Materialize the hash index

Summary:
Materialize the hash index to avoid the soaring cpu/flash usage
when initializing the database.

Test Plan: existing unit tests passed

Reviewers: sdong, haobo

Reviewed By: sdong

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18339

HISTORY.md

@@ -5,6 +5,9 @@
 ### Public API changes
 * Replaced ColumnFamilyOptions::table_properties_collectors with ColumnFamilyOptions::table_properties_collector_factories
 
+### New Features
+* Hash index for block-based table will be materialized and reconstructed more efficiently. Previously hash index is constructed by scanning the whole table during every table open.
+
 ## 3.0.0 (05/05/2014)
 
 ### Public API changes

table/block_based_table_builder.cc

@@ -15,6 +15,8 @@
 
 #include <map>
 #include <memory>
+#include <string>
+#include <unordered_map>
 
 #include "db/dbformat.h"
 
@@ -41,6 +43,8 @@
 
 namespace rocksdb {
 
+extern const std::string kHashIndexPrefixesBlock;
+extern const std::string kHashIndexPrefixesMetadataBlock;
 namespace {
 
 typedef BlockBasedTableOptions::IndexType IndexType;
@@ -57,6 +61,14 @@ typedef BlockBasedTableOptions::IndexType IndexType;
 // design that just works.
 class IndexBuilder {
  public:
+  // Index builder will construct a set of blocks which contain:
+  //  1. One primary index block.
+  //  2. (Optional) a set of metablocks that contains the metadata of the
+  //     primary index.
+  struct IndexBlocks {
+    Slice index_block_contents;
+    std::unordered_map<std::string, Slice> meta_blocks;
+  };
   explicit IndexBuilder(const Comparator* comparator)
       : comparator_(comparator) {}
 
@@ -72,15 +84,19 @@ class IndexBuilder {
   //                           the last one in the table
   //
   // REQUIRES: Finish() has not yet been called.
-  virtual void AddEntry(std::string* last_key_in_current_block,
-                        const Slice* first_key_in_next_block,
-                        const BlockHandle& block_handle) = 0;
+  virtual void AddIndexEntry(std::string* last_key_in_current_block,
+                             const Slice* first_key_in_next_block,
+                             const BlockHandle& block_handle) = 0;
+
+  // This method will be called whenever a key is added. The subclasses may
+  // override OnKeyAdded() if they need to collect additional information.
+  virtual void OnKeyAdded(const Slice& key) {}
 
   // Inform the index builder that all entries has been written. Block builder
   // may therefore perform any operation required for block finalization.
   //
   // REQUIRES: Finish() has not yet been called.
-  virtual Slice Finish() = 0;
+  virtual Status Finish(IndexBlocks* index_blocks) = 0;
 
   // Get the estimated size for index block.
   virtual size_t EstimatedSize() const = 0;
@@ -103,9 +119,9 @@ class ShortenedIndexBuilder : public IndexBuilder {
       : IndexBuilder(comparator),
         index_block_builder_(1 /* block_restart_interval == 1 */, comparator) {}
 
-  virtual void AddEntry(std::string* last_key_in_current_block,
-                        const Slice* first_key_in_next_block,
-                        const BlockHandle& block_handle) override {
+  virtual void AddIndexEntry(std::string* last_key_in_current_block,
+                             const Slice* first_key_in_next_block,
+                             const BlockHandle& block_handle) override {
     if (first_key_in_next_block != nullptr) {
       comparator_->FindShortestSeparator(last_key_in_current_block,
                                          *first_key_in_next_block);
@@ -118,7 +134,10 @@ class ShortenedIndexBuilder : public IndexBuilder {
     index_block_builder_.Add(*last_key_in_current_block, handle_encoding);
   }
 
-  virtual Slice Finish() override { return index_block_builder_.Finish(); }
+  virtual Status Finish(IndexBlocks* index_blocks) {
+    index_blocks->index_block_contents = index_block_builder_.Finish();
+    return Status::OK();
+  }
 
   virtual size_t EstimatedSize() const {
     return index_block_builder_.CurrentSizeEstimate();
@@ -128,38 +147,125 @@ class ShortenedIndexBuilder : public IndexBuilder {
   BlockBuilder index_block_builder_;
 };
 
