Support prefetch last 512KB with direct I/O in block based file reader

Summary:
Right now, if direct I/O is enabled, prefetching the last 512KB cannot be applied, except compaction inputs or readahead is enabled for iterators. This can create a lot of I/O for HDD cases. To solve the problem, the 512KB is prefetched in block based table if direct I/O is enabled. The prefetched buffer is passed in totegher with random access file reader, so that we try to read from the buffer before reading from the file. This can be extended in the future to support flexible user iterator readahead too.
Closes https://github.com/facebook/rocksdb/pull/2708

Differential Revision: D5593091

Pulled By: siying

fbshipit-source-id: ee36ff6d8af11c312a2622272b21957a7b5c81e7

db/db_test2.cc

@@ -2282,12 +2282,15 @@ TEST_F(DBTest2, RateLimitedCompactionReads) {
     // chose 1MB as the upper bound on the total bytes read.
     size_t rate_limited_bytes =
         options.rate_limiter->GetTotalBytesThrough(Env::IO_LOW);
-    ASSERT_GE(
-        rate_limited_bytes,
-        static_cast<size_t>(kNumKeysPerFile * kBytesPerKey * kNumL0Files));
+    // Include the explict prefetch of the footer in direct I/O case.
+    size_t direct_io_extra = use_direct_io ? 512 * 1024 : 0;
+    ASSERT_GE(rate_limited_bytes,
+              static_cast<size_t>(kNumKeysPerFile * kBytesPerKey * kNumL0Files +
+                                  direct_io_extra));
     ASSERT_LT(
         rate_limited_bytes,
-        static_cast<size_t>(2 * kNumKeysPerFile * kBytesPerKey * kNumL0Files));
+        static_cast<size_t>(2 * kNumKeysPerFile * kBytesPerKey * kNumL0Files +
+                            direct_io_extra));
 
     Iterator* iter = db_->NewIterator(ReadOptions());
     for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {

table/adaptive_table_factory.cc

@@ -46,7 +46,8 @@ Status AdaptiveTableFactory::NewTableReader(
     unique_ptr<TableReader>* table,
     bool prefetch_index_and_filter_in_cache) const {
   Footer footer;
-  auto s = ReadFooterFromFile(file.get(), file_size, &footer);
+  auto s = ReadFooterFromFile(file.get(), nullptr /* prefetch_buffer */,
+                              file_size, &footer);
   if (!s.ok()) {
     return s;
   }

table/block_based_table_reader.cc

@@ -70,17 +70,17 @@ namespace {
 // On success fill *result and return OK - caller owns *result
 // @param compression_dict Data for presetting the compression library's
 //    dictionary.
-Status ReadBlockFromFile(RandomAccessFileReader* file, const Footer& footer,
-                         const ReadOptions& options, const BlockHandle& handle,
-                         std::unique_ptr<Block>* result,
-                         const ImmutableCFOptions& ioptions, bool do_uncompress,
-                         const Slice& compression_dict,
-                         const PersistentCacheOptions& cache_options,
-                         SequenceNumber global_seqno,
+Status ReadBlockFromFile(
+    RandomAccessFileReader* file, FilePrefetchBuffer* prefetch_buffer,
+    const Footer& footer, const ReadOptions& options, const BlockHandle& handle,
+    std::unique_ptr<Block>* result, const ImmutableCFOptions& ioptions,
+    bool do_uncompress, const Slice& compression_dict,
+    const PersistentCacheOptions& cache_options, SequenceNumber global_seqno,
     size_t read_amp_bytes_per_bit) {
   BlockContents contents;
-  Status s = ReadBlockContents(file, footer, options, handle, &contents, ioptions,
-                               do_uncompress, compression_dict, cache_options);
+  Status s = ReadBlockContents(file, prefetch_buffer, footer, options, handle,
+                               &contents, ioptions, do_uncompress,
+                               compression_dict, cache_options);
   if (s.ok()) {
     result->reset(new Block(std::move(contents), global_seqno,
                             read_amp_bytes_per_bit, ioptions.statistics));
@@ -157,6 +157,7 @@ class PartitionIndexReader : public IndexReader, public Cleanable {
   // On success, index_reader will be populated; otherwise it will remain
   // unmodified.
   static Status Create(BlockBasedTable* table, RandomAccessFileReader* file,
+                       FilePrefetchBuffer* prefetch_buffer,
                        const Footer& footer, const BlockHandle& index_handle,
                        const ImmutableCFOptions& ioptions,
                        const InternalKeyComparator* icomparator,
@@ -165,8 +166,9 @@ class PartitionIndexReader : public IndexReader, public Cleanable {
                        const int level) {
     std::unique_ptr<Block> index_block;
     auto s = ReadBlockFromFile(
-        file, footer, ReadOptions(), index_handle, &index_block, ioptions,
-        true /* decompress */, Slice() /*compression dict*/, cache_options,
+        file, prefetch_buffer, footer, ReadOptions(), index_handle,
+        &index_block, ioptions, true /* decompress */,
+        Slice() /*compression dict*/, cache_options,
         kDisableGlobalSequenceNumber, 0 /* read_amp_bytes_per_bit */);
 
     if (s.ok()) {
@@ -238,16 +240,18 @@ class BinarySearchIndexReader : public IndexReader {
   // `BinarySearchIndexReader`.
   // On success, index_reader will be populated; otherwise it will remain
   // unmodified.
-  static Status Create(RandomAccessFileReader* file, const Footer& footer,
-                       const BlockHandle& index_handle,
+  static Status Create(RandomAccessFileReader* file,
+                       FilePrefetchBuffer* prefetch_buffer,
+                       const Footer& footer, const BlockHandle& index_handle,
                        const ImmutableCFOptions& ioptions,
                        const InternalKeyComparator* icomparator,
                        IndexReader** index_reader,
                        const PersistentCacheOptions& cache_options) {
     std::unique_ptr<Block> index_block;
     auto s = ReadBlockFromFile(
-        file, footer, ReadOptions(), index_handle, &index_block, ioptions,
-        true /* decompress */, Slice() /*compression dict*/, cache_options,
+        file, prefetch_buffer, footer, ReadOptions(), index_handle,
+        &index_block, ioptions, true /* decompress */,
+        Slice() /*compression dict*/, cache_options,
         kDisableGlobalSequenceNumber, 0 /* read_amp_bytes_per_bit */);
 
