Get() with timestamp should respect snapshot (#7227)

Summary:
If user-defined timestamp is enabled, current implementation can expose
newer data to queries even if an older sequence number is specified via
read_options.snapshot. This PR makes Get() respect sequence-number-based
snapshot.

Solution is simple. Besides using <ukey, ts, seq> to search the index for the key,
we also verify that the candidate result's seq is smaller than or equal to seq. This
requires passing a seq via `GetContext`, which results in the majority of code
change caused by this PR.

Also added a few unit tests to demonstrate standard visibility during point lookup
and range scan when timestamp and snapshot are both present.

Test plan (devserver):
```
make check
$./db_bench --benchmarks=fillseq,readrandom -cache_size=$[64*1024*1024]
```
Result
this PR: readrandom   :       4.827 micros/op 207180 ops/sec;   22.9 MB/s (1000000 of 1000000 found)
master:  readrandom   :       4.936 micros/op 202610 ops/sec;   22.4 MB/s (1000000 of 1000000 found)

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7227

Reviewed By: ltamasi

Differential Revision: D23015242

Pulled By: riversand963

fbshipit-source-id: ea7b85a728654553ba357d2e6a207b5e40f7376a

db/db_impl/db_impl.cc

@@ -1583,19 +1583,32 @@ Status DBImpl::Get(const ReadOptions& read_options,
   return s;
 }
 
+namespace {
+class GetWithTimestampReadCallback : public ReadCallback {
+ public:
+  explicit GetWithTimestampReadCallback(SequenceNumber seq)
+      : ReadCallback(seq) {}
+  bool IsVisibleFullCheck(SequenceNumber seq) override {
+    return seq <= max_visible_seq_;
+  }
+};
+}  // namespace
+
 Status DBImpl::GetImpl(const ReadOptions& read_options, const Slice& key,
                        GetImplOptions& get_impl_options) {
   assert(get_impl_options.value != nullptr ||
          get_impl_options.merge_operands != nullptr);
 
-#ifndef NDEBUG
   assert(get_impl_options.column_family);
-  ColumnFamilyHandle* cf = get_impl_options.column_family;
+  const Comparator* ucmp = get_impl_options.column_family->GetComparator();
-  const Comparator* const ucmp = cf->GetComparator();
   assert(ucmp);
-  if (ucmp->timestamp_size() > 0) {
+  size_t ts_sz = ucmp->timestamp_size();
+  GetWithTimestampReadCallback read_cb(0);  // Will call Refresh
+
+#ifndef NDEBUG
+  if (ts_sz > 0) {
     assert(read_options.timestamp);
-    assert(read_options.timestamp->size() == ucmp->timestamp_size());
+    assert(read_options.timestamp->size() == ts_sz);
   } else {
     assert(!read_options.timestamp);
   }
@@ -1661,6 +1674,12 @@ Status DBImpl::GetImpl(const ReadOptions& read_options, const Slice& key,
       snapshot = get_impl_options.callback->max_visible_seq();
     }
   }
+  // If timestamp is used, we use read callback to ensure <key,t,s> is returned
+  // only if t <= read_opts.timestamp and s <= snapshot.
+  if (ts_sz > 0 && !get_impl_options.callback) {
+    read_cb.Refresh(snapshot);
+    get_impl_options.callback = &read_cb;
+  }
   TEST_SYNC_POINT("DBImpl::GetImpl:3");
   TEST_SYNC_POINT("DBImpl::GetImpl:4");
 
@@ -1678,9 +1697,6 @@ Status DBImpl::GetImpl(const ReadOptions& read_options, const Slice& key,
   bool skip_memtable = (read_options.read_tier == kPersistedTier &&
                         has_unpersisted_data_.load(std::memory_order_relaxed));
   bool done = false;
-  const Comparator* comparator =
-      get_impl_options.column_family->GetComparator();
-  size_t ts_sz = comparator->timestamp_size();
   std::string* timestamp = ts_sz > 0 ? get_impl_options.timestamp : nullptr;
   if (!skip_memtable) {
     // Get value associated with key

db/db_with_timestamp_basic_test.cc

@@ -588,6 +588,324 @@ TEST_F(DBBasicTestWithTimestamp, CompactDeletionWithTimestampMarkerToBottom) {
   Close();
 }
 
