Logically strip timestamp during flush (#11557)

Summary:
Logically strip the user-defined timestamp when L0 files are created during flush when `AdvancedColumnFamilyOptions.persist_user_defined_timestamps` is false. Logically stripping timestamp here means replacing the original user-defined timestamp with a mininum timestamp, which for now is hard coded to be all zeros bytes.

While working on this, I caught a missing piece on the `BlockBuilder` level for this feature. The current quick path `std::min(buffer_size, last_key_size)` needs a bit tweaking to work for this feature. When user-defined timestamp is stripped during block building, on writing first entry or right after resetting, `buffer` is empty and `buffer_size` is zero as usual. However, in follow-up writes, depending on the size of the stripped user-defined timestamp, and the size of the value, what's in `buffer` can sometimes be smaller than `last_key_size`, leading `std::min(buffer_size, last_key_size)` to truncate the `last_key`. Previous test doesn't caught the bug because in those tests, the size of the stripped user-defined timestamps bytes is smaller than the length of the value. In order to avoid the conditional operation, this PR changed the original trivial `std::min` operation into an arithmetic operation. Since this is a change in a hot and performance critical path, I did the following benchmark to check no observable regression is introduced.
```TEST_TMPDIR=/dev/shm/rocksdb1 ./db_bench -benchmarks=fillseq -memtablerep=vector -allow_concurrent_memtable_write=false -num=50000000```
Compiled with DEBUG_LEVEL=0
Test vs. control runs simulaneous for better accuracy, units = ops/sec
                       PR  vs base:
Round 1: 350652 vs 349055
Round 2: 365733 vs 364308
Round 3: 355681 vs 354475

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11557

Test Plan:
New timestamp specific test added or existing tests augmented, both are parameterized with `UserDefinedTimestampTestMode`:
`UserDefinedTimestampTestMode::kNormal` -> UDT feature enabled, write / read with min timestamp
`UserDefinedTimestampTestMode::kStripUserDefinedTimestamps` -> UDT feature enabled, write / read with min timestamp, set Options.persist_user_defined_timestamps to false.

```
make all check
./db_wal_test --gtest_filter="*WithTimestamp*"
./flush_job_test --gtest_filter="*WithTimestamp*"
./repair_test --gtest_filter="*WithTimestamp*"
./block_based_table_reader_test
```

Reviewed By: pdillinger

Differential Revision: D47027664

Pulled By: jowlyzhang

fbshipit-source-id: e729193b6334dfc63aaa736d684d907a022571f5

db/builder.cc

@@ -15,6 +15,7 @@
 
 #include "db/blob/blob_file_builder.h"
 #include "db/compaction/compaction_iterator.h"
+#include "db/dbformat.h"
 #include "db/event_helpers.h"
 #include "db/internal_stats.h"
 #include "db/merge_helper.h"
@@ -205,21 +206,38 @@ Status BuildTable(
         /*compaction=*/nullptr, compaction_filter.get(),
         /*shutting_down=*/nullptr, db_options.info_log, full_history_ts_low);
 
+    const size_t ts_sz = ucmp->timestamp_size();
+    const bool strip_timestamp =
+        ts_sz > 0 && !ioptions.persist_user_defined_timestamps;
+
+    std::string key_after_flush_buf;
     c_iter.SeekToFirst();
     for (; c_iter.Valid(); c_iter.Next()) {
       const Slice& key = c_iter.key();
       const Slice& value = c_iter.value();
       const ParsedInternalKey& ikey = c_iter.ikey();
+      Slice key_after_flush = key;
+      // If user defined timestamps will be stripped from user key after flush,
+      // the in memory version of the key act logically the same as one with a
+      // minimum timestamp. We update the timestamp here so file boundary and
+      // output validator, block builder all see the effect of the stripping.
+      if (strip_timestamp) {
+        key_after_flush_buf.clear();
+        ReplaceInternalKeyWithMinTimestamp(&key_after_flush_buf, key, ts_sz);
+        key_after_flush = key_after_flush_buf;
+      }
+
       //  Generate a rolling 64-bit hash of the key and values
       //  Note :
       //  Here "key" integrates 'sequence_number'+'kType'+'user key'.
