Add crash-recovery correctness check to db_stress

Summary:
Previously, our `db_stress` tool held the expected state of the DB in-memory, so after crash-recovery, there was no way to verify data correctness. This PR adds an option, `--expected_values_file`, which specifies a file holding the expected values.

In black-box testing, the `db_stress` process can be killed arbitrarily, so updates to the `--expected_values_file` must be atomic. We achieve this by `mmap`ing the file and relying on `std::atomic<uint32_t>` for atomicity. Actually this doesn't provide a total guarantee on what we want as `std::atomic<uint32_t>` could, in theory, be translated into multiple stores surrounded by a mutex. We can verify our assumption by looking at `std::atomic::is_always_lock_free`.

For the `mmap`'d file, we didn't have an existing way to expose its contents as a raw memory buffer. This PR adds it in the `Env::NewMemoryMappedFileBuffer` function, and `MemoryMappedFileBuffer` class.

`db_crashtest.py` is updated to use an expected values file for black-box testing. On the first iteration (when the DB is created), an empty file is provided as `db_stress` will populate it when it runs. On subsequent iterations, that same filename is provided so `db_stress` can check the data is as expected on startup.
Closes https://github.com/facebook/rocksdb/pull/3629

Differential Revision: D7463144

Pulled By: ajkr

fbshipit-source-id: c8f3e82c93e045a90055e2468316be155633bd8b

env/env.cc

@@ -87,6 +87,8 @@ RandomAccessFile::~RandomAccessFile() {
 WritableFile::~WritableFile() {
 }
 
+MemoryMappedFileBuffer::~MemoryMappedFileBuffer() {}
+
 Logger::~Logger() {}
 
 Status Logger::Close() {

env/env_posix.cc

@@ -457,6 +457,47 @@ class PosixEnv : public Env {
     return Status::OK();
   }
 
+  virtual Status NewMemoryMappedFileBuffer(
+      const std::string& fname,
+      unique_ptr<MemoryMappedFileBuffer>* result) override {
+    int fd = -1;
+    Status status;
+    while (fd < 0) {
+      IOSTATS_TIMER_GUARD(open_nanos);
+      fd = open(fname.c_str(), O_RDWR, 0644);
+      if (fd < 0) {
+        // Error while opening the file
+        if (errno == EINTR) {
+          continue;
+        }
+        status =
+            IOError("While open file for raw mmap buffer access", fname, errno);
+        break;
+      }
+    }
+    uint64_t size;
+    if (status.ok()) {
+      status = GetFileSize(fname, &size);
+    }
+    void* base;
+    if (status.ok()) {
+      base = mmap(nullptr, static_cast<size_t>(size), PROT_READ | PROT_WRITE,
+                  MAP_SHARED, fd, 0);
+      if (base == MAP_FAILED) {
+        status = IOError("while mmap file for read", fname, errno);
+      }
+    }
+    if (status.ok()) {
+      result->reset(
+          new PosixMemoryMappedFileBuffer(base, static_cast<size_t>(size)));
+    }
+    if (fd >= 0) {
+      // don't need to keep it open after mmap has been called
+      close(fd);
+    }
+    return status;
+  }
+
   virtual Status NewDirectory(const std::string& name,
                               unique_ptr<Directory>* result) override {
     result->reset();

