);
-    const sessionColl = sessionDb.getCollection(collName);
-    const sessionColl2 = sessionDb.getCollection(collName2);
 
-    const session2 = db.getMongo().startSession(sessionOptions);
-    const session2Db = session2.getDatabase(dbName);
-    const session2Coll = session2Db.getCollection(collName);
-    const session2Coll2 = session2Db.getCollection(collName2);
+    function startSessionAndTransaction(readConcernLevel) {
+        let session = db.getMongo().startSession(sessionOptions);
+        jsTestLog("Start a transaction with readConcern " + readConcernLevel.level + ".");
+        session.startTransaction({readConcern: readConcernLevel});
+        return session;
+    };
+
+    let checkReads = (session, collExpected, coll2Expected) => {
+        let sessionDb = session.getDatabase(dbName);
+        let coll = sessionDb.getCollection(collName);
+        let coll2 = sessionDb.getCollection(collName2);
+        assert.sameMembers(collExpected, coll.find().toArray());
+        assert.sameMembers(coll2Expected, coll2.find().toArray());
+    };
 
     // Clear ramlog so checkLog can't find log messages from previous times this fail point was
     // enabled.
@@ -63,21 +69,17 @@
     // the prior uncommitted write is committed.
     assert.commandWorked(testColl.insert([{_id: 1}]));
 
-    jsTestLog("Start a snapshot transaction.");
+    const snapshotSession = startSessionAndTransaction({level: "snapshot"});
+    checkReads(snapshotSession, [{_id: 0}], [{_id: "a"}]);
 
-    session.startTransaction({readConcern: {level: "snapshot"}});
+    const majoritySession = startSessionAndTransaction({level: "majority"});
+    checkReads(majoritySession, [{_id: 0}, {_id: 1}], [{_id: "a"}]);
 
-    assert.sameMembers([{_id: 0}], sessionColl.find().toArray());
+    const localSession = startSessionAndTransaction({level: "local"});
+    checkReads(localSession, [{_id: 0}, {_id: 1}], [{_id: "a"}]);
 
-    assert.sameMembers([{_id: "a"}], sessionColl2.find().toArray());
-
-    jsTestLog("Start a majority-read transaction.");
-
-    session2.startTransaction({readConcern: {level: "majority"}});
-
-    assert.sameMembers([{_id: 0}, {_id: 1}], session2Coll.find().toArray());
-
-    assert.sameMembers([{_id: "a"}], session2Coll2.find().toArray());
+    const defaultSession = startSessionAndTransaction({});
+    checkReads(defaultSession, [{_id: 0}, {_id: 1}], [{_id: "a"}]);
 
     jsTestLog("Allow the uncommitted write to finish.");
     assert.commandWorked(db.adminCommand({
@@ -88,25 +90,25 @@
     joinHungWrite();
 
     jsTestLog("Double-checking that writes not committed at start of snapshot cannot appear.");
-    assert.sameMembers([{_id: 0}], sessionColl.find().toArray());
+    checkReads(snapshotSession, [{_id: 0}], [{_id: "a"}]);
 
-    assert.sameMembers([{_id: "a"}], sessionColl2.find().toArray());
-
-    assert.sameMembers([{_id: 0}, {_id: 1}], session2Coll.find().toArray());
-
-    assert.sameMembers([{_id: "a"}], session2Coll2.find().toArray());
+    jsTestLog(
+        "Double-checking that writes performed before the start of a transaction of 'majority' or lower must appear.");
+    checkReads(majoritySession, [{_id: 0}, {_id: 1}], [{_id: "a"}]);
+    checkReads(localSession, [{_id: 0}, {_id: 1}], [{_id: "a"}]);
+    checkReads(defaultSession, [{_id: 0}, {_id: 1}], [{_id: "a"}]);
 
     jsTestLog("Committing transactions.");
-    session.commitTransaction();
-    session2.commitTransaction();
+    snapshotSession.commitTransaction();
+    majoritySession.commitTransaction();
+    localSession.commitTransaction();
+    defaultSession.commitTransaction();
 
-    assert.sameMembers([{_id: 0}, {_id: 1}], sessionColl.find().toArray());
+    jsTestLog("A new local read must see all committed writes.");
+    checkReads(defaultSession, [{_id: 0}, {_id: 1}], [{_id: "a"}, {_id: "b"}]);
 
