diff --git a/cpp/cdc/CDC.cpp b/cpp/cdc/CDC.cpp
index e76bb595..3e038543 100644
--- a/cpp/cdc/CDC.cpp
+++ b/cpp/cdc/CDC.cpp
@@ -45,6 +45,9 @@ struct CDCShared {
     // when it finished executing.
     std::array<Timings, maxCDCMessageKind+1> timingsProcess;
     std::array<ErrorCount, maxCDCMessageKind+1> errors;
+    // right now we have a max of 200req/s and we send the metrics every minute or so, so
+    // this should cover us for at least 1.5mins. Power of two is good for mod.
+    std::array<std::atomic<size_t>, 0x3FFF> inFlightTxnsWindow;
 
     CDCShared(CDCDB& db_) : db(db_) {
         for (auto& shard: shards) {
@@ -56,6 +59,9 @@ struct CDCShared {
             timingsTotal[(int)kind] = Timings::Standard();
             timingsProcess[(int)kind] = Timings::Standard();
         }
+        for (int i = 0; i < inFlightTxnsWindow.size(); i++) {
+            inFlightTxnsWindow[i] = 0;
+        }
     }
 };
 
@@ -133,6 +139,7 @@ private:
     // The requests we've enqueued, but haven't completed yet, with
     // where to send the response. Indexed by txn id.
     std::unordered_map<uint64_t, InFlightCDCRequest> _inFlightTxns;
+    uint64_t _inFlightTxnsWindowCursor;
     // The enqueued requests, but indexed by req id + ip + port. We
     // store this so that we can drop repeated requests which are
     // still queued, and which will therefore be processed in due
@@ -174,6 +181,7 @@ public:
         _shardRequestIdCounter(0),
         _shardTimeout(options.shardTimeout),
         _maximumEnqueuedRequests(options.maximumEnqueuedRequests),
+        _inFlightTxnsWindowCursor(0),
         _runningTxn(0)
     {
         _currentLogIndex = _shared.db.lastAppliedLogEntry();
@@ -226,6 +234,11 @@ public:
     }
 
 private:
+    void _updateInFlightTxns() {
+        _shared.inFlightTxnsWindow[_inFlightTxnsWindowCursor%_shared.inFlightTxnsWindow.size()].store(_inFlightTxns.size());
+        _inFlightTxnsWindowCursor++;
+    }
+
     bool _waitForShards() {
         bool badShard = false;
         {
@@ -394,6 +407,7 @@ private:
                 inFlight.kind = reqHeader.kind;
                 inFlight.sock = sock;
                 inFlight.receivedAt = receivedAt;
+                _updateInFlightTxns();
                 _inFlightCDCReqs.insert(InFlightCDCRequestKey(reqHeader.requestId, clientAddr));
                 // Go forward
                 _processStep(_step);
@@ -509,6 +523,7 @@ private:
                 }
                 _inFlightCDCReqs.erase(InFlightCDCRequestKey(inFlight->second.cdcRequestId, inFlight->second.clientAddr));
                 _inFlightTxns.erase(inFlight);
+                _updateInFlightTxns();
             }
         }
         if (step.txnNeedsShard != 0) {
@@ -772,6 +787,15 @@ public:
                 _metricsBuilder.timestamp(now);
             }
         }
+        {
+            _metricsBuilder.measurement("eggsfs_cdc_queue");
+            uint64_t sum = 0;
+            for (size_t x: _shared.inFlightTxnsWindow) {
+                sum += x;
+            }
+            _metricsBuilder.fieldFloat("size", (double)sum / (double)_shared.inFlightTxnsWindow.size());
+            _metricsBuilder.timestamp(now);
+        }
         std::string err = sendMetrics(10_sec, _metricsBuilder.payload());
         _metricsBuilder.reset();
         if (err.empty()) {
diff --git a/cpp/core/Metrics.hpp b/cpp/core/Metrics.hpp
index 783fb6f2..6df1fa6b 100644
--- a/cpp/core/Metrics.hpp
+++ b/cpp/core/Metrics.hpp
@@ -45,6 +45,12 @@ public:
         fieldRaw(name, ss.str());
     }
 
+    void fieldFloat(const std::string& name, double x) {
+        std::ostringstream ss;
+        ss << x;
+        fieldRaw(name, ss.str());
+    }
+
     void timestamp(EggsTime t);
 };