SERVER-35713 Add oldestOpenReadTimestamp to serverStatus output

7 files changed, 95 insertions, 18 deletions

diff --git a/jstests/noPassthrough/server_transaction_metrics.js b/jstests/noPassthrough/server_transaction_metrics.js
index f83392a2ea5..1d437caba45 100644
--- a/jstests/noPassthrough/server_transaction_metrics.js
+++ b/jstests/noPassthrough/server_transaction_metrics.js
@@ -7,27 +7,32 @@
     function verifyServerStatusFields(serverStatusResponse) {
         assert(serverStatusResponse.hasOwnProperty("transactions"),
                "Expected the serverStatus response to have a 'transactions' field\n" +
-                   serverStatusResponse);
+                   tojson(serverStatusResponse));
         assert(serverStatusResponse.transactions.hasOwnProperty("currentActive"),
                "The 'transactions' field in serverStatus did not have the 'currentActive' field\n" +
-                   serverStatusResponse.transactions);
+                   tojson(serverStatusResponse.transactions));
         assert(
             serverStatusResponse.transactions.hasOwnProperty("currentInactive"),
             "The 'transactions' field in serverStatus did not have the 'currentInactive' field\n" +
-                serverStatusResponse.transactions);
+                tojson(serverStatusResponse.transactions));
         assert(serverStatusResponse.transactions.hasOwnProperty("currentOpen"),
                "The 'transactions' field in serverStatus did not have the 'currentOpen' field\n" +
-                   serverStatusResponse.transactions);
+                   tojson(serverStatusResponse.transactions));
         assert(serverStatusResponse.transactions.hasOwnProperty("totalAborted"),
                "The 'transactions' field in serverStatus did not have the 'totalAborted' field\n" +
-                   serverStatusResponse.transactions);
+                   tojson(serverStatusResponse.transactions));
         assert(
             serverStatusResponse.transactions.hasOwnProperty("totalCommitted"),
             "The 'transactions' field in serverStatus did not have the 'totalCommitted' field\n" +
-                serverStatusResponse.transactions);
+                tojson(serverStatusResponse.transactions));
         assert(serverStatusResponse.transactions.hasOwnProperty("totalStarted"),
                "The 'transactions' field in serverStatus did not have the 'totalStarted' field\n" +
-                   serverStatusResponse.transactions);
+                   tojson(serverStatusResponse.transactions));
+        assert(
+            serverStatusResponse.transactions.hasOwnProperty("oldestOpenUnpreparedReadTimestamp"),
+            "The 'transactions' field in serverStatus did not have the " +
+                "'oldestOpenUnpreparedReadTimestamp' field\n" +
+                tojson(serverStatusResponse.transactions));
     }
 
     // Verifies that the given value of the server status response is incremented in the way
@@ -68,6 +73,9 @@
     // Compare server status after starting a transaction with the server status before.
     session.startTransaction();
     assert.commandWorked(sessionColl.insert({_id: "insert-1"}));
+    // Trigger the oldestOpenUnpreparedReadTimestamp to be set.
+    assert.eq(sessionColl.find({_id: "insert-1"}).itcount(), 1);
+
     let newStatus = assert.commandWorked(testDB.adminCommand({serverStatus: 1}));
     verifyServerStatusFields(newStatus);
     // Verify that the open transaction counter is incremented while inside the transaction.
@@ -77,6 +85,8 @@
         initialStatus.transactions, newStatus.transactions, "currentActive", 0);
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "currentInactive", 1);
+    // Verify that the oldestOpenUnpreparedReadTimestamp has been set.
+    assert.gt(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
 
     // Compare server status after the transaction commit with the server status before.
     session.commitTransaction();
@@ -92,6 +102,9 @@
         initialStatus.transactions, newStatus.transactions, "currentActive", 0);
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "currentInactive", 0);
+    // Verify that the oldestOpenUnpreparedReadTimestamp is a null timestamp since the transaction
+    // has closed.
+    assert.eq(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
 
