fix Seek with lower_bound

Summary:
When Seek a key less than `lower_bound`, should return `lower_bound`.
ajkr PTAL
Closes https://github.com/facebook/rocksdb/pull/3199

Differential Revision: D6421126

Pulled By: ajkr

fbshipit-source-id: a06c825830573e0040630704f6bcb3f7f48626f7

db/db_iter.cc

@@ -1134,6 +1134,13 @@ void DBIter::Seek(const Slice& target) {
   saved_key_.Clear();
   saved_key_.SetInternalKey(target, sequence_);
 
+  if (iterate_lower_bound_ != nullptr &&
+      user_comparator_->Compare(saved_key_.GetUserKey(),
+                                *iterate_lower_bound_) < 0) {
+    saved_key_.Clear();
+    saved_key_.SetInternalKey(*iterate_lower_bound_, sequence_);
+  }
+
   {
     PERF_TIMER_GUARD(seek_internal_seek_time);
     iter_->Seek(saved_key_.GetInternalKey());
@@ -1177,6 +1184,13 @@ void DBIter::SeekForPrev(const Slice& target) {
   saved_key_.SetInternalKey(target, 0 /* sequence_number */,
                             kValueTypeForSeekForPrev);
 
+  if (iterate_upper_bound_ != nullptr &&
+      user_comparator_->Compare(saved_key_.GetUserKey(),
+                                *iterate_upper_bound_) >= 0) {
+    saved_key_.Clear();
+    saved_key_.SetInternalKey(*iterate_upper_bound_, kMaxSequenceNumber);
+  }
+
   {
     PERF_TIMER_GUARD(seek_internal_seek_time);
     iter_->SeekForPrev(saved_key_.GetInternalKey());

db/db_iter_test.cc

@@ -356,7 +356,7 @@ TEST_F(DBIteratorTest, DBIteratorPrevNext) {
     db_iter->SeekToLast();
 
     ASSERT_TRUE(db_iter->Valid());
-    ASSERT_EQ(static_cast<int>(get_perf_context()->internal_key_skipped_count), 7);
+    ASSERT_EQ(static_cast<int>(get_perf_context()->internal_key_skipped_count), 1);
     ASSERT_EQ(db_iter->key().ToString(), "b");
 
     SetPerfLevel(kDisable);
@@ -475,7 +475,7 @@ TEST_F(DBIteratorTest, DBIteratorPrevNext) {
     db_iter->SeekToLast();
 
     ASSERT_TRUE(db_iter->Valid());
-    ASSERT_EQ(static_cast<int>(get_perf_context()->internal_delete_skipped_count), 1);
+    ASSERT_EQ(static_cast<int>(get_perf_context()->internal_delete_skipped_count), 0);
     ASSERT_EQ(db_iter->key().ToString(), "b");
 
     SetPerfLevel(kDisable);
@@ -2991,6 +2991,33 @@ TEST_F(DBIteratorTest, PrevLowerBound) {
   ASSERT_FALSE(db_iter->Valid());
 }
 
+TEST_F(DBIteratorTest, SeekLessLowerBound) {
+  const int kNumKeys = 3;
+  const int kLowerBound = 2;
+  TestIterator* internal_iter = new TestIterator(BytewiseComparator());
+  for (int j = 1; j <= kNumKeys; ++j) {
+    internal_iter->AddPut(std::to_string(j), "val");
+  }
+  internal_iter->Finish();
+
+  ReadOptions ro;
+  auto lower_bound_str = std::to_string(kLowerBound);
+  Slice lower_bound(lower_bound_str);
+  ro.iterate_lower_bound = &lower_bound;
+  Options options;
+  std::unique_ptr<Iterator> db_iter(NewDBIterator(
+      env_, ro, ImmutableCFOptions(options), BytewiseComparator(),
+      internal_iter, 10 /* sequence */,
+      options.max_sequential_skip_in_iterations, nullptr /* read_callback */));
+
+  auto before_lower_bound_str = std::to_string(kLowerBound - 1);
+  Slice before_lower_bound(lower_bound_str);
+
+  db_iter->Seek(before_lower_bound);
+  ASSERT_TRUE(db_iter->Valid());
+  ASSERT_EQ(lower_bound_str, db_iter->key().ToString());
+}
+
 }  // namespace rocksdb
 
 int main(int argc, char** argv) {

db/db_iterator_test.cc

@@ -2152,8 +2152,8 @@ TEST_F(DBIteratorTest, SkipStatistics) {
   }
   ASSERT_EQ(count, 2);
   delete iter;
-  // 3 deletes + 3 original keys + 2 keys of "b" + lower sequence of "a"
+  // 3 deletes + 3 original keys + lower sequence of "a"
-  skip_count += 9;
+  skip_count += 7;
   ASSERT_EQ(skip_count, TestGetTickerCount(options, NUMBER_ITER_SKIP));
 }