env/env_test.cc

@@ -200,6 +200,41 @@ TEST_F(EnvPosixTest, DISABLED_FilePermission) {
 }
 #endif
 
+TEST_F(EnvPosixTest, MemoryMappedFileBuffer) {
+  const int kFileBytes = 1 << 15;  // 32 KB
+  std::string expected_data;
+  std::string fname = test::TmpDir(env_) + "/" + "testfile";
+  {
+    unique_ptr<WritableFile> wfile;
+    const EnvOptions soptions;
+    ASSERT_OK(env_->NewWritableFile(fname, &wfile, soptions));
+
+    Random rnd(301);
+    test::RandomString(&rnd, kFileBytes, &expected_data);
+    ASSERT_OK(wfile->Append(expected_data));
+  }
+
+  std::unique_ptr<MemoryMappedFileBuffer> mmap_buffer;
+  Status status = env_->NewMemoryMappedFileBuffer(fname, &mmap_buffer);
+  // it should be supported at least on linux
+#if !defined(OS_LINUX)
+  if (status.IsNotSupported()) {
+    fprintf(stderr,
+            "skipping EnvPosixTest.MemoryMappedFileBuffer due to "
+            "unsupported Env::NewMemoryMappedFileBuffer\n");
+    return;
+  }
+#endif  // !defined(OS_LINUX)
+
+  ASSERT_OK(status);
+  ASSERT_NE(nullptr, mmap_buffer.get());
+  ASSERT_NE(nullptr, mmap_buffer->base);
+  ASSERT_EQ(kFileBytes, mmap_buffer->length);
+  std::string actual_data(static_cast<char*>(mmap_buffer->base),
+                          mmap_buffer->length);
+  ASSERT_EQ(expected_data, actual_data);
+}
+
 TEST_P(EnvPosixTestWithParam, UnSchedule) {
   std::atomic<bool> called(false);
   env_->SetBackgroundThreads(1, Env::LOW);

env/io_posix.cc

@@ -1052,6 +1052,11 @@ Status PosixRandomRWFile::Close() {
   return Status::OK();
 }
 
+PosixMemoryMappedFileBuffer::~PosixMemoryMappedFileBuffer() {
+  // TODO should have error handling though not much we can do...
+  munmap(this->base, length);
+}
+
 /*
  * PosixDirectory
  */

env/io_posix.h

@@ -236,6 +236,12 @@ class PosixRandomRWFile : public RandomRWFile {
   int fd_;
 };
 
+struct PosixMemoryMappedFileBuffer : public MemoryMappedFileBuffer {
+  PosixMemoryMappedFileBuffer(void* _base, size_t _length)
+      : MemoryMappedFileBuffer(_base, _length) {}
+  virtual ~PosixMemoryMappedFileBuffer();
+};
+
 class PosixDirectory : public Directory {
  public:
   explicit PosixDirectory(int fd) : fd_(fd) {}

include/rocksdb/env.h

@@ -42,6 +42,7 @@ class SequentialFile;
 class Slice;
 class WritableFile;
 class RandomRWFile;
+struct MemoryMappedFileBuffer;
 class Directory;
 struct DBOptions;
 struct ImmutableDBOptions;
@@ -204,6 +205,16 @@ class Env {
     return Status::NotSupported("RandomRWFile is not implemented in this Env");
   }
 
+  // Opens `fname` as a memory-mapped file for read and write (in-place updates
+  // only, i.e., no appends). On success, stores a raw buffer covering the whole
+  // file in `*result`. The file must exist prior to this call.
+  virtual Status NewMemoryMappedFileBuffer(
+      const std::string& /*fname*/,
+      unique_ptr<MemoryMappedFileBuffer>* /*result*/) {
+    return Status::NotSupported(
+        "MemoryMappedFileBuffer is not implemented in this Env");
+  }
+
   // Create an object that represents a directory. Will fail if directory
   // doesn't exist. If the directory exists, it will open the directory
   // and create a new Directory object.
@@ -804,6 +815,17 @@ class RandomRWFile {
   RandomRWFile& operator=(const RandomRWFile&) = delete;
 };
 
+// MemoryMappedFileBuffer object represents a memory-mapped file's raw buffer.
+// Subclasses should release the mapping upon destruction.
+struct MemoryMappedFileBuffer {
+  MemoryMappedFileBuffer(void* _base, size_t _length)
+      : base(_base), length(_length) {}
+  virtual ~MemoryMappedFileBuffer() = 0;
+
+  void* const base;
+  const size_t length;
+};
+
 // Directory object represents collection of files and implements
 // filesystem operations that can be executed on directories.
 class Directory {

tools/db_crashtest.py

@@ -16,14 +16,19 @@ import argparse
 #   for simple:
 #       simple_default_params < blackbox|whitebox_simple_default_params < args
 
