Reverse sort order in dedup to enable iter checking in callback (#11725)

Summary:
Fix https://github.com/facebook/rocksdb/issues/6470

Ensure TransactionLogIter being initialized correctly with SYNC_POINT API when calling `GetSortedWALFiles`.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11725

Reviewed By: akankshamahajan15

Differential Revision: D48529411

Pulled By: ajkr

fbshipit-source-id: 970ca1a6259ed996c6d87f7fcd40f95acf441517

db/db_impl/db_impl_files.cc

@@ -457,12 +457,12 @@ void DBImpl::PurgeObsoleteFiles(JobContext& state, bool schedule_only) {
   std::sort(candidate_files.begin(), candidate_files.end(),
             [](const JobContext::CandidateFileInfo& lhs,
                const JobContext::CandidateFileInfo& rhs) {
-              if (lhs.file_name > rhs.file_name) {
+              if (lhs.file_name < rhs.file_name) {
                 return true;
-              } else if (lhs.file_name < rhs.file_name) {
+              } else if (lhs.file_name > rhs.file_name) {
                 return false;
               } else {
-                return (lhs.file_path > rhs.file_path);
+                return (lhs.file_path < rhs.file_path);
               }
             });
   candidate_files.erase(

db/db_log_iter_test.cc

@@ -145,6 +145,41 @@ TEST_F(DBTestXactLogIterator, TransactionLogIteratorRace) {
     } while (ChangeCompactOptions());
   }
 }
+
+TEST_F(DBTestXactLogIterator, TransactionLogIteratorCheckWhenArchive) {
+  do {
+    ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->ClearTrace();
+    Options options = OptionsForLogIterTest();
+    DestroyAndReopen(options);
+    ColumnFamilyHandle* cf;
+    auto s = dbfull()->CreateColumnFamily(ColumnFamilyOptions(), "CF", &cf);
+    ASSERT_TRUE(s.ok());
+
+    ASSERT_OK(dbfull()->Put(WriteOptions(), cf, "key1", DummyString(1024)));
+
+    ASSERT_OK(dbfull()->Put(WriteOptions(), "key2", DummyString(1024)));
+
+    ASSERT_OK(dbfull()->Flush(FlushOptions()));
+
+    ASSERT_OK(dbfull()->Put(WriteOptions(), "key3", DummyString(1024)));
+
+    ASSERT_OK(dbfull()->Flush(FlushOptions()));
+
+    ASSERT_OK(dbfull()->Put(WriteOptions(), "key4", DummyString(1024)));
+    ASSERT_OK(dbfull()->Flush(FlushOptions()));
+
+    ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->SetCallBack(
+        "WalManager::PurgeObsoleteFiles:1", [&](void*) {
+          auto iter = OpenTransactionLogIter(0);
+          ExpectRecords(4, iter);
+        });
+
+    ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->EnableProcessing();
+    ASSERT_OK(dbfull()->Flush(FlushOptions(), cf));
+
+    delete cf;
+  } while (ChangeCompactOptions());
+}
 #endif
 
 TEST_F(DBTestXactLogIterator, TransactionLogIteratorStallAtLastRecord) {