Optimize & clean up footer code (#9280)

Summary:
Again, ahead of planned changes in https://github.com/facebook/rocksdb/issues/9058. This change improves
performance (vs. pre-https://github.com/facebook/rocksdb/issues/9240 baseline) by separating a FooterBuilder from
Footer, where FooterBuilder includes (inline owns) the serialized data
so that it can be stack allocated.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9280

Test Plan:
existing tests + performance testing below

Extreme case performance testing as in https://github.com/facebook/rocksdb/issues/9240 with

    TEST_TMPDIR=/dev/shm/ ./db_bench -benchmarks=fillseq -memtablerep=vector -allow_concurrent_memtable_write=false -num=30000000

(Each is ops/s averaged over 50 runs, run simultaneously with competing
configuration for load fairness)
Pre-https://github.com/facebook/rocksdb/issues/9240 baseline (f577458): 436389
With https://github.com/facebook/rocksdb/issues/9240 (653c392): 417946 (-4.2% vs. baseline)
This change: 443762 (+1.7% vs. baseline)

Reviewed By: ajkr

Differential Revision: D33077220

Pulled By: pdillinger

fbshipit-source-id: 7eaa6499589aac1693414a758e8c799216c5016c

table/block_based/block_based_table_builder.cc

@@ -1788,31 +1788,18 @@ void BlockBasedTableBuilder::WriteRangeDelBlock(
 void BlockBasedTableBuilder::WriteFooter(BlockHandle& metaindex_block_handle,
                                          BlockHandle& index_block_handle) {
   Rep* r = rep_;
-  // No need to write out new footer if we're using default checksum.
-  // We're writing legacy magic number because we want old versions of RocksDB
-  // be able to read files generated with new release (just in case if
-  // somebody wants to roll back after an upgrade)
-  // TODO(icanadi) at some point in the future, when we're absolutely sure
-  // nobody will roll back to RocksDB 2.x versions, retire the legacy magic
-  // number and always write new table files with new magic number
-  bool legacy = (r->table_options.format_version == 0);
   // this is guaranteed by BlockBasedTableBuilder's constructor
   assert(r->table_options.checksum == kCRC32c ||
          r->table_options.format_version != 0);
-  Footer footer;
-  footer
-      .set_table_magic_number(legacy ? kLegacyBlockBasedTableMagicNumber
-                                     : kBlockBasedTableMagicNumber)
-      .set_format_version(r->table_options.format_version)
-      .set_metaindex_handle(metaindex_block_handle)
-      .set_index_handle(index_block_handle)
-      .set_checksum_type(r->table_options.checksum);
-  std::string footer_encoding;
-  footer.EncodeTo(&footer_encoding, r->get_offset());
   assert(ok());
-  IOStatus ios = r->file->Append(footer_encoding);
+
+  FooterBuilder footer;
+  footer.Build(kBlockBasedTableMagicNumber, r->table_options.format_version,
+               r->get_offset(), r->table_options.checksum,
+               metaindex_block_handle, index_block_handle);
+  IOStatus ios = r->file->Append(footer.GetSlice());
   if (ios.ok()) {
-    r->set_offset(r->get_offset() + footer_encoding.size());
+    r->set_offset(r->get_offset() + footer.GetSlice().size());
   } else {
     r->SetIOStatus(ios);
     r->SetStatus(ios);

table/cuckoo/cuckoo_table_builder.cc

@@ -393,15 +393,10 @@ Status CuckooTableBuilder::Finish() {
     return status_;
   }
 
