From 6f74f6f0e9f85d55f7c9b5d217d583f9bba308db Mon Sep 17 00:00:00 2001
From: Jason Chan <jason.chan@mongodb.com>
Date: Wed, 6 Jan 2021 21:13:38 +0000
Subject: SERVER-53609 Filter out
 serverStatus.transactions.lastCommittedTransaction from FTDC

(cherry picked from commit 3e5fc29b410b4a0e999f190de5f035e3119f6565)
---
 .../server_transaction_metrics_last_committed_transaction.js  |  7 +++++++
 src/mongo/db/ftdc/ftdc_server.cpp                             |  4 ++++
 src/mongo/db/server_transactions_metrics.cpp                  | 11 ++++++++---
 src/mongo/db/server_transactions_metrics.h                    |  3 ++-
 4 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/jstests/noPassthrough/server_transaction_metrics_last_committed_transaction.js b/jstests/noPassthrough/server_transaction_metrics_last_committed_transaction.js
index bbbd0741c46..d04c697ed00 100644
--- a/jstests/noPassthrough/server_transaction_metrics_last_committed_transaction.js
+++ b/jstests/noPassthrough/server_transaction_metrics_last_committed_transaction.js
@@ -61,6 +61,13 @@ assert(!res.transactions.hasOwnProperty("lastCommittedTransaction"), () => tojso
 assert.commandWorked(PrepareHelpers.commitTransaction(session, prepareTimestampForCommit));
 checkLastCommittedTransaction(1, {});
 
+// Check that we are able to exclude 'lastCommittedTransaction'. FTDC uses this to filter out
+// the section as it frequently triggers scheme changes.
+let filteredRes = assert.commandWorked(
+    primary.adminCommand({serverStatus: 1, transactions: {includeLastCommitted: false}}));
+assert(!filteredRes.transactions.hasOwnProperty("lastCommittedTransaction"),
+       () => tojson(filteredRes));
+
 function runTests(prepare) {
     jsTestLog("Testing server transaction metrics with prepare=" + prepare);
 
diff --git a/src/mongo/db/ftdc/ftdc_server.cpp b/src/mongo/db/ftdc/ftdc_server.cpp
index 0026ccf5864..9068f480a8d 100644
--- a/src/mongo/db/ftdc/ftdc_server.cpp
+++ b/src/mongo/db/ftdc/ftdc_server.cpp
@@ -218,6 +218,10 @@ public:
         commandBuilder.append("defaultRWConcern", false);
         commandBuilder.append(MirrorMaestro::kServerStatusSectionName, true);
 
+        // Exclude 'serverStatus.transactions.lastCommittedTransactions' because it triggers
+        // frequent schema changes.
+        commandBuilder.append("transactions", BSON("includeLastCommitted" << false));
+
         if (gDiagnosticDataCollectionEnableLatencyHistograms.load()) {
             BSONObjBuilder subObjBuilder(commandBuilder.subobjStart("opLatencies"));
             subObjBuilder.append("histograms", true);
diff --git a/src/mongo/db/server_transactions_metrics.cpp b/src/mongo/db/server_transactions_metrics.cpp
index a51ecc0345c..411e898dbe3 100644
--- a/src/mongo/db/server_transactions_metrics.cpp
+++ b/src/mongo/db/server_transactions_metrics.cpp
@@ -161,7 +161,7 @@ void ServerTransactionsMetrics::updateLastTransaction(size_t operationCount,
     _lastCommittedTransaction->setWriteConcern(std::move(writeConcern));
 }
 
-void ServerTransactionsMetrics::updateStats(TransactionsStats* stats) {
+void ServerTransactionsMetrics::updateStats(TransactionsStats* stats, bool includeLastCommitted) {
     stats->setCurrentActive(_currentActive.load());
     stats->setCurrentInactive(_currentInactive.load());
     stats->setCurrentOpen(_currentOpen.load());
@@ -174,7 +174,7 @@ void ServerTransactionsMetrics::updateStats(TransactionsStats* stats) {
     stats->setCurrentPrepared(_currentPrepared.load());
 
     stdx::lock_guard<Latch> lg(_mutex);
-    if (_lastCommittedTransaction) {
+    if (_lastCommittedTransaction && includeLastCommitted) {
         stats->setLastCommittedTransaction(*_lastCommittedTransaction);
     }
 }
@@ -194,12 +194,17 @@ public:
                             const BSONElement& configElement) const override {
         TransactionsStats stats;
 
+        bool includeLastCommitted = true;
+        if (configElement.type() == BSONType::Object) {
+            includeLastCommitted = configElement.Obj()["includeLastCommitted"].trueValue();
+        }
+
         // Retryable writes and multi-document transactions metrics are both included in the same
         // serverStatus section because both utilize similar internal machinery for tracking their
         // 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, includeLastCommitted);
         return stats.toBSON();
     }
 
diff --git a/src/mongo/db/server_transactions_metrics.h b/src/mongo/db/server_transactions_metrics.h
index 78523e5fa36..d17742dd5b6 100644
--- a/src/mongo/db/server_transactions_metrics.h
+++ b/src/mongo/db/server_transactions_metrics.h
@@ -94,8 +94,9 @@ public:
 
     /**
      * Appends the accumulated stats to a transactions stats object.
+     * Include the 'lastCommittedTransactions' field if 'includeLastCommitted' is true.
      */
-    void updateStats(TransactionsStats* stats);
+    void updateStats(TransactionsStats* stats, bool includeLastCommitted);
 
 private:
     // The number of multi-document transactions currently active.
-- 
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