-      s = output_validator.Add(key, value);
+      s = output_validator.Add(key_after_flush, value);
       if (!s.ok()) {
         break;
       }
-      builder->Add(key, value);
+      builder->Add(key_after_flush, value);
 
-      s = meta->UpdateBoundaries(key, value, ikey.sequence, ikey.type);
+      s = meta->UpdateBoundaries(key_after_flush, value, ikey.sequence,
+                                 ikey.type);
       if (!s.ok()) {
         break;
       }
@@ -244,6 +262,7 @@ Status BuildTable(
            range_del_it->Next()) {
         auto tombstone = range_del_it->Tombstone();
         auto kv = tombstone.Serialize();
+        // TODO(yuzhangyu): handle range deletion for UDT in memtables only.
         builder->Add(kv.first.Encode(), kv.second);
         InternalKey tombstone_end = tombstone.SerializeEndKey();
         meta->UpdateBoundariesForRange(kv.first, tombstone_end, tombstone.seq_,
@@ -354,6 +373,8 @@ Status BuildTable(
       s = *io_status;
     }
 
+    // TODO(yuzhangyu): handle the key copy in the blob when ts should be
+    // stripped.
     if (blob_file_builder) {
       if (s.ok()) {
         s = blob_file_builder->Finish();

db/db_wal_test.cc

@@ -311,7 +311,9 @@ TEST_F(DBWALTest, Recover) {
   } while (ChangeWalOptions());
 }
 
-class DBWALTestWithTimestamp : public DBBasicTestWithTimestampBase {
+class DBWALTestWithTimestamp
+    : public DBBasicTestWithTimestampBase,
+      public testing::WithParamInterface<test::UserDefinedTimestampTestMode> {
  public:
   DBWALTestWithTimestamp()
       : DBBasicTestWithTimestampBase("db_wal_test_with_timestamp") {}
@@ -401,6 +403,54 @@ TEST_F(DBWALTestWithTimestamp, RecoverInconsistentTimestamp) {
       ReopenColumnFamiliesWithTs({"pikachu"}, ts_options).IsInvalidArgument());
 }
 
+TEST_P(DBWALTestWithTimestamp, RecoverAndFlush) {
+  // Set up the option that enables user defined timestmp size.
+  std::string min_ts = Timestamp(0, 0);
+  std::string write_ts = Timestamp(1, 0);
+  const size_t kTimestampSize = write_ts.size();
+  TestComparator test_cmp(kTimestampSize);
+  Options ts_options;
+  ts_options.create_if_missing = true;
+  ts_options.comparator = &test_cmp;
+  bool persist_udt = test::ShouldPersistUDT(GetParam());
+  ts_options.persist_user_defined_timestamps = persist_udt;
+
+  std::string smallest_ukey_without_ts = "baz";
+  std::string largest_ukey_without_ts = "foo";
+
+  ASSERT_OK(CreateAndReopenWithCFWithTs({"pikachu"}, ts_options));
+  ASSERT_OK(Put(1, largest_ukey_without_ts, write_ts, "v1"));
+  ASSERT_OK(Put(1, smallest_ukey_without_ts, write_ts, "v5"));
+
+  // Very small write buffer size to force flush memtables recovered from WAL.
+  ts_options.write_buffer_size = 16;
+  ts_options.arena_block_size = 16;
+  ASSERT_OK(ReopenColumnFamiliesWithTs({"pikachu"}, ts_options));
+  ASSERT_EQ(GetNumberOfSstFilesForColumnFamily(db_, "pikachu"),
+            static_cast<uint64_t>(1));
+
+  std::vector<std::vector<FileMetaData>> level_to_files;
+  dbfull()->TEST_GetFilesMetaData(handles_[1], &level_to_files);
+  ASSERT_GT(level_to_files.size(), 1);
+  // L0 only has one SST file.