-    assert.sameMembers([{_id: "a"}, {_id: "b"}], sessionColl2.find().toArray());
-
-    assert.sameMembers([{_id: 0}, {_id: 1}], session2Coll.find().toArray());
-
-    assert.sameMembers([{_id: "a"}, {_id: "b"}], session2Coll2.find().toArray());
-
-    session.endSession();
+    snapshotSession.endSession();
+    majoritySession.endSession();
+    localSession.endSession();
+    defaultSession.endSession();
 }());

jstests/noPassthrough/server_transaction_metrics.js

@@ -71,7 +71,7 @@
     jsTest.log("Start a transaction and then commit it.");
 
     // Compare server status after starting a transaction with the server status before.
-    session.startTransaction();
+    session.startTransaction({readConcern: {level: 'snapshot'}});
     assert.commandWorked(sessionColl.insert({_id: "insert-1"}));
     // Trigger the oldestOpenUnpreparedReadTimestamp to be set.
     assert.eq(sessionColl.find({_id: "insert-1"}).itcount(), 1);
@@ -110,7 +110,7 @@
     jsTest.log("Start a transaction and then abort it.");
 
     // Compare server status after starting a transaction with the server status before.
-    session.startTransaction();
+    session.startTransaction({readConcern: {level: 'snapshot'}});
     assert.commandWorked(sessionColl.insert({_id: "insert-2"}));
     // Trigger the oldestOpenUnpreparedReadTimestamp to be set.
     assert.eq(sessionColl.find({_id: "insert-2"}).itcount(), 1);
@@ -150,7 +150,7 @@
     jsTest.log("Start a transaction that will abort on a duplicated key error.");
 
     // Compare server status after starting a transaction with the server status before.
-    session.startTransaction();
+    session.startTransaction({readConcern: {level: 'snapshot'}});
     // Inserting a new document will work fine, and the transaction starts.
     assert.commandWorked(sessionColl.insert({_id: "insert-3"}));
     // Trigger the oldestOpenUnpreparedReadTimestamp to be set.

jstests/noPassthrough/server_transaction_metrics_for_prepared_transactions.js

@@ -69,7 +69,7 @@
     const doc1 = {_id: 1, x: 1};
 
     // Start transaction and prepare transaction.
-    session.startTransaction();
+    session.startTransaction({readConcern: {level: 'snapshot'}});
     assert.commandWorked(sessionColl.insert(doc1));
 
     // Trigger the oldestOpenUnpreparedReadTimestamp to be set.
@@ -118,7 +118,7 @@
     const doc2 = {_id: 2, x: 2};
 
     // Start transaction and prepare transaction.
-    session.startTransaction();
+    session.startTransaction({readConcern: {level: 'snapshot'}});
     assert.commandWorked(sessionColl.insert(doc2));
 
     // Trigger the oldestOpenUnpreparedReadTimestamp to be set.

jstests/noPassthrough/transaction_write_with_snapshot_unavailable.js

@@ -35,7 +35,7 @@
         jsTestLog(
             `Testing that SnapshotUnavailable during ${op} is labelled TransientTransactionError`);
 
-        session.startTransaction();
+        session.startTransaction({readConcern: {level: "snapshot"}});
         assert.commandWorked(sessionDB.runCommand({insert: collName, documents: [{}]}));
         // Create collection outside transaction, cannot write to it in the transaction
         assert.commandWorked(primaryDB.getSiblingDB(dbNameB).runCommand({create: collNameB}));

src/mongo/db/repl/read_concern_args.cpp

@@ -106,7 +106,8 @@ ReadConcernLevel ReadConcernArgs::getLevel() const {
 }
 
 ReadConcernLevel ReadConcernArgs::getOriginalLevel() const {
-    return _originalLevel.value_or(getLevel());
+    // If no read concern specified, default to "local"
+    return _originalLevel.value_or(ReadConcernLevel::kLocalReadConcern);
 }
 
 bool ReadConcernArgs::hasLevel() const {

src/mongo/db/repl/read_concern_args_test.cpp

@@ -510,6 +510,7 @@ TEST(UpconvertReadConcernLevelToSnapshot, EmptyLevel) {
 
     ASSERT_OK(readConcern.upconvertReadConcernLevelToSnapshot());
     ASSERT(ReadConcernLevel::kSnapshotReadConcern == readConcern.getLevel());
+    ASSERT(ReadConcernLevel::kLocalReadConcern == readConcern.getOriginalLevel());
 }
 
