Return error if trying to open secondary on missing or inaccessible primary (#8200)

Summary:
If the primary's CURRENT file is missing or inaccessible, the secondary should not hang
trying repeatedly to switch to the next MANIFEST.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8200

Test Plan: make check

Reviewed By: jay-zhuang

Differential Revision: D27840627

Pulled By: riversand963

fbshipit-source-id: 071fed97cbab1bc5cdefd1dc235e5cd406c174e1

HISTORY.md

@@ -1,4 +1,8 @@
 # Rocksdb Change Log
+## Unreleased
+### Bug Fixes
+* If the primary's CURRENT file is missing or inaccessible, the secondary instance should not hang repeatedly trying to switch to a new MANIFEST. It should instead return the error code encountered while accessing the file.
+
 ## 6.23.0 (2021-07-16)
 ### Behavior Changes
 * Obsolete keys in the bottommost level that were preserved for a snapshot will now be cleaned upon snapshot release in all cases. This form of compaction (snapshot release triggered compaction) previously had an artificial limitation that multiple tombstones needed to be present.

db/db_impl/db_impl_open.cc

@@ -1674,6 +1674,7 @@ Status DBImpl::Open(const DBOptions& db_options, const std::string& dbname,
 
       impl->DeleteObsoleteFiles();
       s = impl->directories_.GetDbDir()->Fsync(IOOptions(), nullptr);
+      TEST_SYNC_POINT("DBImpl::Open:AfterDeleteFilesAndSyncDir");
     }
     if (s.ok()) {
       // In WritePrepared there could be gap in sequence numbers. This breaks

db/db_impl/db_impl_secondary.cc

@@ -41,6 +41,9 @@ Status DBImplSecondary::Recover(
           ->Recover(column_families, &manifest_reader_, &manifest_reporter_,
                     &manifest_reader_status_);
   if (!s.ok()) {
+    if (manifest_reader_status_) {
+      manifest_reader_status_->PermitUncheckedError();
+    }
     return s;
   }
   if (immutable_db_options_.paranoid_checks && s.ok()) {

db/db_secondary_test.cc

@@ -115,6 +115,18 @@ void DBSecondaryTest::CheckFileTypeCounts(const std::string& dir,
   ASSERT_EQ(expected_manifest, manifest_cnt);
 }
 
+TEST_F(DBSecondaryTest, NonExistingDb) {
+  Destroy(last_options_);
+
+  Options options = GetDefaultOptions();
+  options.env = env_;
+  options.max_open_files = -1;
+  const std::string dbname = "/doesnt/exist";
+  Status s =
+      DB::OpenAsSecondary(options, dbname, secondary_path_, &db_secondary_);
+  ASSERT_TRUE(s.IsIOError());
+}
+
 TEST_F(DBSecondaryTest, ReopenAsSecondary) {
   Options options;
   options.env = env_;
@@ -599,17 +611,19 @@ TEST_F(DBSecondaryTest, SwitchToNewManifestDuringOpen) {
   SyncPoint::GetInstance()->LoadDependency(
       {{"ReactiveVersionSet::MaybeSwitchManifest:AfterGetCurrentManifestPath:0",
         "VersionSet::ProcessManifestWrites:BeforeNewManifest"},
-       {"VersionSet::ProcessManifestWrites:AfterNewManifest",
+       {"DBImpl::Open:AfterDeleteFilesAndSyncDir",
         "ReactiveVersionSet::MaybeSwitchManifest:AfterGetCurrentManifestPath:"
         "1"}});
   SyncPoint::GetInstance()->EnableProcessing();
 