+expected_values_file = tempfile.NamedTemporaryFile()
+
 default_params = {
     "acquire_snapshot_one_in": 10000,
     "block_size": 16384,
     "cache_size": 1048576,
+    "clear_column_family_one_in": 0,
+    "compression_type": "snappy",
     "use_clock_cache": "false",
     "delpercent": 5,
     "destroy_db_initially": 0,
     "disable_wal": 0,
+    "expected_values_path": expected_values_file.name,
     "allow_concurrent_memtable_write": 0,
     "iterpercent": 10,
     "max_background_compactions": 20,
@@ -88,10 +93,13 @@ simple_default_params = {
     "block_size": 16384,
     "cache_size": 1048576,
     "use_clock_cache": "false",
+    "clear_column_family_one_in": 0,
     "column_families": 1,
+    "compression_type": "snappy",
     "delpercent": 5,
     "destroy_db_initially": 0,
     "disable_wal": 0,
+    "expected_values_path": expected_values_file.name,
     "allow_concurrent_memtable_write": lambda: random.randint(0, 1),
     "iterpercent": 10,
     "max_background_compactions": 1,
@@ -190,13 +198,16 @@ def blackbox_crash_main(args):
           + "threads=" + str(cmd_params['threads']) + "\n"
           + "ops_per_thread=" + str(cmd_params['ops_per_thread']) + "\n"
           + "write_buffer_size=" + str(cmd_params['write_buffer_size']) + "\n"
-          + "subcompactions=" + str(cmd_params['subcompactions']) + "\n")
+          + "subcompactions=" + str(cmd_params['subcompactions']) + "\n"
+          + "expected_values_path=" + str(cmd_params['expected_values_path']) + "\n")
 
     while time.time() < exit_time:
         run_had_errors = False
         killtime = time.time() + cmd_params['interval']
 
-        cmd = gen_cmd(dict(cmd_params.items() + {'db': dbname}.items()))
+        cmd = gen_cmd(dict(
+            cmd_params.items() +
+            {'db': dbname}.items()))
 
         child = subprocess.Popen(cmd, stderr=subprocess.PIPE)
         print("Running db_stress with pid=%d: %s\n\n"
@@ -253,7 +264,8 @@ def whitebox_crash_main(args):
           + "threads=" + str(cmd_params['threads']) + "\n"
           + "ops_per_thread=" + str(cmd_params['ops_per_thread']) + "\n"
           + "write_buffer_size=" + str(cmd_params['write_buffer_size']) + "\n"
-          + "subcompactions=" + str(cmd_params['subcompactions']) + "\n")
+          + "subcompactions=" + str(cmd_params['subcompactions']) + "\n"
+          + "expected_values_path=" + str(cmd_params['expected_values_path']) + "\n")
 
     total_check_mode = 4
     check_mode = 0

tools/db_stress.cc

@@ -297,6 +297,14 @@ DEFINE_bool(use_block_based_filter, false, "use block based filter"
 
 DEFINE_string(db, "", "Use the db with the following name.");
 
+DEFINE_string(
+    expected_values_path, "",
+    "File where the array of expected uint32_t values will be stored. If "
+    "provided and non-empty, the DB state will be verified against these "
+    "values after recovery. --max_key and --column_family must be kept the "
+    "same across invocations of this program that use the same "
+    "--expected_values_path.");
+
 DEFINE_bool(verify_checksum, false,
             "Verify checksum for every block read from storage");
 
@@ -768,7 +776,11 @@ class Stats {
 // State shared by all concurrent executions of the same benchmark.
 class SharedState {
  public:
-  static const uint32_t SENTINEL;
+  // indicates a key may have any value (or not be present) as an operation on
+  // it is incomplete.
+  static const uint32_t UNKNOWN_SENTINEL;
+  // indicates a key should definitely be deleted
+  static const uint32_t DELETION_SENTINEL;
 
   explicit SharedState(StressTest* stress_test)
       : cv_(&mu_),
@@ -786,7 +798,8 @@ class SharedState {
         bg_thread_finished_(false),
         stress_test_(stress_test),
         verification_failure_(false),
-        no_overwrite_ids_(FLAGS_column_families) {
+        no_overwrite_ids_(FLAGS_column_families),
+        values_(nullptr) {
     // Pick random keys in each column family that will not experience
     // overwrite
 
@@ -820,15 +833,69 @@ class SharedState {
     }
     delete[] permutation;
 