+  ASSERT_EQ(level_to_files[0].size(), 1);
+  auto meta = level_to_files[0][0];
+  if (persist_udt) {
+    ASSERT_EQ(smallest_ukey_without_ts + write_ts, meta.smallest.user_key());
+    ASSERT_EQ(largest_ukey_without_ts + write_ts, meta.largest.user_key());
+  } else {
+    ASSERT_EQ(smallest_ukey_without_ts + min_ts, meta.smallest.user_key());
+    ASSERT_EQ(largest_ukey_without_ts + min_ts, meta.largest.user_key());
+  }
+}
+
+// Param 0: test mode for the user-defined timestamp feature
+INSTANTIATE_TEST_CASE_P(
+    RecoverAndFlush, DBWALTestWithTimestamp,
+    ::testing::Values(
+        test::UserDefinedTimestampTestMode::kStripUserDefinedTimestamp,
+        test::UserDefinedTimestampTestMode::kNormal));
+
 TEST_F(DBWALTest, RecoverWithTableHandle) {
   do {
     Options options = CurrentOptions();

db/dbformat.cc

@@ -120,6 +120,16 @@ void StripTimestampFromInternalKey(std::string* result, const Slice& key,
                  kNumInternalBytes);
 }
 
+void ReplaceInternalKeyWithMinTimestamp(std::string* result, const Slice& key,
+                                        size_t ts_sz) {
+  const size_t key_sz = key.size();
+  assert(key_sz >= ts_sz + kNumInternalBytes);
+  result->reserve(key_sz);
+  result->append(key.data(), key_sz - kNumInternalBytes - ts_sz);
+  result->append(ts_sz, static_cast<unsigned char>(0));
+  result->append(key.data() + key_sz - kNumInternalBytes, kNumInternalBytes);
+}
+
 std::string ParsedInternalKey::DebugString(bool log_err_key, bool hex) const {
   std::string result = "'";
   if (log_err_key) {

db/dbformat.h

@@ -168,51 +168,57 @@ inline void UnPackSequenceAndType(uint64_t packed, uint64_t* seq,
 EntryType GetEntryType(ValueType value_type);
 
 // Append the serialization of "key" to *result.
-extern void AppendInternalKey(std::string* result,
-                              const ParsedInternalKey& key);
+void AppendInternalKey(std::string* result, const ParsedInternalKey& key);
 
 // Append the serialization of "key" to *result, replacing the original
 // timestamp with argument ts.
-extern void AppendInternalKeyWithDifferentTimestamp(
-    std::string* result, const ParsedInternalKey& key, const Slice& ts);
+void AppendInternalKeyWithDifferentTimestamp(std::string* result,
+                                             const ParsedInternalKey& key,
+                                             const Slice& ts);
 
 // Serialized internal key consists of user key followed by footer.
 // This function appends the footer to *result, assuming that *result already
 // contains the user key at the end.
-extern void AppendInternalKeyFooter(std::string* result, SequenceNumber s,
+void AppendInternalKeyFooter(std::string* result, SequenceNumber s,
                              ValueType t);
 
 // Append the key and a minimal timestamp to *result
-extern void AppendKeyWithMinTimestamp(std::string* result, const Slice& key,
+void AppendKeyWithMinTimestamp(std::string* result, const Slice& key,
                                size_t ts_sz);
 
 // Append the key and a maximal timestamp to *result
-extern void AppendKeyWithMaxTimestamp(std::string* result, const Slice& key,
+void AppendKeyWithMaxTimestamp(std::string* result, const Slice& key,
                                size_t ts_sz);
 
 // `key` is a user key with timestamp. Append the user key without timestamp
 // and the maximal timestamp to *result.
-extern void AppendUserKeyWithMaxTimestamp(std::string* result, const Slice& key,
+void AppendUserKeyWithMaxTimestamp(std::string* result, const Slice& key,
                                    size_t ts_sz);
 
 // `key` is an internal key containing a user key without timestamp. Create a
 // new key in *result by padding a min timestamp of size `ts_sz` to the user key
 // and copying the remaining internal key bytes.
-extern void PadInternalKeyWithMinTimestamp(std::string* result,
-                                           const Slice& key, size_t ts_sz);
+void PadInternalKeyWithMinTimestamp(std::string* result, const Slice& key,
+                                    size_t ts_sz);
 
 // `key` is an internal key containing a user key with timestamp of size
 // `ts_sz`. Create a new internal key in *result by stripping the timestamp from
 // the user key and copying the remaining internal key bytes.
-extern void StripTimestampFromInternalKey(std::string* result, const Slice& key,
+void StripTimestampFromInternalKey(std::string* result, const Slice& key,
+                                   size_t ts_sz);
+
+// `key` is an internal key containing a user key with timestamp of size
+// `ts_sz`. Create a new internal key in *result while replace the original
+// timestamp with min timestamp.
+void ReplaceInternalKeyWithMinTimestamp(std::string* result, const Slice& key,
                                         size_t ts_sz);
 
 // Attempt to parse an internal key from "internal_key".  On success,
 // stores the parsed data in "*result", and returns true.
 //
 // On error, returns false, leaves "*result" in an undefined state.