-// FullKeyIndexBuilder is also based on BlockBuilder. It works pretty much like
-// ShortenedIndexBuilder, but preserves the full key instead the substitude key.
-class FullKeyIndexBuilder : public IndexBuilder {
+// HashIndexBuilder contains a binary-searchable primary index and the
+// metadata for secondary hash index construction.
+// The metadata for hash index consists two parts:
+//  - a metablock that compactly contains a sequence of prefixes. All prefixes
+//    are stored consectively without any metadata (like, prefix sizes) being
+//    stored, which is kept in the other metablock.
+//  - a metablock contains the metadata of the prefixes, including prefix size,
+//    restart index and number of block it spans. The format looks like:
+//
+// +-----------------+---------------------------+---------------------+ <=prefix 1
+// | length: 4 bytes | restart interval: 4 bytes | num-blocks: 4 bytes |
+// +-----------------+---------------------------+---------------------+ <=prefix 2
+// | length: 4 bytes | restart interval: 4 bytes | num-blocks: 4 bytes |
+// +-----------------+---------------------------+---------------------+
+// |                                                                   |
+// | ....                                                              |
+// |                                                                   |
+// +-----------------+---------------------------+---------------------+ <=prefix n
+// | length: 4 bytes | restart interval: 4 bytes | num-blocks: 4 bytes |
+// +-----------------+---------------------------+---------------------+
+//
+// The reason of separating these two metablocks is to enable the efficiently
+// reuse the first metablock during hash index construction without unnecessary
+// data copy or small heap allocations for prefixes.
+class HashIndexBuilder : public IndexBuilder {
  public:
-  explicit FullKeyIndexBuilder(const Comparator* comparator)
+  explicit HashIndexBuilder(const Comparator* comparator,
+                            const SliceTransform* hash_key_extractor)
       : IndexBuilder(comparator),
-        index_block_builder_(1 /* block_restart_interval == 1 */, comparator) {}
+        primary_index_builder(comparator),
+        hash_key_extractor_(hash_key_extractor) {}
+
+  virtual void AddIndexEntry(std::string* last_key_in_current_block,
+                             const Slice* first_key_in_next_block,
+                             const BlockHandle& block_handle) override {
+    ++current_restart_index_;
+    primary_index_builder.AddIndexEntry(last_key_in_current_block,
+                                        first_key_in_next_block, block_handle);
+  }
 
-  virtual void AddEntry(std::string* last_key_in_current_block,
-                        const Slice* first_key_in_next_block,
-                        const BlockHandle& block_handle) override {
-    std::string handle_encoding;
-    block_handle.EncodeTo(&handle_encoding);
-    index_block_builder_.Add(*last_key_in_current_block, handle_encoding);
+  virtual void OnKeyAdded(const Slice& key) override {
+    auto key_prefix = hash_key_extractor_->Transform(key);
+    bool is_first_entry = pending_block_num_ == 0;
+
+    // Keys may share the prefix
+    if (is_first_entry || pending_entry_prefix_ != key_prefix) {
+      if (!is_first_entry) {
+        FlushPendingPrefix();
+      }
+
+      // need a hard copy otherwise the underlying data changes all the time.
+      // TODO(kailiu) ToString() is expensive. We may speed up can avoid data
+      // copy.
+      pending_entry_prefix_ = key_prefix.ToString();
+      pending_block_num_ = 1;
+      pending_entry_index_ = current_restart_index_;
+    } else {
+      // entry number increments when keys share the prefix reside in
+      // differnt data blocks.
+      auto last_restart_index = pending_entry_index_ + pending_block_num_ - 1;
+      assert(last_restart_index <= current_restart_index_);
+      if (last_restart_index != current_restart_index_) {
+        ++pending_block_num_;
+      }
+    }
   }
 
-  virtual Slice Finish() override { return index_block_builder_.Finish(); }
+  virtual Status Finish(IndexBlocks* index_blocks) {
+    FlushPendingPrefix();
+    primary_index_builder.Finish(index_blocks);
+    index_blocks->meta_blocks.insert(
+        {kHashIndexPrefixesBlock.c_str(), prefix_block_});
+    index_blocks->meta_blocks.insert(
+        {kHashIndexPrefixesMetadataBlock.c_str(), prefix_meta_block_});
+    return Status::OK();
+  }
 
   virtual size_t EstimatedSize() const {
-    return index_block_builder_.CurrentSizeEstimate();
+    return primary_index_builder.EstimatedSize() + prefix_block_.size() +
+           prefix_meta_block_.size();
   }
 
  private:
-  BlockBuilder index_block_builder_;
+  void FlushPendingPrefix() {
+    prefix_block_.append(pending_entry_prefix_.data(),
+                         pending_entry_prefix_.size());
+    PutVarint32(&prefix_meta_block_, pending_entry_prefix_.size());
+    PutVarint32(&prefix_meta_block_, pending_entry_index_);
+    PutVarint32(&prefix_meta_block_, pending_block_num_);
+  }
+
+  ShortenedIndexBuilder primary_index_builder;
+  const SliceTransform* hash_key_extractor_;
+
+  // stores a sequence of prefixes
+  std::string prefix_block_;
+  // stores the metadata of prefixes
+  std::string prefix_meta_block_;
+
+  // The following 3 variables keeps unflushed prefix and its metadata.
+  // The details of block_num and entry_index can be found in
+  // "block_hash_index.{h,cc}"
+  uint32_t pending_block_num_ = 0;
+  uint32_t pending_entry_index_ = 0;
+  std::string pending_entry_prefix_;
+
+  uint64_t current_restart_index_ = 0;
 };
 
