Remove the contstaint that iterator upper bound needs to be within a prefix

Summary: There is a check to fail the iterator if prefix extractor is specified but upper bound is out of the prefix for the seek key. Relax this constraint to allow users to set upper bound to the next prefix of the current one.

Test Plan: make commit-prereq

Reviewers: igor, anthony, kradhakrishnan, yhchiang, rven

Reviewed By: rven

Subscribers: tnovak, leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D44949

db/db_iter.cc

@@ -625,21 +625,6 @@ void DBIter::FindParseableKey(ParsedInternalKey* ikey, Direction direction) {
 
 void DBIter::Seek(const Slice& target) {
   StopWatch sw(env_, statistics_, DB_SEEK);
-
-  // total ordering is not guaranteed if prefix_extractor is set
-  // hence prefix based seeks will not give correct results
-  if (iterate_upper_bound_ != nullptr && prefix_extractor_ != nullptr) {
-    if (!prefix_extractor_->InDomain(*iterate_upper_bound_) ||
-        !prefix_extractor_->InDomain(target) ||
-        prefix_extractor_->Transform(*iterate_upper_bound_).compare(
-          prefix_extractor_->Transform(target)) != 0) {
-      status_ = Status::InvalidArgument("read_options.iterate_*_bound "
-                  " and seek target need to have the same prefix.");
-      valid_ = false;
-      return;
-    }
-  }
-
   saved_key_.Clear();
   // now savved_key is used to store internal key.
   saved_key_.SetInternalKey(target, sequence_);

db/db_test.cc

@@ -5844,15 +5844,22 @@ TEST_F(DBTest, DBIteratorBoundTest) {
   // This should be an error
   {
     ReadOptions ro;
-    Slice prefix("g1");
-    ro.iterate_upper_bound = &prefix;
+    Slice upper_bound("g");
+    ro.iterate_upper_bound = &upper_bound;
 
     std::unique_ptr<Iterator> iter(db_->NewIterator(ro));
 
     iter->Seek("foo");
 
+    ASSERT_TRUE(iter->Valid());
+    ASSERT_EQ("foo", iter->key().ToString());
+
+    iter->Next();
+    ASSERT_TRUE(iter->Valid());
+    ASSERT_EQ("foo1", iter->key().ToString());
+
+    iter->Next();
     ASSERT_TRUE(!iter->Valid());
-    ASSERT_TRUE(iter->status().IsInvalidArgument());
   }
 
   // testing that iterate_upper_bound prevents iterating over deleted items