-extern Status ParseInternalKey(const Slice& internal_key,
-                               ParsedInternalKey* result, bool log_err_key);
+Status ParseInternalKey(const Slice& internal_key, ParsedInternalKey* result,
+                        bool log_err_key);
 
 // Returns the user key portion of an internal key.
 inline Slice ExtractUserKey(const Slice& internal_key) {
@@ -783,8 +789,7 @@ class InternalKeySliceTransform : public SliceTransform {
 // Read the key of a record from a write batch.
 // if this record represent the default column family then cf_record
 // must be passed as false, otherwise it must be passed as true.
-extern bool ReadKeyFromWriteBatchEntry(Slice* input, Slice* key,
-                                       bool cf_record);
+bool ReadKeyFromWriteBatchEntry(Slice* input, Slice* key, bool cf_record);
 
 // Read record from a write batch piece from input.
 // tag, column_family, key, value and blob are return values. Callers own the
@@ -793,7 +798,7 @@ extern bool ReadKeyFromWriteBatchEntry(Slice* input, Slice* key,
 // input will be advanced to after the record.
 // If user-defined timestamp is enabled for a column family, then the `key`
 // resulting from this call will include timestamp.
-extern Status ReadRecordFromWriteBatch(Slice* input, char* tag,
+Status ReadRecordFromWriteBatch(Slice* input, char* tag,
                                 uint32_t* column_family, Slice* key,
                                 Slice* value, Slice* blob, Slice* xid);
 

db/dbformat_test.cc

@@ -312,6 +312,27 @@ TEST_F(FormatTest, StripTimestampFromInternalKey) {
   ASSERT_EQ(kTypeValue, key_without_timestamp.type);
 }
 
+TEST_F(FormatTest, ReplaceInternalKeyWithMinTimestamp) {
+  std::string orig_user_key = "foo";
+  size_t ts_sz = 8;
+  orig_user_key.append(ts_sz, static_cast<unsigned char>(1));
+  std::string orig_internal_key = IKey(orig_user_key, 100, kTypeValue);
+
+  std::string key_buf;
+  ReplaceInternalKeyWithMinTimestamp(&key_buf, orig_internal_key, ts_sz);
+  ParsedInternalKey new_key;
+  Slice in(key_buf);
+  ASSERT_OK(ParseInternalKey(in, &new_key, true /*log_err_key*/));
+
+  std::string min_timestamp(ts_sz, static_cast<unsigned char>(0));
+  size_t ukey_diff_offset = new_key.user_key.difference_offset(orig_user_key);
+  ASSERT_EQ(min_timestamp,
+            Slice(new_key.user_key.data() + ukey_diff_offset, ts_sz));
+  ASSERT_EQ(orig_user_key.size(), new_key.user_key.size());
+  ASSERT_EQ(100, new_key.sequence);
+  ASSERT_EQ(kTypeValue, new_key.type);
+}
+
 }  // namespace ROCKSDB_NAMESPACE
 
 int main(int argc, char** argv) {

db/flush_job_test.cc

@@ -117,6 +117,8 @@ class FlushJobTestBase : public testing::Test {
     db_options_.statistics = CreateDBStatistics();
 
     cf_options_.comparator = ucmp_;
+    cf_options_.persist_user_defined_timestamps = persist_udt_;
+    cf_options_.paranoid_file_checks = paranoid_file_checks_;
 
     std::vector<ColumnFamilyDescriptor> column_families;
     cf_options_.table_factory = mock_table_factory_;
@@ -149,6 +151,9 @@ class FlushJobTestBase : public testing::Test {
   std::atomic<bool> shutting_down_;
   std::shared_ptr<mock::MockTableFactory> mock_table_factory_;
 
+  bool persist_udt_ = true;
+  bool paranoid_file_checks_ = false;
+
   SeqnoToTimeMapping empty_seqno_to_time_mapping_;
 };
 
@@ -600,7 +605,13 @@ TEST_F(FlushJobTest, GetRateLimiterPriorityForWrite) {
   }
 }
 
-class FlushJobTimestampTest : public FlushJobTestBase {
+// Test parameters:
+// param 0): paranoid file check
