Do readahead in VerifyChecksum() (#5713)

Summary:
Right now VerifyChecksum() doesn't do read-ahead. In some use cases, users won't be able to achieve good performance. With this change, by default, RocksDB will do a default readahead, and users will be able to overwrite the readahead size by passing in a ReadOptions.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5713

Test Plan: Add a new unit test.

Differential Revision: D16860874

fbshipit-source-id: 0cff0fe79ac855d3d068e6ccd770770854a68413

HISTORY.md

@@ -2,6 +2,8 @@
 ## Unreleased
 ### Bug Fixes
 * Fixed a number of data races in BlobDB.
+### New Features
+* VerifyChecksum() by default will issue readahead. Allow ReadOptions to be passed in to those functions to override the readhead size.
 
 ## 6.4.0 (7/30/2019)
 ### Default Option Change

Makefile

@@ -1226,7 +1226,7 @@ histogram_test: monitoring/histogram_test.o $(LIBOBJECTS) $(TESTHARNESS)
 thread_local_test: util/thread_local_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
-corruption_test: db/corruption_test.o $(LIBOBJECTS) $(TESTHARNESS)
+corruption_test: db/corruption_test.o db/db_test_util.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
 crc32c_test: util/crc32c_test.o $(LIBOBJECTS) $(TESTHARNESS)

db/convenience.cc

@@ -35,6 +35,12 @@ Status DeleteFilesInRanges(DB* db, ColumnFamilyHandle* column_family,
 Status VerifySstFileChecksum(const Options& options,
                              const EnvOptions& env_options,
                              const std::string& file_path) {
+  return VerifySstFileChecksum(options, env_options, ReadOptions(), file_path);
+}
+Status VerifySstFileChecksum(const Options& options,
+                             const EnvOptions& env_options,
+                             const ReadOptions& read_options,
+                             const std::string& file_path) {
   std::unique_ptr<RandomAccessFile> file;
   uint64_t file_size;
   InternalKeyComparator internal_comparator(options.comparator);
@@ -59,7 +65,8 @@ Status VerifySstFileChecksum(const Options& options,
   if (!s.ok()) {
     return s;
   }
-  s = table_reader->VerifyChecksum(TableReaderCaller::kUserVerifyChecksum);
+  s = table_reader->VerifyChecksum(read_options,
+                                   TableReaderCaller::kUserVerifyChecksum);
   return s;
 }
 

db/corruption_test.cc

@@ -13,10 +13,11 @@
 
 #include <errno.h>
 #include <fcntl.h>
-#include <cinttypes>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <cinttypes>
 #include "db/db_impl/db_impl.h"
+#include "db/db_test_util.h"
 #include "db/log_format.h"
 #include "db/version_set.h"
 #include "file/filename.h"
@@ -76,7 +77,11 @@ class CorruptionTest : public testing::Test {
     delete db_;
     db_ = nullptr;
     Options opt = (options ? *options : options_);
-    opt.env = &env_;
+    if (opt.env == Options().env) {
+      // If env is not overridden, replace it with ErrorEnv.
+      // Otherwise, the test already uses a non-default Env.
+      opt.env = &env_;
+    }
     opt.arena_block_size = 4096;
     BlockBasedTableOptions table_options;
     table_options.block_cache = tiny_cache_;
@@ -321,6 +326,52 @@ TEST_F(CorruptionTest, TableFile) {
   ASSERT_NOK(dbi->VerifyChecksum());
 }
 
