RUBY-2520 Change estimatedDocumentCount() to use the $collStats Agg S…

…tage Instead of Count Command

.evergreen/config.yml

@@ -928,7 +928,7 @@ buildvariants:
     tasks:
       - name: "test-mlaunch"
 
-  - matrix_name: "mongo-4.9"
+  - matrix_name: "mongo-4.9-api-version"
     matrix_spec:
       auth-and-ssl: ["auth-and-ssl", "noauth-and-nossl"]
       ruby: "ruby-2.7"

.evergreen/config/standard.yml.erb

@@ -131,7 +131,7 @@ buildvariants:
     tasks:
       - name: "test-mlaunch"
 
-  - matrix_name: "mongo-4.9"
+  - matrix_name: "mongo-4.9-api-version"
     matrix_spec:
       auth-and-ssl: ["auth-and-ssl", "noauth-and-nossl"]
       ruby: "ruby-2.7"

lib/mongo/collection/view/readable.rb

@@ -230,24 +230,36 @@ def estimated_document_count(opts = {})
             raise ArgumentError, "Cannot call estimated_document_count when querying with a filter"
           end
 
-          cmd = { count: collection.name }
-          cmd[:maxTimeMS] = opts[:max_time_ms] if opts[:max_time_ms]
-          if read_concern
-            cmd[:readConcern] = Options::Mapper.transform_values_to_strings(
-              read_concern)
-          end
           Mongo::Lint.validate_underscore_read_preference(opts[:read])
           read_pref = opts[:read] || read_preference
           selector = ServerSelector.get(read_pref || server_selector)
           with_session(opts) do |session|
+            context = Operation::Context.new(client: client, session: session)
             read_with_retry(session, selector) do |server|
-              Operation::Count.new(
-                selector: cmd,
-                db_name: database.name,
-                read: read_pref,
-                session: session,
-              ).execute(server, context: Operation::Context.new(client: client, session: session))
-            end.n.to_i
+              if server.description.server_version_gte?('5.0')
+                pipeline = [
+                  {'$collStats' => {'count' => {}}},
+                  {'$group' => {'_id' => 1, 'n' => {'$sum' => '$count'}}},
+                ]
+                spec = Builder::Aggregation.new(pipeline, self, options.merge(session: session)).specification
+                result = Operation::Aggregate.new(spec).execute(server, context: context)
+                result.documents.first.fetch('n')
+              else
+                cmd = { count: collection.name }
+                cmd[:maxTimeMS] = opts[:max_time_ms] if opts[:max_time_ms]
+                if read_concern
+                  cmd[:readConcern] = Options::Mapper.transform_values_to_strings(
+                    read_concern)
+                end
+                result = Operation::Count.new(
+                  selector: cmd,
+                  db_name: database.name,
+                  read: read_pref,
+                  session: session,
+                ).execute(server, context: context)
+                result.n.to_i
+              end
+            end
           end
         end
 

lib/mongo/operation.rb

@@ -6,6 +6,7 @@
 require 'mongo/operation/shared/executable_no_validate'
 require 'mongo/operation/shared/executable_transaction_label'
 require 'mongo/operation/shared/polymorphic_lookup'
+require 'mongo/operation/shared/polymorphic_operation'
 require 'mongo/operation/shared/polymorphic_result'
 require 'mongo/operation/shared/read_preference_supported'
 require 'mongo/operation/shared/bypass_document_validation'
@@ -19,8 +20,6 @@
 require 'mongo/operation/shared/object_id_generator'
 require 'mongo/operation/shared/op_msg_or_command'
 require 'mongo/operation/shared/op_msg_or_find_command'
-require 'mongo/operation/shared/op_msg_or_list_indexes_command'
-require 'mongo/operation/shared/collections_info_or_list_collections'
 
 require 'mongo/operation/op_msg_base'
 require 'mongo/operation/command'

lib/mongo/operation/collections_info.rb

@@ -25,7 +25,24 @@ module Operation
     # @since 2.0.0
     class CollectionsInfo
       include Specifiable
-      include CollectionsInfoOrListCollections
+      include PolymorphicOperation
+      include PolymorphicLookup
+
+      private
+
+      def final_operation(connection)
+         op_class = if connection.features.list_collections_enabled?
+          if connection.features.op_msg_enabled?
+            ListCollections::OpMsg
+          else
+            ListCollections::Command
+          end
+        else
+          CollectionsInfo::Command
+        end
+
+        op_class.new(spec)
+      end
     end
   end
 end

lib/mongo/operation/indexes.rb

@@ -27,7 +27,21 @@ module Operation
     # @since 2.0.0
     class Indexes
       include Specifiable
-      include OpMsgOrListIndexesCommand
+      include PolymorphicOperation
+      include PolymorphicLookup
+
+      private
+
+      def final_operation(connection)
+        cls = if connection.features.op_msg_enabled?
+          polymorphic_class(self.class.name, :OpMsg)
+        elsif connection.features.list_indexes_enabled?
+          polymorphic_class(self.class.name, :Command)
+        else
+          polymorphic_class(self.class.name, :Legacy)
+        end
+        cls.new(spec)
+      end
     end
   end
 end

lib/mongo/operation/shared/op_msg_or_command.rb

@@ -20,15 +20,9 @@ module Operation
     #
     # @api private
     module OpMsgOrCommand
+      include PolymorphicOperation
       include PolymorphicLookup
 
-      def execute(server, context:, options: {})
-        server.with_connection do |connection|
-          operation = final_operation(connection)
-          operation.execute(connection, context: context, options: options)
-        end
-      end
-
       private
 
       def final_operation(connection)

lib/mongo/operation/shared/op_msg_or_find_command.rb

@@ -21,15 +21,9 @@ module Operation
     #
     # @api private
     module OpMsgOrFindCommand
+      include PolymorphicOperation
       include PolymorphicLookup
 