+// param 1): user-defined timestamp test mode
+class FlushJobTimestampTest
+    : public FlushJobTestBase,
+      public testing::WithParamInterface<
+          std::tuple<bool, test::UserDefinedTimestampTestMode>> {
  public:
   FlushJobTimestampTest()
       : FlushJobTestBase(test::PerThreadDBPath("flush_job_ts_gc_test"),
@@ -616,13 +627,36 @@ class FlushJobTimestampTest : public FlushJobTestBase {
   }
 
  protected:
+  void SetUp() override {
+    paranoid_file_checks_ = std::get<0>(GetParam());
+    auto udt_test_mode = std::get<1>(GetParam());
+    persist_udt_ = test::ShouldPersistUDT(udt_test_mode);
+    FlushJobTestBase::SetUp();
+  }
   static constexpr uint64_t kStartTs = 10;
   static constexpr SequenceNumber kStartSeq = 0;
   SequenceNumber curr_seq_{kStartSeq};
   std::atomic<uint64_t> curr_ts_{kStartTs};
+
+  void CheckFileMetaData(ColumnFamilyData* cfd,
+                         const InternalKey& expected_smallest,
+                         const InternalKey& expected_largest,
+                         const FileMetaData* meta_from_flush) const {
+    ASSERT_EQ(expected_smallest.Encode(), meta_from_flush->smallest.Encode());
+    ASSERT_EQ(expected_largest.Encode(), meta_from_flush->largest.Encode());
+
+    const VersionStorageInfo* storage_info = cfd->current()->storage_info();
+    const std::vector<FileMetaData*>& l0_files = storage_info->LevelFiles(0);
+
+    ASSERT_EQ(l0_files.size(), 1);
+    auto installed_file_meta = l0_files[0];
+    ASSERT_EQ(expected_smallest.Encode(),
+              installed_file_meta->smallest.Encode());
+    ASSERT_EQ(expected_largest.Encode(), installed_file_meta->largest.Encode());
+  }
 };
 
-TEST_F(FlushJobTimestampTest, AllKeysExpired) {
+TEST_P(FlushJobTimestampTest, AllKeysExpired) {
   ColumnFamilyData* cfd = versions_->GetColumnFamilySet()->GetDefault();
   autovector<MemTable*> to_delete;
 
@@ -669,17 +703,24 @@ TEST_F(FlushJobTimestampTest, AllKeysExpired) {
 
   {
     std::string key = test::EncodeInt(0);
+    if (!persist_udt_) {
+      // When `AdvancedColumnFamilyOptions.persist_user_defined_timestamps` flag
+      // is set to false. The user-defined timestamp is stripped from user key
+      // during flush, making the user key logically containing the minimum
+      // timestamp.
+      key.append(test::EncodeInt(0));
+    } else {
       key.append(test::EncodeInt(curr_ts_.load(std::memory_order_relaxed) - 1));
+    }
     InternalKey ikey(key, curr_seq_ - 1, ValueType::kTypeDeletionWithTimestamp);
-    ASSERT_EQ(ikey.Encode(), fmeta.smallest.Encode());
-    ASSERT_EQ(ikey.Encode(), fmeta.largest.Encode());
+    CheckFileMetaData(cfd, ikey, ikey, &fmeta);
   }
 
   job_context.Clean();
   ASSERT_TRUE(to_delete.empty());
 }
 
-TEST_F(FlushJobTimestampTest, NoKeyExpired) {
+TEST_P(FlushJobTimestampTest, NoKeyExpired) {
   ColumnFamilyData* cfd = versions_->GetColumnFamilySet()->GetDefault();
   autovector<MemTable*> to_delete;
 
@@ -722,18 +763,38 @@ TEST_F(FlushJobTimestampTest, NoKeyExpired) {
 
   {
     std::string ukey = test::EncodeInt(0);
-    std::string smallest_key =
+    std::string smallest_key;
+    std::string largest_key;
+    if (!persist_udt_) {
+      // When `AdvancedColumnFamilyOptions.persist_user_defined_timestamps` flag
+      // is set to false. The user-defined timestamp is stripped from user key
+      // during flush, making the user key logically containing the minimum
+      // timestamp, which is hardcoded to be all zeros for now.
