SERVER-40755 Expose statistics which indicate how many collection scans have executed

3 files changed, 17 insertions, 1 deletions

diff --git a/src/mongo/db/query/explain.cpp b/src/mongo/db/query/explain.cpp
index 709d8ffda4a..eb109928be4 100644
--- a/src/mongo/db/query/explain.cpp
+++ b/src/mongo/db/query/explain.cpp
@@ -34,6 +34,7 @@
 #include "mongo/base/owned_pointer_vector.h"
 #include "mongo/bson/util/builder.h"
 #include "mongo/db/exec/cached_plan.h"
+#include "mongo/db/exec/collection_scan.h"
 #include "mongo/db/exec/count_scan.h"
 #include "mongo/db/exec/distinct_scan.h"
 #include "mongo/db/exec/idhack.h"
@@ -1015,6 +1016,13 @@ void Explain::getSummaryStats(const PlanExecutor& exec, PlanSummaryStats* statsO
             statsOut->replanned = cachedStats->replanned;
         } else if (STAGE_MULTI_PLAN == stages[i]->stageType()) {
             statsOut->fromMultiPlanner = true;
+        } else if (STAGE_COLLSCAN == stages[i]->stageType()) {
+            statsOut->collectionScans++;
+            const auto collScan = static_cast<const CollectionScan*>(stages[i]);
+            const auto collScanStats =
+                static_cast<const CollectionScanStats*>(collScan->getSpecificStats());
+            if (!collScanStats->tailable)
+                statsOut->collectionScansNonTailable++;
         }
     }
 }
diff --git a/src/mongo/db/query/find.cpp b/src/mongo/db/query/find.cpp
index 8f4132b1eaf..f9de0152b5c 100644
--- a/src/mongo/db/query/find.cpp
+++ b/src/mongo/db/query/find.cpp
@@ -150,7 +150,7 @@ void endQueryOp(OperationContext* opCtx,
     curOp->debug().setPlanSummaryMetrics(summaryStats);
 
     if (collection) {
-        collection->infoCache()->notifyOfQuery(opCtx, summaryStats.indexesUsed);
+        collection->infoCache()->notifyOfQuery(opCtx, summaryStats);
     }
 
     if (curOp->shouldDBProfile()) {
diff --git a/src/mongo/db/query/plan_summary_stats.h b/src/mongo/db/query/plan_summary_stats.h
index 35deb4d83c0..a0ded1f2755 100644
--- a/src/mongo/db/query/plan_summary_stats.h
+++ b/src/mongo/db/query/plan_summary_stats.h
@@ -50,6 +50,14 @@ struct PlanSummaryStats {
     // The number of milliseconds spent inside the root stage's work() method.
     long long executionTimeMillis = 0;
 
+    // The number of collection scans that occur during execution. Note that more than one
+    // collection scan may happen during execution (e.g. for $lookup execution).
+    long long collectionScans = 0;
+
+    // The number of collection scans that occur during execution which are nontailable. Note that
+    // more than one collection scan may happen during execution (e.g. for $lookup execution).
+    long long collectionScansNonTailable = 0;
+
     // Did this plan use an in-memory sort stage?
     bool hasSortStage = false;