-  // Make sure db calls RecoverLogFiles so as to trigger a manifest write,
-  // which causes the db to switch to a new MANIFEST upon start.
   port::Thread ro_db_thread([&]() {
     Options options1;
     options1.env = env_;
     options1.max_open_files = -1;
+    Status s = TryOpenSecondary(options1);
+    ASSERT_TRUE(s.IsTryAgain());
+
+    // Try again
     OpenSecondary(options1);
     CloseSecondary();
   });

db/version_set.cc

@@ -4224,7 +4224,6 @@ Status VersionSet::ProcessManifestWrites(
       if (!io_s.ok()) {
         s = io_s;
       }
-      TEST_SYNC_POINT("VersionSet::ProcessManifestWrites:AfterNewManifest");
     }
 
     if (s.ok()) {
@@ -5716,6 +5715,9 @@ Status ReactiveVersionSet::Recover(
   static_cast_with_check<LogReporter>(manifest_reporter->get())->status =
       manifest_reader_status->get();
   Status s = MaybeSwitchManifest(manifest_reporter->get(), manifest_reader);
+  if (!s.ok()) {
+    return s;
+  }
   log::Reader* reader = manifest_reader->get();
   assert(reader);
 
@@ -5757,43 +5759,62 @@ Status ReactiveVersionSet::MaybeSwitchManifest(
     std::unique_ptr<log::FragmentBufferedReader>* manifest_reader) {
   assert(manifest_reader != nullptr);
   Status s;
-  do {
   std::string manifest_path;
   s = GetCurrentManifestPath(dbname_, fs_.get(), &manifest_path,
                              &manifest_file_number_);
+  if (!s.ok()) {
+    return s;
+  }
   std::unique_ptr<FSSequentialFile> manifest_file;
-    if (s.ok()) {
-      if (nullptr == manifest_reader->get() ||
-          manifest_reader->get()->file()->file_name() != manifest_path) {
+  if (manifest_reader->get() != nullptr &&
+      manifest_reader->get()->file()->file_name() == manifest_path) {
+    // CURRENT points to the same MANIFEST as before, no need to switch
+    // MANIFEST.
+    return s;
+  }
+  assert(nullptr == manifest_reader->get() ||
+         manifest_reader->get()->file()->file_name() != manifest_path);
+  s = fs_->FileExists(manifest_path, IOOptions(), nullptr);
+  if (s.IsNotFound()) {
+    return Status::TryAgain(
+        "The primary may have switched to a new MANIFEST and deleted the old "
+        "one.");
+  } else if (!s.ok()) {
+    return s;
+  }
   TEST_SYNC_POINT(
       "ReactiveVersionSet::MaybeSwitchManifest:"
       "AfterGetCurrentManifestPath:0");
   TEST_SYNC_POINT(
       "ReactiveVersionSet::MaybeSwitchManifest:"
       "AfterGetCurrentManifestPath:1");
+  // The primary can also delete the MANIFEST while the secondary is reading
+  // it. This is OK on POSIX. For other file systems, maybe create a hard link
+  // to MANIFEST. The hard link should be cleaned up later by the secondary.
   s = fs_->NewSequentialFile(manifest_path,
                              fs_->OptimizeForManifestRead(file_options_),
                              &manifest_file, nullptr);
-      } else {
-        // No need to switch manifest.
-        break;
-      }
-    }
   std::unique_ptr<SequentialFileReader> manifest_file_reader;
   if (s.ok()) {
-      manifest_file_reader.reset(new SequentialFileReader(
-          std::move(manifest_file), manifest_path,
+    manifest_file_reader.reset(
+        new SequentialFileReader(std::move(manifest_file), manifest_path,
                                  db_options_->log_readahead_size, io_tracer_));
     manifest_reader->reset(new log::FragmentBufferedReader(
-          nullptr, std::move(manifest_file_reader), reporter,
-          true /* checksum */, 0 /* log_number */));
+        nullptr, std::move(manifest_file_reader), reporter, true /* checksum */,
+        0 /* log_number */));
     ROCKS_LOG_INFO(db_options_->info_log, "Switched to new manifest: %s\n",
                    manifest_path.c_str());
     if (manifest_tailer_) {
       manifest_tailer_->PrepareToReadNewManifest();
     }
+  } else if (s.IsPathNotFound()) {
+    // This can happen if the primary switches to a new MANIFEST after the
+    // secondary reads the CURRENT file but before the secondary actually tries
+    // to open the MANIFEST.
+    s = Status::TryAgain(
+        "The primary may have switched to a new MANIFEST and deleted the old "
+        "one.");
   }
-  } while (s.IsPathNotFound());
   return s;
 }