+      smallest_key = ukey + test::EncodeInt(0);
+      largest_key = ukey + test::EncodeInt(0);
+    } else {
+      smallest_key =
           ukey + test::EncodeInt(curr_ts_.load(std::memory_order_relaxed) - 1);
-    std::string largest_key = ukey + test::EncodeInt(kStartTs);
+      largest_key = ukey + test::EncodeInt(kStartTs);
+    }
     InternalKey smallest(smallest_key, curr_seq_ - 1, ValueType::kTypeValue);
     InternalKey largest(largest_key, kStartSeq, ValueType::kTypeValue);
-    ASSERT_EQ(smallest.Encode(), fmeta.smallest.Encode());
-    ASSERT_EQ(largest.Encode(), fmeta.largest.Encode());
+    CheckFileMetaData(cfd, smallest, largest, &fmeta);
   }
   job_context.Clean();
   ASSERT_TRUE(to_delete.empty());
 }
 
+// Param 0: paranoid file check
+// Param 1: test mode for the user-defined timestamp feature
+INSTANTIATE_TEST_CASE_P(
+    FlushJobTimestampTest, FlushJobTimestampTest,
+    ::testing::Combine(
+        ::testing::Bool(),
+        ::testing::Values(
+            test::UserDefinedTimestampTestMode::kStripUserDefinedTimestamp,
+            test::UserDefinedTimestampTestMode::kNormal)));
+
 }  // namespace ROCKSDB_NAMESPACE
 
 int main(int argc, char** argv) {

db/repair_test.cc

@@ -315,7 +315,13 @@ TEST_F(RepairTest, UnflushedSst) {
   ASSERT_EQ(Get("key"), "val");
 }
 
-class RepairTestWithTimestamp : public DBBasicTestWithTimestampBase {
+// Test parameters:
+// param 0): paranoid file check
+// param 1): user-defined timestamp test mode
+class RepairTestWithTimestamp
+    : public DBBasicTestWithTimestampBase,
+      public testing::WithParamInterface<
+          std::tuple<bool, test::UserDefinedTimestampTestMode>> {
  public:
   RepairTestWithTimestamp()
       : DBBasicTestWithTimestampBase("repair_test_with_timestamp") {}
@@ -326,23 +332,46 @@ class RepairTestWithTimestamp : public DBBasicTestWithTimestampBase {
   }
 
   void CheckGet(const ReadOptions& read_opts, const Slice& key,
-                const std::string& expected_value) {
+                const std::string& expected_value,
+                const std::string& expected_ts) {
     std::string actual_value;
-    ASSERT_OK(db_->Get(read_opts, handles_[0], key, &actual_value));
+    std::string actual_ts;
+    ASSERT_OK(db_->Get(read_opts, handles_[0], key, &actual_value, &actual_ts));
     ASSERT_EQ(expected_value, actual_value);
+    ASSERT_EQ(expected_ts, actual_ts);
+  }
+
+  void CheckFileBoundaries(const Slice& smallest_user_key,
+                           const Slice& largest_user_key) {
+    std::vector<std::vector<FileMetaData>> level_to_files;
+    dbfull()->TEST_GetFilesMetaData(dbfull()->DefaultColumnFamily(),
+                                    &level_to_files);
+    ASSERT_GT(level_to_files.size(), 1);
+    // L0 only has one SST file.
+    ASSERT_EQ(level_to_files[0].size(), 1);
+    auto file_meta = level_to_files[0][0];
+    ASSERT_EQ(smallest_user_key, file_meta.smallest.user_key());
+    ASSERT_EQ(largest_user_key, file_meta.largest.user_key());
   }
 };
 
-TEST_F(RepairTestWithTimestamp, UnflushedSst) {
+TEST_P(RepairTestWithTimestamp, UnflushedSst) {
   Destroy(last_options_);
 
+  bool paranoid_file_checks = std::get<0>(GetParam());
+  bool persist_udt = test::ShouldPersistUDT(std::get<1>(GetParam()));
+  std::string smallest_ukey_without_ts = "bar";
+  std::string largest_ukey_without_ts = "foo";
   Options options = CurrentOptions();
   options.env = env_;
   options.create_if_missing = true;
-  std::string ts = Timestamp(0, 0);
-  const size_t kTimestampSize = ts.size();
+  std::string min_ts = Timestamp(0, 0);
+  std::string write_ts = Timestamp(1, 0);
+  const size_t kTimestampSize = write_ts.size();
   TestComparator test_cmp(kTimestampSize);
   options.comparator = &test_cmp;
+  options.persist_user_defined_timestamps = persist_udt;
+  options.paranoid_file_checks = paranoid_file_checks;
 
   ColumnFamilyOptions cf_options(options);
   std::vector<ColumnFamilyDescriptor> column_families;
@@ -351,7 +380,10 @@ TEST_F(RepairTestWithTimestamp, UnflushedSst) {
 
   ASSERT_OK(DB::Open(options, dbname_, column_families, &handles_, &db_));
 
-  ASSERT_OK(Put("key", ts, "val"));
+  ASSERT_OK(Put(smallest_ukey_without_ts, write_ts,
+                smallest_ukey_without_ts + ":val"));
+  ASSERT_OK(
+      Put(largest_ukey_without_ts, write_ts, largest_ukey_without_ts + ":val"));
   VectorLogPtr wal_files;
   ASSERT_OK(dbfull()->GetSortedWalFiles(wal_files));
   ASSERT_EQ(wal_files.size(), 1);
@@ -381,12 +413,46 @@ TEST_F(RepairTestWithTimestamp, UnflushedSst) {
     ASSERT_GT(total_ssts_size, 0);
   }
 
+  // Check file boundaries are correct for different
+  // `persist_user_defined_timestamps` option values.