-  Footer footer;
-  footer.set_table_magic_number(kCuckooTableMagicNumber)
-      .set_format_version(1)
-      .set_metaindex_handle(meta_index_block_handle)
-      .set_index_handle(BlockHandle::NullBlockHandle())
-      .set_checksum_type(kNoChecksum);
-  std::string footer_encoding;
-  footer.EncodeTo(&footer_encoding, offset);
-  io_status_ = file_->Append(footer_encoding);
+  FooterBuilder footer;
+  footer.Build(kCuckooTableMagicNumber, /* format_version */ 1, offset,
+               kNoChecksum, meta_index_block_handle);
+  io_status_ = file_->Append(footer.GetSlice());
   status_ = io_status_;
   return status_;
 }

table/format.cc

@@ -173,21 +173,25 @@ inline uint64_t UpconvertLegacyFooterFormat(uint64_t magic_number) {
     return kPlainTableMagicNumber;
   }
   assert(false);
-  return 0;
+  return magic_number;
 }
-}  // namespace
-
-Footer& Footer::set_table_magic_number(uint64_t magic_number) {
-  assert(table_magic_number_ == kNullTableMagicNumber);
-  table_magic_number_ = magic_number;
+inline uint64_t DownconvertToLegacyFooterFormat(uint64_t magic_number) {
+  if (magic_number == kBlockBasedTableMagicNumber) {
+    return kLegacyBlockBasedTableMagicNumber;
+  }
+  if (magic_number == kPlainTableMagicNumber) {
+    return kLegacyPlainTableMagicNumber;
+  }
+  assert(false);
+  return magic_number;
+}
+inline uint8_t BlockTrailerSizeForMagicNumber(uint64_t magic_number) {
   if (magic_number == kBlockBasedTableMagicNumber ||
       magic_number == kLegacyBlockBasedTableMagicNumber) {
-    block_trailer_size_ =
-        static_cast<uint8_t>(BlockBasedTable::kBlockTrailerSize);
+    return static_cast<uint8_t>(BlockBasedTable::kBlockTrailerSize);
   } else {
-    block_trailer_size_ = 0;
+    return 0;
   }
-  return *this;
 }
 
 // Footer format, in three parts:
@@ -206,60 +210,69 @@ Footer& Footer::set_table_magic_number(uint64_t magic_number) {
 //   -> format_version >= 1 (inferred from NOT legacy magic number)
 //      format_version (uint32LE, 4 bytes), also called "footer version"
 //      newer magic number (8 bytes)
-void Footer::EncodeTo(std::string* dst, uint64_t footer_offset) const {
-  (void)footer_offset;  // Future use
 
-  // Sanitize magic numbers & format versions
-  assert(table_magic_number_ != kNullTableMagicNumber);
-  uint64_t magic = table_magic_number_;
-  uint32_t fv = format_version_;
-  assert(fv != kInvalidFormatVersion);
-  assert(IsLegacyFooterFormat(magic) == (fv == 0));
+constexpr size_t kFooterPart2Size = 2 * BlockHandle::kMaxEncodedLength;
+}  // namespace
 
-  ChecksumType ct = checksum_type();
+void FooterBuilder::Build(uint64_t magic_number, uint32_t format_version,
+                          uint64_t footer_offset, ChecksumType checksum_type,
+                          const BlockHandle& metaindex_handle,
+                          const BlockHandle& index_handle) {
+  (void)footer_offset;  // Future use
+
+  assert(magic_number != Footer::kNullTableMagicNumber);
+  assert(IsSupportedFormatVersion(format_version));
 