+TEST_F(CorruptionTest, VerifyChecksumReadahead) {
+  Options options;
+  SpecialEnv senv(Env::Default());
+  options.env = &senv;
+  // Disable block cache as we are going to check checksum for
+  // the same file twice and measure number of reads.
+  BlockBasedTableOptions table_options_no_bc;
+  table_options_no_bc.no_block_cache = true;
+  options.table_factory.reset(NewBlockBasedTableFactory(table_options_no_bc));
+
+  Reopen(&options);
+
+  Build(10000);
+  DBImpl* dbi = reinterpret_cast<DBImpl*>(db_);
+  dbi->TEST_FlushMemTable();
+  dbi->TEST_CompactRange(0, nullptr, nullptr);
+  dbi->TEST_CompactRange(1, nullptr, nullptr);
+
+  senv.count_random_reads_ = true;
+  senv.random_read_counter_.Reset();
+  ASSERT_OK(dbi->VerifyChecksum());
+
+  // Make sure the counter is enabled.
+  ASSERT_GT(senv.random_read_counter_.Read(), 0);
+
+  // The SST file is about 10MB. Default readahead size is 256KB.
+  // Give a conservative 20 reads for metadata blocks, The number
+  // of random reads should be within 10 MB / 256KB + 20 = 60.
+  ASSERT_LT(senv.random_read_counter_.Read(), 60);
+
+  senv.random_read_bytes_counter_ = 0;
+  ReadOptions ro;
+  ro.readahead_size = size_t{32 * 1024};
+  ASSERT_OK(dbi->VerifyChecksum(ro));
+  // The SST file is about 10MB. We set readahead size to 32KB.
+  // Give 0 to 20 reads for metadata blocks, and allow real read
+  // to range from 24KB to 48KB. The lower bound would be:
+  //   10MB / 48KB + 0 = 213
+  // The higher bound is
+  //   10MB / 24KB + 20 = 447.
+  ASSERT_GE(senv.random_read_counter_.Read(), 213);
+  ASSERT_LE(senv.random_read_counter_.Read(), 447);
+
+  CloseDb();
+}
+
 TEST_F(CorruptionTest, TableFileIndexData) {
   Options options;
   // very big, we'll trigger flushes manually

db/db_impl/db_impl.cc

@@ -4112,7 +4112,7 @@ Status DBImpl::CreateColumnFamilyWithImport(
   return status;
 }
 
-Status DBImpl::VerifyChecksum() {
+Status DBImpl::VerifyChecksum(const ReadOptions& read_options) {
   Status s;
   std::vector<ColumnFamilyData*> cfd_list;
   {
@@ -4143,7 +4143,8 @@ Status DBImpl::VerifyChecksum() {
         const auto& fd = vstorage->LevelFilesBrief(i).files[j].fd;
         std::string fname = TableFileName(cfd->ioptions()->cf_paths,
                                           fd.GetNumber(), fd.GetPathId());
-        s = rocksdb::VerifySstFileChecksum(opts, env_options_, fname);
+        s = rocksdb::VerifySstFileChecksum(opts, env_options_, read_options,
+                                           fname);
       }
     }
     if (!s.ok()) {

db/db_impl/db_impl.h

@@ -380,7 +380,8 @@ class DBImpl : public DB {
       const ExportImportFilesMetaData& metadata,
       ColumnFamilyHandle** handle) override;
 
-  virtual Status VerifyChecksum() override;
+  using DB::VerifyChecksum;
+  virtual Status VerifyChecksum(const ReadOptions& /*read_options*/) override;
 
   using DB::StartTrace;
   virtual Status StartTrace(

db/db_test.cc

@@ -2585,7 +2585,8 @@ class ModelDB : public DB {
     return Status::NotSupported("Not implemented.");
   }
 
-  Status VerifyChecksum() override {
+  using DB::VerifyChecksum;
+  Status VerifyChecksum(const ReadOptions&) override {
     return Status::NotSupported("Not implemented.");
   }
 

db/external_sst_file_ingestion_job.cc

@@ -347,8 +347,11 @@ Status ExternalSstFileIngestionJob::GetIngestedFileInfo(
   }
 
   if (ingestion_options_.verify_checksums_before_ingest) {
-    status =
+    // If customized readahead size is needed, we can pass a user option
-        table_reader->VerifyChecksum(TableReaderCaller::kExternalSSTIngestion);
+    // all the way to here. Right now we just rely on the default readahead
+    // to keep things simple.
+    status = table_reader->VerifyChecksum(
+        ReadOptions(), TableReaderCaller::kExternalSSTIngestion);
   }
   if (!status.ok()) {
     return status;

include/rocksdb/convenience.h

@@ -339,6 +339,13 @@ Status DeleteFilesInRanges(DB* db, ColumnFamilyHandle* column_family,
 Status VerifySstFileChecksum(const Options& options,
                              const EnvOptions& env_options,
                              const std::string& file_path);
+
+// Verify the checksum of file
+Status VerifySstFileChecksum(const Options& options,
+                             const EnvOptions& env_options,
+                             const ReadOptions& read_options,
+                             const std::string& file_path);
+
 #endif  // ROCKSDB_LITE
 