     if (s.ok()) {
@@ -289,6 +293,7 @@ class HashIndexReader : public IndexReader {
  public:
   static Status Create(const SliceTransform* hash_key_extractor,
                        const Footer& footer, RandomAccessFileReader* file,
+                       FilePrefetchBuffer* prefetch_buffer,
                        const ImmutableCFOptions& ioptions,
                        const InternalKeyComparator* icomparator,
                        const BlockHandle& index_handle,
@@ -298,8 +303,9 @@ class HashIndexReader : public IndexReader {
                        const PersistentCacheOptions& cache_options) {
     std::unique_ptr<Block> index_block;
     auto s = ReadBlockFromFile(
-        file, footer, ReadOptions(), index_handle, &index_block, ioptions,
-        true /* decompress */, Slice() /*compression dict*/, cache_options,
+        file, prefetch_buffer, footer, ReadOptions(), index_handle,
+        &index_block, ioptions, true /* decompress */,
+        Slice() /*compression dict*/, cache_options,
         kDisableGlobalSequenceNumber, 0 /* read_amp_bytes_per_bit */);
 
     if (!s.ok()) {
@@ -335,15 +341,17 @@ class HashIndexReader : public IndexReader {
 
     // Read contents for the blocks
     BlockContents prefixes_contents;
-    s = ReadBlockContents(file, footer, ReadOptions(), prefixes_handle,
-                          &prefixes_contents, ioptions, true /* decompress */,
-                          Slice() /*compression dict*/, cache_options);
+    s = ReadBlockContents(file, prefetch_buffer, footer, ReadOptions(),
+                          prefixes_handle, &prefixes_contents, ioptions,
+                          true /* decompress */, Slice() /*compression dict*/,
+                          cache_options);
     if (!s.ok()) {
       return s;
     }
     BlockContents prefixes_meta_contents;
-    s = ReadBlockContents(file, footer, ReadOptions(), prefixes_meta_handle,
-                          &prefixes_meta_contents, ioptions, true /* decompress */,
+    s = ReadBlockContents(file, prefetch_buffer, footer, ReadOptions(),
+                          prefixes_meta_handle, &prefixes_meta_contents,
+                          ioptions, true /* decompress */,
                           Slice() /*compression dict*/, cache_options);
     if (!s.ok()) {
       // TODO: log error
@@ -535,11 +543,28 @@ Status BlockBasedTable::Open(const ImmutableCFOptions& ioptions,
 
   Footer footer;
 
+  std::unique_ptr<FilePrefetchBuffer> prefetch_buffer;
+
   // Before read footer, readahead backwards to prefetch data
-  Status s =
-      file->Prefetch((file_size < 512 * 1024 ? 0 : file_size - 512 * 1024),
-                     512 * 1024 /* 512 KB prefetching */);
-  s = ReadFooterFromFile(file.get(), file_size, &footer,
+  const size_t kTailPrefetchSize = 512 * 1024;
+  size_t prefetch_off;
+  size_t prefetch_len;
+  if (file_size < kTailPrefetchSize) {
+    prefetch_off = 0;
+    prefetch_len = file_size;
+  } else {
+    prefetch_off = file_size - kTailPrefetchSize;
+    prefetch_len = kTailPrefetchSize;
+  }
+  Status s;
+  // TODO should not have this special logic in the future.
+  if (!file->use_direct_io()) {
+    s = file->Prefetch(prefetch_off, prefetch_len);
+  } else {
+    prefetch_buffer.reset(new FilePrefetchBuffer());
+    s = prefetch_buffer->Prefetch(file.get(), prefetch_off, prefetch_len);
+  }
+  s = ReadFooterFromFile(file.get(), prefetch_buffer.get(), file_size, &footer,
                          kBlockBasedTableMagicNumber);
   if (!s.ok()) {
     return s;
@@ -577,7 +602,7 @@ Status BlockBasedTable::Open(const ImmutableCFOptions& ioptions,
   // Read meta index
   std::unique_ptr<Block> meta;
   std::unique_ptr<InternalIterator> meta_iter;
-  s = ReadMetaBlock(rep, &meta, &meta_iter);
+  s = ReadMetaBlock(rep, prefetch_buffer.get(), &meta, &meta_iter);
   if (!s.ok()) {
     return s;
   }
@@ -623,8 +648,9 @@ Status BlockBasedTable::Open(const ImmutableCFOptions& ioptions,
     s = meta_iter->status();
     TableProperties* table_properties = nullptr;
     if (s.ok()) {
-      s = ReadProperties(meta_iter->value(), rep->file.get(), rep->footer,
-                         rep->ioptions, &table_properties);
+      s = ReadProperties(meta_iter->value(), rep->file.get(),
+                         prefetch_buffer.get(), rep->footer, rep->ioptions,
+                         &table_properties);
     }
 
     if (!s.ok()) {
@@ -655,9 +681,9 @@ Status BlockBasedTable::Open(const ImmutableCFOptions& ioptions,
     // TODO(andrewkr): ReadMetaBlock repeats SeekToCompressionDictBlock().
     // maybe decode a handle from meta_iter
     // and do ReadBlockContents(handle) instead
-    s = rocksdb::ReadMetaBlock(rep->file.get(), file_size,
-                               kBlockBasedTableMagicNumber, rep->ioptions,
-                               rocksdb::kCompressionDictBlock,
+    s = rocksdb::ReadMetaBlock(rep->file.get(), prefetch_buffer.get(),
+                               file_size, kBlockBasedTableMagicNumber,
+                               rep->ioptions, rocksdb::kCompressionDictBlock,
                                compression_dict_block.get());
     if (!s.ok()) {
       ROCKS_LOG_WARN(
@@ -682,6 +708,7 @@ Status BlockBasedTable::Open(const ImmutableCFOptions& ioptions,
   } else {
     if (found_range_del_block && !rep->range_del_handle.IsNull()) {
       ReadOptions read_options;
+      // TODO: try to use prefetched buffer too.
       s = MaybeLoadDataBlockToCache(rep, read_options, rep->range_del_handle,
                                     Slice() /* compression_dict */,
                                     &rep->range_del_entry);
@@ -753,7 +780,8 @@ Status BlockBasedTable::Open(const ImmutableCFOptions& ioptions,
     // pre-load these blocks, which will kept in member variables in Rep
     // and with a same life-time as this table object.
     IndexReader* index_reader = nullptr;
-    s = new_table->CreateIndexReader(&index_reader, meta_iter.get(), level);
+    s = new_table->CreateIndexReader(prefetch_buffer.get(), &index_reader,
+                                     meta_iter.get(), level);
 