-  // Allocate destination data and generate parts 1 and 3
-  const size_t original_size = dst->size();
   char* part2;
-  if (fv > 0) {
-    dst->resize(original_size + kNewVersionsEncodedLength);
-    char* part1 = &(*dst)[original_size];
-    part2 = part1 + 1;
-    char* part3 = part2 + 2 * BlockHandle::kMaxEncodedLength;
-    assert(&(*dst)[dst->size() - 1] + 1 - part3 == /* part 3 size */ 12);
+  char* part3;
+  if (format_version > 0) {
+    slice_ = Slice(data_.data(), Footer::kNewVersionsEncodedLength);
     // Generate parts 1 and 3
-    part1[0] = ct;
-    EncodeFixed32(part3, fv);
-    EncodeFixed64(part3 + 4, magic);
+    char* cur = data_.data();
+    // Part 1
+    *(cur++) = checksum_type;
+    // Part 2
+    part2 = cur;
+    // Skip over part 2 for now
+    cur += kFooterPart2Size;
+    // Part 3
+    part3 = cur;
+    EncodeFixed32(cur, format_version);
+    cur += 4;
+    EncodeFixed64(cur, magic_number);
+    assert(cur + 8 == slice_.data() + slice_.size());
   } else {
-    dst->resize(original_size + kVersion0EncodedLength);
-    part2 = &(*dst)[original_size];
-    char* part3 = part2 + 2 * BlockHandle::kMaxEncodedLength;
-    assert(&(*dst)[dst->size() - 1] + 1 - part3 == /* part 3 size */ 8);
+    slice_ = Slice(data_.data(), Footer::kVersion0EncodedLength);
     // Legacy SST files use kCRC32c checksum but it's not stored in footer.
-    assert(ct == kNoChecksum || ct == kCRC32c);
-    // Generate part 3 (part 1 empty)
-    EncodeFixed64(part3, magic);
+    assert(checksum_type == kNoChecksum || checksum_type == kCRC32c);
+    // Generate part 3 (part 1 empty, skip part 2 for now)
+    part2 = data_.data();
+    part3 = part2 + kFooterPart2Size;
+    char* cur = part3;
+    // Use legacy magic numbers to indicate format_version=0, for
+    // compatibility. No other cases should use format_version=0.
+    EncodeFixed64(cur, DownconvertToLegacyFooterFormat(magic_number));
+    assert(cur + 8 == slice_.data() + slice_.size());
   }
 
-  // Generate Part2
-  // Variable size encode handles (sigh)
-  part2 = metaindex_handle_.EncodeTo(part2);
-  /*part2 = */ index_handle_.EncodeTo(part2);
-
-  // remainder of part2 is already zero padded
+  {
+    char* cur = part2;
+    cur = metaindex_handle.EncodeTo(cur);
+    cur = index_handle.EncodeTo(cur);
+    // Zero pad remainder
+    std::fill(cur, part3, char{0});
+  }
 }
 
-Status Footer::DecodeFrom(Slice* input, uint64_t input_offset) {
+Status Footer::DecodeFrom(Slice input, uint64_t input_offset) {
   (void)input_offset;  // Future use
 
   // Only decode to unused Footer
   assert(table_magic_number_ == kNullTableMagicNumber);
   assert(input != nullptr);
-  assert(input->size() >= kMinEncodedLength);
+  assert(input.size() >= kMinEncodedLength);
 
-  const char* magic_ptr =
-      input->data() + input->size() - kMagicNumberLengthByte;
+  const char* magic_ptr = input.data() + input.size() - kMagicNumberLengthByte;
   uint64_t magic = DecodeFixed64(magic_ptr);
 
   // We check for legacy formats here and silently upconvert them
@@ -267,13 +280,14 @@ Status Footer::DecodeFrom(Slice* input, uint64_t input_offset) {
   if (legacy) {
     magic = UpconvertLegacyFooterFormat(magic);
   }
-  set_table_magic_number(magic);
+  table_magic_number_ = magic;
+  block_trailer_size_ = BlockTrailerSizeForMagicNumber(magic);
 