 // Create a index builder based on its type.
-IndexBuilder* CreateIndexBuilder(IndexType type, const Comparator* comparator) {
+IndexBuilder* CreateIndexBuilder(IndexType type, const Comparator* comparator,
+                                 const SliceTransform* prefix_extractor) {
   switch (type) {
     case BlockBasedTableOptions::kBinarySearch: {
       return new ShortenedIndexBuilder(comparator);
     }
+    case BlockBasedTableOptions::kHashSearch: {
+      return new HashIndexBuilder(comparator, prefix_extractor);
+    }
     default: {
       assert(!"Do not recognize the index type ");
       return nullptr;
@@ -249,7 +355,7 @@ extern const uint64_t kLegacyBlockBasedTableMagicNumber = 0xdb4775248b80fb57ull;
 class BlockBasedTableBuilder::BlockBasedTablePropertiesCollector
     : public TablePropertiesCollector {
  public:
-  BlockBasedTablePropertiesCollector(
+  explicit BlockBasedTablePropertiesCollector(
       BlockBasedTableOptions::IndexType index_type)
       : index_type_(index_type) {}
 
@@ -288,6 +394,8 @@ struct BlockBasedTableBuilder::Rep {
   uint64_t offset = 0;
   Status status;
   BlockBuilder data_block;
+
+  InternalKeySliceTransform internal_prefix_transform;
   std::unique_ptr<IndexBuilder> index_builder;
 
   std::string last_key;
@@ -316,8 +424,9 @@ struct BlockBasedTableBuilder::Rep {
         internal_comparator(icomparator),
         file(f),
         data_block(options, &internal_comparator),
-        index_builder(
-            CreateIndexBuilder(index_block_type, &internal_comparator)),
+        internal_prefix_transform(options.prefix_extractor.get()),
+        index_builder(CreateIndexBuilder(index_block_type, &internal_comparator,
+                                         &this->internal_prefix_transform)),
         compression_type(compression_type),
         checksum_type(checksum_type),
         filter_block(opt.filter_policy == nullptr
@@ -335,16 +444,13 @@ struct BlockBasedTableBuilder::Rep {
   }
 };
 
-// TODO(sdong): Currently only write out binary search index. In
-// BlockBasedTableReader, Hash index will be built using binary search index.
 BlockBasedTableBuilder::BlockBasedTableBuilder(
     const Options& options, const BlockBasedTableOptions& table_options,
     const InternalKeyComparator& internal_comparator, WritableFile* file,
     CompressionType compression_type)
     : rep_(new Rep(options, internal_comparator, file,
                    table_options.flush_block_policy_factory.get(),
-                   compression_type,
-                   BlockBasedTableOptions::IndexType::kBinarySearch,
+                   compression_type, table_options.index_type,
                    table_options.checksum)) {
   if (rep_->filter_block != nullptr) {
     rep_->filter_block->StartBlock(0);
@@ -370,7 +476,7 @@ void BlockBasedTableBuilder::Add(const Slice& key, const Slice& value) {
   if (r->props.num_entries > 0) {
     assert(r->internal_comparator.Compare(key, Slice(r->last_key)) > 0);
   }
-
+  r->index_builder->OnKeyAdded(key);
   auto should_flush = r->flush_block_policy->Update(key, value);
   if (should_flush) {
     assert(!r->data_block.empty());
@@ -385,7 +491,7 @@ void BlockBasedTableBuilder::Add(const Slice& key, const Slice& value) {
     // entries in the first block and < all entries in subsequent
     // blocks.
     if (ok()) {
-      r->index_builder->AddEntry(&r->last_key, &key, r->pending_handle);
+      r->index_builder->AddIndexEntry(&r->last_key, &key, r->pending_handle);
     }
   }
 
@@ -561,24 +667,36 @@ Status BlockBasedTableBuilder::Finish() {
   // block, we will finish writing all index entries here and flush them
   // to storage after metaindex block is written.
   if (ok() && !empty_data_block) {
-    r->index_builder->AddEntry(&r->last_key, nullptr /* no next data block */,
-                               r->pending_handle);
+    r->index_builder->AddIndexEntry(
+        &r->last_key, nullptr /* no next data block */, r->pending_handle);
+  }
+
+  IndexBuilder::IndexBlocks index_blocks;
+  auto s = r->index_builder->Finish(&index_blocks);
+  if (!s.ok()) {
+    return s;
   }
 
   // Write meta blocks and metaindex block with the following order.
   //    1. [meta block: filter]
-  //    2. [meta block: properties]
-  //    3. [metaindex block]
-  if (ok()) {
-    MetaIndexBuilder meta_index_builer;
+  //    2. [other meta blocks]
+  //    3. [meta block: properties]
+  //    4. [metaindex block]
+  // write meta blocks
+  MetaIndexBuilder meta_index_builder;
+  for (const auto& item : index_blocks.meta_blocks) {
+    BlockHandle block_handle;
+    WriteBlock(item.second, &block_handle);
+    meta_index_builder.Add(item.first, block_handle);
+  }
 
