1 files changed, 9 insertions, 3 deletions
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_begin_transaction_block.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_begin_transaction_block.cpp
index 1ad70b3d11b..c3421f81987 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_begin_transaction_block.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_begin_transaction_block.cpp
@@ -91,10 +91,16 @@ WiredTigerBeginTxnBlock::~WiredTigerBeginTxnBlock() {
 
 Status WiredTigerBeginTxnBlock::setReadSnapshot(Timestamp readTimestamp) {
     invariant(_rollback);
-    std::string readTSConfigString = "read_timestamp={:x}"_format(readTimestamp.asULL());
+    // Avoid heap allocation in favour of a stack allocation for the configuration string.
+    constexpr auto configFmtString = "read_timestamp={:x}";
+    constexpr auto numBytesRequired = std::char_traits<char>::length(configFmtString) +
+        (sizeof(decltype(readTimestamp.asULL())) * 2) + 1;
+    std::array<char, numBytesRequired> configString;
+    auto end =
+        fmt::format_to(configString.begin(), FMT_STRING(configFmtString), readTimestamp.asULL());
+    *end = '\0';
 
-    return wtRCToStatus(_session->timestamp_transaction(_session, readTSConfigString.c_str()),
-                        _session);
+    return wtRCToStatus(_session->timestamp_transaction(_session, configString.begin()), _session);
 }
 
 void WiredTigerBeginTxnBlock::done() {