     if (s.ok()) {
       rep->index_reader.reset(index_reader);
@@ -761,8 +789,8 @@ Status BlockBasedTable::Open(const ImmutableCFOptions& ioptions,
       // Set filter block
       if (rep->filter_policy) {
         const bool is_a_filter_partition = true;
-        rep->filter.reset(
-            new_table->ReadFilter(rep->filter_handle, !is_a_filter_partition));
+        rep->filter.reset(new_table->ReadFilter(
+            prefetch_buffer.get(), rep->filter_handle, !is_a_filter_partition));
         if (rep->filter.get()) {
           rep->filter->SetLevel(level);
         }
@@ -816,13 +844,14 @@ size_t BlockBasedTable::ApproximateMemoryUsage() const {
 // Load the meta-block from the file. On success, return the loaded meta block
 // and its iterator.
 Status BlockBasedTable::ReadMetaBlock(Rep* rep,
+                                      FilePrefetchBuffer* prefetch_buffer,
                                       std::unique_ptr<Block>* meta_block,
                                       std::unique_ptr<InternalIterator>* iter) {
   // TODO(sanjay): Skip this if footer.metaindex_handle() size indicates
   // it is an empty block.
   std::unique_ptr<Block> meta;
   Status s = ReadBlockFromFile(
-      rep->file.get(), rep->footer, ReadOptions(),
+      rep->file.get(), prefetch_buffer, rep->footer, ReadOptions(),
       rep->footer.metaindex_handle(), &meta, rep->ioptions,
       true /* decompress */, Slice() /*compression dict*/,
       rep->persistent_cache_options, kDisableGlobalSequenceNumber,
@@ -1021,7 +1050,8 @@ Status BlockBasedTable::PutDataBlockToCache(
 }
 
 FilterBlockReader* BlockBasedTable::ReadFilter(
-    const BlockHandle& filter_handle, const bool is_a_filter_partition) const {
+    FilePrefetchBuffer* prefetch_buffer, const BlockHandle& filter_handle,
+    const bool is_a_filter_partition) const {
   auto& rep = rep_;
   // TODO: We might want to unify with ReadBlockFromFile() if we start
   // requiring checksum verification in Table::Open.
@@ -1029,8 +1059,8 @@ FilterBlockReader* BlockBasedTable::ReadFilter(
     return nullptr;
   }
   BlockContents block;
-  if (!ReadBlockContents(rep->file.get(), rep->footer, ReadOptions(),
-                         filter_handle, &block, rep->ioptions,
+  if (!ReadBlockContents(rep->file.get(), prefetch_buffer, rep->footer,
+                         ReadOptions(), filter_handle, &block, rep->ioptions,
                          false /* decompress */, Slice() /*compression dict*/,
                          rep->persistent_cache_options)
            .ok()) {
@@ -1127,7 +1157,8 @@ BlockBasedTable::CachableEntry<FilterBlockReader> BlockBasedTable::GetFilter(
     // Do not invoke any io.
     return CachableEntry<FilterBlockReader>();
   } else {
-    filter = ReadFilter(filter_blk_handle, is_a_filter_partition);
+    filter = ReadFilter(nullptr /* prefetch_buffer */, filter_blk_handle,
+                        is_a_filter_partition);
     if (filter != nullptr) {
       assert(filter->size() > 0);
       Status s = block_cache->Insert(
@@ -1195,7 +1226,7 @@ InternalIterator* BlockBasedTable::NewIndexIterator(
     // Create index reader and put it in the cache.
     Status s;
     TEST_SYNC_POINT("BlockBasedTable::NewIndexIterator::thread2:2");
-    s = CreateIndexReader(&index_reader);
+    s = CreateIndexReader(nullptr /* prefetch_buffer */, &index_reader);
     TEST_SYNC_POINT("BlockBasedTable::NewIndexIterator::thread1:1");
     TEST_SYNC_POINT("BlockBasedTable::NewIndexIterator::thread2:3");
     TEST_SYNC_POINT("BlockBasedTable::NewIndexIterator::thread1:4");
@@ -1290,10 +1321,11 @@ InternalIterator* BlockBasedTable::NewDataBlockIterator(
       }
     }
     std::unique_ptr<Block> block_value;
-    s = ReadBlockFromFile(
-        rep->file.get(), rep->footer, ro, handle, &block_value, rep->ioptions,
-        true /* compress */, compression_dict, rep->persistent_cache_options,
-        rep->global_seqno, rep->table_options.read_amp_bytes_per_bit);
+    s = ReadBlockFromFile(rep->file.get(), nullptr /* prefetch_buffer */,
+                          rep->footer, ro, handle, &block_value, rep->ioptions,
+                          true /* compress */, compression_dict,
+                          rep->persistent_cache_options, rep->global_seqno,
+                          rep->table_options.read_amp_bytes_per_bit);
     if (s.ok()) {
       block.value = block_value.release();
     }
@@ -1360,10 +1392,11 @@ Status BlockBasedTable::MaybeLoadDataBlockToCache(
       std::unique_ptr<Block> raw_block;
       {
         StopWatch sw(rep->ioptions.env, statistics, READ_BLOCK_GET_MICROS);
-        s = ReadBlockFromFile(
-            rep->file.get(), rep->footer, ro, handle, &raw_block, rep->ioptions,
-            block_cache_compressed == nullptr, compression_dict,
-            rep->persistent_cache_options, rep->global_seqno,
+        s = ReadBlockFromFile(rep->file.get(), nullptr /* prefetch_buffer*/,
+                              rep->footer, ro, handle, &raw_block,
+                              rep->ioptions, block_cache_compressed == nullptr,
+                              compression_dict, rep->persistent_cache_options,
+                              rep->global_seqno,
                               rep->table_options.read_amp_bytes_per_bit);
       }
 