 TEST(UpconvertReadConcernLevelToSnapshot, LevelLocal) {
@@ -522,6 +523,7 @@ TEST(UpconvertReadConcernLevelToSnapshot, LevelLocal) {
 
     ASSERT_OK(readConcern.upconvertReadConcernLevelToSnapshot());
     ASSERT(ReadConcernLevel::kSnapshotReadConcern == readConcern.getLevel());
+    ASSERT(ReadConcernLevel::kLocalReadConcern == readConcern.getOriginalLevel());
 }
 
 TEST(UpconvertReadConcernLevelToSnapshot, LevelMajority) {
@@ -535,6 +537,7 @@ TEST(UpconvertReadConcernLevelToSnapshot, LevelMajority) {
 
     ASSERT_OK(readConcern.upconvertReadConcernLevelToSnapshot());
     ASSERT(ReadConcernLevel::kSnapshotReadConcern == readConcern.getLevel());
+    ASSERT(ReadConcernLevel::kMajorityReadConcern == readConcern.getOriginalLevel());
 }
 
 TEST(UpconvertReadConcernLevelToSnapshot, LevelSnapshot) {
@@ -548,6 +551,7 @@ TEST(UpconvertReadConcernLevelToSnapshot, LevelSnapshot) {
 
     ASSERT_OK(readConcern.upconvertReadConcernLevelToSnapshot());
     ASSERT(ReadConcernLevel::kSnapshotReadConcern == readConcern.getLevel());
+    ASSERT(ReadConcernLevel::kSnapshotReadConcern == readConcern.getOriginalLevel());
 }
 
 TEST(UpconvertReadConcernLevelToSnapshot, LevelSnapshotWithAtClusterTime) {
@@ -565,6 +569,7 @@ TEST(UpconvertReadConcernLevelToSnapshot, LevelSnapshotWithAtClusterTime) {
 
     ASSERT_OK(readConcern.upconvertReadConcernLevelToSnapshot());
     ASSERT(ReadConcernLevel::kSnapshotReadConcern == readConcern.getLevel());
+    ASSERT(ReadConcernLevel::kSnapshotReadConcern == readConcern.getOriginalLevel());
     ASSERT_TRUE(readConcern.getArgsAtClusterTime());
 }
 
@@ -581,6 +586,7 @@ TEST(UpconvertReadConcernLevelToSnapshot, AfterClusterTime) {
 
     ASSERT_OK(readConcern.upconvertReadConcernLevelToSnapshot());
     ASSERT(ReadConcernLevel::kSnapshotReadConcern == readConcern.getLevel());
+    ASSERT(ReadConcernLevel::kLocalReadConcern == readConcern.getOriginalLevel());
     ASSERT_TRUE(readConcern.getArgsAfterClusterTime());
 }
 
@@ -595,6 +601,7 @@ TEST(UpconvertReadConcernLevelToSnapshot, LevelAvailable) {
 
     ASSERT_NOT_OK(readConcern.upconvertReadConcernLevelToSnapshot());
     ASSERT(ReadConcernLevel::kAvailableReadConcern == readConcern.getLevel());
+    ASSERT(ReadConcernLevel::kAvailableReadConcern == readConcern.getOriginalLevel());
 }
 
 TEST(UpconvertReadConcernLevelToSnapshot, LevelLinearizable) {
@@ -608,6 +615,7 @@ TEST(UpconvertReadConcernLevelToSnapshot, LevelLinearizable) {
 
     ASSERT_NOT_OK(readConcern.upconvertReadConcernLevelToSnapshot());
     ASSERT(ReadConcernLevel::kLinearizableReadConcern == readConcern.getLevel());
+    ASSERT(ReadConcernLevel::kLinearizableReadConcern == readConcern.getOriginalLevel());
 }
 
 TEST(UpconvertReadConcernLevelToSnapshot, AfterOpTime) {
@@ -624,6 +632,7 @@ TEST(UpconvertReadConcernLevelToSnapshot, AfterOpTime) {
 
     ASSERT_NOT_OK(readConcern.upconvertReadConcernLevelToSnapshot());
     ASSERT(ReadConcernLevel::kLocalReadConcern == readConcern.getLevel());
+    ASSERT(ReadConcernLevel::kLocalReadConcern == readConcern.getOriginalLevel());
     ASSERT_TRUE(readConcern.getArgsOpTime());
 }