Revert "SERVER-33966 Removed Redundant Sort"r4.4.0

This reverts commit ed966606c2e5eb82f447c81986c64f8cfa0c74d7.

3 files changed, 8 insertions, 264 deletions

diff --git a/jstests/aggregation/mongos_merge.js b/jstests/aggregation/mongos_merge.js
index 633df86ab4b..e99dd77eb02 100644
--- a/jstests/aggregation/mongos_merge.js
+++ b/jstests/aggregation/mongos_merge.js
@@ -15,7 +15,6 @@
  *   requires_sharding,
  *   requires_spawning_own_processes,
  *   requires_profiling,
- *   requires_fcv_46,
  * ]
  */
 
@@ -346,6 +345,14 @@ function runTestCasesWhoseMergeLocationDependsOnAllowDiskUse(allowDiskUse) {
     // All test cases should merge on mongoD if allowDiskUse is true, mongoS otherwise.
     const assertMergeOnMongoX = (allowDiskUse ? assertMergeOnMongoD : assertMergeOnMongoS);
 
+    // Test that a blocking $sort is only merged on mongoS if 'allowDiskUse' is not set.
+    assertMergeOnMongoX({
+        testName: "agg_mongos_merge_blocking_sort_no_disk_use",
+        pipeline: [{$match: {_id: {$gte: -200, $lte: 200}}}, {$sort: {_id: -1}}, {$sort: {a: 1}}],
+        allowDiskUse: allowDiskUse,
+        expectedCount: 400
+    });
+
     // Test that $group is only merged on mongoS if 'allowDiskUse' is not set.
     assertMergeOnMongoX({
         testName: "agg_mongos_merge_group_allow_disk_use",
@@ -355,20 +362,6 @@ function runTestCasesWhoseMergeLocationDependsOnAllowDiskUse(allowDiskUse) {
         expectedCount: 299
     });
 
-    // Adjacent $sort stages will be coalesced and merge sort will occur on anyShard when disk use
-    // is allowed, and on mongos otherwise.
-    assertMergeOnMongoX({
-        testName: "agg_mongos_merge_blocking_sort_allow_disk_use",
-        pipeline: [
-            {$match: {_id: {$gte: -200, $lte: 200}}},
-            {$sort: {_id: 1}},
-            {$_internalSplitPipeline: {}},
-            {$sort: {a: 1}}
-        ],
-        allowDiskUse: allowDiskUse,
-        expectedCount: 400
-    });
-
     // Test that a blocking $sample is only merged on mongoS if 'allowDiskUse' is not set.
     assertMergeOnMongoX({
         testName: "agg_mongos_merge_blocking_sample_allow_disk_use",
diff --git a/src/mongo/db/pipeline/document_source_sort.cpp b/src/mongo/db/pipeline/document_source_sort.cpp
index 02290179439..dcf40ba110b 100644
--- a/src/mongo/db/pipeline/document_source_sort.cpp
+++ b/src/mongo/db/pipeline/document_source_sort.cpp
@@ -169,23 +169,6 @@ Pipeline::SourceContainer::iterator DocumentSourceSort::doOptimizeAt(
         _sortExecutor->setLimit(*limit);
     }
 
-    if (std::next(itr) == container->end()) {
-        return container->end();
-    }
-
-    if (auto nextSort = dynamic_cast<DocumentSourceSort*>((*std::next(itr)).get())) {
-        // If subsequent $sort stage exists, optimize by erasing the initial one.
-        // Since $sort is not guaranteed to be stable, we can blindly remove the first $sort.
-        auto thisLim = _sortExecutor->getLimit();
-        auto otherLim = nextSort->_sortExecutor->getLimit();
-        // When coalescing subsequent $sort stages, retain the existing/lower limit.
-        if (thisLim && (!otherLim || otherLim > thisLim)) {
-            nextSort->_sortExecutor->setLimit(thisLim);
-        }
-        Pipeline::SourceContainer::iterator ret = std::next(itr);
-        container->erase(itr);
-        return ret;
-    }
     return std::next(itr);
 }
 
diff --git a/src/mongo/db/pipeline/pipeline_test.cpp b/src/mongo/db/pipeline/pipeline_test.cpp
index a23c5d8a7f6..1715379912b 100644
--- a/src/mongo/db/pipeline/pipeline_test.cpp
+++ b/src/mongo/db/pipeline/pipeline_test.cpp
@@ -293,238 +293,6 @@ TEST(PipelineOptimizationTest, SortMatchProjSkipLimBecomesMatchTopKSortSkipProj)
     assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
 }
 