 }  // namespace rocksdb

include/rocksdb/db.h

@@ -1225,7 +1225,9 @@ class DB {
       const ExportImportFilesMetaData& metadata,
       ColumnFamilyHandle** handle) = 0;
 
-  virtual Status VerifyChecksum() = 0;
+  virtual Status VerifyChecksum(const ReadOptions& read_options) = 0;
+
+  virtual Status VerifyChecksum() { return VerifyChecksum(ReadOptions()); }
 
   // AddFile() is deprecated, please use IngestExternalFile()
   ROCKSDB_DEPRECATED_FUNC virtual Status AddFile(

include/rocksdb/sst_file_reader.h

@@ -33,7 +33,9 @@ class SstFileReader {
   std::shared_ptr<const TableProperties> GetTableProperties() const;
 
   // Verifies whether there is corruption in this table.
-  Status VerifyChecksum();
+  Status VerifyChecksum(const ReadOptions& /*read_options*/);
+
+  Status VerifyChecksum() { return VerifyChecksum(ReadOptions()); }
 
  private:
   struct Rep;

include/rocksdb/utilities/stackable_db.h

@@ -143,6 +143,10 @@ class StackableDB : public DB {
 
   virtual Status VerifyChecksum() override { return db_->VerifyChecksum(); }
 
+  virtual Status VerifyChecksum(const ReadOptions& options) override {
+    return db_->VerifyChecksum(options);
+  }
+
   using DB::KeyMayExist;
   virtual bool KeyMayExist(const ReadOptions& options,
                            ColumnFamilyHandle* column_family, const Slice& key,

table/block_based/block_based_table_reader.cc

@@ -62,6 +62,10 @@ extern const std::string kHashIndexPrefixesMetadataBlock;
 
 typedef BlockBasedTable::IndexReader IndexReader;
 
+// Found that 256 KB readahead size provides the best performance, based on
+// experiments, for auto readahead. Experiment data is in PR #3282.
+const size_t BlockBasedTable::kMaxAutoReadaheadSize = 256 * 1024;
+
 BlockBasedTable::~BlockBasedTable() {
   delete rep_;
 }
@@ -2854,13 +2858,6 @@ void BlockBasedTableIterator<TBlockIter, TValue>::Prev() {
   FindKeyBackward();
 }
 
-// Found that 256 KB readahead size provides the best performance, based on
-// experiments, for auto readahead. Experiment data is in PR #3282.
-template <class TBlockIter, typename TValue>
-const size_t
-    BlockBasedTableIterator<TBlockIter, TValue>::kMaxAutoReadaheadSize =
-        256 * 1024;
-
 template <class TBlockIter, typename TValue>
 void BlockBasedTableIterator<TBlockIter, TValue>::InitDataBlock() {
   BlockHandle data_block_handle = index_iter_->value().handle;
@@ -2883,7 +2880,8 @@ void BlockBasedTableIterator<TBlockIter, TValue>::InitDataBlock() {
       if (read_options_.readahead_size == 0) {
         // Implicit auto readahead
         num_file_reads_++;
-        if (num_file_reads_ > kMinNumFileReadsToStartAutoReadahead) {
+        if (num_file_reads_ >
+            BlockBasedTable::kMinNumFileReadsToStartAutoReadahead) {
           if (!rep->file->use_direct_io() &&
               (data_block_handle.offset() +
                    static_cast<size_t>(data_block_handle.size()) +
@@ -2897,14 +2895,14 @@ void BlockBasedTableIterator<TBlockIter, TValue>::InitDataBlock() {
                                                    readahead_size_);
             // Keep exponentially increasing readahead size until
             // kMaxAutoReadaheadSize.
-            readahead_size_ =
+            readahead_size_ = std::min(BlockBasedTable::kMaxAutoReadaheadSize,
-                std::min(kMaxAutoReadaheadSize, readahead_size_ * 2);
+                                       readahead_size_ * 2);
           } else if (rep->file->use_direct_io() && !prefetch_buffer_) {
             // Direct I/O
             // Let FilePrefetchBuffer take care of the readahead.
-            prefetch_buffer_.reset(
+            prefetch_buffer_.reset(new FilePrefetchBuffer(
-                new FilePrefetchBuffer(rep->file.get(), kInitAutoReadaheadSize,
+                rep->file.get(), BlockBasedTable::kInitAutoReadaheadSize,
-                                       kMaxAutoReadaheadSize));
+                BlockBasedTable::kMaxAutoReadaheadSize));
           }
         }
       } else if (!prefetch_buffer_) {
@@ -3707,7 +3705,8 @@ Status BlockBasedTable::Prefetch(const Slice* const begin,
   return Status::OK();
 }
 
