SERVER-40337: Remove oldestOpenUnpreparedReadTimestamp from serverStatus.transactions

This reverts most of the work done in 3bb72042c29ceac96ec628ee643cbc4db8e982ab

5 files changed, 9 insertions, 83 deletions

diff --git a/jstests/noPassthrough/server_transaction_metrics.js b/jstests/noPassthrough/server_transaction_metrics.js
index 191619ca3fc..a3d870f8a50 100644
--- a/jstests/noPassthrough/server_transaction_metrics.js
+++ b/jstests/noPassthrough/server_transaction_metrics.js
@@ -28,11 +28,6 @@
         assert(serverStatusResponse.transactions.hasOwnProperty("totalStarted"),
                "The 'transactions' field in serverStatus did not have the 'totalStarted' field\n" +
                    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
@@ -71,10 +66,8 @@
     jsTest.log("Start a transaction and then commit it.");
 
     // Compare server status after starting a transaction with the server status before.
-    session.startTransaction({readConcern: {level: 'snapshot'}});
+    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);
@@ -85,8 +78,6 @@
         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();
@@ -102,18 +93,13 @@
         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.");
 
     // Compare server status after starting a transaction with the server status before.
-    session.startTransaction({readConcern: {level: 'snapshot'}});
+    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);
@@ -124,8 +110,6 @@
         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();
@@ -142,19 +126,14 @@
         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.");
 
     // Compare server status after starting a transaction with the server status before.
-    session.startTransaction({readConcern: {level: 'snapshot'}});
+    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);
@@ -165,8 +144,6 @@
         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.
@@ -236,9 +213,6 @@
         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 ba599d711cf..74a3f0a347e 100644
--- a/jstests/noPassthrough/server_transaction_metrics_for_prepared_transactions.js
+++ b/jstests/noPassthrough/server_transaction_metrics_for_prepared_transactions.js
@@ -25,10 +25,6 @@
         assert(serverStatusResponse.transactions.hasOwnProperty("currentPrepared"),
                "Expected the serverStatus response to have a 'currentPrepared' field: " +
                    tojson(serverStatusResponse));
-        assert(
-            serverStatusResponse.transactions.hasOwnProperty("oldestOpenUnpreparedReadTimestamp"),
-            "Expected the serverStatus response to have a 'oldestOpenUnpreparedReadTimestamp' " +
-                "field: " + tojson(serverStatusResponse));
     }
 
     /**
@@ -93,29 +89,20 @@
     const doc1 = {_id: 1, x: 1};
 
     // Start transaction and prepare transaction.
-    session.startTransaction({readConcern: {level: 'snapshot'}});
+    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.
-    newStatus = assert.commandWorked(testDB.adminCommand({serverStatus: 1}));
+    let newStatus = assert.commandWorked(testDB.adminCommand({serverStatus: 1}));
     verifyServerStatusFields(newStatus);
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "totalPrepared", 1);
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "currentPrepared", 1);
 
-    // Verify that the oldestOpenUnpreparedReadTimestamp is a null timestamp since the transaction
-    // has been prepared.
-    assert.eq(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
-
     // Verify that the prepare entry has the oldest timestamp of any active transaction
     // in the transactions table.
     verifyOldestActiveTransactionTimestamp(testDB, prepareTimestampForCommit);
@@ -135,9 +122,6 @@
         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");
@@ -145,14 +129,9 @@
     const doc2 = {_id: 2, x: 2};
 
     // Start transaction and prepare transaction.
-    session.startTransaction({readConcern: {level: 'snapshot'}});
+    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
@@ -164,10 +143,6 @@
     verifyServerStatusChange(
         initialStatus.transactions, newStatus.transactions, "currentPrepared", 1);
 
-    // Verify that the oldestOpenUnpreparedReadTimestamp is a null timestamp since the transaction
-    // has been prepared.
-    assert.eq(newStatus.transactions.oldestOpenUnpreparedReadTimestamp, Timestamp(0, 0));
-
     // Verify that the prepare entry has the oldest timestamp of any active transaction
     // in the transactions table.
     verifyOldestActiveTransactionTimestamp(testDB, prepareTimestampForAbort);
@@ -182,10 +157,6 @@
     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 54300a1ca26..1daa320782d 100644
--- a/src/mongo/db/server_transactions_metrics.cpp
+++ b/src/mongo/db/server_transactions_metrics.cpp
@@ -149,15 +149,7 @@ void ServerTransactionsMetrics::decrementCurrentPrepared() {
     _currentPrepared.fetchAndSubtract(1);
 }
 
-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) {
+void ServerTransactionsMetrics::updateStats(TransactionsStats* stats) {
     stats->setCurrentActive(_currentActive.load());
     stats->setCurrentInactive(_currentInactive.load());
     stats->setCurrentOpen(_currentOpen.load());
@@ -168,8 +160,6 @@ void ServerTransactionsMetrics::updateStats(TransactionsStats* stats, OperationC
     stats->setTotalPreparedThenCommitted(_totalPreparedThenCommitted.load());
     stats->setTotalPreparedThenAborted(_totalPreparedThenAborted.load());
     stats->setCurrentPrepared(_currentPrepared.load());
-    stats->setOldestOpenUnpreparedReadTimestamp(
-        ServerTransactionsMetrics::_getOldestOpenUnpreparedReadTimestamp(opCtx));
 }
 
 namespace {
@@ -192,7 +182,7 @@ 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, opCtx);
+        ServerTransactionsMetrics::get(opCtx)->updateStats(&stats);
         return stats.toBSON();
     }
 
diff --git a/src/mongo/db/server_transactions_metrics.h b/src/mongo/db/server_transactions_metrics.h
index d5b829f6845..250b2c41931 100644
--- a/src/mongo/db/server_transactions_metrics.h
+++ b/src/mongo/db/server_transactions_metrics.h
@@ -90,16 +90,9 @@ public:
     /**
      * Appends the accumulated stats to a transactions stats object.
      */
-    void updateStats(TransactionsStats* stats, OperationContext* opCtx);
+    void updateStats(TransactionsStats* stats);
 
 private:
-    /**
-     * 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);
-
     // The number of multi-document transactions currently active.
     AtomicWord<unsigned long long> _currentActive{0};
 
diff --git a/src/mongo/db/transactions_stats.idl b/src/mongo/db/transactions_stats.idl
index ad70e141d6f..c2a269d4a79 100644
--- a/src/mongo/db/transactions_stats.idl
+++ b/src/mongo/db/transactions_stats.idl
@@ -83,5 +83,3 @@ structs:
       currentPrepared:
         type: long
         default: 0
-      oldestOpenUnpreparedReadTimestamp:
-        type: timestamp