     // This transaction will abort.
     jsTest.log("Start a transaction and then abort it.");
@@ -99,6 +112,9 @@
     // Compare server status after starting a transaction with the server status before.
     session.startTransaction();
     assert.commandWorked(sessionColl.insert({_id: "insert-2"}));
+    // Trigger the oldestOpenUnpreparedReadTimestamp to be set.
+    assert.eq(sessionColl.find({_id: "insert-2"}).itcount(), 1);
+
     newStatus = assert.commandWorked(testDB.adminCommand({serverStatus: 1}));
     verifyServerStatusFields(newStatus);
     // Verify that the open transaction counter is incremented while inside the transaction.
@@ -108,6 +124,8 @@
         initialStatus.transactions, newStatus.transactions, "currentActive", 0);
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "currentInactive", 1);
+    // Verify that the oldestOpenUnpreparedReadTimestamp has been set.
+    assert.gt(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
 
     // Compare server status after the transaction abort with the server status before.
     session.abortTransaction_forTesting();
@@ -124,6 +142,9 @@
         initialStatus.transactions, newStatus.transactions, "currentActive", 0);
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "currentInactive", 0);
+    // Verify that the oldestOpenUnpreparedReadTimestamp is a null timestamp since the transaction
+    // has closed.
+    assert.eq(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
 
     // This transaction will abort due to a duplicate key insert.
     jsTest.log("Start a transaction that will abort on a duplicated key error.");
@@ -132,6 +153,9 @@
     session.startTransaction();
     // Inserting a new document will work fine, and the transaction starts.
     assert.commandWorked(sessionColl.insert({_id: "insert-3"}));
+    // Trigger the oldestOpenUnpreparedReadTimestamp to be set.
+    assert.eq(sessionColl.find({_id: "insert-3"}).itcount(), 1);
+
     newStatus = assert.commandWorked(testDB.adminCommand({serverStatus: 1}));
     verifyServerStatusFields(newStatus);
     // Verify that the open transaction counter is incremented while inside the transaction.
@@ -141,6 +165,8 @@
         initialStatus.transactions, newStatus.transactions, "currentActive", 0);
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "currentInactive", 1);
+    // Verify that the oldestOpenUnpreparedReadTimestamp has been set.
+    assert.gt(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
 
     // Compare server status after the transaction abort with the server status before.
     // The duplicated insert will fail, causing the transaction to abort.
@@ -212,6 +238,9 @@
         initialStatus.transactions, newStatus.transactions, "currentActive", 0);
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "currentInactive", 0);
+    // Verify that the oldestOpenUnpreparedReadTimestamp is a null timestamp since the transaction
+    // has closed.
+    assert.eq(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
 
     // End the session and stop the replica set.
     session.endSession();
diff --git a/jstests/noPassthrough/server_transaction_metrics_for_prepared_transactions.js b/jstests/noPassthrough/server_transaction_metrics_for_prepared_transactions.js
index f59ba448b39..4924143dfc9 100644
--- a/jstests/noPassthrough/server_transaction_metrics_for_prepared_transactions.js
+++ b/jstests/noPassthrough/server_transaction_metrics_for_prepared_transactions.js
@@ -10,19 +10,23 @@
     function verifyServerStatusFields(serverStatusResponse) {
         assert(serverStatusResponse.hasOwnProperty("transactions"),
                "Expected the serverStatus response to have a 'transactions' field: " +
-                   serverStatusResponse);
+                   tojson(serverStatusResponse));
         assert(serverStatusResponse.transactions.hasOwnProperty("totalPrepared"),
                "Expected the serverStatus response to have a 'totalPrepared' field: " +
-                   serverStatusResponse);
+                   tojson(serverStatusResponse));
         assert(serverStatusResponse.transactions.hasOwnProperty("totalPreparedThenCommitted"),
                "Expected the serverStatus response to have a 'totalPreparedThenCommitted' field: " +
-                   serverStatusResponse);
+                   tojson(serverStatusResponse));
         assert(serverStatusResponse.transactions.hasOwnProperty("totalPreparedThenAborted"),
                "Expected the serverStatus response to have a 'totalPreparedThenAborted' field: " +
-                   serverStatusResponse);
+                   tojson(serverStatusResponse));
         assert(serverStatusResponse.transactions.hasOwnProperty("currentPrepared"),
                "Expected the serverStatus response to have a 'currentPrepared' field: " +
-                   serverStatusResponse);
+                   tojson(serverStatusResponse));
+        assert(
+            serverStatusResponse.transactions.hasOwnProperty("oldestOpenUnpreparedReadTimestamp"),
+            "Expected the serverStatus response to have a 'oldestOpenUnpreparedReadTimestamp' " +
+                "field: " + tojson(serverStatusResponse));
     }
 