-Status BlockBasedTable::VerifyChecksum(TableReaderCaller caller) {
+Status BlockBasedTable::VerifyChecksum(const ReadOptions& read_options,
+                                       TableReaderCaller caller) {
   Status s;
   // Check Meta blocks
   std::unique_ptr<Block> meta;
@@ -3725,7 +3724,7 @@ Status BlockBasedTable::VerifyChecksum(TableReaderCaller caller) {
   IndexBlockIter iiter_on_stack;
   BlockCacheLookupContext context{caller};
   InternalIteratorBase<IndexValue>* iiter = NewIndexIterator(
-      ReadOptions(), /*need_upper_bound_check=*/false, &iiter_on_stack,
+      read_options, /*disable_prefix_seek=*/false, &iiter_on_stack,
       /*get_context=*/nullptr, &context);
   std::unique_ptr<InternalIteratorBase<IndexValue>> iiter_unique_ptr;
   if (iiter != &iiter_on_stack) {
@@ -3735,13 +3734,22 @@ Status BlockBasedTable::VerifyChecksum(TableReaderCaller caller) {
     // error opening index iterator
     return iiter->status();
   }
-  s = VerifyChecksumInBlocks(iiter);
+  s = VerifyChecksumInBlocks(read_options, iiter);
   return s;
 }
 
 Status BlockBasedTable::VerifyChecksumInBlocks(
+    const ReadOptions& read_options,
     InternalIteratorBase<IndexValue>* index_iter) {
   Status s;
+  // We are scanning the whole file, so no need to do exponential
+  // increasing of the buffer size.
+  size_t readahead_size = (read_options.readahead_size != 0)
+                              ? read_options.readahead_size
+                              : kMaxAutoReadaheadSize;
+  FilePrefetchBuffer prefetch_buffer(rep_->file.get(), readahead_size,
+                                     readahead_size);
+
   for (index_iter->SeekToFirst(); index_iter->Valid(); index_iter->Next()) {
     s = index_iter->status();
     if (!s.ok()) {
@@ -3750,9 +3758,9 @@ Status BlockBasedTable::VerifyChecksumInBlocks(
     BlockHandle handle = index_iter->value().handle;
     BlockContents contents;
     BlockFetcher block_fetcher(
-        rep_->file.get(), nullptr /* prefetch buffer */, rep_->footer,
+        rep_->file.get(), &prefetch_buffer, rep_->footer, ReadOptions(), handle,
-        ReadOptions(), handle, &contents, rep_->ioptions,
+        &contents, rep_->ioptions, false /* decompress */,
-        false /* decompress */, false /*maybe_compressed*/, BlockType::kData,
+        false /*maybe_compressed*/, BlockType::kData,
         UncompressionDict::GetEmptyDict(), rep_->persistent_cache_options);
     s = block_fetcher.ReadBlockContents();
     if (!s.ok()) {

table/block_based/block_based_table_reader.h

@@ -82,6 +82,13 @@ class BlockBasedTable : public TableReader {
   // For Posix files the unique ID is three varints.
   static const size_t kMaxCacheKeyPrefixSize = kMaxVarint64Length * 3 + 1;
 