-    // Write filter block.
+  if (ok()) {
     if (r->filter_block != nullptr) {
       // Add mapping from "<filter_block_prefix>.Name" to location
       // of filter data.
       std::string key = BlockBasedTable::kFilterBlockPrefix;
       key.append(r->options.filter_policy->Name());
-      meta_index_builer.Add(key, filter_block_handle);
+      meta_index_builder.Add(key, filter_block_handle);
     }
 
     // Write properties block.
@@ -605,20 +723,16 @@ Status BlockBasedTableBuilder::Finish() {
           &properties_block_handle
       );
 
-      meta_index_builer.Add(kPropertiesBlock,
-                            properties_block_handle);
+      meta_index_builder.Add(kPropertiesBlock, properties_block_handle);
     }  // end of properties block writing
-
-    WriteRawBlock(
-        meta_index_builer.Finish(),
-        kNoCompression,
-        &metaindex_block_handle
-    );
-  }  // meta blocks and metaindex block.
+  }    // meta blocks
 
   // Write index block
   if (ok()) {
-    WriteBlock(r->index_builder->Finish(), &index_block_handle);
+    // flush the meta index block
+    WriteRawBlock(meta_index_builder.Finish(), kNoCompression,
+                  &metaindex_block_handle);
+    WriteBlock(index_blocks.index_block_contents, &index_block_handle);
   }
 
   // Write footer
@@ -685,7 +799,6 @@ uint64_t BlockBasedTableBuilder::FileSize() const {
   return rep_->offset;
 }
 
-const std::string BlockBasedTable::kFilterBlockPrefix =
-    "filter.";
+const std::string BlockBasedTable::kFilterBlockPrefix = "filter.";
 
 }  // namespace rocksdb

table/block_based_table_factory.cc

@@ -56,5 +56,8 @@ TableFactory* NewBlockBasedTableFactory(
 
 const std::string BlockBasedTablePropertyNames::kIndexType =
     "rocksdb.block.based.table.index.type";
+const std::string kHashIndexPrefixesBlock = "rocksdb.hashindex.prefixes";
+const std::string kHashIndexPrefixesMetadataBlock =
+    "rocksdb.hashindex.metadata";
 
 }  // namespace rocksdb

table/block_based_table_factory.h

@@ -8,9 +8,11 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
 #pragma once
-#include <memory>
 #include <stdint.h>
 
+#include <memory>
+#include <string>
+
 #include "rocksdb/flush_block_policy.h"
 #include "rocksdb/options.h"
 #include "rocksdb/table.h"
@@ -45,4 +47,7 @@ class BlockBasedTableFactory : public TableFactory {
   BlockBasedTableOptions table_options_;
 };
 
+extern const std::string kHashIndexPrefixesBlock;
+extern const std::string kHashIndexPrefixesMetadataBlock;
+
 }  // namespace rocksdb

table/block_based_table_reader.cc

@@ -38,6 +38,8 @@
 namespace rocksdb {
 
 extern const uint64_t kBlockBasedTableMagicNumber;
+extern const std::string kHashIndexPrefixesBlock;
+extern const std::string kHashIndexPrefixesMetadataBlock;
 using std::unique_ptr;
 
 typedef BlockBasedTable::IndexReader IndexReader;
@@ -186,19 +188,13 @@ class BinarySearchIndexReader : public IndexReader {
 
 // Index that leverages an internal hash table to quicken the lookup for a given
 // key.
-// @param data_iter_gen, equavalent to BlockBasedTable::NewIterator(). But that
-// functions requires index to be initalized. To avoid this problem external
-// caller will pass a function that can create the iterator over the entries
-// without the table to be fully initialized.
 class HashIndexReader : public IndexReader {
  public:
-  static Status Create(RandomAccessFile* file, const Footer& footer,
-                       const BlockHandle& index_handle, Env* env,
+  static Status Create(const SliceTransform* hash_key_extractor,
+                       const Footer& footer, RandomAccessFile* file, Env* env,
                        const Comparator* comparator,
-                       std::function<Iterator*(Iterator*)> data_iter_gen,
-                       const SliceTransform* prefix_extractor,
-                       IndexReader** index_reader) {
-    assert(prefix_extractor);
+                       const BlockHandle& index_handle,
+                       Iterator* meta_index_iter, IndexReader** index_reader) {
     Block* index_block = nullptr;
     auto s = ReadBlockFromFile(file, footer, ReadOptions(), index_handle,
                                &index_block, env);
@@ -207,14 +203,57 @@ class HashIndexReader : public IndexReader {
       return s;
     }
 