@@ -1750,7 +1783,7 @@ Status BlockBasedTable::VerifyChecksum() {
   // Check Meta blocks
   std::unique_ptr<Block> meta;
   std::unique_ptr<InternalIterator> meta_iter;
-  s = ReadMetaBlock(rep_, &meta, &meta_iter);
+  s = ReadMetaBlock(rep_, nullptr /* prefetch buffer */, &meta, &meta_iter);
   if (s.ok()) {
     s = VerifyChecksumInBlocks(meta_iter.get());
     if (!s.ok()) {
@@ -1788,9 +1821,10 @@ Status BlockBasedTable::VerifyChecksumInBlocks(InternalIterator* index_iter) {
       break;
     }
     BlockContents contents;
-    s = ReadBlockContents(rep_->file.get(), rep_->footer, ReadOptions(),
-                          handle, &contents, rep_->ioptions,
-                          false /* decompress */, Slice() /*compression dict*/,
+    s = ReadBlockContents(rep_->file.get(), nullptr /* prefetch buffer */,
+                          rep_->footer, ReadOptions(), handle, &contents,
+                          rep_->ioptions, false /* decompress */,
+                          Slice() /*compression dict*/,
                           rep_->persistent_cache_options);
     if (!s.ok()) {
       break;
@@ -1840,8 +1874,8 @@ bool BlockBasedTable::TEST_KeyInCache(const ReadOptions& options,
 //  4. internal_comparator
 //  5. index_type
 Status BlockBasedTable::CreateIndexReader(
-    IndexReader** index_reader, InternalIterator* preloaded_meta_index_iter,
-    int level) {
+    FilePrefetchBuffer* prefetch_buffer, IndexReader** index_reader,
+    InternalIterator* preloaded_meta_index_iter, int level) {
   // 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;
@@ -1869,20 +1903,22 @@ Status BlockBasedTable::CreateIndexReader(
   switch (index_type_on_file) {
     case BlockBasedTableOptions::kTwoLevelIndexSearch: {
       return PartitionIndexReader::Create(
-          this, file, footer, footer.index_handle(), rep_->ioptions,
-          icomparator, index_reader, rep_->persistent_cache_options, level);
+          this, file, prefetch_buffer, footer, footer.index_handle(),
+          rep_->ioptions, icomparator, index_reader,
+          rep_->persistent_cache_options, level);
     }
     case BlockBasedTableOptions::kBinarySearch: {
       return BinarySearchIndexReader::Create(
-          file, footer, footer.index_handle(), rep_->ioptions, icomparator,
-          index_reader, rep_->persistent_cache_options);
+          file, prefetch_buffer, footer, footer.index_handle(), rep_->ioptions,
+          icomparator, index_reader, rep_->persistent_cache_options);
     }
     case BlockBasedTableOptions::kHashSearch: {
       std::unique_ptr<Block> meta_guard;
       std::unique_ptr<InternalIterator> 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);
+        auto s =
+            ReadMetaBlock(rep_, prefetch_buffer, &meta_guard, &meta_iter_guard);
         if (!s.ok()) {
           // we simply fall back to binary search in case there is any
           // problem with prefix hash index loading.
@@ -1890,16 +1926,18 @@ Status BlockBasedTable::CreateIndexReader(
                          "Unable to read the metaindex block."
                          " Fall back to binary search index.");
           return BinarySearchIndexReader::Create(
-              file, footer, footer.index_handle(), rep_->ioptions, icomparator,
-              index_reader, rep_->persistent_cache_options);
+              file, prefetch_buffer, footer, footer.index_handle(),
+              rep_->ioptions, icomparator, index_reader,
+              rep_->persistent_cache_options);
         }
         meta_index_iter = meta_iter_guard.get();
       }
 
       return HashIndexReader::Create(
-          rep_->internal_prefix_transform.get(), footer, file, rep_->ioptions,
-          icomparator, footer.index_handle(), meta_index_iter, index_reader,
-          rep_->hash_index_allow_collision, rep_->persistent_cache_options);
+          rep_->internal_prefix_transform.get(), footer, file, prefetch_buffer,
+          rep_->ioptions, icomparator, footer.index_handle(), meta_index_iter,
+          index_reader, rep_->hash_index_allow_collision,
+          rep_->persistent_cache_options);
     }
     default: {
       std::string error_message =
@@ -2015,7 +2053,8 @@ Status BlockBasedTable::DumpTable(WritableFile* out_file) {
       "--------------------------------------\n");
   std::unique_ptr<Block> meta;
   std::unique_ptr<InternalIterator> meta_iter;
-  Status s = ReadMetaBlock(rep_, &meta, &meta_iter);
+  Status s =
+      ReadMetaBlock(rep_, nullptr /* prefetch_buffer */, &meta, &meta_iter);
   if (s.ok()) {
     for (meta_iter->SeekToFirst(); meta_iter->Valid(); meta_iter->Next()) {
       s = meta_iter->status();
@@ -2071,10 +2110,11 @@ Status BlockBasedTable::DumpTable(WritableFile* out_file) {
       BlockHandle handle;
       if (FindMetaBlock(meta_iter.get(), filter_block_key, &handle).ok()) {
         BlockContents block;
-        if (ReadBlockContents(
-                rep_->file.get(), rep_->footer, ReadOptions(), handle, &block,
+        if (ReadBlockContents(rep_->file.get(), nullptr /* prefetch_buffer */,
+                              rep_->footer, ReadOptions(), handle, &block,
                               rep_->ioptions, false /*decompress*/,
-                Slice() /*compression dict*/, rep_->persistent_cache_options)
+                              Slice() /*compression dict*/,
+                              rep_->persistent_cache_options)
                 .ok()) {
           rep_->filter.reset(new BlockBasedFilterBlockReader(
               rep_->ioptions.prefix_extractor, table_options,

table/block_based_table_reader.h

@@ -300,7 +300,7 @@ class BlockBasedTable : public TableReader {
   // 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,
+      FilePrefetchBuffer* prefetch_buffer, IndexReader** index_reader,
       InternalIterator* preloaded_meta_index_iter = nullptr,
       const int level = -1);
 