+class DataVisibilityTest : public DBBasicTestWithTimestampBase {
+ public:
+  DataVisibilityTest() : DBBasicTestWithTimestampBase("data_visibility_test") {}
+};
+
+// Application specifies timestamp but not snapshot.
+//           reader              writer
+//                               ts'=90
+//           ts=100
+//           seq=10
+//                               seq'=11
+//                               write finishes
+//         GetImpl(ts,seq)
+// It is OK to return <k, t1, s1> if ts>=t1 AND seq>=s1. If ts>=1t1 but seq<s1,
+// the key should not be returned.
+TEST_F(DataVisibilityTest, PointLookupWithoutSnapshot1) {
+  Options options = CurrentOptions();
+  const size_t kTimestampSize = Timestamp(0, 0).size();
+  TestComparator test_cmp(kTimestampSize);
+  options.comparator = &test_cmp;
+  DestroyAndReopen(options);
+  SyncPoint::GetInstance()->DisableProcessing();
+  SyncPoint::GetInstance()->LoadDependency({
+      {"DBImpl::GetImpl:3",
+       "DataVisibilityTest::PointLookupWithoutSnapshot1:BeforePut"},
+      {"DataVisibilityTest::PointLookupWithoutSnapshot1:AfterPut",
+       "DBImpl::GetImpl:4"},
+  });
+  SyncPoint::GetInstance()->EnableProcessing();
+  port::Thread writer_thread([this]() {
+    std::string write_ts_str = Timestamp(1, 0);
+    Slice write_ts = write_ts_str;
+    WriteOptions write_opts;
+    write_opts.timestamp = &write_ts;
+    TEST_SYNC_POINT(
+        "DataVisibilityTest::PointLookupWithoutSnapshot1:BeforePut");
+    Status s = db_->Put(write_opts, "foo", "value");
+    ASSERT_OK(s);
+    TEST_SYNC_POINT("DataVisibilityTest::PointLookupWithoutSnapshot1:AfterPut");
+  });
+  ReadOptions read_opts;
+  std::string read_ts_str = Timestamp(3, 0);
+  Slice read_ts = read_ts_str;
+  read_opts.timestamp = &read_ts;
+  std::string value;
+  Status s = db_->Get(read_opts, "foo", &value);
+
+  writer_thread.join();
+  ASSERT_TRUE(s.IsNotFound());
+  Close();
+}
+
+// Application specifies timestamp but not snapshot.
+//           reader              writer
+//                               ts'=90
+//           ts=100
+//           seq=10
+//                               seq'=11
+//                               write finishes
+//                               Flush
+//         GetImpl(ts,seq)
+// It is OK to return <k, t1, s1> if ts>=t1 AND seq>=s1. If ts>=t1 but seq<s1,
+// the key should not be returned.
+TEST_F(DataVisibilityTest, PointLookupWithoutSnapshot2) {
+  Options options = CurrentOptions();
+  const size_t kTimestampSize = Timestamp(0, 0).size();
+  TestComparator test_cmp(kTimestampSize);
+  options.comparator = &test_cmp;
+  DestroyAndReopen(options);
+  SyncPoint::GetInstance()->DisableProcessing();
+  SyncPoint::GetInstance()->LoadDependency({
+      {"DBImpl::GetImpl:3",
+       "DataVisibilityTest::PointLookupWithoutSnapshot2:BeforePut"},
+      {"DataVisibilityTest::PointLookupWithoutSnapshot2:AfterPut",
+       "DBImpl::GetImpl:4"},
+  });
+  SyncPoint::GetInstance()->EnableProcessing();
+  port::Thread writer_thread([this]() {
+    std::string write_ts_str = Timestamp(1, 0);