+    size_t expected_values_size =
+        sizeof(std::atomic<uint32_t>) * FLAGS_column_families * max_key_;
+    bool values_init_needed = false;
+    Status status;
+    if (!FLAGS_expected_values_path.empty()) {
+      if (!std::atomic<uint32_t>{}.is_lock_free()) {
+        status = Status::InvalidArgument(
+            "Cannot use --expected_values_path on platforms without lock-free "
+            "std::atomic<uint32_t>");
+      }
+      if (status.ok() && FLAGS_clear_column_family_one_in > 0) {
+        status = Status::InvalidArgument(
+            "Cannot use --expected_values_path on when "
+            "--clear_column_family_one_in is greater than zero.");
+      }
+      size_t size;
+      if (status.ok()) {
+        status = FLAGS_env->GetFileSize(FLAGS_expected_values_path, &size);
+      }
+      unique_ptr<WritableFile> wfile;
+      if (status.ok() && size == 0) {
+        const EnvOptions soptions;
+        status = FLAGS_env->NewWritableFile(FLAGS_expected_values_path, &wfile,
+                                            soptions);
+      }
+      if (status.ok() && size == 0) {
+        std::string buf(expected_values_size, '\0');
+        status = wfile->Append(buf);
+        values_init_needed = true;
+      }
+      if (status.ok()) {
+        status = FLAGS_env->NewMemoryMappedFileBuffer(
+            FLAGS_expected_values_path, &expected_mmap_buffer_);
+      }
+      if (status.ok()) {
+        assert(expected_mmap_buffer_->length == expected_values_size);
+        values_ =
+            static_cast<std::atomic<uint32_t>*>(expected_mmap_buffer_->base);
+        assert(values_ != nullptr);
+      } else {
+        fprintf(stderr, "Failed opening shared file '%s' with error: %s\n",
+                FLAGS_expected_values_path.c_str(), status.ToString().c_str());
+        assert(values_ == nullptr);
+      }
+    }
+    if (values_ == nullptr) {
+      values_ =
+          static_cast<std::atomic<uint32_t>*>(malloc(expected_values_size));
+      values_init_needed = true;
+    }
+    assert(values_ != nullptr);
+    if (values_init_needed) {
+      for (int i = 0; i < FLAGS_column_families; ++i) {
+        for (int j = 0; j < max_key_; ++j) {
+          Delete(i, j, false /* pending */);
+        }
+      }
+    }
+
     if (FLAGS_test_batches_snapshots) {
       fprintf(stdout, "No lock creation because test_batches_snapshots set\n");
       return;
     }
-    values_.resize(FLAGS_column_families);
-
-    for (int i = 0; i < FLAGS_column_families; ++i) {
-      values_[i] = std::vector<uint32_t>(max_key_, SENTINEL);
-    }
 
     long num_locks = static_cast<long>(max_key_ >> log2_keys_per_lock_);
     if (max_key_ & ((1 << log2_keys_per_lock_) - 1)) {
@@ -935,27 +1002,57 @@ class SharedState {
     }
   }
 
+  std::atomic<uint32_t>& Value(int cf, int64_t key) const {
+    return values_[cf * max_key_ + key];
+  }
+
   void ClearColumnFamily(int cf) {
-    std::fill(values_[cf].begin(), values_[cf].end(), SENTINEL);
+    std::fill(&Value(cf, 0 /* key */), &Value(cf + 1, 0 /* key */),
+              DELETION_SENTINEL);
   }
 
-  void Put(int cf, int64_t key, uint32_t value_base) {
+  // @param pending True if the update may have started but is not yet
-    values_[cf][key] = value_base;
+  //    guaranteed finished. This is useful for crash-recovery testing when the
+  //    process may crash before updating the expected values array.
+  void Put(int cf, int64_t key, uint32_t value_base, bool pending) {
+    if (!pending) {
+      // prevent expected-value update from reordering before Write
+      std::atomic_thread_fence(std::memory_order_release);
+    }
+    Value(cf, key).store(pending ? UNKNOWN_SENTINEL : value_base,
+                         std::memory_order_relaxed);
+    if (pending) {
+      // prevent Write from reordering before expected-value update
+      std::atomic_thread_fence(std::memory_order_release);
+    }
   }
 
-  uint32_t Get(int cf, int64_t key) const { return values_[cf][key]; }
+  uint32_t Get(int cf, int64_t key) const { return Value(cf, key); }
 
-  void Delete(int cf, int64_t key) { values_[cf][key] = SENTINEL; }
+  // @param pending See comment above Put()
+  // Returns true if the key was not yet deleted.
+  bool Delete(int cf, int64_t key, bool pending) {
+    if (Value(cf, key) == DELETION_SENTINEL) {
+      return false;
+    }
+    Put(cf, key, DELETION_SENTINEL, pending);
+    return true;
+  }
 