@@ -309,13 +309,15 @@ class BlockBasedTable : public TableReader {
                              const bool no_io) const;
 
   // Read the meta block from sst.
-  static Status ReadMetaBlock(Rep* rep, std::unique_ptr<Block>* meta_block,
+  static Status ReadMetaBlock(Rep* rep, FilePrefetchBuffer* prefetch_buffer,
+                              std::unique_ptr<Block>* meta_block,
                               std::unique_ptr<InternalIterator>* iter);
 
   Status VerifyChecksumInBlocks(InternalIterator* index_iter);
 
   // Create the filter from the filter block.
-  FilterBlockReader* ReadFilter(const BlockHandle& filter_handle,
+  FilterBlockReader* ReadFilter(FilePrefetchBuffer* prefetch_buffer,
+                                const BlockHandle& filter_handle,
                                 const bool is_a_filter_partition) const;
 
   static void SetupCacheKeyPrefix(Rep* rep, uint64_t file_size);

table/format.cc

@@ -216,8 +216,10 @@ std::string Footer::ToString() const {
   return result;
 }
 
-Status ReadFooterFromFile(RandomAccessFileReader* file, uint64_t file_size,
-                          Footer* footer, uint64_t enforce_table_magic_number) {
+Status ReadFooterFromFile(RandomAccessFileReader* file,
+                          FilePrefetchBuffer* prefetch_buffer,
+                          uint64_t file_size, Footer* footer,
+                          uint64_t enforce_table_magic_number) {
   if (file_size < Footer::kMinEncodedLength) {
     return Status::Corruption(
       "file is too short (" + ToString(file_size) + " bytes) to be an "
@@ -230,9 +232,14 @@ Status ReadFooterFromFile(RandomAccessFileReader* file, uint64_t file_size,
       (file_size > Footer::kMaxEncodedLength)
           ? static_cast<size_t>(file_size - Footer::kMaxEncodedLength)
           : 0;
-  Status s = file->Read(read_offset, Footer::kMaxEncodedLength, &footer_input,
+  Status s;
+  if (prefetch_buffer == nullptr ||
+      !prefetch_buffer->TryReadFromCache(read_offset, Footer::kMaxEncodedLength,
+                                         &footer_input)) {
+    s = file->Read(read_offset, Footer::kMaxEncodedLength, &footer_input,
                    footer_space);
     if (!s.ok()) return s;
+  }
 
   // Check that we actually read the whole footer from the file. It may be
   // that size isn't correct.
@@ -259,6 +266,43 @@ Status ReadFooterFromFile(RandomAccessFileReader* file, uint64_t file_size,
 
 // Without anonymous namespace here, we fail the warning -Wmissing-prototypes
 namespace {
+Status CheckBlockChecksum(const ReadOptions& options, const Footer& footer,
+                          const Slice& contents, size_t block_size,
+                          RandomAccessFileReader* file,
+                          const BlockHandle& handle) {
+  Status s;
+  // Check the crc of the type and the block contents
+  if (options.verify_checksums) {
+    const char* data = contents.data();  // Pointer to where Read put the data
+    PERF_TIMER_GUARD(block_checksum_time);
+    uint32_t value = DecodeFixed32(data + block_size + 1);
+    uint32_t actual = 0;
+    switch (footer.checksum()) {
+      case kCRC32c:
+        value = crc32c::Unmask(value);
+        actual = crc32c::Value(data, block_size + 1);
+        break;
+      case kxxHash:
+        actual = XXH32(data, static_cast<int>(block_size) + 1, 0);
+        break;
+      default:
+        s = Status::Corruption(
+            "unknown checksum type " + ToString(footer.checksum()) + " in " +
+            file->file_name() + " offset " + ToString(handle.offset()) +
+            " size " + ToString(block_size));
+    }
+    if (s.ok() && actual != value) {
+      s = Status::Corruption(
+          "block checksum mismatch: expected " + ToString(actual) + ", got " +
+          ToString(value) + "  in " + file->file_name() + " offset " +
+          ToString(handle.offset()) + " size " + ToString(block_size));
+    }
+    if (!s.ok()) {
+      return s;
+    }
+  }
+  return s;
+}
 
 // Read a block and check its CRC
 // contents is the result of reading.
@@ -281,51 +325,19 @@ Status ReadBlock(RandomAccessFileReader* file, const Footer& footer,
     return s;
   }
   if (contents->size() != n + kBlockTrailerSize) {
-    return Status::Corruption(
-      "truncated block read from " + file->file_name() + " offset "
-      + ToString(handle.offset()) + ", expected "
-      + ToString(n + kBlockTrailerSize) + " bytes, got "
-      + ToString(contents->size()));
-  }
-
-  // Check the crc of the type and the block contents
-  const char* data = contents->data();  // Pointer to where Read put the data
-  if (options.verify_checksums) {
-    PERF_TIMER_GUARD(block_checksum_time);
-    uint32_t value = DecodeFixed32(data + n + 1);
-    uint32_t actual = 0;
-    switch (footer.checksum()) {
-      case kCRC32c:
-        value = crc32c::Unmask(value);
-        actual = crc32c::Value(data, n + 1);
-        break;
-      case kxxHash:
-        actual = XXH32(data, static_cast<int>(n) + 1, 0);
-        break;
-      default:
-        s = Status::Corruption(
-          "unknown checksum type " + ToString(footer.checksum())
-          + " in " + file->file_name() + " offset "
-          + ToString(handle.offset()) + " size " + ToString(n));
+    return Status::Corruption("truncated block read from " + file->file_name() +
+                              " offset " + ToString(handle.offset()) +
+                              ", expected " + ToString(n + kBlockTrailerSize) +
+                              " bytes, got " + ToString(contents->size()));
   }
-    if (s.ok() && actual != value) {
-      s = Status::Corruption(
-        "block checksum mismatch: expected " + ToString(actual)
-        + ", got " + ToString(value) + "  in " + file->file_name()
-        + " offset " + ToString(handle.offset())
-        + " size " + ToString(n));
-    }
-    if (!s.ok()) {
-      return s;
-    }
-  }
-  return s;
+  return CheckBlockChecksum(options, footer, *contents, n, file, handle);
 }
 
