Best efforts recovery to skip empty MANIFEST (#10416)

Summary:
Skip empty MANIFEST fie during best_efforts_recovery.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10416

Test Plan: make failed db_stress test pass

Reviewed By: riversand963

Differential Revision: D38126273

Pulled By: jay-zhuang

fbshipit-source-id: 4498d322b09eaa194dd2cbf9c683d62ab54bfb01

HISTORY.md

@@ -16,6 +16,7 @@
 * Fix race conditions in `GenericRateLimiter`.
 * Fix a bug in `FIFOCompactionPicker::PickTTLCompaction` where total_size calculating might cause underflow
 * Fix data race bug in hash linked list memtable. With this bug, read request might temporarily miss an old record in the memtable in a race condition to the hash bucket.
+* Fix a bug that `best_efforts_recovery` may fail to open the db with mmap read.
 
 ### Behavior Change
 * Added checksum handshake during the copying of decompressed WAL fragment. This together with #9875, #10037, #10212, #10114 and #10319 provides end-to-end integrity protection for write batch during recovery.

db/db_impl/db_impl_open.cc

@@ -441,11 +441,14 @@ Status DBImpl::Recover(
         uint64_t number = 0;
         FileType type = kWalFile;  // initialize
         if (ParseFileName(file, &number, &type) && type == kDescriptorFile) {
-          // Found MANIFEST (descriptor log), thus best-efforts recovery does
-          // not have to treat the db as empty.
-          s = Status::OK();
-          manifest_path = dbname_ + "/" + file;
-          break;
+          uint64_t bytes;
+          s = env_->GetFileSize(DescriptorFileName(dbname_, number), &bytes);
+          if (s.ok() && bytes != 0) {
+            // Found non-empty MANIFEST (descriptor log), thus best-efforts
+            // recovery does not have to treat the db as empty.
+            manifest_path = dbname_ + "/" + file;
+            break;
+          }
         }
       }
     }