BlockBasedTable::PrefixMayMatch: no need to find data block after full bloom checking

Summary:
Full block checking should be a good enough indication of prefix existance. No need to further check data block.
This also fixes wrong results when using prefix bloom and reverse bitwise comparator.

Test Plan: Will add a unit test.

Reviewers: yhchiang, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: hermanlee4, yoshinorim, yiwu, kradhakrishnan, leveldb, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D56625

db/db_test2.cc

@@ -23,6 +23,45 @@ class DBTest2 : public DBTestBase {
   DBTest2() : DBTestBase("/db_test2") {}
 };
 
+TEST_F(DBTest2, PrefixFullBloomWithReverseComparator) {
+  Options options = last_options_;
+  options.comparator = ReverseBytewiseComparator();
+  options.prefix_extractor.reset(NewCappedPrefixTransform(3));
+  options.statistics = rocksdb::CreateDBStatistics();
+  BlockBasedTableOptions bbto;
+  bbto.filter_policy.reset(NewBloomFilterPolicy(10, false));
+  bbto.whole_key_filtering = false;
+  options.table_factory.reset(NewBlockBasedTableFactory(bbto));
+  DestroyAndReopen(options);
+
+  ASSERT_OK(dbfull()->Put(WriteOptions(), "bar123", "foo"));
+  ASSERT_OK(dbfull()->Put(WriteOptions(), "bar234", "foo2"));
+  ASSERT_OK(dbfull()->Put(WriteOptions(), "foo123", "foo3"));
+
+  dbfull()->Flush(FlushOptions());
+
+  unique_ptr<Iterator> iter(db_->NewIterator(ReadOptions()));
+  iter->Seek("bar345");
+  ASSERT_OK(iter->status());
+  ASSERT_TRUE(iter->Valid());
+  ASSERT_EQ("bar234", iter->key().ToString());
+  ASSERT_EQ("foo2", iter->value().ToString());
+  iter->Next();
+  ASSERT_TRUE(iter->Valid());
+  ASSERT_EQ("bar123", iter->key().ToString());
+  ASSERT_EQ("foo", iter->value().ToString());
+
+  iter->Seek("foo234");
+  ASSERT_OK(iter->status());
+  ASSERT_TRUE(iter->Valid());
+  ASSERT_EQ("foo123", iter->key().ToString());
+  ASSERT_EQ("foo3", iter->value().ToString());
+
+  iter->Seek("bar");
+  ASSERT_OK(iter->status());
+  ASSERT_TRUE(!iter->Valid());
+}
+
 TEST_F(DBTest2, IteratorPropertyVersionNumber) {
   Put("", "");
   Iterator* iter1 = db_->NewIterator(ReadOptions());

table/block_based_table_reader.cc

@@ -1226,10 +1226,8 @@ bool BlockBasedTable::PrefixMayMatch(const Slice& internal_key) {
   FilterBlockReader* filter = filter_entry.value;
   if (filter != nullptr && !filter->IsBlockBased()) {
     may_match = filter->PrefixMayMatch(prefix);
-  }
+  } else {
-
+    // Then, try find it within each block
-  // Then, try find it within each block
-  if (may_match) {
     unique_ptr<InternalIterator> iiter(NewIndexIterator(no_io_read_options));
     iiter->Seek(internal_prefix);