Improve two error messages on WAL recovery (facebook#13876)

Summary:
**Context/Summary:** ... for better readability

Pull Request resolved: facebook#13876

Test Plan: Existing UT

Reviewed By: mszeszko-meta

Differential Revision: D80185817

Pulled By: hx235

fbshipit-source-id: 534d37dd747369da48fc5903acc66bb9c8f5206d

Author: hx235

db/db_impl/db_impl_open.cc

@@ -1755,8 +1755,12 @@ Status DBImpl::MaybeHandleStopReplayForCorruptionForInconsistency(
         ROCKS_LOG_ERROR(immutable_db_options_.info_log,
                         "Column family inconsistency: SST file contains data"
                         " beyond the point of corruption.");
-        status = Status::Corruption("SST file is ahead of WALs in CF " +
-                                    cfd->GetName());
+        status = Status::Corruption(
+            "Column family inconsistency: SST file contains data"
+            " beyond the point of corruption in CF " +
+            cfd->GetName() +
+            ". WAL recovery stopped at corruption point, but SST files"
+            " contain newer data.");
         return status;
       }
     }

db/log_reader.cc

@@ -380,8 +380,11 @@ void Reader::MaybeVerifyPredecessorWALInfo(
   } else {
     if (observed_predecessor_wal_info_.GetLogNumber() !=
         recorded_predecessor_log_number) {
-      std::string reason = "Missing WAL of log number " +
-                           std::to_string(recorded_predecessor_log_number);
+      std::string reason =
+          "Mismatched predecessor log number of WAL file " +
+          file_->file_name() + " Recorded " +
+          std::to_string(recorded_predecessor_log_number) + ". Observed " +
+          std::to_string(observed_predecessor_wal_info_.GetLogNumber());
       ReportCorruption(fragment.size(), reason.c_str(),
                        recorded_predecessor_log_number);
     } else if (observed_predecessor_wal_info_.GetLastSeqnoRecorded() !=