-      def execute(server, context:)
-        server.with_connection do |connection|
-          operation = final_operation(connection)
-          operation.execute(connection, context: context)
-        end
-      end
-
       private
 
       def final_operation(connection)

lib/mongo/operation/shared/collections_info_or_list_collections.rb → lib/mongo/operation/shared/polymorphic_operation.rb

@@ -1,4 +1,4 @@
-# Copyright (C) 2020 MongoDB Inc.
+# Copyright (C) 2021 MongoDB Inc.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -15,39 +15,25 @@
 module Mongo
   module Operation
 
+    # Shared behavior of implementing an operation differently based on
+    # the server that will be executing the operation.
+    #
     # @api private
-    module CollectionsInfoOrListCollections
-      include PolymorphicLookup
+    module PolymorphicOperation
 
       # Execute the operation.
       #
       # @param [ Mongo::Server ] server The server to send the operation to.
       # @param [ Operation::Context ] context The operation context.
+      # @param [ Hash ] options Operation execution options.
       #
-      # @return [ Mongo::Operation::CollectionsInfo::Result,
-      #           Mongo::Operation::ListCollections::Result ] The operation result.
-      def execute(server, context:)
+      # @return [ Mongo::Operation::Result ] The operation result.
+      def execute(server, context:, options: {})
         server.with_connection do |connection|
           operation = final_operation(connection)
-          operation.execute(connection, context: context)
+          operation.execute(connection, context: context, options: options)
         end
       end
-
-      private
-
-      def final_operation(connection)
-         op_class = if connection.features.list_collections_enabled?
-          if connection.features.op_msg_enabled?
-            ListCollections::OpMsg
-          else
-            ListCollections::Command
-          end
-        else
-          CollectionsInfo::Command
-        end
-
-        op_class.new(spec)
-      end
     end
   end
 end

lib/mongo/server/description.rb

@@ -790,6 +790,10 @@ def ==(other)
       # @api private
       def server_version_gte?(version)
         required_wv = case version
+          when '5.0'
+            12
+          when '4.4'
+            9
           when '4.2'
             8
           when '4.0'

lib/mongo/server/description/features.rb

@@ -23,14 +23,15 @@ class Features
         # List of features and the wire protocol version they appear in.
         #
         # Wire protocol versions map to server releases as follows:
-        # - 2 => 2.6
-        # - 3 => 3.0
-        # - 4 => 3.2
-        # - 5 => 3.4
-        # - 6 => 3.6
-        # - 7 => 4.0
-        # - 8 => 4.2
-        # - 9 => 4.4
+        # -  2 => 2.6
+        # -  3 => 3.0
+        # -  4 => 3.2
+        # -  5 => 3.4
+        # -  6 => 3.6
+        # -  7 => 4.0
+        # -  8 => 4.2
+        # -  9 => 4.4
+        # - 12 => 5.0
         #
         # @since 2.0.0
         MAPPINGS = {

spec/spec_tests/data/retryable_reads/estimatedDocumentCount-4.9.yml

@@ -0,0 +1,60 @@
+runOn:
+    - minServerVersion: "4.9.0"
+
+database_name: &database_name "retryable-reads-tests"
+collection_name: &collection_name "coll"
+
+data:
+    - { _id: 1, x: 11 }
+    - { _id: 2, x: 22 }
+
+tests:
+    -
+        description: "EstimatedDocumentCount succeeds on first attempt"
+        operations:
+            - &retryable_operation_succeeds
+                <<: &retryable_operation
+                    name: estimatedDocumentCount
+                    object: collection
+                result: 2
+        expectations:
+            - &retryable_command_started_event
+                command_started_event:
+                    command:
+                        aggregate: *collection_name
+                        pipeline: &pipeline
+                          - $collStats: { count: {} }
+                          - $group: { _id: 1, n: { $sum: $count }}
+                    database_name: *database_name
+    -
+        description: "EstimatedDocumentCount succeeds on second attempt"
+        failPoint:  &failCommand_failPoint
+            configureFailPoint: failCommand
+            mode: { times: 1 }
+            data:
+                failCommands: [aggregate]
+                closeConnection: true
+        operations: [*retryable_operation_succeeds]
+        expectations:
+             - *retryable_command_started_event
+             - *retryable_command_started_event
+    -
+        description: "EstimatedDocumentCount fails on first attempt"
+        clientOptions:
+            retryReads: false
+        failPoint: *failCommand_failPoint
+        operations:
+            - &retryable_operation_fails
+                <<: *retryable_operation
+                error: true
+        expectations:
+             - *retryable_command_started_event
+    -
+        description: "EstimatedDocumentCount fails on second attempt"
+        failPoint:
+          <<: *failCommand_failPoint
+          mode: { times: 2 }
+        operations: [*retryable_operation_fails]
+        expectations:
+             - *retryable_command_started_event
+             - *retryable_command_started_event

spec/spec_tests/data/retryable_reads/estimatedDocumentCount.yml → spec/spec_tests/data/retryable_reads/estimatedDocumentCount-pre4.9.yml

@@ -1,9 +1,11 @@
 runOn:
     -
         minServerVersion: "4.0"
+        maxServerVersion: "4.8.99"
         topology: ["single", "replicaset"]
     -
         minServerVersion: "4.1.7"
+        maxServerVersion: "4.8.99"
         topology: ["sharded"]
 
 database_name: &database_name "retryable-reads-tests"