Ensure VerifyFileChecksums reads don't exceed readahead_size

HISTORY.md

@@ -9,6 +9,9 @@
 * For level compaction with `level_compaction_dynamic_level_bytes=true`, RocksDB now trivially moves levels down to fill LSM starting from bottommost level during DB open. See more in comments for option `level_compaction_dynamic_level_bytes`.
 * User-provided `ReadOptions` take effect for more reads of non-`CacheEntryRole::kDataBlock` blocks.
 
+### Bug Fixes
+* In the DB::VerifyFileChecksums API, ensure that file system reads of SST files are equal to the readahead_size in ReadOptions, if specified. Previously, each read was 2x the readahead_size.
+
 ### New Features
 * Add experimental `PerfContext` counters `iter_{next|prev|seek}_count` for db iterator, each counting the times of corresponding API being called.
 * Allow runtime changes to whether `WriteBufferManager` allows stall or not by calling `SetAllowStall()`

db/db_basic_test.cc

@@ -4494,6 +4494,63 @@ TEST_F(DBBasicTest, VerifyFileChecksums) {
   ASSERT_TRUE(db_->VerifyFileChecksums(ReadOptions()).IsInvalidArgument());
 }
 
+TEST_F(DBBasicTest, VerifyFileChecksumsReadahead) {
+  Options options = GetDefaultOptions();
+  options.create_if_missing = true;
+  options.env = env_;
+  options.file_checksum_gen_factory = GetFileChecksumGenCrc32cFactory();
+  DestroyAndReopen(options);
+
+  Random rnd(301);
+  int alignment = 256 * 1024;
+  for (int i = 0; i < 16; ++i) {
+    ASSERT_OK(Put("key" + std::to_string(i), rnd.RandomString(alignment)));
+  }
+  ASSERT_OK(Flush());
+
+  std::vector<std::string> filenames;
+  int sst_cnt = 0;
+  std::string sst_name;
+  uint64_t sst_size;
+  uint64_t number;
+  FileType type;
+  ASSERT_OK(env_->GetChildren(dbname_, &filenames));
+  for (auto name : filenames) {
+    if (ParseFileName(name, &number, &type)) {
+      if (type == kTableFile) {
+        sst_cnt++;
+        sst_name = name;
+      }
+    }
+  }
+  ASSERT_EQ(sst_cnt, 1);
+  ASSERT_OK(env_->GetFileSize(dbname_ + '/' + sst_name, &sst_size));
+
+  bool last_read = false;
+  ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->SetCallBack(
+      "GenerateOneFileChecksum::Chunk:0", [&](void* /*arg*/) {
+        if (env_->random_read_bytes_counter_.load() == sst_size) {
+          EXPECT_FALSE(last_read);
+          last_read = true;
+        } else {
+          ASSERT_EQ(env_->random_read_bytes_counter_.load() & (alignment - 1),
+                    0);
+        }
+      });
+  ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->EnableProcessing();
+  env_->count_random_reads_ = true;
+  env_->random_read_bytes_counter_ = 0;
+  env_->random_read_counter_.Reset();
+
+  ReadOptions ro;
+  ro.readahead_size = alignment;
+  ASSERT_OK(db_->VerifyFileChecksums(ro));
+  ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->DisableProcessing();
+  ASSERT_TRUE(last_read);
+  ASSERT_EQ(env_->random_read_counter_.Read(),
+            (sst_size + alignment - 1) / (alignment));
+}
+
 // TODO: re-enable after we provide finer-grained control for WAL tracking to
 // meet the needs of different use cases, durability levels and recovery modes.
 TEST_F(DBBasicTest, DISABLED_ManualWalSync) {

file/file_util.cc

@@ -135,7 +135,7 @@ IOStatus GenerateOneFileChecksum(
     FileChecksumGenFactory* checksum_factory,
     const std::string& requested_checksum_func_name, std::string* file_checksum,
     std::string* file_checksum_func_name,
-    size_t verify_checksums_readahead_size, bool allow_mmap_reads,
+    size_t verify_checksums_readahead_size, bool /*allow_mmap_reads*/,
     std::shared_ptr<IOTracer>& io_tracer, RateLimiter* rate_limiter,
     Env::IOPriority rate_limiter_priority) {
   if (checksum_factory == nullptr) {
@@ -196,29 +196,33 @@ IOStatus GenerateOneFileChecksum(
   size_t readahead_size = (verify_checksums_readahead_size != 0)
                               ? verify_checksums_readahead_size
                               : default_max_read_ahead_size;
-
-  FilePrefetchBuffer prefetch_buffer(readahead_size /* readahead_size */,
-                                     readahead_size /* max_readahead_size */,
-                                     !allow_mmap_reads /* enable */);
+  std::unique_ptr<char[]> buf;
+  if (reader->use_direct_io()) {
+    size_t alignment = reader->file()->GetRequiredBufferAlignment();
+    readahead_size = (readahead_size + alignment - 1) & ~(alignment - 1);
+  }
+  buf.reset(new char[readahead_size]);
 
   Slice slice;
   uint64_t offset = 0;
   IOOptions opts;
   while (size > 0) {
     size_t bytes_to_read =
         static_cast<size_t>(std::min(uint64_t{readahead_size}, size));
-    if (!prefetch_buffer.TryReadFromCache(
-            opts, reader.get(), offset, bytes_to_read, &slice,
-            nullptr /* status */, rate_limiter_priority,
-            false /* for_compaction */)) {
-      return IOStatus::Corruption("file read failed");
+    io_s = reader->Read(opts, offset, bytes_to_read, &slice, buf.get(), nullptr,
+                        rate_limiter_priority);
+    if (!io_s.ok()) {
+      return IOStatus::Corruption("file read failed with error: " +
+                                  io_s.ToString());
     }
     if (slice.size() == 0) {
       return IOStatus::Corruption("file too small");
     }
     checksum_generator->Update(slice.data(), slice.size());
     size -= slice.size();
     offset += slice.size();
+
+    TEST_SYNC_POINT("GenerateOneFileChecksum::Chunk:0");
   }
   checksum_generator->Finalize();
   *file_checksum = checksum_generator->GetChecksum();