+    Slice write_ts = write_ts_str;
+    WriteOptions write_opts;
+    write_opts.timestamp = &write_ts;
+    TEST_SYNC_POINT(
+        "DataVisibilityTest::PointLookupWithoutSnapshot2:BeforePut");
+    Status s = db_->Put(write_opts, "foo", "value");
+    ASSERT_OK(s);
+    ASSERT_OK(Flush());
+
+    write_ts_str = Timestamp(2, 0);
+    write_ts = write_ts_str;
+    write_opts.timestamp = &write_ts;
+    s = db_->Put(write_opts, "bar", "value");
+    ASSERT_OK(s);
+    TEST_SYNC_POINT("DataVisibilityTest::PointLookupWithoutSnapshot2:AfterPut");
+  });
+  ReadOptions read_opts;
+  std::string read_ts_str = Timestamp(3, 0);
+  Slice read_ts = read_ts_str;
+  read_opts.timestamp = &read_ts;
+  std::string value;
+  Status s = db_->Get(read_opts, "foo", &value);
+  writer_thread.join();
+  ASSERT_TRUE(s.IsNotFound());
+  Close();
+}
+
+// Application specifies both timestamp and snapshot.
+//       reader               writer
+//       seq=10
+//                            ts'=90
+//       ts=100
+//                            seq'=11
+//                            write finishes
+//       GetImpl(ts,seq)
+// Since application specifies both timestamp and snapshot, application expects
+// to see data that visible in BOTH timestamp and sequence number. Therefore,
+// <k, t1, s1> can be returned only if t1<=ts AND s1<=seq.
+TEST_F(DataVisibilityTest, PointLookupWithSnapshot1) {
+  Options options = CurrentOptions();
+  const size_t kTimestampSize = Timestamp(0, 0).size();
+  TestComparator test_cmp(kTimestampSize);
+  options.comparator = &test_cmp;
+  DestroyAndReopen(options);
+  SyncPoint::GetInstance()->DisableProcessing();
+  SyncPoint::GetInstance()->LoadDependency({
+      {"DataVisibilityTest::PointLookupWithSnapshot1:AfterTakingSnap",
+       "DataVisibilityTest::PointLookupWithSnapshot1:BeforePut"},
+      {"DataVisibilityTest::PointLookupWithSnapshot1:AfterPut",
+       "DBImpl::GetImpl:1"},
+  });
+  SyncPoint::GetInstance()->EnableProcessing();
+  port::Thread writer_thread([this]() {
+    std::string write_ts_str = Timestamp(1, 0);
+    Slice write_ts = write_ts_str;
+    WriteOptions write_opts;
+    write_opts.timestamp = &write_ts;
+    TEST_SYNC_POINT("DataVisibilityTest::PointLookupWithSnapshot1:BeforePut");
+    Status s = db_->Put(write_opts, "foo", "value");
+    TEST_SYNC_POINT("DataVisibilityTest::PointLookupWithSnapshot1:AfterPut");
+    ASSERT_OK(s);
+  });
+  ReadOptions read_opts;
+  const Snapshot* snap = db_->GetSnapshot();
+  TEST_SYNC_POINT(
+      "DataVisibilityTest::PointLookupWithSnapshot1:AfterTakingSnap");
+  read_opts.snapshot = snap;
+  std::string read_ts_str = Timestamp(3, 0);
+  Slice read_ts = read_ts_str;
+  read_opts.timestamp = &read_ts;
+  std::string value;
+  Status s = db_->Get(read_opts, "foo", &value);
+  writer_thread.join();
+
+  ASSERT_TRUE(s.IsNotFound());
+
+  db_->ReleaseSnapshot(snap);
+  Close();
+}
+
+// Application specifies both timestamp and snapshot.
+//       reader               writer
+//       seq=10
+//                            ts'=90
+//       ts=100
+//                            seq'=11