-    *index_reader = new HashIndexReader(comparator, index_block);
-    std::unique_ptr<Iterator> index_iter(index_block->NewIterator(nullptr));
-    std::unique_ptr<Iterator> data_iter(
-        data_iter_gen(index_block->NewIterator(nullptr)));
-    auto hash_index = CreateBlockHashIndex(index_iter.get(), data_iter.get(),
-                                           index_block->NumRestarts(),
-                                           comparator, prefix_extractor);
-    index_block->SetBlockHashIndex(hash_index);
+    // Get prefixes block
+    BlockHandle prefixes_handle;
+    s = FindMetaBlock(meta_index_iter, kHashIndexPrefixesBlock,
+                      &prefixes_handle);
+    if (!s.ok()) {
+      return s;
+    }
+
+    // Get index metadata block
+    BlockHandle prefixes_meta_handle;
+    s = FindMetaBlock(meta_index_iter, kHashIndexPrefixesMetadataBlock,
+                      &prefixes_meta_handle);
+    if (!s.ok()) {
+      return s;
+    }
+
+    // Read contents for the blocks
+    BlockContents prefixes_contents;
+    s = ReadBlockContents(file, footer, ReadOptions(), prefixes_handle,
+                          &prefixes_contents, env, true /* do decompression */);
+    if (!s.ok()) {
+      return s;
+    }
+    BlockContents prefixes_meta_contents;
+    s = ReadBlockContents(file, footer, ReadOptions(), prefixes_meta_handle,
+                          &prefixes_meta_contents, env,
+                          true /* do decompression */);
+    if (!s.ok()) {
+      if (prefixes_contents.heap_allocated) {
+        delete[] prefixes_contents.data.data();
+      }
+      return s;
+    }
+
+    auto new_index_reader =
+        new HashIndexReader(comparator, index_block, prefixes_contents);
+    BlockHashIndex* hash_index = nullptr;
+    s = CreateBlockHashIndex(hash_key_extractor, prefixes_contents.data,
+                             prefixes_meta_contents.data, &hash_index);
+    if (!s.ok()) {
+      return s;
+    }
+
+    new_index_reader->index_block_->SetBlockHashIndex(hash_index);
+
+    *index_reader = new_index_reader;
+
+    // release resources
+    if (prefixes_meta_contents.heap_allocated) {
+      delete[] prefixes_meta_contents.data.data();
+    }
     return s;
   }
 
@@ -225,11 +264,22 @@ class HashIndexReader : public IndexReader {
   virtual size_t size() const override { return index_block_->size(); }
 
  private:
-  HashIndexReader(const Comparator* comparator, Block* index_block)
-      : IndexReader(comparator), index_block_(index_block) {
+  HashIndexReader(const Comparator* comparator, Block* index_block,
+                  const BlockContents& prefixes_contents)
+      : IndexReader(comparator),
+        index_block_(index_block),
+        prefixes_contents_(prefixes_contents) {
     assert(index_block_ != nullptr);
   }
+
+  ~HashIndexReader() {
+    if (prefixes_contents_.heap_allocated) {
+      delete[] prefixes_contents_.data.data();
+    }
+  }
+
   std::unique_ptr<Block> index_block_;
+  BlockContents prefixes_contents_;
 };
 
 
@@ -408,7 +458,7 @@ Status BlockBasedTable::Open(const Options& options, const EnvOptions& soptions,
     // and with a same life-time as this table object.
     IndexReader* index_reader = nullptr;
     // TODO: we never really verify check sum for index block
-    s = new_table->CreateIndexReader(&index_reader);
+    s = new_table->CreateIndexReader(&index_reader, meta_iter.get());
 
     if (s.ok()) {
       rep->index_reader.reset(index_reader);
@@ -417,10 +467,9 @@ Status BlockBasedTable::Open(const Options& options, const EnvOptions& soptions,
       if (rep->options.filter_policy) {
         std::string key = kFilterBlockPrefix;
         key.append(rep->options.filter_policy->Name());
-        meta_iter->Seek(key);
-
-        if (meta_iter->Valid() && meta_iter->key() == Slice(key)) {
-          rep->filter.reset(ReadFilter(meta_iter->value(), rep));
+        BlockHandle handle;
+        if (FindMetaBlock(meta_iter.get(), key, &handle).ok()) {
+          rep->filter.reset(ReadFilter(handle, rep));
         }
       }
     } else {
@@ -617,16 +666,9 @@ Status BlockBasedTable::PutDataBlockToCache(
   return s;
 }
 