     /**
@@ -67,11 +71,17 @@
     // Start transaction and prepare transaction.
     session.startTransaction();
     assert.commandWorked(sessionColl.insert(doc1));
+
+    // Trigger the oldestOpenUnpreparedReadTimestamp to be set.
+    assert.eq(sessionColl.find(doc1).itcount(), 1);
+    let newStatus = assert.commandWorked(testDB.adminCommand({serverStatus: 1}));
+    assert.gt(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
+
     const prepareTimestampForCommit = PrepareHelpers.prepareTransaction(session);
 
     // Verify the total and current prepared transaction counter is updated and the oldest active
     // oplog entry timestamp is shown.
-    let newStatus = assert.commandWorked(testDB.adminCommand({serverStatus: 1}));
+    newStatus = assert.commandWorked(testDB.adminCommand({serverStatus: 1}));
     verifyServerStatusFields(newStatus);
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "totalPrepared", 1);
@@ -79,6 +89,9 @@
         initialStatus.transactions, newStatus.transactions, "currentPrepared", 1);
 
     assert.eq(newStatus.transactions.oldestActiveOplogEntryTimestamp, prepareTimestampForCommit);
+    // Verify that the oldestOpenUnpreparedReadTimestamp is a null timestamp since the transaction
+    // has been prepared.
+    assert.eq(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
 
     // Verify the total prepared and committed transaction counters are updated after a commit
     // and that the current prepared counter is decremented.
@@ -95,6 +108,9 @@
         initialStatus.transactions, newStatus.transactions, "totalPreparedThenAborted", 0);
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "totalPrepared", 1);
+    // Verify that the oldestOpenUnpreparedReadTimestamp is a null timestamp since the transaction
+    // is closed.
+    assert.eq(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
 
     // Test server metrics for a prepared transaction that is aborted.
     jsTest.log("Prepare a transaction and then abort it");
@@ -104,6 +120,12 @@
     // Start transaction and prepare transaction.
     session.startTransaction();
     assert.commandWorked(sessionColl.insert(doc2));
+
+    // Trigger the oldestOpenUnpreparedReadTimestamp to be set.
+    assert.eq(sessionColl.find(doc2).itcount(), 1);
+    newStatus = assert.commandWorked(testDB.adminCommand({serverStatus: 1}));
+    assert.gt(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
+
     const prepareTimestampForAbort = PrepareHelpers.prepareTransaction(session);
 
     // Verify that the total and current prepared counter is updated and the oldest active oplog
@@ -116,6 +138,9 @@
         initialStatus.transactions, newStatus.transactions, "currentPrepared", 1);
 
     assert.eq(newStatus.transactions.oldestActiveOplogEntryTimestamp, prepareTimestampForAbort);
+    // Verify that the oldestOpenUnpreparedReadTimestamp is a null timestamp since the transaction
+    // has been prepared.
+    assert.eq(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
 
     // Verify the total prepared and aborted transaction counters are updated after an abort and the
     // current prepared counter is decremented.
@@ -127,6 +152,10 @@
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "currentPrepared", 0);
 
+    // Verify that the oldestOpenUnpreparedReadTimestamp is a null timestamp since the transaction
+    // is closed.
+    assert.eq(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
+
     // Verify that other prepared transaction metrics have not changed.
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "totalPreparedThenCommitted", 1);
diff --git a/src/mongo/db/server_transactions_metrics.cpp b/src/mongo/db/server_transactions_metrics.cpp
index 6afdd053532..e71f7a25d31 100644
--- a/src/mongo/db/server_transactions_metrics.cpp
+++ b/src/mongo/db/server_transactions_metrics.cpp
@@ -273,7 +273,15 @@ unsigned int ServerTransactionsMetrics::getTotalActiveOpTimes() const {
     return _oldestActiveOplogEntryOpTimes.size();
 }
 