+//                            write finishes
+//                            Flush
+//       GetImpl(ts,seq)
+// Since application specifies both timestamp and snapshot, application expects
+// to see data that visible in BOTH timestamp and sequence number. Therefore,
+// <k, t1, s1> can be returned only if t1<=ts AND s1<=seq.
+TEST_F(DataVisibilityTest, PointLookupWithSnapshot2) {
+  Options options = CurrentOptions();
+  const size_t kTimestampSize = Timestamp(0, 0).size();
+  TestComparator test_cmp(kTimestampSize);
+  options.comparator = &test_cmp;
+  DestroyAndReopen(options);
+  SyncPoint::GetInstance()->DisableProcessing();
+  SyncPoint::GetInstance()->LoadDependency({
+      {"DataVisibilityTest::PointLookupWithSnapshot2:AfterTakingSnap",
+       "DataVisibilityTest::PointLookupWithSnapshot2:BeforePut"},
+  });
+  SyncPoint::GetInstance()->EnableProcessing();
+  port::Thread writer_thread([this]() {
+    std::string write_ts_str = Timestamp(1, 0);
+    Slice write_ts = write_ts_str;
+    WriteOptions write_opts;
+    write_opts.timestamp = &write_ts;
+    TEST_SYNC_POINT("DataVisibilityTest::PointLookupWithSnapshot2:BeforePut");
+    Status s = db_->Put(write_opts, "foo", "value1");
+    ASSERT_OK(s);
+    ASSERT_OK(Flush());
+
+    write_ts_str = Timestamp(2, 0);
+    write_ts = write_ts_str;
+    write_opts.timestamp = &write_ts;
+    s = db_->Put(write_opts, "bar", "value2");
+    ASSERT_OK(s);
+  });
+  const Snapshot* snap = db_->GetSnapshot();
+  TEST_SYNC_POINT(
+      "DataVisibilityTest::PointLookupWithSnapshot2:AfterTakingSnap");
+  writer_thread.join();
+  std::string read_ts_str = Timestamp(3, 0);
+  Slice read_ts = read_ts_str;
+  ReadOptions read_opts;
+  read_opts.snapshot = snap;
+  read_opts.timestamp = &read_ts;
+  std::string value;
+  Status s = db_->Get(read_opts, "foo", &value);
+  ASSERT_TRUE(s.IsNotFound());
+  db_->ReleaseSnapshot(snap);
+  Close();
+}
+
+// Application specifies timestamp but not snapshot.
+//      reader                writer
+//                            ts'=90
+//      ts=100
+//      seq=10
+//                            seq'=11
+//                            write finishes
+//      scan(ts,seq)
+// <k, t1, s1> can be seen in scan as long as ts>=t1 AND seq>=s1. If ts>=t1 but
+// seq<s1, then the key should not be returned.
+TEST_F(DataVisibilityTest, RangeScanWithoutSnapshot) {
+  Options options = CurrentOptions();
+  const size_t kTimestampSize = Timestamp(0, 0).size();
+  TestComparator test_cmp(kTimestampSize);
+  options.comparator = &test_cmp;
+  DestroyAndReopen(options);
+  SyncPoint::GetInstance()->DisableProcessing();
+  SyncPoint::GetInstance()->LoadDependency({
+      {"DBImpl::NewIterator:3",
+       "DataVisibilityTest::RangeScanWithoutSnapshot:BeforePut"},
+  });
+  SyncPoint::GetInstance()->EnableProcessing();
+  port::Thread writer_thread([this]() {
+    WriteOptions write_opts;
+    TEST_SYNC_POINT("DataVisibilityTest::RangeScanWithoutSnapshot:BeforePut");
+    for (int i = 0; i < 3; ++i) {
+      std::string write_ts_str = Timestamp(i + 1, 0);