-FilterBlockReader* BlockBasedTable::ReadFilter (
-    const Slice& filter_handle_value,
-    BlockBasedTable::Rep* rep,
-    size_t* filter_size) {
-  Slice v = filter_handle_value;
-  BlockHandle filter_handle;
-  if (!filter_handle.DecodeFrom(&v).ok()) {
-    return nullptr;
-  }
-
+FilterBlockReader* BlockBasedTable::ReadFilter(const BlockHandle& filter_handle,
+                                               BlockBasedTable::Rep* rep,
+                                               size_t* filter_size) {
   // TODO: We might want to unify with ReadBlockFromFile() if we start
   // requiring checksum verification in Table::Open.
   ReadOptions opt;
@@ -687,10 +729,9 @@ BlockBasedTable::CachableEntry<FilterBlockReader> BlockBasedTable::GetFilter(
     if (s.ok()) {
       std::string filter_block_key = kFilterBlockPrefix;
       filter_block_key.append(rep_->options.filter_policy->Name());
-      iter->Seek(filter_block_key);
-
-      if (iter->Valid() && iter->key() == Slice(filter_block_key)) {
-        filter = ReadFilter(iter->value(), rep_, &filter_size);
+      BlockHandle handle;
+      if (FindMetaBlock(iter.get(), filter_block_key, &handle).ok()) {
+        filter = ReadFilter(handle, rep_, &filter_size);
         assert(filter);
         assert(filter_size > 0);
 
@@ -1032,7 +1073,8 @@ bool BlockBasedTable::TEST_KeyInCache(const ReadOptions& options,
 //  3. options
 //  4. internal_comparator
 //  5. index_type
-Status BlockBasedTable::CreateIndexReader(IndexReader** index_reader) {
+Status BlockBasedTable::CreateIndexReader(IndexReader** index_reader,
+                                          Iterator* preloaded_meta_index_iter) {
   // Some old version of block-based tables don't have index type present in
   // table properties. If that's the case we can safely use the kBinarySearch.
   auto index_type_on_file = BlockBasedTableOptions::kBinarySearch;
@@ -1045,41 +1087,45 @@ Status BlockBasedTable::CreateIndexReader(IndexReader** index_reader) {
     }
   }
 
-  // TODO(sdong): Currently binary index is the only index type we support in
-  // files. Hash index is built on top of binary index too.
-  if (index_type_on_file != BlockBasedTableOptions::kBinarySearch) {
-    return Status::NotSupported("File Contains not supported index type: ",
-                                std::to_string(index_type_on_file));
-  }
-
   auto file = rep_->file.get();
   auto env = rep_->options.env;
   auto comparator = &rep_->internal_comparator;
   const Footer& footer = rep_->footer;
 
-  switch (rep_->index_type) {
+  switch (index_type_on_file) {
     case BlockBasedTableOptions::kBinarySearch: {
       return BinarySearchIndexReader::Create(
           file, footer, footer.index_handle(), env, comparator, index_reader);
     }
     case BlockBasedTableOptions::kHashSearch: {
+      std::unique_ptr<Block> meta_guard;
+      std::unique_ptr<Iterator> meta_iter_guard;
+      auto meta_index_iter = preloaded_meta_index_iter;
+      if (meta_index_iter == nullptr) {
+        auto s = ReadMetaBlock(rep_, &meta_guard, &meta_iter_guard);
+        if (!s.ok()) {
+          return Status::Corruption("Unable to read the metaindex block");
+        }
+        meta_index_iter = meta_iter_guard.get();
+      }
+
       // We need to wrap data with internal_prefix_transform to make sure it can
       // handle prefix correctly.
+      if (rep_->options.prefix_extractor == nullptr) {
+        return Status::InvalidArgument(
+            "BlockBasedTableOptions::kHashSearch requires "
+            "options.prefix_extractor to be set.");
+      }
+
       rep_->internal_prefix_transform.reset(
           new InternalKeySliceTransform(rep_->options.prefix_extractor.get()));
       return HashIndexReader::Create(
-          file, footer, footer.index_handle(), env, comparator,
-          [&](Iterator* index_iter) {
-            return NewTwoLevelIterator(new BlockEntryIteratorState(this,
-                ReadOptions(), nullptr), index_iter);
-          },
-          rep_->internal_prefix_transform.get(), index_reader);
+          rep_->internal_prefix_transform.get(), footer, file, env, comparator,
+          footer.index_handle(), meta_index_iter, index_reader);
     }
     default: {
       std::string error_message =
           "Unrecognized index type: " + std::to_string(rep_->index_type);
-      // equivalent to assert(false), but more informative.
-      assert(!error_message.c_str());
       return Status::InvalidArgument(error_message.c_str());
     }
   }

table/block_based_table_reader.h

@@ -160,8 +160,13 @@ class BlockBasedTable : public TableReader {
   friend class BlockBasedTableBuilder;
 
   void ReadMeta(const Footer& footer);
-  void ReadFilter(const Slice& filter_handle_value);
-  Status CreateIndexReader(IndexReader** index_reader);
+
+  // Create a index reader based on the index type stored in the table.
+  // Optionally, user can pass a preloaded meta_index_iter for the index that
+  // need to access extra meta blocks for index construction. This parameter
+  // helps avoid re-reading meta index block if caller already created one.
+  Status CreateIndexReader(IndexReader** index_reader,
+                           Iterator* preloaded_meta_index_iter = nullptr);
 
   // Read the meta block from sst.
   static Status ReadMetaBlock(
@@ -170,10 +175,8 @@ class BlockBasedTable : public TableReader {
       std::unique_ptr<Iterator>* iter);
 
   // Create the filter from the filter block.
-  static FilterBlockReader* ReadFilter(
-      const Slice& filter_handle_value,
-      Rep* rep,
-      size_t* filter_size = nullptr);
+  static FilterBlockReader* ReadFilter(const BlockHandle& filter_handle,
+                                       Rep* rep, size_t* filter_size = nullptr);
 
   static void SetupCacheKeyPrefix(Rep* rep);
 

table/block_hash_index.cc

@@ -3,21 +3,62 @@
 // LICENSE file in the root directory of this source tree. An additional grant
 // of patent rights can be found in the PATENTS file in the same directory.
 