 }  // namespace
 
-Status ReadBlockContents(RandomAccessFileReader* file, const Footer& footer,
-                         const ReadOptions& read_options,
+Status ReadBlockContents(RandomAccessFileReader* file,
+                         FilePrefetchBuffer* prefetch_buffer,
+                         const Footer& footer, const ReadOptions& read_options,
                          const BlockHandle& handle, BlockContents* contents,
                          const ImmutableCFOptions& ioptions,
                          bool decompression_requested,
@@ -357,7 +369,20 @@ Status ReadBlockContents(RandomAccessFileReader* file, const Footer& footer,
     }
   }
 
-  if (cache_options.persistent_cache &&
+  bool got_from_prefetch_buffer = false;
+  if (prefetch_buffer != nullptr &&
+      prefetch_buffer->TryReadFromCache(
+          handle.offset(),
+          static_cast<size_t>(handle.size()) + kBlockTrailerSize, &slice)) {
+    status =
+        CheckBlockChecksum(read_options, footer, slice,
+                           static_cast<size_t>(handle.size()), file, handle);
+    if (!status.ok()) {
+      return status;
+    }
+    got_from_prefetch_buffer = true;
+    used_buf = const_cast<char*>(slice.data());
+  } else if (cache_options.persistent_cache &&
              cache_options.persistent_cache->IsCompressed()) {
     // lookup uncompressed cache mode p-cache
     status = PersistentCacheHelper::LookupRawPage(
@@ -366,6 +391,7 @@ Status ReadBlockContents(RandomAccessFileReader* file, const Footer& footer,
     status = Status::NotFound();
   }
 
+  if (!got_from_prefetch_buffer) {
     if (status.ok()) {
       // cache hit
       used_buf = heap_buf.get();
@@ -401,6 +427,7 @@ Status ReadBlockContents(RandomAccessFileReader* file, const Footer& footer,
     if (!status.ok()) {
       return status;
     }
+  }
 
   PERF_TIMER_GUARD(block_decompress_time);
 
@@ -416,14 +443,14 @@ Status ReadBlockContents(RandomAccessFileReader* file, const Footer& footer,
     *contents = BlockContents(Slice(slice.data(), n), false, compression_type);
   } else {
     // page is uncompressed, the buffer either stack or heap provided
-    if (used_buf == &stack_buf[0]) {
+    if (got_from_prefetch_buffer || used_buf == &stack_buf[0]) {
       heap_buf = std::unique_ptr<char[]>(new char[n]);
-      memcpy(heap_buf.get(), stack_buf, n);
+      memcpy(heap_buf.get(), used_buf, n);
     }
     *contents = BlockContents(std::move(heap_buf), n, true, compression_type);
   }
 
-  if (status.ok() && read_options.fill_cache &&
+  if (status.ok() && !got_from_prefetch_buffer && read_options.fill_cache &&
       cache_options.persistent_cache &&
       !cache_options.persistent_cache->IsCompressed()) {
     // insert to uncompressed cache

table/format.h

@@ -18,6 +18,7 @@
 #include "options/cf_options.h"
 #include "port/port.h"  // noexcept
 #include "table/persistent_cache_options.h"
+#include "util/file_reader_writer.h"
 
 namespace rocksdb {
 
@@ -173,8 +174,9 @@ class Footer {
 // Read the footer from file
 // If enforce_table_magic_number != 0, ReadFooterFromFile() will return
 // corruption if table_magic number is not equal to enforce_table_magic_number
-Status ReadFooterFromFile(RandomAccessFileReader* file, uint64_t file_size,
-                          Footer* footer,
+Status ReadFooterFromFile(RandomAccessFileReader* file,
+                          FilePrefetchBuffer* prefetch_buffer,
+                          uint64_t file_size, Footer* footer,
                           uint64_t enforce_table_magic_number = 0);
 
 // 1-byte type + 32-bit crc
@@ -213,8 +215,8 @@ struct BlockContents {
 // Read the block identified by "handle" from "file".  On failure
 // return non-OK.  On success fill *result and return OK.
 extern Status ReadBlockContents(
-    RandomAccessFileReader* file, const Footer& footer,
-    const ReadOptions& options, const BlockHandle& handle,
+    RandomAccessFileReader* file, FilePrefetchBuffer* prefetch_buffer,
+    const Footer& footer, const ReadOptions& options, const BlockHandle& handle,
     BlockContents* contents, const ImmutableCFOptions& ioptions,
     bool do_uncompress = true, const Slice& compression_dict = Slice(),
     const PersistentCacheOptions& cache_options = PersistentCacheOptions());

table/meta_blocks.cc

@@ -16,6 +16,7 @@
 #include "table/persistent_cache_helper.h"
 #include "table/table_properties_internal.h"
 #include "util/coding.h"
+#include "util/file_reader_writer.h"
 
 namespace rocksdb {
 
@@ -159,7 +160,8 @@ bool NotifyCollectTableCollectorsOnFinish(
 }
 
 Status ReadProperties(const Slice& handle_value, RandomAccessFileReader* file,
-                      const Footer& footer, const ImmutableCFOptions& ioptions,
+                      FilePrefetchBuffer* prefetch_buffer, const Footer& footer,
+                      const ImmutableCFOptions& ioptions,
                       TableProperties** table_properties) {
   assert(table_properties);
 
@@ -173,8 +175,8 @@ Status ReadProperties(const Slice& handle_value, RandomAccessFileReader* file,
   ReadOptions read_options;
   read_options.verify_checksums = false;
   Status s;
-  s = ReadBlockContents(file, footer, read_options, handle, &block_contents,
-                        ioptions, false /* decompress */);
+  s = ReadBlockContents(file, prefetch_buffer, footer, read_options, handle,
+                        &block_contents, ioptions, false /* decompress */);
 
   if (!s.ok()) {
     return s;
@@ -277,7 +279,8 @@ Status ReadTableProperties(RandomAccessFileReader* file, uint64_t file_size,
                            TableProperties** properties) {
   // -- Read metaindex block
   Footer footer;
-  auto s = ReadFooterFromFile(file, file_size, &footer, table_magic_number);
+  auto s = ReadFooterFromFile(file, nullptr /* prefetch_buffer */, file_size,
+                              &footer, table_magic_number);
   if (!s.ok()) {
     return s;
   }
@@ -286,8 +289,9 @@ Status ReadTableProperties(RandomAccessFileReader* file, uint64_t file_size,
   BlockContents metaindex_contents;
   ReadOptions read_options;
   read_options.verify_checksums = false;
-  s = ReadBlockContents(file, footer, read_options, metaindex_handle,
-                        &metaindex_contents, ioptions, false /* decompress */);
+  s = ReadBlockContents(file, nullptr /* prefetch_buffer */, footer,
+                        read_options, metaindex_handle, &metaindex_contents,
+                        ioptions, false /* decompress */);
   if (!s.ok()) {
     return s;
   }
@@ -305,7 +309,8 @@ Status ReadTableProperties(RandomAccessFileReader* file, uint64_t file_size,
 