-void ServerTransactionsMetrics::updateStats(TransactionsStats* stats) {
+Timestamp ServerTransactionsMetrics::_getOldestOpenUnpreparedReadTimestamp(
+    OperationContext* opCtx) {
+    // The history is not pinned in memory once a transaction has been prepared since reads
+    // are no longer possible. Therefore, the timestamp returned by the storage engine refers
+    // to the oldest read timestamp for any open unprepared transaction.
+    return opCtx->getServiceContext()->getStorageEngine()->getOldestOpenReadTimestamp();
+}
+
+void ServerTransactionsMetrics::updateStats(TransactionsStats* stats, OperationContext* opCtx) {
     stats->setCurrentActive(_currentActive.load());
     stats->setCurrentInactive(_currentInactive.load());
     stats->setCurrentOpen(_currentOpen.load());
@@ -284,6 +292,8 @@ void ServerTransactionsMetrics::updateStats(TransactionsStats* stats) {
     stats->setTotalPreparedThenCommitted(_totalPreparedThenCommitted.load());
     stats->setTotalPreparedThenAborted(_totalPreparedThenAborted.load());
     stats->setCurrentPrepared(_currentPrepared.load());
+    stats->setOldestOpenUnpreparedReadTimestamp(
+        ServerTransactionsMetrics::_getOldestOpenUnpreparedReadTimestamp(opCtx));
     // Acquire _mutex before reading _oldestActiveOplogEntryOpTime.
     stdx::lock_guard<stdx::mutex> lm(_mutex);
     // To avoid compression loss, we have Timestamp(0, 0) be the default value if no oldest active
@@ -313,7 +323,7 @@ public:
         // lifecycle within a session. Both are assigned transaction numbers, and so both are often
         // referred to as “transactions”.
         RetryableWritesStats::get(opCtx)->updateStats(&stats);
-        ServerTransactionsMetrics::get(opCtx)->updateStats(&stats);
+        ServerTransactionsMetrics::get(opCtx)->updateStats(&stats, opCtx);
         return stats.toBSON();
     }
 
diff --git a/src/mongo/db/server_transactions_metrics.h b/src/mongo/db/server_transactions_metrics.h
index c29dd2b12f2..5bbcb661e8f 100644
--- a/src/mongo/db/server_transactions_metrics.h
+++ b/src/mongo/db/server_transactions_metrics.h
@@ -141,7 +141,7 @@ public:
     /**
      * Appends the accumulated stats to a transactions stats object.
      */
-    void updateStats(TransactionsStats* stats);
+    void updateStats(TransactionsStats* stats, OperationContext* opCtx);
 
 private:
     /**
@@ -150,6 +150,13 @@ private:
      */
     boost::optional<repl::OpTime> _calculateOldestActiveOpTime(WithLock) const;
 
+    /**
+     * Returns the oldest read timestamp in use by any open unprepared transaction. This will
+     * return a null timestamp if there is no oldest open unprepared read timestamp to be
+     * returned.
+     */
+    static Timestamp _getOldestOpenUnpreparedReadTimestamp(OperationContext* opCtx);
+
     //
     // Member variables, excluding atomic variables, are labeled with the following code to
     // indicate the synchronization rules for accessing them.
diff --git a/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_engine.h b/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_engine.h
index a52d175bdc1..c6111a553d8 100644
--- a/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_engine.h
+++ b/src/mongo/db/storage/ephemeral_for_test/ephemeral_for_test_engine.h
@@ -120,7 +120,7 @@ public:
     }
 
     virtual Timestamp getOldestOpenReadTimestamp() const override {
-        MONGO_UNREACHABLE;
+        return Timestamp();
     }
 
 private:
diff --git a/src/mongo/db/storage/mobile/mobile_kv_engine.h b/src/mongo/db/storage/mobile/mobile_kv_engine.h
index 716b2f97d74..6cb5cf42661 100644
--- a/src/mongo/db/storage/mobile/mobile_kv_engine.h
+++ b/src/mongo/db/storage/mobile/mobile_kv_engine.h
@@ -130,7 +130,7 @@ public:
     }
 
     virtual Timestamp getOldestOpenReadTimestamp() const override {
-        MONGO_UNREACHABLE;
+        return Timestamp();
     }
 
 private:
diff --git a/src/mongo/db/transactions_stats.idl b/src/mongo/db/transactions_stats.idl
index e2eebd0e7e6..834399a331c 100644
--- a/src/mongo/db/transactions_stats.idl
+++ b/src/mongo/db/transactions_stats.idl
@@ -84,3 +84,5 @@ structs:
         default: 0
       oldestActiveOplogEntryTimestamp:
         type: timestamp
+      oldestOpenUnpreparedReadTimestamp:
+        type: timestamp