+  if (persist_udt) {
+    CheckFileBoundaries(smallest_ukey_without_ts + write_ts,
+                        largest_ukey_without_ts + write_ts);
+  } else {
+    CheckFileBoundaries(smallest_ukey_without_ts + min_ts,
+                        largest_ukey_without_ts + min_ts);
+  }
+
   ReadOptions read_opts;
-  Slice read_ts_slice = ts;
+  Slice read_ts_slice = write_ts;
   read_opts.timestamp = &read_ts_slice;
-  CheckGet(read_opts, "key", "val");
+  if (persist_udt) {
+    CheckGet(read_opts, smallest_ukey_without_ts,
+             smallest_ukey_without_ts + ":val", write_ts);
+    CheckGet(read_opts, largest_ukey_without_ts,
+             largest_ukey_without_ts + ":val", write_ts);
+  } else {
+    // TODO(yuzhangyu): currently when `persist_user_defined_timestamps` is
+    //  false, ts is unconditionally stripped during flush.
+    //  When `full_history_ts_low` is set and respected during flush.
+    //  We should prohibit reading below `full_history_ts_low` all together.
+    CheckGet(read_opts, smallest_ukey_without_ts,
+             smallest_ukey_without_ts + ":val", min_ts);
+    CheckGet(read_opts, largest_ukey_without_ts,
+             largest_ukey_without_ts + ":val", min_ts);
+  }
 }
 
+// Param 0: paranoid file check
+// Param 1: test mode for the user-defined timestamp feature
+INSTANTIATE_TEST_CASE_P(
+    UnflushedSst, RepairTestWithTimestamp,
+    ::testing::Combine(
+        ::testing::Bool(),
+        ::testing::Values(
+            test::UserDefinedTimestampTestMode::kStripUserDefinedTimestamp,
+            test::UserDefinedTimestampTestMode::kNormal)));
+
 TEST_F(RepairTest, SeparateWalDir) {
   do {
     Options options = CurrentOptions();

include/rocksdb/advanced_options.h

@@ -1120,11 +1120,30 @@ struct AdvancedColumnFamilyOptions {
   //
   // When it's false, the user-defined timestamps will be removed from the user
   // keys when data is flushed from memtables to SST files. Other places that
-  // user keys can be persisted like WAL and blob files go through a similar
-  // process. Users should call `DB::IncreaseFullHistoryTsLow` to set a cutoff
-  // timestamp. RocksDB refrains from flushing a memtable with data still above
-  // the cutoff timestamp with best effort. When users try to read below the
-  // cutoff timestamp, an error will be returned.
+  // user keys can be persisted like file boundaries in file metadata and blob
+  // files go through a similar process. There are two major motivations
+  // for this flag:
+  // 1) backward compatibility: if the user later decides to
+  // disable the user-defined timestamp feature for the column family, these SST
+  // files can be handled by a user comparator that is not aware of user-defined
+  // timestamps.
+  // 2) enable user-defined timestamp feature for an existing column family
+  // while set this flag to be `false`: user keys in the newly generated SST
+  // files are of the same format as the existing SST files.
+  //
+  // When setting this flag to `false`, users should also call
+  // `DB::IncreaseFullHistoryTsLow` to set a cutoff timestamp for flush. RocksDB
+  // refrains from flushing a memtable with data still above
+  // the cutoff timestamp with best effort. Users can do user-defined
+  // multi-versioned read above the cutoff timestamp. When users try to read
+  // below the cutoff timestamp, an error will be returned.
