From 90d3ce821b6faa28c68b515bfacb4ce63388759d Mon Sep 17 00:00:00 2001
From: Misha Tyulenev <misha@mongodb.com>
Date: Fri, 28 Feb 2020 14:59:17 -0500
Subject: SERVER-46463 add logging for hedged reads

---
 src/mongo/executor/network_interface_tl.cpp | 15 ++++++++++++++-
 src/mongo/executor/network_interface_tl.h   |  4 +++-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/mongo/executor/network_interface_tl.cpp b/src/mongo/executor/network_interface_tl.cpp
index afe86fa7ae7..76ff8e8cc7d 100644
--- a/src/mongo/executor/network_interface_tl.cpp
+++ b/src/mongo/executor/network_interface_tl.cpp
@@ -334,12 +334,14 @@ void NetworkInterfaceTL::RequestState::returnConnection(Status status) noexcept
 void NetworkInterfaceTL::CommandStateBase::tryFinish(Status status) noexcept {
     invariant(finishLine.isReady());
 
+    LOGV2_DEBUG(4646302, 2, "Finished request {request_id}", "request_id"_attr = requestOnAny.id);
+
     if (timer) {
         // The command has resolved one way or another,
         timer->cancel(baton);
     }
 
-    if (!status.isOK()) {
+    if (!status.isOK()) {  // TODO: SERVER-46469: || (requestManager && requestManager->isHedging))
         if (requestManager) {
             requestManager->cancelRequests();
         }
@@ -552,6 +554,11 @@ void NetworkInterfaceTL::RequestManager::cancelRequests() {
     for (size_t i = 0; i < requests.size(); i++) {
         auto requestState = requests[i].lock();
         if (requestState) {
+            LOGV2_DEBUG(4646301,
+                        2,
+                        "Cancelling request {request_id} with index {idx}",
+                        "request_id"_attr = cmdState.lock()->requestOnAny.id,
+                        "idx"_attr = i);
             requestState->cancel();
         }
     }
@@ -594,6 +601,12 @@ void NetworkInterfaceTL::RequestManager::trySend(
         }
     }
 
+    LOGV2_DEBUG(4646300,
+                2,
+                "Sending request {request_id} with index {idx}",
+                "request_id"_attr = cmdState.lock()->requestOnAny.id,
+                "idx"_attr = idx);
+
     auto req = getNextRequest();
     if (req) {
         req->send(std::move(swConn), {cmdStatePtr->requestOnAny, idx});
diff --git a/src/mongo/executor/network_interface_tl.h b/src/mongo/executor/network_interface_tl.h
index fc4d40c194d..9d599452af3 100644
--- a/src/mongo/executor/network_interface_tl.h
+++ b/src/mongo/executor/network_interface_tl.h
@@ -211,7 +211,8 @@ private:
         RequestManager(size_t numHedges, std::shared_ptr<CommandStateBase> cmdState_)
             : connStatus(cmdState_->requestOnAny.target.size(), ConnStatus::Unset),
               requests(numHedges),
-              cmdState(cmdState_) {}
+              cmdState(cmdState_),
+              isHedging(numHedges > 1) {}
 
         std::shared_ptr<RequestState> makeRequest(RequestManager* mgr) {
             auto req = std::make_shared<RequestState>(mgr, cmdState.lock());
@@ -248,6 +249,7 @@ private:
         AtomicWord<size_t> requestCnt{0};
         // blocks sending requests
         bool isLocked{false};
+        bool isHedging{false};
 
         Mutex mutex = MONGO_MAKE_LATCH("NetworkInterfaceTL::RequestManager::mutex");
     };
-- 
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