-  void SingleDelete(int cf, int64_t key) { values_[cf][key] = SENTINEL; }
+  // @param pending See comment above Put()
+  // Returns true if the key was not yet deleted.
+  bool SingleDelete(int cf, int64_t key, bool pending) {
+    return Delete(cf, key, pending);
+  }
 
-  int DeleteRange(int cf, int64_t begin_key, int64_t end_key) {
+  // @param pending See comment above Put()
+  // Returns number of keys deleted by the call.
+  int DeleteRange(int cf, int64_t begin_key, int64_t end_key, bool pending) {
     int covered = 0;
     for (int64_t key = begin_key; key < end_key; ++key) {
-      if (values_[cf][key] != SENTINEL) {
+      if (Delete(cf, key, pending)) {
         ++covered;
       }
-      values_[cf][key] = SENTINEL;
     }
     return covered;
   }
@@ -964,7 +1061,11 @@ class SharedState {
     return no_overwrite_ids_[cf].find(key) == no_overwrite_ids_[cf].end();
   }
 
-  bool Exists(int cf, int64_t key) { return values_[cf][key] != SENTINEL; }
+  bool Exists(int cf, int64_t key) {
+    uint32_t expected_value = Value(cf, key).load();
+    assert(expected_value != UNKNOWN_SENTINEL);
+    return expected_value != DELETION_SENTINEL;
+  }
 
   uint32_t GetSeed() const { return seed_; }
 
@@ -976,6 +1077,10 @@ class SharedState {
 
   bool BgThreadFinished() const { return bg_thread_finished_; }
 
+  bool ShouldVerifyAtBeginning() const {
+    return expected_mmap_buffer_.get() != nullptr;
+  }
+
  private:
   port::Mutex mu_;
   port::CondVar cv_;
@@ -997,13 +1102,15 @@ class SharedState {
   // Keys that should not be overwritten
   std::vector<std::unordered_set<size_t> > no_overwrite_ids_;
 
-  std::vector<std::vector<uint32_t>> values_;
+  std::atomic<uint32_t>* values_;
   // Has to make it owned by a smart ptr as port::Mutex is not copyable
   // and storing it in the container may require copying depending on the impl.
   std::vector<std::vector<std::unique_ptr<port::Mutex> > > key_locks_;
+  std::unique_ptr<MemoryMappedFileBuffer> expected_mmap_buffer_;
 };
 
-const uint32_t SharedState::SENTINEL = 0xffffffff;
+const uint32_t SharedState::UNKNOWN_SENTINEL = 0xfffffffe;
+const uint32_t SharedState::DELETION_SENTINEL = 0xffffffff;
 
 // Per-thread state for concurrent executions of the same benchmark.
 struct ThreadState {
@@ -1311,6 +1418,13 @@ class StressTest {
       while (!shared.AllInitialized()) {
         shared.GetCondVar()->Wait();
       }
+      if (shared.ShouldVerifyAtBeginning()) {
+        if (shared.HasVerificationFailedYet()) {
+          printf("Crash-recovery verification failed :(\n");
+        } else {
+          printf("Crash-recovery verification passed :)\n");
+        }
+      }
 
       auto now = FLAGS_env->NowMicros();
       fprintf(stdout, "%s Starting database operations\n",
@@ -1406,6 +1520,9 @@ class StressTest {
     ThreadState* thread = reinterpret_cast<ThreadState*>(v);
     SharedState* shared = thread->shared;
 