   // Parse Part3
   if (legacy) {
     // The size is already asserted to be at least kMinEncodedLength
     // at the beginning of the function
-    input->remove_prefix(input->size() - kVersion0EncodedLength);
+    input.remove_prefix(input.size() - kVersion0EncodedLength);
     format_version_ = 0 /* legacy */;
     checksum_type_ = kCRC32c;
   } else {
@@ -284,14 +298,14 @@ Status Footer::DecodeFrom(Slice* input, uint64_t input_offset) {
                                 ROCKSDB_NAMESPACE::ToString(format_version_));
     }
     // All known format versions >= 1 occupy exactly this many bytes.
-    if (input->size() < kNewVersionsEncodedLength) {
+    if (input.size() < kNewVersionsEncodedLength) {
       return Status::Corruption("Input is too short to be an SST file");
     }
-    uint64_t adjustment = input->size() - kNewVersionsEncodedLength;
-    input->remove_prefix(adjustment);
+    uint64_t adjustment = input.size() - kNewVersionsEncodedLength;
+    input.remove_prefix(adjustment);
 
     // Parse Part1
-    char chksum = input->data()[0];
+    char chksum = input.data()[0];
     checksum_type_ = lossless_cast<ChecksumType>(chksum);
     if (!IsSupportedChecksumType(checksum_type())) {
       return Status::Corruption(
@@ -299,21 +313,16 @@ Status Footer::DecodeFrom(Slice* input, uint64_t input_offset) {
           ROCKSDB_NAMESPACE::ToString(lossless_cast<uint8_t>(chksum)));
     }
     // Consume checksum type field
-    input->remove_prefix(1);
+    input.remove_prefix(1);
   }
 
   // Parse Part2
-  Status result = metaindex_handle_.DecodeFrom(input);
+  Status result = metaindex_handle_.DecodeFrom(&input);
   if (result.ok()) {
-    result = index_handle_.DecodeFrom(input);
+    result = index_handle_.DecodeFrom(&input);
   }
-  if (!result.ok()) {
-    return result;
-  }
-
-  // Mark all input consumed (skip padding & part3)
-  *input = Slice(input->data() + input->size(), 0U);
-  return Status::OK();
+  return result;
+  // Padding in part2 is ignored
 }
 
 std::string Footer::ToString() const {
@@ -384,7 +393,7 @@ Status ReadFooterFromFile(const IOOptions& opts, RandomAccessFileReader* file,
                               file->file_name());
   }
 
-  s = footer->DecodeFrom(&footer_input, read_offset);
+  s = footer->DecodeFrom(footer_input, read_offset);
   if (!s.ok()) {
     return s;
   }

table/format.h

@@ -9,6 +9,7 @@
 
 #pragma once
 
+#include <array>
 #include <cstdint>
 #include <string>
 
@@ -128,66 +129,45 @@ inline bool IsSupportedFormatVersion(uint32_t version) {
 // elsewhere under the metaindex block. For example, checksum_type is
 // required for verifying metaindex block checksum (when applicable), but
 // index block handle can easily go in metaindex block (possible future).
+// See also FooterBuilder below.
 class Footer {
  public:
+  // Create empty. Populate using DecodeFrom.
   Footer() {}
 
-  // Uses builder pattern rather than distinctive ctors
+  // Deserialize a footer (populate fields) from `input` and check for various
+  // corruptions. `input_offset` is the offset within the target file of
+  // `input` buffer (future use).
+  Status DecodeFrom(Slice input, uint64_t input_offset);
 
   // Table magic number identifies file as RocksDB SST file and which kind of
   // SST format is use.
-  Footer& set_table_magic_number(uint64_t tmn);
   uint64_t table_magic_number() const { return table_magic_number_; }
 
   // A version (footer and more) within a kind of SST. (It would add more
   // unnecessary complexity to separate footer versions and
   // BBTO::format_version.)
-  Footer& set_format_version(uint32_t fv) {
-    format_version_ = fv;
-    return *this;
-  }
   uint32_t format_version() const { return format_version_; }
 
   // Block handle for metaindex block.
-  Footer& set_metaindex_handle(const BlockHandle& h) {
-    metaindex_handle_ = h;
-    return *this;
-  }
   const BlockHandle& metaindex_handle() const { return metaindex_handle_; }
 