   TableProperties table_properties;
   if (found_properties_block == true) {
-    s = ReadProperties(meta_iter->value(), file, footer, ioptions, properties);
+    s = ReadProperties(meta_iter->value(), file, nullptr /* prefetch_buffer */,
+                       footer, ioptions, properties);
   } else {
     s = Status::NotFound();
   }
@@ -332,7 +337,8 @@ Status FindMetaBlock(RandomAccessFileReader* file, uint64_t file_size,
                      const std::string& meta_block_name,
                      BlockHandle* block_handle) {
   Footer footer;
-  auto s = ReadFooterFromFile(file, file_size, &footer, table_magic_number);
+  auto s = ReadFooterFromFile(file, nullptr /* prefetch_buffer */, file_size,
+                              &footer, table_magic_number);
   if (!s.ok()) {
     return s;
   }
@@ -341,8 +347,9 @@ Status FindMetaBlock(RandomAccessFileReader* file, uint64_t file_size,
   BlockContents metaindex_contents;
   ReadOptions read_options;
   read_options.verify_checksums = false;
-  s = ReadBlockContents(file, footer, read_options, metaindex_handle,
-                        &metaindex_contents, ioptions, false /* do decompression */);
+  s = ReadBlockContents(file, nullptr /* prefetch_buffer */, footer,
+                        read_options, metaindex_handle, &metaindex_contents,
+                        ioptions, false /* do decompression */);
   if (!s.ok()) {
     return s;
   }
@@ -355,14 +362,16 @@ Status FindMetaBlock(RandomAccessFileReader* file, uint64_t file_size,
   return FindMetaBlock(meta_iter.get(), meta_block_name, block_handle);
 }
 
-Status ReadMetaBlock(RandomAccessFileReader* file, uint64_t file_size,
+Status ReadMetaBlock(RandomAccessFileReader* file,
+                     FilePrefetchBuffer* prefetch_buffer, uint64_t file_size,
                      uint64_t table_magic_number,
                      const ImmutableCFOptions& ioptions,
                      const std::string& meta_block_name,
                      BlockContents* contents) {
   Status status;
   Footer footer;
-  status = ReadFooterFromFile(file, file_size, &footer, table_magic_number);
+  status = ReadFooterFromFile(file, prefetch_buffer, file_size, &footer,
+                              table_magic_number);
   if (!status.ok()) {
     return status;
   }
@@ -372,8 +381,8 @@ Status ReadMetaBlock(RandomAccessFileReader* file, uint64_t file_size,
   BlockContents metaindex_contents;
   ReadOptions read_options;
   read_options.verify_checksums = false;
-  status = ReadBlockContents(file, footer, read_options, metaindex_handle,
-                             &metaindex_contents, ioptions,
+  status = ReadBlockContents(file, prefetch_buffer, footer, read_options,
+                             metaindex_handle, &metaindex_contents, ioptions,
                              false /* decompress */);
   if (!status.ok()) {
     return status;
@@ -394,8 +403,9 @@ Status ReadMetaBlock(RandomAccessFileReader* file, uint64_t file_size,
   }
 
   // Reading metablock
-  return ReadBlockContents(file, footer, read_options, block_handle, contents,
-                           ioptions, false /* decompress */);
+  return ReadBlockContents(file, prefetch_buffer, footer, read_options,
+                           block_handle, contents, ioptions,
+                           false /* decompress */);
 }
 
 }  // namespace rocksdb

table/meta_blocks.h

@@ -94,7 +94,8 @@ bool NotifyCollectTableCollectorsOnFinish(
 //          *table_properties will point to a heap-allocated TableProperties
 //          object, otherwise value of `table_properties` will not be modified.
 Status ReadProperties(const Slice& handle_value, RandomAccessFileReader* file,
-                      const Footer& footer, const ImmutableCFOptions &ioptions,
+                      FilePrefetchBuffer* prefetch_buffer, const Footer& footer,
+                      const ImmutableCFOptions& ioptions,
                       TableProperties** table_properties);
 
 // Directly read the properties from the properties block of a plain table.
@@ -121,7 +122,8 @@ Status FindMetaBlock(RandomAccessFileReader* file, uint64_t file_size,
 // Read the specified meta block with name meta_block_name
 // from `file` and initialize `contents` with contents of this block.
 // Return Status::OK in case of success.
-Status ReadMetaBlock(RandomAccessFileReader* file, uint64_t file_size,
+Status ReadMetaBlock(RandomAccessFileReader* file,
+                     FilePrefetchBuffer* prefetch_buffer, uint64_t file_size,
                      uint64_t table_magic_number,
                      const ImmutableCFOptions& ioptions,
                      const std::string& meta_block_name,

table/partitioned_filter_block.cc

@@ -132,7 +132,8 @@ bool PartitionedFilterBlockReader::KeyMayMatch(
     return false;
   }
   bool cached = false;
-  auto filter_partition = GetFilterPartition(&filter_handle, no_io, &cached);
+  auto filter_partition = GetFilterPartition(nullptr /* prefetch_buffer */,
+                                             &filter_handle, no_io, &cached);
   if (UNLIKELY(!filter_partition.value)) {
     return true;
   }
@@ -164,7 +165,8 @@ bool PartitionedFilterBlockReader::PrefixMayMatch(
     return false;
   }
   bool cached = false;
-  auto filter_partition = GetFilterPartition(&filter_handle, no_io, &cached);
+  auto filter_partition = GetFilterPartition(nullptr /* prefetch_buffer */,
+                                             &filter_handle, no_io, &cached);
   if (UNLIKELY(!filter_partition.value)) {
     return true;
   }
@@ -194,8 +196,8 @@ Slice PartitionedFilterBlockReader::GetFilterPartitionHandle(
 }
 