+  //
+  // Note that if WAL is enabled, unlike SST files, user-defined timestamps are
+  // persisted to WAL even if this flag is set to `false`. The benefit of this
+  // is that user-defined timestamps can be recovered with the caveat that users
+  // should flush all memtables so there is no active WAL files before doing a
+  // downgrade or toggling on / off the user-defined timestamp feature on a
+  // column family.
   //
   // Default: true (user-defined timestamps are persisted)
   // Not dynamically changeable, change it requires db restart and

table/block_based/block_builder.cc

@@ -53,8 +53,7 @@ BlockBuilder::BlockBuilder(
     : block_restart_interval_(block_restart_interval),
       use_delta_encoding_(use_delta_encoding),
       use_value_delta_encoding_(use_value_delta_encoding),
-      ts_sz_(ts_sz),
-      persist_user_defined_timestamps_(persist_user_defined_timestamps),
+      strip_ts_sz_(persist_user_defined_timestamps ? 0 : ts_sz),
       is_user_key_(is_user_key),
       restarts_(1, 0),  // First restart point is at offset 0
       counter_(0),
@@ -100,8 +99,8 @@ size_t BlockBuilder::EstimateSizeAfterKV(const Slice& key,
   // Note: this is an imprecise estimate as it accounts for the whole key size
   // instead of non-shared key size.
   estimate += key.size();
-  if (ts_sz_ > 0 && !persist_user_defined_timestamps_) {
-    estimate -= ts_sz_;
+  if (strip_ts_sz_ > 0) {
+    estimate -= strip_ts_sz_;
   }
   // In value delta encoding we estimate the value delta size as half the full
   // value size since only the size field of block handle is encoded.
@@ -175,13 +174,13 @@ void BlockBuilder::AddWithLastKey(const Slice& key, const Slice& value,
   // or Reset. This is more convenient for the caller and we can be more
   // clever inside BlockBuilder. On this hot code path, we want to avoid
   // conditional jumps like `buffer_.empty() ? ... : ...` so we can use a
-  // fast min operation instead, with an assertion to be sure our logic is
-  // sound.
+  // fast arithmetic operation instead, with an assertion to be sure our logic
+  // is sound.
   size_t buffer_size = buffer_.size();
   size_t last_key_size = last_key_param.size();
-  assert(buffer_size == 0 || buffer_size >= last_key_size);
+  assert(buffer_size == 0 || buffer_size >= last_key_size - strip_ts_sz_);
 
-  Slice last_key(last_key_param.data(), std::min(buffer_size, last_key_size));
+  Slice last_key(last_key_param.data(), last_key_size * (buffer_size > 0));
 
   AddWithLastKeyImpl(key, value, last_key, delta_value, buffer_size);
 }
@@ -255,11 +254,11 @@ inline void BlockBuilder::AddWithLastKeyImpl(const Slice& key,
 const Slice BlockBuilder::MaybeStripTimestampFromKey(std::string* key_buf,
                                                      const Slice& key) {
   Slice stripped_key = key;
-  if (ts_sz_ > 0 && !persist_user_defined_timestamps_) {
+  if (strip_ts_sz_ > 0) {
     if (is_user_key_) {
-      stripped_key.remove_suffix(ts_sz_);
+      stripped_key.remove_suffix(strip_ts_sz_);
     } else {
-      StripTimestampFromInternalKey(key_buf, key, ts_sz_);
+      StripTimestampFromInternalKey(key_buf, key, strip_ts_sz_);
       stripped_key = *key_buf;
     }
   }

table/block_based/block_builder.h

@@ -94,11 +94,10 @@ class BlockBuilder {
   const bool use_delta_encoding_;
   // Refer to BlockIter::DecodeCurrentValue for format of delta encoded values
   const bool use_value_delta_encoding_;
-  // Size in bytes for the user-defined timestamp in a user key.
-  const size_t ts_sz_;
-  // Whether the user-defined timestamp part in user keys should be persisted.
-  // If false, it will be stripped from the key before it's encoded.
-  const bool persist_user_defined_timestamps_;
+  // Size in bytes for the user-defined timestamp to strip in a user key.
+  // This is non-zero if there is user-defined timestamp in the user key and it
+  // should not be persisted.
+  const size_t strip_ts_sz_;
   // Whether the keys provided to build this block are user keys. If not,
   // the keys are internal keys. This will affect how timestamp stripping is
   // done for the key if `persisted_user_defined_timestamps_` is false and