   // Block handle for (top-level) index block.
-  Footer& set_index_handle(const BlockHandle& h) {
-    index_handle_ = h;
-    return *this;
-  }
   const BlockHandle& index_handle() const { return index_handle_; }
 
   // Checksum type used in the file.
-  Footer& set_checksum_type(ChecksumType ct) {
-    checksum_type_ = ct;
-    return *this;
-  }
   ChecksumType checksum_type() const {
     return static_cast<ChecksumType>(checksum_type_);
   }
 
-  // Appends serialized footer to `dst`. The starting offset of the footer
-  // within the file is required for future work.
-  void EncodeTo(std::string* dst, uint64_t footer_offset) const;
-
-  // Deserialize a footer (populate fields) from `input` and check for various
-  // corruptions. On success (and some error cases) `input` is advanced past
-  // the footer. Like EncodeTo, the offset within the file will be nedded for
-  // future work
-  Status DecodeFrom(Slice* input, uint64_t input_offset);
+  // Block trailer size used by file with this footer (e.g. 5 for block-based
+  // table and 0 for plain table). This is inferred from magic number so
+  // not in the serialized form.
+  inline size_t GetBlockTrailerSize() const { return block_trailer_size_; }
 
   // Convert this object to a human readable form
   std::string ToString() const;
 
-  // Block trailer size used by file with this footer (e.g. 5 for block-based
-  // table and 0 for plain table)
-  inline size_t GetBlockTrailerSize() const { return block_trailer_size_; }
-
   // Encoded lengths of Footers. Bytes for serialized Footer will always be
   // >= kMinEncodedLength and <= kMaxEncodedLength.
   //
@@ -207,8 +187,9 @@ class Footer {
 
   static constexpr uint64_t kNullTableMagicNumber = 0;
 
- private:
   static constexpr uint32_t kInvalidFormatVersion = 0xffffffffU;
+
+ private:
   static constexpr int kInvalidChecksumType =
       (1 << (sizeof(ChecksumType) * 8)) | kNoChecksum;
 
@@ -217,7 +198,40 @@ class Footer {
   BlockHandle metaindex_handle_;
   BlockHandle index_handle_;
   int checksum_type_ = kInvalidChecksumType;
-  uint8_t block_trailer_size_ = 0;  // set based on magic number
+  uint8_t block_trailer_size_ = 0;
+};
+
+// Builder for Footer
+class FooterBuilder {
+ public:
+  // Run builder in inputs. This is a single step with lots of parameters for
+  // efficiency (based on perf testing).
+  // * table_magic_number identifies file as RocksDB SST file and which kind of
+  // SST format is use.
+  // * format_version is a version for the footer and can also apply to other
+  // aspects of the SST file (see BlockBasedTableOptions::format_version).
+  // NOTE: To save complexity in the caller, when format_version == 0 and
+  // there is a corresponding legacy magic number to the one specified, the
+  // legacy magic number will be written for forward compatibility.
+  // * footer_offset is the file offset where the footer will be written
+  // (for future use).
+  // * checksum_type is for formats using block checksums.
+  // * index_handle is optional for some kinds of SST files.
+  void Build(uint64_t table_magic_number, uint32_t format_version,
+             uint64_t footer_offset, ChecksumType checksum_type,
+             const BlockHandle& metaindex_handle,
+             const BlockHandle& index_handle = BlockHandle::NullBlockHandle());
+
+  // After Builder, get a Slice for the serialized Footer, backed by this
+  // FooterBuilder.
+  const Slice& GetSlice() const {
+    assert(slice_.size());
+    return slice_;
+  }
+
+ private:
+  Slice slice_;
+  std::array<char, Footer::kMaxEncodedLength> data_;
 };
 
