Use the generic iterator interface instead of multi_cf_iterator for u…

…nified experience

db/db_impl/db_impl.cc

@@ -8,8 +8,9 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 #include "db/db_impl/db_impl.h"
 
-#include <cstdint>
 #include <stdint.h>
+
+#include <cstdint>
 #ifdef OS_SOLARIS
 #include <alloca.h>
 #endif
@@ -81,7 +82,6 @@
 #include "rocksdb/db.h"
 #include "rocksdb/env.h"
 #include "rocksdb/merge_operator.h"
-#include "rocksdb/multi_cf_iterator.h"
 #include "rocksdb/statistics.h"
 #include "rocksdb/stats_history.h"
 #include "rocksdb/status.h"
@@ -3737,20 +3737,20 @@ ArenaWrappedDBIter* DBImpl::NewIteratorImpl(
   return db_iter;
 }
 
-std::unique_ptr<MultiCfIterator> DBImpl::NewMultiCfIterator(
+std::unique_ptr<Iterator> DBImpl::NewMultiCfIterator(
     const ReadOptions& _read_options,
     const std::vector<ColumnFamilyHandle*>& column_families) {
-  if (column_families.size() < 2) {
-    return std::make_unique<EmptyMultiCfIterator>(
-        Status::InvalidArgument("Less than 2 CFs were provided"));
+  if (column_families.size() == 0) {
+    return std::unique_ptr<Iterator>(NewErrorIterator(
+        Status::InvalidArgument("No Column Family was provided")));
   }
   const Comparator* first_comparator = column_families[0]->GetComparator();
   for (size_t i = 1; i < column_families.size(); ++i) {
     const Comparator* cf_comparator = column_families[i]->GetComparator();
     if (first_comparator != cf_comparator &&
         first_comparator->GetId().compare(cf_comparator->GetId()) != 0) {
-      return std::make_unique<EmptyMultiCfIterator>(Status::InvalidArgument(
-          "Different comparators are being used across CFs"));
+      return std::unique_ptr<Iterator>(NewErrorIterator(Status::InvalidArgument(
+          "Different comparators are being used across CFs")));
     }
   }
   std::vector<Iterator*> child_iterators;
@@ -3759,7 +3759,7 @@ std::unique_ptr<MultiCfIterator> DBImpl::NewMultiCfIterator(
     return std::make_unique<MultiCfIteratorImpl>(
         first_comparator, column_families, std::move(child_iterators));
   }
-  return std::make_unique<EmptyMultiCfIterator>(s);
+  return std::unique_ptr<Iterator>(NewErrorIterator(s));
 }
 
 Status DBImpl::NewIterators(

db/db_impl/db_impl.h

@@ -354,7 +354,7 @@ class DBImpl : public DB {
 
   // UNDER CONSTRUCTION - DO NOT USE
   // Return a cross-column-family iterator from a consistent database state.
-  std::unique_ptr<MultiCfIterator> NewMultiCfIterator(
+  std::unique_ptr<Iterator> NewMultiCfIterator(
       const ReadOptions& options,
       const std::vector<ColumnFamilyHandle*>& column_families) override;
 

db/db_test.cc

@@ -3201,7 +3201,7 @@ class ModelDB : public DB {
   }
 
   // UNDER CONSTRUCTION - DO NOT USE
-  std::unique_ptr<MultiCfIterator> NewMultiCfIterator(
+  std::unique_ptr<Iterator> NewMultiCfIterator(
       const ReadOptions& /*options*/,
       const std::vector<ColumnFamilyHandle*>& /*column_families*/) override {
     return nullptr;

db/multi_cf_iterator_impl.h

@@ -5,7 +5,9 @@
 
 #pragma once
 
-#include "rocksdb/multi_cf_iterator.h"
+#include "rocksdb/comparator.h"
+#include "rocksdb/iterator.h"
+#include "rocksdb/options.h"
 #include "util/heap.h"
 
 namespace ROCKSDB_NAMESPACE {
@@ -15,7 +17,7 @@ namespace ROCKSDB_NAMESPACE {
 // When the same key exists in more than one column families, the iterator
 // selects the value from the first column family containing the key, in the
 // order provided in the `column_families` parameter.
-class MultiCfIteratorImpl : public MultiCfIterator {
+class MultiCfIteratorImpl : public Iterator {
  public:
   MultiCfIteratorImpl(const Comparator* comparator,
                       const std::vector<ColumnFamilyHandle*>& column_families,
@@ -116,32 +118,4 @@ class MultiCfIteratorImpl : public MultiCfIterator {
   }
 };
 
