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diff --git a/src/rocksdb/table/block_based/partitioned_index_reader.h b/src/rocksdb/table/block_based/partitioned_index_reader.h
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+//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+#pragma once
+#include "table/block_based/index_reader_common.h"
+#include "util/hash_containers.h"
+
+namespace ROCKSDB_NAMESPACE {
+// Index that allows binary search lookup in a two-level index structure.
+class PartitionIndexReader : public BlockBasedTable::IndexReaderCommon {
+ public:
+  // Read the partition index from the file and create an instance for
+  // `PartitionIndexReader`.
+  // On success, index_reader will be populated; otherwise it will remain
+  // unmodified.
+  static Status Create(const BlockBasedTable* table, const ReadOptions& ro,
+                       FilePrefetchBuffer* prefetch_buffer, bool use_cache,
+                       bool prefetch, bool pin,
+                       BlockCacheLookupContext* lookup_context,
+                       std::unique_ptr<IndexReader>* index_reader);
+
+  // return a two-level iterator: first level is on the partition index
+  InternalIteratorBase<IndexValue>* NewIterator(
+      const ReadOptions& read_options, bool /* disable_prefix_seek */,
+      IndexBlockIter* iter, GetContext* get_context,
+      BlockCacheLookupContext* lookup_context) override;
+
+  Status CacheDependencies(const ReadOptions& ro, bool pin) override;
+  size_t ApproximateMemoryUsage() const override {
+    size_t usage = ApproximateIndexBlockMemoryUsage();
+#ifdef ROCKSDB_MALLOC_USABLE_SIZE
+    usage += malloc_usable_size(const_cast<PartitionIndexReader*>(this));
+#else
+    usage += sizeof(*this);
+#endif  // ROCKSDB_MALLOC_USABLE_SIZE
+    // TODO(myabandeh): more accurate estimate of partition_map_ mem usage
+    return usage;
+  }
+
+ private:
+  PartitionIndexReader(const BlockBasedTable* t,
+                       CachableEntry<Block>&& index_block)
+      : IndexReaderCommon(t, std::move(index_block)) {}
+
+  // For partition blocks pinned in cache. This is expected to be "all or
+  // none" so that !partition_map_.empty() can use an iterator expecting
+  // all partitions to be saved here.
+  UnorderedMap<uint64_t, CachableEntry<Block>> partition_map_;
+};
+}  // namespace ROCKSDB_NAMESPACE