Revert "SERVER-41872 PlanEnumerator AndAssignment::choices ordering not stable and is relevant to set of plans generated"r3.6.21-rc1

This reverts commit b010331e00cb46efe4e98e0f74150854b4407d67.

2 files changed, 2 insertions, 71 deletions

diff --git a/src/mongo/db/query/plan_enumerator.h b/src/mongo/db/query/plan_enumerator.h
index 8b563ed145b..53643b2a95c 100644
--- a/src/mongo/db/query/plan_enumerator.h
+++ b/src/mongo/db/query/plan_enumerator.h
@@ -430,16 +430,10 @@ private:
      */
     bool alreadyCompounded(const std::set<MatchExpression*>& ixisectAssigned,
                            const AndAssignment* andAssignment);
-
-    struct CmpByIndexID {
-        bool operator()(IndexID a, IndexID b) const {
-            return a < b;
-        }
-    };
     /**
-     * Maps from index id to the list of predicates assigned to that index.
+     * Output index intersection assignments inside of an AND node.
      */
-    typedef std::map<IndexID, std::vector<MatchExpression*>, CmpByIndexID> IndexToPredMap;
+    typedef unordered_map<IndexID, std::vector<MatchExpression*>> IndexToPredMap;
 
     /**
      * Generate index intersection assignments given the predicate/index structure in idxToFirst
diff --git a/src/mongo/db/query/query_planner_test.cpp b/src/mongo/db/query/query_planner_test.cpp
index 58645fc9efc..f27c7a1e46c 100644
--- a/src/mongo/db/query/query_planner_test.cpp
+++ b/src/mongo/db/query/query_planner_test.cpp
@@ -5624,69 +5624,6 @@ TEST_F(QueryPlannerTest, EmptyQueryWithProjectionUsesCollscanIfIndexCollationDif
         "{cscan: {dir: 1}}}}");
 }
 
-// SERVER-41872 fixed a case where variable "choice" ordering in the PlanEnumerator memo could lead
-// to different sets of solutions generated for the same input. This would occur in the case where
-// we only enumerate a subset of possible plans due to reaching internal limits and enumerate plans
-// in a non-stable order. With the fix for SERVER-41872, PlanEnumerator ordering is stable and
-// expected to always return the same set of solutions for a given input.
-TEST_F(QueryPlannerTest, SolutionSetStableWhenOrEnumerationLimitIsReached) {
-    params.options = QueryPlannerParams::NO_TABLE_SCAN;
-    addIndex(BSON("d" << 1));
-    addIndex(BSON("e" << 1));
-    addIndex(BSON("f" << 1));
-    addIndex(BSON("f" << 1 << "y" << 1));
-    addIndex(BSON("a" << 1));
-    addIndex(BSON("b" << 1));
-    addIndex(BSON("c" << 1));
-    addIndex(BSON("c" << 1 << "x" << 1));
-
-    runQueryAsCommand(
-        fromjson("{find: 'testns', filter: {$or: [{a: 1, b: 1, c: 1}, {d: 1, e: 1, f: 1}]}}"));
-
-    assertNumSolutions(10U);
-
-    assertSolutionExists(
-        "{or: {nodes: [{fetch: {filter: {b: {$eq: 1}, c: {$eq: 1} }, node: {ixscan: {pattern: {a: "
-        "1}}}}}, {fetch: {filter: {e: {$eq: 1}, f: {$eq: 1} }, node: {ixscan: {pattern: {d: "
-        "1}}}}}]}}");
-    assertSolutionExists(
-        "{or: {nodes: [{fetch: {filter: {a: {$eq: 1}, c: {$eq: 1} }, node: {ixscan: {pattern: {b: "
-        "1}}}}}, {fetch: {filter: {e: {$eq: 1}, f: {$eq: 1} }, node: {ixscan: {pattern: {d: "
-        "1}}}}}]}}");
-    assertSolutionExists(
-        "{or: {nodes: [{fetch: {filter: {a: {$eq: 1}, b: {$eq: 1} }, node: {ixscan: {pattern: {c: "
-        "1}}}}}, {fetch: {filter: {e: {$eq: 1}, f: {$eq: 1} }, node: {ixscan: {pattern: {d: "
-        "1}}}}}]}}");
-    assertSolutionExists(
-        "{or: {nodes: [{fetch: {filter: {a: {$eq: 1}, b: {$eq: 1} }, node: {ixscan: {pattern: {c: "
-        "1, x: 1}}}}}, {fetch: {filter: {e: {$eq: 1}, f: {$eq: 1} }, node: {ixscan: {pattern: {d: "
-        "1}}}}}]}}");
-    assertSolutionExists(
-        "{or: {nodes: [{fetch: {filter: {b: {$eq: 1}, c: {$eq: 1} }, node: {ixscan: {pattern: {a: "
-        "1}}}}}, {fetch: {filter: {d: {$eq: 1}, f: {$eq: 1} }, node: {ixscan: {pattern: {e: "
-        "1}}}}}]}}");
-    assertSolutionExists(
-        "{or: {nodes: [{fetch: {filter: {a: {$eq: 1}, c: {$eq: 1} }, node: {ixscan: {pattern: {b: "
-        "1}}}}}, {fetch: {filter: {d: {$eq: 1}, f: {$eq: 1} }, node: {ixscan: {pattern: {e: "
-        "1}}}}}]}}");
-    assertSolutionExists(
-        "{or: {nodes: [{fetch: {filter: {a: {$eq: 1}, b: {$eq: 1} }, node: {ixscan: {pattern: {c: "
-        "1}}}}}, {fetch: {filter: {d: {$eq: 1}, f: {$eq: 1} }, node: {ixscan: {pattern: {e: "
-        "1}}}}}]}}");
-    assertSolutionExists(
-        "{or: {nodes: [{fetch: {filter: {a: {$eq: 1}, b: {$eq: 1} }, node: {ixscan: {pattern: {c: "
-        "1, x: 1}}}}}, {fetch: {filter: {d: {$eq: 1}, f: {$eq: 1} }, node: {ixscan: {pattern: {e: "
-        "1}}}}}]}}");
-    assertSolutionExists(
-        "{or: {nodes: [{fetch: {filter: {b: {$eq: 1}, c: {$eq: 1} }, node: {ixscan: {pattern: {a: "
-        "1}}}}}, {fetch: {filter: {d: {$eq: 1}, e: {$eq: 1} }, node: {ixscan: {pattern: {f: "
-        "1}}}}}]}}");
-    assertSolutionExists(
-        "{or: {nodes: [{fetch: {filter: {a: {$eq: 1}, c: {$eq: 1} }, node: {ixscan: {pattern: {b: "
-        "1}}}}}, {fetch: {filter: {d: {$eq: 1}, e: {$eq: 1} }, node: {ixscan: {pattern: {f: "
-        "1}}}}}]}}");
-}
-
 TEST_F(QueryPlannerTest, InvalidUtf8CodePointDoesNotLeadToInvalidIndexBoundsInvariantFailure) {
     params.options &= ~QueryPlannerParams::INCLUDE_COLLSCAN;
     addIndex(BSON("a" << 1));