SERVER-50895 Fix leak of $unionWith cached pipeline for explain when execution does not read from sub-pipeline

2 files changed, 3 insertions, 4 deletions

diff --git a/src/mongo/db/pipeline/document_source_union_with.cpp b/src/mongo/db/pipeline/document_source_union_with.cpp
index 294b16accc3..3191468d65b 100644
--- a/src/mongo/db/pipeline/document_source_union_with.cpp
+++ b/src/mongo/db/pipeline/document_source_union_with.cpp
@@ -267,7 +267,7 @@ Value DocumentSourceUnionWith::serialize(boost::optional<ExplainOptions::Verbosi
             // We've either exhausted the sub-pipeline or at least started iterating it. Use the
             // cached pipeline to get the explain output since the '_pipeline' may have been
             // modified for any optimizations or pushdowns into the initial $cursor stage.
-            pipeCopy = _cachedPipeline;
+            pipeCopy = Pipeline::create(_cachedPipeline, _pipeline->getContext()).release();
         } else {
             // The plan does not require reading from the sub-pipeline, so just include the
             // serialization in the explain output.
diff --git a/src/mongo/db/pipeline/document_source_union_with.h b/src/mongo/db/pipeline/document_source_union_with.h
index 5686f569374..38f5eeeb804 100644
--- a/src/mongo/db/pipeline/document_source_union_with.h
+++ b/src/mongo/db/pipeline/document_source_union_with.h
@@ -66,8 +66,7 @@ public:
         // If this pipeline is being run as part of explain, then cache a copy to use later during
         // serialization.
         if (expCtx->explain >= ExplainOptions::Verbosity::kExecStats) {
-            _cachedPipeline =
-                Pipeline::create(_pipeline->getSources(), _pipeline->getContext()).release();
+            _cachedPipeline = _pipeline->getSources();
         }
     }
 
@@ -162,7 +161,7 @@ private:
     void addViewDefinition(NamespaceString nss, std::vector<BSONObj> viewPipeline);
 
     std::unique_ptr<Pipeline, PipelineDeleter> _pipeline;
-    Pipeline* _cachedPipeline = nullptr;
+    Pipeline::SourceContainer _cachedPipeline;
     bool _usedDisk = false;
     ExecutionProgress _executionState = ExecutionProgress::kIteratingSource;
 };