SERVER-35693 Pre-sort $in elements to avoid O(n^2) boost::flat_set() complexity.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/mongo/db/matcher/expression_leaf.cpp b/src/mongo/db/matcher/expression_leaf.cpp
index dce381e8a27..843f086bf58 100644
--- a/src/mongo/db/matcher/expression_leaf.cpp
+++ b/src/mongo/db/matcher/expression_leaf.cpp
@@ -551,7 +551,10 @@ Status ArrayFilterEntries::setEqualities(std::vector<BSONElement> equalities) {
         }
     }
 
-    _equalities = BSONElementFlatSet(equalities.begin(), equalities.end());
+    // Sort the list of equalities to work around https://svn.boost.org/trac10/ticket/13140.
+    std::sort(equalities.begin(), equalities.end(), BSONElementCmpWithoutField());
+    _equalities =
+        BSONElementFlatSet(equalities.begin(), equalities.end(), BSONElementCmpWithoutField());
     return Status::OK();
 }