Fix data block upper bound checking for iterator reseek case (facebook#5883)

Summary:
When an iterator reseek happens with the user specifying a new iterate_upper_bound in ReadOptions, and the new seek position is at the end of the same data block, the Seek() ends up using a stale value of data_block_within_upper_bound_ and may return incorrect results.
Pull Request resolved: facebook#5883

Test Plan: Added a new test case DBIteratorTest.IterReseekNewUpperBound. Verified that it failed due to the assertion failure without the fix, and passes with the fix.

Differential Revision: D17752740

Pulled By: anand1976

fbshipit-source-id: f9b635ff5d6aeb0e1bef102cf8b2f900efd378e3

Author: anand76

db/db_iterator_test.cc

@@ -182,6 +182,33 @@ TEST_P(DBIteratorTest, IterSeekBeforePrev) {
   delete iter;
 }
 
+TEST_P(DBIteratorTest, IterReseekNewUpperBound) {
+  Random rnd(301);
+  Options options = CurrentOptions();
+  BlockBasedTableOptions table_options;
+  table_options.block_size = 1024;
+  table_options.block_size_deviation = 50;
+  options.table_factory.reset(NewBlockBasedTableFactory(table_options));
+  options.compression = kNoCompression;
+  Reopen(options);
+
+  ASSERT_OK(Put("a", RandomString(&rnd, 400)));
+  ASSERT_OK(Put("aabb", RandomString(&rnd, 400)));
+  ASSERT_OK(Put("aaef", RandomString(&rnd, 400)));
+  ASSERT_OK(Put("b", RandomString(&rnd, 400)));
+  dbfull()->Flush(FlushOptions());
+  ReadOptions opts;
+  Slice ub = Slice("aa");
+  opts.iterate_upper_bound = &ub;
+  auto iter = NewIterator(opts);
+  iter->Seek(Slice("a"));
+  ub = Slice("b");
+  iter->Seek(Slice("aabc"));
+  ASSERT_TRUE(iter->Valid());
+  ASSERT_EQ(iter->key().ToString(), "aaef");
+  delete iter;
+}
+
 TEST_P(DBIteratorTest, IterSeekForPrevBeforeNext) {
   ASSERT_OK(Put("a", "b"));
   ASSERT_OK(Put("c", "d"));

table/block_based/block_based_table_reader.cc

@@ -2706,11 +2706,21 @@ void BlockBasedTableIterator<TBlockIter, TValue>::SeekImpl(
     // Index contains the first key of the block, and it's >= target.
     // We can defer reading the block.
     is_at_first_key_from_index_ = true;
+    // ResetDataIter() will invalidate block_iter_. Thus, there is no need to
+    // call CheckDataBlockWithinUpperBound() to check for iterate_upper_bound
+    // as that will be done later when the data block is actually read.
     ResetDataIter();
   } else {
     // Need to use the data block.
     if (!same_block) {
       InitDataBlock();
+    } else {
+      // When the user does a reseek, the iterate_upper_bound might have
+      // changed. CheckDataBlockWithinUpperBound() needs to be called
+      // explicitly if the reseek ends up in the same data block.
+      // If the reseek ends up in a different block, InitDataBlock() will do
+      // the iterator upper bound check.
+      CheckDataBlockWithinUpperBound();
     }
 
     if (target) {
@@ -2721,7 +2731,6 @@ void BlockBasedTableIterator<TBlockIter, TValue>::SeekImpl(
     FindKeyForward();
   }
 
-  CheckDataBlockWithinUpperBound();
   CheckOutOfBound();
 
   if (target) {