+#include "table/block_hash_index.h"
+
 #include <algorithm>
 
-#include "table/block_hash_index.h"
 #include "rocksdb/comparator.h"
 #include "rocksdb/iterator.h"
 #include "rocksdb/slice_transform.h"
+#include "util/coding.h"
 
 namespace rocksdb {
 
-BlockHashIndex* CreateBlockHashIndex(Iterator* index_iter, Iterator* data_iter,
-                                     const uint32_t num_restarts,
-                                     const Comparator* comparator,
-                                     const SliceTransform* hash_key_extractor) {
+Status CreateBlockHashIndex(const SliceTransform* hash_key_extractor,
+                            const Slice& prefixes, const Slice& prefix_meta,
+                            BlockHashIndex** hash_index) {
+  uint64_t pos = 0;
+  auto meta_pos = prefix_meta;
+  Status s;
+  *hash_index = new BlockHashIndex(
+      hash_key_extractor,
+      false /* external module manages memory space for prefixes */);
+
+  while (!meta_pos.empty()) {
+    uint32_t prefix_size = 0;
+    uint32_t entry_index = 0;
+    uint32_t num_blocks = 0;
+    if (!GetVarint32(&meta_pos, &prefix_size) ||
+        !GetVarint32(&meta_pos, &entry_index) ||
+        !GetVarint32(&meta_pos, &num_blocks)) {
+      s = Status::Corruption(
+          "Corrupted prefix meta block: unable to read from it.");
+      break;
+    }
+    Slice prefix(prefixes.data() + pos, prefix_size);
+    (*hash_index)->Add(prefix, entry_index, num_blocks);
+
+    pos += prefix_size;
+  }
+
+  if (s.ok() && pos != prefixes.size()) {
+    s = Status::Corruption("Corrupted prefix meta block");
+  }
+
+  if (!s.ok()) {
+    delete *hash_index;
+  }
+
+  return s;
+}
+
+BlockHashIndex* CreateBlockHashIndexOnTheFly(
+    Iterator* index_iter, Iterator* data_iter, const uint32_t num_restarts,
+    const Comparator* comparator, const SliceTransform* hash_key_extractor) {
   assert(hash_key_extractor);
-  auto hash_index = new BlockHashIndex(hash_key_extractor);
+  auto hash_index = new BlockHashIndex(
+      hash_key_extractor,
+      true /* hash_index will copy prefix when Add() is called */);
   uint64_t current_restart_index = 0;
 
   std::string pending_entry_prefix;
@@ -88,12 +129,16 @@ BlockHashIndex* CreateBlockHashIndex(Iterator* index_iter, Iterator* data_iter,
 
 bool BlockHashIndex::Add(const Slice& prefix, uint32_t restart_index,
                          uint32_t num_blocks) {
-  auto prefix_ptr = arena_.Allocate(prefix.size());
-  std::copy(prefix.data() /* begin */, prefix.data() + prefix.size() /* end */,
-            prefix_ptr /* destination */);
-  auto result =
-      restart_indices_.insert({Slice(prefix_ptr, prefix.size()),
-                               RestartIndex(restart_index, num_blocks)});
+  auto prefix_to_insert = prefix;
+  if (kOwnPrefixes) {
+    auto prefix_ptr = arena_.Allocate(prefix.size());
+    std::copy(prefix.data() /* begin */,
+              prefix.data() + prefix.size() /* end */,
+              prefix_ptr /* destination */);
+    prefix_to_insert = Slice(prefix_ptr, prefix.size());
+  }
+  auto result = restart_indices_.insert(
+      {prefix_to_insert, RestartIndex(restart_index, num_blocks)});
   return result.second;
 }
 

table/block_hash_index.h

@@ -7,6 +7,7 @@
 #include <string>
 #include <unordered_map>
 
+#include "rocksdb/status.h"
 #include "util/arena.h"
 #include "util/murmurhash.h"
 
@@ -35,8 +36,12 @@ class BlockHashIndex {
     uint32_t num_blocks = 1;
   };
 