+  // All the below fields control iterator readahead
+  static const size_t kInitAutoReadaheadSize = 8 * 1024;
+  // Found that 256 KB readahead size provides the best performance, based on
+  // experiments, for auto readahead. Experiment data is in PR #3282.
+  static const size_t kMaxAutoReadaheadSize;
+  static const int kMinNumFileReadsToStartAutoReadahead = 2;
+
   // Attempt to open the table that is stored in bytes [0..file_size)
   // of "file", and read the metadata entries necessary to allow
   // retrieving data from the table.
@@ -182,7 +189,8 @@ class BlockBasedTable : public TableReader {
   // convert SST file to a human readable form
   Status DumpTable(WritableFile* out_file) override;
 
-  Status VerifyChecksum(TableReaderCaller caller) override;
+  Status VerifyChecksum(const ReadOptions& readOptions,
+                        TableReaderCaller caller) override;
 
   ~BlockBasedTable();
 
@@ -430,7 +438,8 @@ class BlockBasedTable : public TableReader {
   static BlockType GetBlockTypeForMetaBlockByName(const Slice& meta_block_name);
 
   Status VerifyChecksumInMetaBlocks(InternalIteratorBase<Slice>* index_iter);
-  Status VerifyChecksumInBlocks(InternalIteratorBase<IndexValue>* index_iter);
+  Status VerifyChecksumInBlocks(const ReadOptions& read_options,
+                                InternalIteratorBase<IndexValue>* index_iter);
 
   // Create the filter from the filter block.
   std::unique_ptr<FilterBlockReader> CreateFilterBlockReader(
@@ -772,13 +781,7 @@ class BlockBasedTableIterator : public InternalIteratorBase<TValue> {
   // lookup_context_.caller = kCompaction.
   size_t compaction_readahead_size_;
 
-  // All the below fields control iterator readahead
+  size_t readahead_size_ = BlockBasedTable::kInitAutoReadaheadSize;
-  static const size_t kInitAutoReadaheadSize = 8 * 1024;
-  // Found that 256 KB readahead size provides the best performance, based on
-  // experiments, for auto readahead. Experiment data is in PR #3282.
-  static const size_t kMaxAutoReadaheadSize;
-  static const int kMinNumFileReadsToStartAutoReadahead = 2;
-  size_t readahead_size_ = kInitAutoReadaheadSize;
   size_t readahead_limit_ = 0;
   int64_t num_file_reads_ = 0;
   std::unique_ptr<FilePrefetchBuffer> prefetch_buffer_;

table/sst_file_reader.cc

@@ -79,8 +79,9 @@ std::shared_ptr<const TableProperties> SstFileReader::GetTableProperties()
   return rep_->table_reader->GetTableProperties();
 }
 
-Status SstFileReader::VerifyChecksum() {
+Status SstFileReader::VerifyChecksum(const ReadOptions& read_options) {
-  return rep_->table_reader->VerifyChecksum(TableReaderCaller::kSSTFileReader);
+  return rep_->table_reader->VerifyChecksum(read_options,
+                                            TableReaderCaller::kSSTFileReader);
 }
 
 }  // namespace rocksdb

table/table_reader.h

@@ -127,7 +127,8 @@ class TableReader {
   }
 
   // check whether there is corruption in this db file
-  virtual Status VerifyChecksum(TableReaderCaller /*caller*/) {
+  virtual Status VerifyChecksum(const ReadOptions& /*read_options*/,
+                                TableReaderCaller /*caller*/) {
     return Status::NotSupported("VerifyChecksum() not supported");
   }
 };

tools/sst_dump_tool.cc

@@ -143,7 +143,9 @@ Status SstFileDumper::NewTableReader(
 }
 
 Status SstFileDumper::VerifyChecksum() {
-  return table_reader_->VerifyChecksum(TableReaderCaller::kSSTDumpTool);
+  // We could pass specific readahead setting into read options if needed.
+  return table_reader_->VerifyChecksum(ReadOptions(),
+                                       TableReaderCaller::kSSTDumpTool);
 }
 
 Status SstFileDumper::DumpTable(const std::string& out_filename) {