 // Read the footer from file

table/plain/plain_table_builder.cc

@@ -292,16 +292,12 @@ Status PlainTableBuilder::Finish() {
 
   // Write Footer
   // no need to write out new footer if we're using default checksum
-  Footer footer;
-  footer.set_table_magic_number(kLegacyPlainTableMagicNumber)
-      .set_format_version(0)
-      .set_metaindex_handle(metaindex_block_handle)
-      .set_index_handle(BlockHandle::NullBlockHandle());
-  std::string footer_encoding;
-  footer.EncodeTo(&footer_encoding, offset_);
-  io_status_ = file_->Append(footer_encoding);
+  FooterBuilder footer;
+  footer.Build(kPlainTableMagicNumber, /* format_version */ 0, offset_,
+               kNoChecksum, metaindex_block_handle);
+  io_status_ = file_->Append(footer.GetSlice());
   if (io_status_.ok()) {
-    offset_ += footer_encoding.size();
+    offset_ += footer.GetSlice().size();
   }
   status_ = io_status_;
   return status_;

table/table_test.cc

@@ -4175,17 +4175,12 @@ TEST(TableTest, FooterTests) {
   BlockHandle meta_index(data_size + index_size + 2 * 5, metaindex_size);
   uint64_t footer_offset = data_size + metaindex_size + index_size + 3 * 5;
   {
-    // upconvert legacy block based
-    std::string encoded;
-    Footer footer;
-    footer.set_table_magic_number(kLegacyBlockBasedTableMagicNumber)
-        .set_format_version(0)
-        .set_metaindex_handle(meta_index)
-        .set_index_handle(index);
-    footer.EncodeTo(&encoded, footer_offset);
+    // legacy block based
+    FooterBuilder footer;
+    footer.Build(kBlockBasedTableMagicNumber, /* format_version */ 0,
+                 footer_offset, kCRC32c, meta_index, index);
     Footer decoded_footer;
-    Slice encoded_slice(encoded);
-    ASSERT_OK(decoded_footer.DecodeFrom(&encoded_slice, footer_offset));
+    ASSERT_OK(decoded_footer.DecodeFrom(footer.GetSlice(), footer_offset));
     ASSERT_EQ(decoded_footer.table_magic_number(), kBlockBasedTableMagicNumber);
     ASSERT_EQ(decoded_footer.checksum_type(), kCRC32c);
     ASSERT_EQ(decoded_footer.metaindex_handle().offset(), meta_index.offset());
@@ -4194,21 +4189,19 @@ TEST(TableTest, FooterTests) {
     ASSERT_EQ(decoded_footer.index_handle().size(), index.size());
     ASSERT_EQ(decoded_footer.format_version(), 0U);
     ASSERT_EQ(decoded_footer.GetBlockTrailerSize(), 5U);
+    // Ensure serialized with legacy magic
+    ASSERT_EQ(
+        DecodeFixed64(footer.GetSlice().data() + footer.GetSlice().size() - 8),
+        kLegacyBlockBasedTableMagicNumber);
   }
   // block based, various checksums, various versions
   for (auto t : GetSupportedChecksums()) {
     for (uint32_t fv = 1; IsSupportedFormatVersion(fv); ++fv) {
-      std::string encoded;
-      Footer footer;
-      footer.set_table_magic_number(kBlockBasedTableMagicNumber)
-          .set_format_version(fv)
-          .set_metaindex_handle(meta_index)
-          .set_index_handle(index)
-          .set_checksum_type(t);
-      footer.EncodeTo(&encoded, footer_offset);
+      FooterBuilder footer;
+      footer.Build(kBlockBasedTableMagicNumber, fv, footer_offset, t,
+                   meta_index, index);
       Footer decoded_footer;
-      Slice encoded_slice(encoded);
-      ASSERT_OK(decoded_footer.DecodeFrom(&encoded_slice, footer_offset));