-  explicit BlockHashIndex(const SliceTransform* hash_key_extractor)
-      : hash_key_extractor_(hash_key_extractor) {}
+  // @params own_prefixes indicate if we should take care the memory space for
+  // the `key_prefix`
+  // passed by Add()
+  explicit BlockHashIndex(const SliceTransform* hash_key_extractor,
+                          bool own_prefixes)
+      : hash_key_extractor_(hash_key_extractor), kOwnPrefixes(own_prefixes) {}
 
   // Maps a key to its restart first_index.
   // Returns nullptr if the restart first_index is found
@@ -52,9 +57,18 @@ class BlockHashIndex {
  private:
   const SliceTransform* hash_key_extractor_;
   std::unordered_map<Slice, RestartIndex, murmur_hash> restart_indices_;
+
   Arena arena_;
+  bool kOwnPrefixes;
 };
 
+// Create hash index by reading from the metadata blocks.
+// @params prefixes: a sequence of prefixes.
+// @params prefix_meta: contains the "metadata" to of the prefixes.
+Status CreateBlockHashIndex(const SliceTransform* hash_key_extractor,
+                            const Slice& prefixes, const Slice& prefix_meta,
+                            BlockHashIndex** hash_index);
+
 // Create hash index by scanning the entries in index as well as the whole
 // dataset.
 // @params index_iter: an iterator with the pointer to the first entry in a
@@ -64,9 +78,8 @@ class BlockHashIndex {
 // @params num_restarts: used for correctness verification.
 // @params hash_key_extractor: extract the hashable part of a given key.
 // On error, nullptr will be returned.
-BlockHashIndex* CreateBlockHashIndex(Iterator* index_iter, Iterator* data_iter,
-                                     const uint32_t num_restarts,
-                                     const Comparator* comparator,
-                                     const SliceTransform* hash_key_extractor);
+BlockHashIndex* CreateBlockHashIndexOnTheFly(
+    Iterator* index_iter, Iterator* data_iter, const uint32_t num_restarts,
+    const Comparator* comparator, const SliceTransform* hash_key_extractor);
 
 }  // namespace rocksdb

table/block_hash_index_test.cc

@@ -81,9 +81,9 @@ TEST(BlockTest, BasicTest) {
   MapIterator index_iter(index_entries);
 
   auto prefix_extractor = NewFixedPrefixTransform(prefix_size);
-  std::unique_ptr<BlockHashIndex> block_hash_index(
-      CreateBlockHashIndex(&index_iter, &data_iter, index_entries.size(),
-                           BytewiseComparator(), prefix_extractor));
+  std::unique_ptr<BlockHashIndex> block_hash_index(CreateBlockHashIndexOnTheFly(
+      &index_iter, &data_iter, index_entries.size(), BytewiseComparator(),
+      prefix_extractor));
 
   std::map<std::string, BlockHashIndex::RestartIndex> expected = {
       {"01xx", BlockHashIndex::RestartIndex(0, 1)},

table/block_test.cc

@@ -163,9 +163,9 @@ void CheckBlockContents(BlockContents contents, const int max_key,
   {
     auto iter1 = reader1.NewIterator(nullptr);
     auto iter2 = reader1.NewIterator(nullptr);
-    reader1.SetBlockHashIndex(CreateBlockHashIndex(iter1, iter2, keys.size(),
-                                                   BytewiseComparator(),
-                                                   prefix_extractor.get()));
+    reader1.SetBlockHashIndex(CreateBlockHashIndexOnTheFly(
+        iter1, iter2, keys.size(), BytewiseComparator(),
+        prefix_extractor.get()));
 
     delete iter1;
     delete iter2;

table/meta_blocks.cc

@@ -254,11 +254,23 @@ Status ReadTableProperties(RandomAccessFile* file, uint64_t file_size,
                        properties);
   } else {
     s = Status::Corruption("Unable to read the property block.");
-    Log(WARN_LEVEL, info_log,
-        "Cannot find Properties block from file.");
+    Log(WARN_LEVEL, info_log, "Cannot find Properties block from file.");
   }
 
   return s;
 }
 
+Status FindMetaBlock(Iterator* meta_index_iter,
+                     const std::string& meta_block_name,
+                     BlockHandle* block_handle) {
+  meta_index_iter->Seek(meta_block_name);
+  if (meta_index_iter->status().ok() && meta_index_iter->Valid() &&
+      meta_index_iter->key() == meta_block_name) {
+    Slice v = meta_index_iter->value();
+    return block_handle->DecodeFrom(&v);
+  } else {
+    return Status::Corruption("Cannot find the meta block", meta_block_name);
+  }
+}
+
 }  // namespace rocksdb

table/meta_blocks.h

@@ -123,4 +123,9 @@ Status ReadTableProperties(RandomAccessFile* file, uint64_t file_size,
 // set to true.
 extern Status SeekToPropertiesBlock(Iterator* meta_iter, bool* is_found);
 
+// Find the meta block from the meta index block.
+Status FindMetaBlock(Iterator* meta_index_iter,
+                     const std::string& meta_block_name,
+                     BlockHandle* block_handle);
+
 }  // namespace rocksdb