-TEST(PipelineOptimizationTest, IdenticalSortSortBecomesSort) {
-    std::string inputPipe =
-        "[{$sort: {a: 1}}"
-        ",{$sort: {a: 1}}"
-        "]";
-
-    std::string outputPipe =
-        "[{$sort: {sortKey: {a: 1}}}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$sort: {a: 1}}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
-TEST(PipelineOptimizationTest, IdenticalSortSortSortBecomesSort) {
-    std::string inputPipe =
-        "[{$sort: {a: 1}}"
-        ",{$sort: {a: 1}}"
-        ",{$sort: {a: 1}}"
-        "]";
-
-    std::string outputPipe =
-        "[{$sort: {sortKey: {a: 1}}}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$sort: {a: 1}}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
-TEST(PipelineOptimizationTest, NonIdenticalSortsOnlySortOnFinalKey) {
-    std::string inputPipe =
-        "[{$sort: {a: -1}}"
-        ",{$sort: {a: 1}}"
-        ",{$sort: {a: -1}}"
-        "]";
-
-    std::string outputPipe =
-        "[{$sort: {sortKey: {a: -1}}}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$sort: {a: -1}}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
-TEST(PipelineOptimizationTest, SortSortLimitBecomesFinalKeyTopKSort) {
-    std::string inputPipe =
-        "[{$sort: {a: -1}}"
-        ",{$sort: {a: 1}}"
-        ",{$limit: 5}"
-        "]";
-
-    std::string outputPipe =
-        "[{$sort: {sortKey: {a: 1}, limit: 5}}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$sort: {a: 1}}"
-        ",{$limit: 5}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
-TEST(PipelineOptimizationTest, SortSortSkipLimitBecomesTopKSortSkip) {
-    std::string inputPipe =
-        "[{$sort: {b: 1}}"
-        ",{$sort: {a: 1}}"
-        ",{$skip : 3}"
-        ",{$limit: 5}"
-        "]";
-
-    std::string outputPipe =
-        "[{$sort: {sortKey: {a: 1}, limit: 8}}"
-        ",{$skip: 3}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$sort: {a: 1}}"
-        ",{$limit: 8}"
-        ",{$skip : 3}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
-TEST(PipelineOptimizationTest, SortLimitSortLimitBecomesTopKSort) {
-    std::string inputPipe =
-        "[{$sort: {a: 1}}"
-        ",{$limit: 12}"
-        ",{$sort: {a: 1}}"
-        ",{$limit: 20}"
-        "]";
-
-    std::string outputPipe =
-        "[{$sort: {sortKey: {a: 1}, limit: 12}}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$sort: {a: 1}}"
-        ",{$limit: 12}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
-TEST(PipelineOptimizationTest, SortLimitSortRetainsLimit) {
-    std::string inputPipe =
-        "[{$sort: {a: 1}}"
-        ",{$limit: 12}"
-        ",{$sort: {a: 1}}"
-        "]";
-
-    std::string outputPipe =
-        "[{$sort: {sortKey: {a: 1}, limit: 12}}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$sort: {a: 1}}"
-        ",{$limit: 12}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
-TEST(PipelineOptimizationTest, SortSortLimitRetainsLimit) {
-    std::string inputPipe =
-        "[{$sort: {a: 1}}"
-        ",{$sort: {a: 1}}"
-        ",{$limit: 20}"
-        "]";
-
-    std::string outputPipe =
-        "[{$sort: {sortKey: {a: 1}, limit: 20}}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$sort: {a: 1}}"
-        ",{$limit: 20}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
-TEST(PipelineOptimizationTest, SortSortSortMatchProjSkipLimBecomesMatchTopKSortSkipProj) {
-    std::string inputPipe =
-        "[{$sort: {a: 1}}"
-        ",{$sort: {a: 1}}"
-        ",{$sort: {a: 1}}"
-        ",{$match: {a: 1}}"
-        ",{$project : {a: 1}}"
-        ",{$skip : 3}"
-        ",{$limit: 5}"
-        "]";
-
-    std::string outputPipe =
-        "[{$match: {a: {$eq: 1}}}"
-        ",{$sort: {sortKey: {a: 1}, limit: 8}}"
-        ",{$skip: 3}"
-        ",{$project: {_id: true, a: true}}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$match: {a: 1}}"
-        ",{$sort: {a: 1}}"
-        ",{$limit: 8}"
-        ",{$skip : 3}"
-        ",{$project : {_id: true, a: true}}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
-TEST(PipelineOptimizationTest, NonIdenticalSortsBecomeFinalKeyTopKSort) {
-    std::string inputPipe =
-        "[{$sort: {a: -1}}"
-        ",{$sort: {b: -1}}"
-        ",{$sort: {b: 1}}"
-        ",{$sort: {a: 1}}"
-        ",{$limit: 7}"
-        ",{$project : {a: 1}}"
-        ",{$limit: 5}"
-        "]";
-
-    std::string outputPipe =
-        "[{$sort: {sortKey: {a: 1}, limit: 5}}"
-        ",{$project: {_id: true, a: true}}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$sort: {a: 1}}"
-        ",{$limit: 5}"
-        ",{$project : {_id: true, a: true}}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
-TEST(PipelineOptimizationTest, SubsequentSortsMergeAndBecomeTopKSortWithFinalKeyAndLowestLimit) {
-    std::string inputPipe =
-        "[{$sort: {a: 1}}"
-        ",{$sort: {a: -1}}"
-        ",{$limit: 8}"
-        ",{$limit: 7}"
-        ",{$project : {a: 1}}"
-        ",{$unwind: {path: '$a'}}"
-        "]";
-
-    std::string outputPipe =
-        "[{$sort: {sortKey: {a: -1}, limit: 7}}"
-        ",{$project: {_id: true, a: true}}"
-        ",{$unwind: {path: '$a'}}"
-        "]";
-
-    std::string serializedPipe =
-        "[{$sort: {a: -1}}"
-        ",{$limit: 7}"
-        ",{$project : {_id: true, a: true}}"
-        ",{$unwind: {path: '$a'}}"
-        "]";
-
-    assertPipelineOptimizesAndSerializesTo(inputPipe, outputPipe, serializedPipe);
-}
-
 TEST(PipelineOptimizationTest, RemoveSkipZero) {
     assertPipelineOptimizesTo("[{$skip: 0}]", "[]");
 }