+    if (shared->ShouldVerifyAtBeginning()) {
+      thread->shared->GetStressTest()->VerifyDb(thread);
+    }
     {
       MutexLock l(shared->GetMutex());
       shared->IncInitialized();
@@ -1987,7 +2104,7 @@ class StressTest {
         }
       } else if (prefixBound <= prob_op && prob_op < writeBound) {
         // OPERATION write
-        uint32_t value_base = thread->rand.Next();
+        uint32_t value_base = thread->rand.Next() % shared->UNKNOWN_SENTINEL;
         size_t sz = GenerateValue(value_base, value, sizeof(value));
         Slice v(value, sz);
         if (!FLAGS_test_batches_snapshots) {
@@ -2015,7 +2132,8 @@ class StressTest {
               break;
             }
           }
-          shared->Put(rand_column_family, rand_key, value_base);
+          shared->Put(rand_column_family, rand_key, value_base,
+                      true /* pending */);
           Status s;
           if (FLAGS_use_merge) {
             if (!FLAGS_use_txn) {
@@ -2048,6 +2166,8 @@ class StressTest {
 #endif
             }
           }
+          shared->Put(rand_column_family, rand_key, value_base,
+                      false /* pending */);
           if (!s.ok()) {
             fprintf(stderr, "put or merge error: %s\n", s.ToString().c_str());
             std::terminate();
@@ -2079,7 +2199,7 @@ class StressTest {
           // Use delete if the key may be overwritten and a single deletion
           // otherwise.
           if (shared->AllowsOverwrite(rand_column_family, rand_key)) {
-            shared->Delete(rand_column_family, rand_key);
+            shared->Delete(rand_column_family, rand_key, true /* pending */);
             Status s;
             if (!FLAGS_use_txn) {
               s = db_->Delete(write_opts, column_family, key);
@@ -2095,13 +2215,15 @@ class StressTest {
               }
 #endif
             }
+            shared->Delete(rand_column_family, rand_key, false /* pending */);
             thread->stats.AddDeletes(1);
             if (!s.ok()) {
               fprintf(stderr, "delete error: %s\n", s.ToString().c_str());
               std::terminate();
             }
           } else {
-            shared->SingleDelete(rand_column_family, rand_key);
+            shared->SingleDelete(rand_column_family, rand_key,
+                                 true /* pending */);
             Status s;
             if (!FLAGS_use_txn) {
               s = db_->SingleDelete(write_opts, column_family, key);
@@ -2117,6 +2239,8 @@ class StressTest {
               }
 #endif
             }
+            shared->SingleDelete(rand_column_family, rand_key,
+                                 false /* pending */);
             thread->stats.AddSingleDeletes(1);
             if (!s.ok()) {
               fprintf(stderr, "single delete error: %s\n",
@@ -2150,21 +2274,24 @@ class StressTest {
                     shared->GetMutexForKey(rand_column_family, rand_key + j)));
             }
           }
+          shared->DeleteRange(rand_column_family, rand_key,
+                              rand_key + FLAGS_range_deletion_width,
+                              true /* pending */);
 
           keystr = Key(rand_key);
           key = keystr;
           column_family = column_families_[rand_column_family];
           std::string end_keystr = Key(rand_key + FLAGS_range_deletion_width);
           Slice end_key = end_keystr;
-          int covered = shared->DeleteRange(
-              rand_column_family, rand_key,
-              rand_key + FLAGS_range_deletion_width);
           Status s = db_->DeleteRange(write_opts, column_family, key, end_key);
           if (!s.ok()) {
             fprintf(stderr, "delete range error: %s\n",
                     s.ToString().c_str());
             std::terminate();
           }
+          int covered = shared->DeleteRange(
+              rand_column_family, rand_key,
+              rand_key + FLAGS_range_deletion_width, false /* pending */);
           thread->stats.AddRangeDeletions(1);
           thread->stats.AddCoveredByRangeDeletions(covered);
         }
@@ -2276,12 +2403,15 @@ class StressTest {
     // compare value_from_db with the value in the shared state
     char value[kValueMaxLen];
     uint32_t value_base = shared->Get(cf, key);
-    if (value_base == SharedState::SENTINEL && !strict) {
+    if (value_base == SharedState::UNKNOWN_SENTINEL) {
+      return true;
+    }
+    if (value_base == SharedState::DELETION_SENTINEL && !strict) {
       return true;
     }
 
     if (s.ok()) {
-      if (value_base == SharedState::SENTINEL) {
+      if (value_base == SharedState::DELETION_SENTINEL) {
         VerificationAbort(shared, "Unexpected value found", cf, key);
         return false;
       }
@@ -2296,7 +2426,7 @@ class StressTest {
         return false;
       }
     } else {
-      if (value_base != SharedState::SENTINEL) {
+      if (value_base != SharedState::DELETION_SENTINEL) {
         VerificationAbort(shared, "Value not found: " + s.ToString(), cf, key);
         return false;
       }