-class EmptyMultiCfIterator : public MultiCfIterator {
- public:
-  explicit EmptyMultiCfIterator(const Status& s) : status_(s) {}
-  bool Valid() const override { return false; }
-  void Seek(const Slice& /*target*/) override {}
-  void SeekForPrev(const Slice& /*target*/) override {}
-  void SeekToFirst() override {}
-  void SeekToLast() override {}
-  void Next() override { assert(false); }
-  void Prev() override { assert(false); }
-  Slice key() const override {
-    assert(false);
-    return Slice();
-  }
-  Slice value() const override {
-    assert(false);
-    return Slice();
-  }
-  const AttributeGroups& attribute_groups() const override {
-    assert(false);
-    return kNoAttributeGroups;
-  }
-  Status status() const override { return status_; }
-
- private:
-  Status status_;
-};
-
 }  // namespace ROCKSDB_NAMESPACE

db/multi_cf_iterator_test.cc

@@ -23,7 +23,7 @@ class MultiCfIteratorTest : public DBTestBase {
       const std::optional<std::vector<AttributeGroups>>&
           expected_attribute_groups = std::nullopt) {
     int i = 0;
-    std::unique_ptr<MultiCfIterator> iter =
+    std::unique_ptr<Iterator> iter =
         db_->NewMultiCfIterator(ReadOptions(), cfhs);
     for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
       ASSERT_EQ(expected_keys[i], iter->key());
@@ -66,16 +66,10 @@ TEST_F(MultiCfIteratorTest, InvalidArguments) {
     CreateAndReopenWithCF({"cf_1", "cf_2", "cf_3"}, options);
 
     // Invalid - No CF is provided
-    std::unique_ptr<MultiCfIterator> iter_with_no_cf =
+    std::unique_ptr<Iterator> iter_with_no_cf =
         db_->NewMultiCfIterator(ReadOptions(), {});
     ASSERT_NOK(iter_with_no_cf->status());
     ASSERT_TRUE(iter_with_no_cf->status().IsInvalidArgument());
-
-    // Invalid - Only one CF is provided
-    std::unique_ptr<MultiCfIterator> iter_with_one_cf =
-        db_->NewMultiCfIterator(ReadOptions(), {handles_[0]});
-    ASSERT_NOK(iter_with_one_cf->status());
-    ASSERT_TRUE(iter_with_one_cf->status().IsInvalidArgument());
   }
 }
 
@@ -233,7 +227,7 @@ TEST_F(MultiCfIteratorTest, DifferentComparatorsInMultiCFs) {
   verifyExpectedKeys(handles_[0], {"key_1", "key_2", "key_3"});
   verifyExpectedKeys(handles_[1], {"key_3", "key_2", "key_1"});
 
-  std::unique_ptr<MultiCfIterator> iter =
+  std::unique_ptr<Iterator> iter =
       db_->NewMultiCfIterator(ReadOptions(), handles_);
   ASSERT_NOK(iter->status());
   ASSERT_TRUE(iter->status().IsInvalidArgument());
@@ -286,7 +280,7 @@ TEST_F(MultiCfIteratorTest, CustomComparatorsInMultiCFs) {
                                         "value_0_4", "value_0_5", "value_0_6",
                                         "value_1_4", "value_1_5", "value_1_6"};
   int i = 0;
-  std::unique_ptr<MultiCfIterator> iter =
+  std::unique_ptr<Iterator> iter =
       db_->NewMultiCfIterator(ReadOptions(), handles_);
   for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
     ASSERT_EQ(expected_keys[i], iter->key());

include/rocksdb/db.h

@@ -21,7 +21,6 @@
 #include "rocksdb/iterator.h"
 #include "rocksdb/listener.h"
 #include "rocksdb/metadata.h"
-#include "rocksdb/multi_cf_iterator.h"
 #include "rocksdb/options.h"
 #include "rocksdb/snapshot.h"
 #include "rocksdb/sst_file_writer.h"
@@ -961,7 +960,7 @@ class DB {
   // When the same key is present in multiple column families, the iterator
   // selects the value or columns from the first column family containing the
   // key, in the order specified by the `column_families` parameter.
-  virtual std::unique_ptr<MultiCfIterator> NewMultiCfIterator(
+  virtual std::unique_ptr<Iterator> NewMultiCfIterator(
       const ReadOptions& options,
       const std::vector<ColumnFamilyHandle*>& column_families) = 0;
 

include/rocksdb/iterator.h

@@ -24,6 +24,7 @@
 #include "rocksdb/slice.h"
 #include "rocksdb/status.h"
 #include "rocksdb/wide_columns.h"
+#include "wide_columns.h"
 
 namespace ROCKSDB_NAMESPACE {
 
@@ -102,6 +103,12 @@ class Iterator : public Cleanable {
     return kNoWideColumns;
   }
 
+  // UNDER CONSTRUCTION - DO NOT USE
+  virtual const AttributeGroups& attribute_groups() const {
+    assert(false);
+    return kNoAttributeGroups;
+  }
+
   // If an error has occurred, return it.  Else return an ok status.
   // If non-blocking IO is requested and this operation cannot be
   // satisfied without doing some IO, then this returns Status::Incomplete().

include/rocksdb/utilities/stackable_db.h

@@ -260,7 +260,7 @@ class StackableDB : public DB {
   }
 
   using DB::NewMultiCfIterator;
-  std::unique_ptr<MultiCfIterator> NewMultiCfIterator(
+  std::unique_ptr<Iterator> NewMultiCfIterator(
       const ReadOptions& options,
       const std::vector<ColumnFamilyHandle*>& column_families) override {
     return db_->NewMultiCfIterator(options, column_families);