SERVER-35905 Add logic to detect when $out is eligible for an exchange

1 files changed, 22 insertions, 0 deletions

diff --git a/src/mongo/db/pipeline/pipeline.h b/src/mongo/db/pipeline/pipeline.h
index d3e99daae31..4874126b398 100644
--- a/src/mongo/db/pipeline/pipeline.h
+++ b/src/mongo/db/pipeline/pipeline.h
@@ -132,6 +132,19 @@ public:
      */
     static bool aggSupportsWriteConcern(const BSONObj& cmd);
 
+    /**
+     * Given 'pathsOfInterest' which describes a set of paths which the caller is interested in,
+     * returns boost::none if any of those paths are modified by the section of a pipeline
+     * described by 'rstart' and 'rend', or a mapping from their name at the end of the pipeline to
+     * their name at the beginning of the pipeline if they are preserved but possibly renamed by
+     * this pipeline. Note that the analysis proceeds backwards, so the iterators must be reverse
+     * iterators.
+     */
+    static boost::optional<StringMap<std::string>> renamedPaths(
+        SourceContainer::const_reverse_iterator rstart,
+        SourceContainer::const_reverse_iterator rend,
+        std::set<std::string> pathsOfInterest);
+
     const boost::intrusive_ptr<ExpressionContext>& getContext() const {
         return pCtx;
     }
@@ -250,6 +263,15 @@ public:
      */
     DepsTracker getDependencies(DepsTracker::MetadataAvailable metadataAvailable) const;
 
+    /**
+     * Given 'pathsOfInterest' which describes a set of paths which the caller is interested in,
+     * returns boost::none if any of those paths are modified by this pipeline, or a mapping from
+     * their name at the end of the pipeline to their name at the beginning of the pipeline if they
+     * are preserved but possibly renamed by this pipeline.
+     */
+    boost::optional<StringMap<std::string>> renamedPaths(
+        std::set<std::string> pathsOfInterest) const;
+
     const SourceContainer& getSources() const {
         return _sources;
     }