Add a GetComparator() function to the ColumnFamilyHandle base class so that the user's comparator can be retrieved.

Summary: MyRocks is adding support for the user of the SstFileWriter which needs a comparator.  It would be more convenient to get the comparator from the column family (which already has to have it) than to have caller keep track of it.

Test Plan: Standard tests (adding one for the new method)

Reviewers: IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D61155

db/column_family.cc

@@ -81,7 +81,7 @@ Status ColumnFamilyHandleImpl::GetDescriptor(ColumnFamilyDescriptor* desc) {
 #endif  // !ROCKSDB_LITE
 }
 
-const Comparator* ColumnFamilyHandleImpl::user_comparator() const {
+const Comparator* ColumnFamilyHandleImpl::GetComparator() const {
   return cfd()->user_comparator();
 }
 
@@ -1007,8 +1007,7 @@ uint32_t GetColumnFamilyID(ColumnFamilyHandle* column_family) {
 const Comparator* GetColumnFamilyUserComparator(
     ColumnFamilyHandle* column_family) {
   if (column_family != nullptr) {
-    auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
+    return column_family->GetComparator();
-    return cfh->user_comparator();
   }
   return nullptr;
 }

db/column_family.h

@@ -55,11 +55,11 @@ class ColumnFamilyHandleImpl : public ColumnFamilyHandle {
   // destroy without mutex
   virtual ~ColumnFamilyHandleImpl();
   virtual ColumnFamilyData* cfd() const { return cfd_; }
-  virtual const Comparator* user_comparator() const;
 
   virtual uint32_t GetID() const override;
   virtual const std::string& GetName() const override;
   virtual Status GetDescriptor(ColumnFamilyDescriptor* desc) override;
+  virtual const Comparator* GetComparator() const override;
 
  private:
   ColumnFamilyData* cfd_;

db/column_family_test.cc

@@ -1072,6 +1072,39 @@ TEST_F(ColumnFamilyTest, MemtableNotSupportSnapshot) {
 }
 #endif  // !ROCKSDB_LITE
 
+class TestComparator : public Comparator {
+  int Compare(const rocksdb::Slice& a, const rocksdb::Slice& b) const override {
+    return 0;
+  }
+  const char* Name() const override { return "Test"; }
+  void FindShortestSeparator(std::string* start,
+                             const rocksdb::Slice& limit) const override {}
+  void FindShortSuccessor(std::string* key) const override {}
+};
+
+static TestComparator third_comparator;
+static TestComparator fourth_comparator;
+
+// Test that we can retrieve the comparator from a created CF
+TEST_F(ColumnFamilyTest, GetComparator) {
+  Open();
+  // Add a column family with no comparator specified
+  CreateColumnFamilies({"first"});
+  const Comparator* comp = handles_[0]->GetComparator();
+  ASSERT_EQ(comp, BytewiseComparator());
+
+  // Add three column families - one with no comparator and two
+  // with comparators specified
+  ColumnFamilyOptions second, third, fourth;
+  second.comparator = &third_comparator;
+  third.comparator = &fourth_comparator;
+  CreateColumnFamilies({"second", "third", "fourth"}, {second, third, fourth});
+  ASSERT_EQ(handles_[1]->GetComparator(), BytewiseComparator());
+  ASSERT_EQ(handles_[2]->GetComparator(), &third_comparator);
+  ASSERT_EQ(handles_[3]->GetComparator(), &fourth_comparator);
+  Close();
+}
+
 TEST_F(ColumnFamilyTest, DifferentMergeOperators) {
   Open();
   CreateColumnFamilies({"first", "second"});

db/write_batch_test.cc

@@ -546,7 +546,7 @@ class ColumnFamilyHandleImplDummy : public ColumnFamilyHandleImpl {
   explicit ColumnFamilyHandleImplDummy(int id)
       : ColumnFamilyHandleImpl(nullptr, nullptr, nullptr), id_(id) {}
   uint32_t GetID() const override { return id_; }
-  const Comparator* user_comparator() const override {
+  const Comparator* GetComparator() const override {
     return BytewiseComparator();
   }
 

include/rocksdb/db.h

@@ -77,6 +77,9 @@ class ColumnFamilyHandle {
   //
   // Note that this function is not supported in RocksDBLite.
   virtual Status GetDescriptor(ColumnFamilyDescriptor* desc) = 0;
+  // Returns the comparator of the column family associated with the
+  // current handle.
+  virtual const Comparator* GetComparator() const = 0;
 };
 
 static const int kMajorVersion = __ROCKSDB_MAJOR__;

utilities/write_batch_with_index/write_batch_with_index_test.cc

@@ -29,7 +29,7 @@ class ColumnFamilyHandleImplDummy : public ColumnFamilyHandleImpl {
         id_(id),
         comparator_(comparator) {}
   uint32_t GetID() const override { return id_; }
-  const Comparator* user_comparator() const override { return comparator_; }
+  const Comparator* GetComparator() const override { return comparator_; }
 
  private:
   uint32_t id_;