 BlockBasedTable::CachableEntry<FilterBlockReader>
-PartitionedFilterBlockReader::GetFilterPartition(Slice* handle_value,
-                                                 const bool no_io,
+PartitionedFilterBlockReader::GetFilterPartition(
+    FilePrefetchBuffer* prefetch_buffer, Slice* handle_value, const bool no_io,
     bool* cached) {
   BlockHandle fltr_blk_handle;
   auto s = fltr_blk_handle.DecodeFrom(handle_value);
@@ -232,7 +234,8 @@ PartitionedFilterBlockReader::GetFilterPartition(Slice* handle_value,
     }
     return filter;
   } else {
-    auto filter = table_->ReadFilter(fltr_blk_handle, is_a_filter_partition);
+    auto filter = table_->ReadFilter(prefetch_buffer, fltr_blk_handle,
+                                     is_a_filter_partition);
     return {filter, nullptr};
   }
 }

table/partitioned_filter_block.h

@@ -86,7 +86,8 @@ class PartitionedFilterBlockReader : public FilterBlockReader {
  private:
   Slice GetFilterPartitionHandle(const Slice& entry);
   BlockBasedTable::CachableEntry<FilterBlockReader> GetFilterPartition(
-      Slice* handle, const bool no_io, bool* cached);
+      FilePrefetchBuffer* prefetch_buffer, Slice* handle, const bool no_io,
+      bool* cached);
 
   const SliceTransform* prefix_extractor_;
   std::unique_ptr<Block> idx_on_fltr_blk_;

table/plain_table_reader.cc

@@ -291,9 +291,10 @@ Status PlainTableReader::PopulateIndex(TableProperties* props,
   table_properties_.reset(props);
 
   BlockContents index_block_contents;
-  Status s = ReadMetaBlock(
-      file_info_.file.get(), file_size_, kPlainTableMagicNumber, ioptions_,
-      PlainTableIndexBuilder::kPlainTableIndexBlock, &index_block_contents);
+  Status s = ReadMetaBlock(file_info_.file.get(), nullptr /* prefetch_buffer */,
+                           file_size_, kPlainTableMagicNumber, ioptions_,
+                           PlainTableIndexBuilder::kPlainTableIndexBlock,
+                           &index_block_contents);
 
   bool index_in_file = s.ok();
 
@@ -301,9 +302,9 @@ Status PlainTableReader::PopulateIndex(TableProperties* props,
   bool bloom_in_file = false;
   // We only need to read the bloom block if index block is in file.
   if (index_in_file) {
-    s = ReadMetaBlock(file_info_.file.get(), file_size_, kPlainTableMagicNumber,
-                      ioptions_, BloomBlockBuilder::kBloomBlock,
-                      &bloom_block_contents);
+    s = ReadMetaBlock(file_info_.file.get(), nullptr /* prefetch_buffer */,
+                      file_size_, kPlainTableMagicNumber, ioptions_,
+                      BloomBlockBuilder::kBloomBlock, &bloom_block_contents);
     bloom_in_file = s.ok() && bloom_block_contents.data.size() > 0;
   }
 

tools/sst_dump_tool.cc

@@ -79,7 +79,8 @@ Status SstFileReader::GetTableReader(const std::string& file_path) {
   file_.reset(new RandomAccessFileReader(std::move(file), file_path));
 
   if (s.ok()) {
-    s = ReadFooterFromFile(file_.get(), file_size, &footer);
+    s = ReadFooterFromFile(file_.get(), nullptr /* prefetch_buffer */,
+                           file_size, &footer);
   }
   if (s.ok()) {
     magic_number = footer.table_magic_number();

util/file_reader_writer.cc

@@ -603,6 +603,34 @@ class ReadaheadRandomAccessFile : public RandomAccessFile {
 };
 }  // namespace
 
+Status FilePrefetchBuffer::Prefetch(RandomAccessFileReader* reader,
+                                    uint64_t offset, size_t n) {
+  size_t alignment = reader->file()->GetRequiredBufferAlignment();
+  uint64_t roundup_offset = Roundup(offset, alignment);
+  uint64_t roundup_len = Roundup(n, alignment);
+  buffer_.Alignment(alignment);
+  buffer_.AllocateNewBuffer(roundup_len);
+
+  Slice result;
+  Status s =
+      reader->Read(roundup_offset, roundup_len, &result, buffer_.BufferStart());
+  if (s.ok()) {
+    buffer_offset_ = roundup_offset;
+    buffer_len_ = result.size();
+  }
+  return s;
+}
+
+bool FilePrefetchBuffer::TryReadFromCache(uint64_t offset, size_t n,
+                                          Slice* result) const {
+  if (offset < buffer_offset_ || offset + n > buffer_offset_ + buffer_len_) {
+    return false;
+  }
+  uint64_t offset_in_buffer = offset - buffer_offset_;
+  *result = Slice(buffer_.BufferStart() + offset_in_buffer, n);
+  return true;
+}
+
 std::unique_ptr<RandomAccessFile> NewReadaheadRandomAccessFile(
     std::unique_ptr<RandomAccessFile>&& file, size_t readahead_size) {
   std::unique_ptr<RandomAccessFile> result(

util/file_reader_writer.h

@@ -196,6 +196,17 @@ class WritableFileWriter {
   Status SyncInternal(bool use_fsync);
 };
 
+class FilePrefetchBuffer {
+ public:
+  Status Prefetch(RandomAccessFileReader* reader, uint64_t offset, size_t n);
+  bool TryReadFromCache(uint64_t offset, size_t n, Slice* result) const;
+
+ private:
+  AlignedBuffer buffer_;
+  uint64_t buffer_offset_;
+  size_t buffer_len_;
+};
+
 extern Status NewWritableFile(Env* env, const std::string& fname,
                               unique_ptr<WritableFile>* result,
                               const EnvOptions& options);