+      Slice write_ts = write_ts_str;
+      write_opts.timestamp = &write_ts;
+      Status s = db_->Put(write_opts, "key" + std::to_string(i),
+                          "value" + std::to_string(i));
+      ASSERT_OK(s);
+    }
+  });
+  std::string read_ts_str = Timestamp(10, 0);
+  Slice read_ts = read_ts_str;
+  ReadOptions read_opts;
+  read_opts.total_order_seek = true;
+  read_opts.timestamp = &read_ts;
+  Iterator* it = db_->NewIterator(read_opts);
+  ASSERT_NE(nullptr, it);
+  writer_thread.join();
+  it->SeekToFirst();
+  ASSERT_FALSE(it->Valid());
+  delete it;
+  Close();
+}
+
+// Application specifies both timestamp and snapshot.
+//       reader         writer
+//       seq=10
+//                      ts'=90
+//       ts=100         seq'=11
+//                      write finishes
+//       scan(ts,seq)
+// <k, t1, s1> can be seen by the scan only if t1<=ts AND s1<=seq. If t1<=ts
+// but s1>seq, then the key should not be returned.
+TEST_F(DataVisibilityTest, RangeScanWithSnapshot) {
+  Options options = CurrentOptions();
+  const size_t kTimestampSize = Timestamp(0, 0).size();
+  TestComparator test_cmp(kTimestampSize);
+  options.comparator = &test_cmp;
+  DestroyAndReopen(options);
+  SyncPoint::GetInstance()->DisableProcessing();
+  SyncPoint::GetInstance()->LoadDependency({
+      {"DataVisibilityTest::RangeScanWithSnapshot:AfterTakingSnapshot",
+       "DataVisibilityTest::RangeScanWithSnapshot:BeforePut"},
+  });
+  SyncPoint::GetInstance()->EnableProcessing();
+  port::Thread writer_thread([this]() {
+    WriteOptions write_opts;
+    TEST_SYNC_POINT("DataVisibilityTest::RangeScanWithSnapshot:BeforePut");
+    for (int i = 0; i < 3; ++i) {
+      std::string write_ts_str = Timestamp(i + 1, 0);
+      Slice write_ts = write_ts_str;
+      write_opts.timestamp = &write_ts;
+      Status s = db_->Put(write_opts, "key" + std::to_string(i),
+                          "value" + std::to_string(i));
+      ASSERT_OK(s);
+    }
+  });
+  const Snapshot* snap = db_->GetSnapshot();
+  TEST_SYNC_POINT(
+      "DataVisibilityTest::RangeScanWithSnapshot:AfterTakingSnapshot");
+
+  writer_thread.join();
+
+  std::string read_ts_str = Timestamp(10, 0);
+  Slice read_ts = read_ts_str;
+  ReadOptions read_opts;
+  read_opts.snapshot = snap;
+  read_opts.total_order_seek = true;
+  read_opts.timestamp = &read_ts;
+  Iterator* it = db_->NewIterator(read_opts);
+  ASSERT_NE(nullptr, it);
+  it->Seek("key0");
+  ASSERT_FALSE(it->Valid());
+
+  delete it;
+  db_->ReleaseSnapshot(snap);
+  Close();
+}
+
 class DBBasicTestWithTimestampCompressionSettings
     : public DBBasicTestWithTimestampBase,
       public testing::WithParamInterface<

db/read_callback.h

@@ -11,7 +11,7 @@ namespace ROCKSDB_NAMESPACE {
 
 class ReadCallback {
  public:
-  ReadCallback(SequenceNumber last_visible_seq)
+  explicit ReadCallback(SequenceNumber last_visible_seq)
       : max_visible_seq_(last_visible_seq) {}
   ReadCallback(SequenceNumber last_visible_seq, SequenceNumber min_uncommitted)
       : max_visible_seq_(last_visible_seq), min_uncommitted_(min_uncommitted) {}