+      ASSERT_OK(decoded_footer.DecodeFrom(footer.GetSlice(), footer_offset));
       ASSERT_EQ(decoded_footer.table_magic_number(),
                 kBlockBasedTableMagicNumber);
       ASSERT_EQ(decoded_footer.checksum_type(), t);
@@ -4224,45 +4217,38 @@ TEST(TableTest, FooterTests) {
 // Plain table is not supported in ROCKSDB_LITE
 #ifndef ROCKSDB_LITE
   {
-    // upconvert legacy plain table
-    std::string encoded;
-    Footer footer;
-    footer.set_table_magic_number(kLegacyPlainTableMagicNumber)
-        .set_format_version(0)
-        .set_metaindex_handle(meta_index)
-        .set_index_handle(index);
-    footer.EncodeTo(&encoded, footer_offset);
+    // legacy plain table
+    FooterBuilder footer;
+    footer.Build(kPlainTableMagicNumber, /* format_version */ 0, footer_offset,
+                 kNoChecksum, meta_index);
     Footer decoded_footer;
-    Slice encoded_slice(encoded);
-    ASSERT_OK(decoded_footer.DecodeFrom(&encoded_slice, footer_offset));
+    ASSERT_OK(decoded_footer.DecodeFrom(footer.GetSlice(), footer_offset));
     ASSERT_EQ(decoded_footer.table_magic_number(), kPlainTableMagicNumber);
     ASSERT_EQ(decoded_footer.checksum_type(), kCRC32c);
     ASSERT_EQ(decoded_footer.metaindex_handle().offset(), meta_index.offset());
     ASSERT_EQ(decoded_footer.metaindex_handle().size(), meta_index.size());
-    ASSERT_EQ(decoded_footer.index_handle().offset(), index.offset());
-    ASSERT_EQ(decoded_footer.index_handle().size(), index.size());
+    ASSERT_EQ(decoded_footer.index_handle().offset(), 0U);
+    ASSERT_EQ(decoded_footer.index_handle().size(), 0U);
     ASSERT_EQ(decoded_footer.format_version(), 0U);
     ASSERT_EQ(decoded_footer.GetBlockTrailerSize(), 0U);
+    // Ensure serialized with legacy magic
+    ASSERT_EQ(
+        DecodeFixed64(footer.GetSlice().data() + footer.GetSlice().size() - 8),
+        kLegacyPlainTableMagicNumber);
   }
   {
     // xxhash plain table (not currently used)
-    std::string encoded;
-    Footer footer;
-    footer.set_table_magic_number(kPlainTableMagicNumber)
-        .set_format_version(1)
-        .set_metaindex_handle(meta_index)
-        .set_index_handle(index)
-        .set_checksum_type(kxxHash);
-    footer.EncodeTo(&encoded, footer_offset);
+    FooterBuilder footer;
+    footer.Build(kPlainTableMagicNumber, /* format_version */ 1, footer_offset,
+                 kxxHash, meta_index);
     Footer decoded_footer;
-    Slice encoded_slice(encoded);
-    ASSERT_OK(decoded_footer.DecodeFrom(&encoded_slice, footer_offset));
+    ASSERT_OK(decoded_footer.DecodeFrom(footer.GetSlice(), footer_offset));
     ASSERT_EQ(decoded_footer.table_magic_number(), kPlainTableMagicNumber);
     ASSERT_EQ(decoded_footer.checksum_type(), kxxHash);
     ASSERT_EQ(decoded_footer.metaindex_handle().offset(), meta_index.offset());
     ASSERT_EQ(decoded_footer.metaindex_handle().size(), meta_index.size());
-    ASSERT_EQ(decoded_footer.index_handle().offset(), index.offset());
-    ASSERT_EQ(decoded_footer.index_handle().size(), index.size());
+    ASSERT_EQ(decoded_footer.index_handle().offset(), 0U);
+    ASSERT_EQ(decoded_footer.index_handle().size(), 0U);
     ASSERT_EQ(decoded_footer.format_version(), 1U);
     ASSERT_EQ(decoded_footer.GetBlockTrailerSize(), 0U);
   }