Track WAL in MANIFEST: Update logic for computing min_log_number_to_keep in atomic flush (#7660)

Summary:
The logic for computing min_log_number_to_keep in atomic flush was incorrect.

For example, when all column families are flushed, the min_log_number_to_keep should be the latest new log. But the incorrect logic calls `PrecomputeMinLogNumberToKeepNon2PC` for each column family, and returns the minimum of them. However, `PrecomputeMinLogNumberToKeepNon2PC(cf)` assumes column families other than `cf` are flushed, but in case all column families are flushed, this assumption is incorrect.

Without this fix, the WAL referenced by the computed min_log_number_to_keep may actually contain no unflushed data, so the WAL might have actually been deleted from disk on recovery, then an incorrect error `Corruption: missing WAL` will be reported.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7660

Test Plan:
run `make crash_test_with_atomic_flush`  on devserver
added a unit test in `db_flush_test`

Reviewed By: riversand963

Differential Revision: D24906265

Pulled By: cheng-chang

fbshipit-source-id: 08deda62e71f67f59e3b7925cdd86dd09bd4f430

db/db_flush_test.cc

@@ -646,6 +646,63 @@ TEST_P(DBAtomicFlushTest, ManualAtomicFlush) {
   }
 }
 
+TEST_P(DBAtomicFlushTest, PrecomputeMinLogNumberToKeepNon2PC) {
+  Options options = CurrentOptions();
+  options.create_if_missing = true;
+  options.atomic_flush = GetParam();
+  options.write_buffer_size = (static_cast<size_t>(64) << 20);
+  CreateAndReopenWithCF({"pikachu"}, options);
+
+  const size_t num_cfs = handles_.size();
+  ASSERT_EQ(num_cfs, 2);
+  WriteOptions wopts;
+  for (size_t i = 0; i != num_cfs; ++i) {
+    ASSERT_OK(Put(static_cast<int>(i) /*cf*/, "key", "value", wopts));
+  }
+
+  {
+    // Flush the default CF only.
+    std::vector<int> cf_ids{0};
+    ASSERT_OK(Flush(cf_ids));
+
+    autovector<ColumnFamilyData*> flushed_cfds;
+    autovector<autovector<VersionEdit*>> flush_edits;
+    auto flushed_cfh = static_cast<ColumnFamilyHandleImpl*>(handles_[0]);
+    flushed_cfds.push_back(flushed_cfh->cfd());
+    flush_edits.push_back({});
+    auto unflushed_cfh = static_cast<ColumnFamilyHandleImpl*>(handles_[1]);
+
+    ASSERT_EQ(PrecomputeMinLogNumberToKeepNon2PC(dbfull()->TEST_GetVersionSet(),
+                                                 flushed_cfds, flush_edits),
+              unflushed_cfh->cfd()->GetLogNumber());
+  }
+
+  {
+    // Flush all CFs.
+    std::vector<int> cf_ids;
+    for (size_t i = 0; i != num_cfs; ++i) {
+      cf_ids.emplace_back(static_cast<int>(i));
+    }
+    ASSERT_OK(Flush(cf_ids));
+    uint64_t log_num_after_flush = dbfull()->TEST_GetCurrentLogNumber();
+
+    uint64_t min_log_number_to_keep = port::kMaxUint64;
+    autovector<ColumnFamilyData*> flushed_cfds;
+    autovector<autovector<VersionEdit*>> flush_edits;
+    for (size_t i = 0; i != num_cfs; ++i) {
+      auto cfh = static_cast<ColumnFamilyHandleImpl*>(handles_[i]);
+      flushed_cfds.push_back(cfh->cfd());
+      flush_edits.push_back({});
+      min_log_number_to_keep =
+          std::min(min_log_number_to_keep, cfh->cfd()->GetLogNumber());
+    }
+    ASSERT_EQ(min_log_number_to_keep, log_num_after_flush);
+    ASSERT_EQ(PrecomputeMinLogNumberToKeepNon2PC(dbfull()->TEST_GetVersionSet(),
+                                                 flushed_cfds, flush_edits),
+              min_log_number_to_keep);
+  }
+}
+
 TEST_P(DBAtomicFlushTest, AtomicFlushTriggeredByMemTableFull) {
   Options options = CurrentOptions();
   options.create_if_missing = true;

db/db_impl/db_impl.h

@@ -1017,6 +1017,12 @@ class DBImpl : public DB {
 
   VersionSet* TEST_GetVersionSet() const { return versions_.get(); }
 
+  uint64_t TEST_GetCurrentLogNumber() const {
+    InstrumentedMutexLock l(mutex());
+    assert(!logs_.empty());
+    return logs_.back().number;
+  }
+
   const std::unordered_set<uint64_t>& TEST_GetFilesGrabbedForPurge() const {
     return files_grabbed_for_purge_;
   }
@@ -2225,6 +2231,10 @@ extern uint64_t PrecomputeMinLogNumberToKeep2PC(
 extern uint64_t PrecomputeMinLogNumberToKeepNon2PC(
     VersionSet* vset, const ColumnFamilyData& cfd_to_flush,
     const autovector<VersionEdit*>& edit_list);
+// For atomic flush.
+extern uint64_t PrecomputeMinLogNumberToKeepNon2PC(
+    VersionSet* vset, const autovector<ColumnFamilyData*>& cfds_to_flush,
+    const autovector<autovector<VersionEdit*>>& edit_lists);
 
 // `cfd_to_flush` is the column family whose memtable will be flushed and thus
 // will not depend on any WAL file. nullptr means no memtable is being flushed.

db/db_impl/db_impl_files.cc

@@ -6,16 +6,17 @@
 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
-#include "db/db_impl/db_impl.h"
-
 #include <cinttypes>
 #include <set>
 #include <unordered_set>
+
+#include "db/db_impl/db_impl.h"
 #include "db/event_helpers.h"
 #include "db/memtable_list.h"
 #include "file/file_util.h"
 #include "file/filename.h"
 #include "file/sst_file_manager_impl.h"
+#include "port/port.h"
 #include "util/autovector.h"
 
 namespace ROCKSDB_NAMESPACE {
@@ -710,6 +711,42 @@ uint64_t PrecomputeMinLogNumberToKeepNon2PC(
   return min_log_number_to_keep;
 }
 
+uint64_t PrecomputeMinLogNumberToKeepNon2PC(
+    VersionSet* vset, const autovector<ColumnFamilyData*>& cfds_to_flush,
+    const autovector<autovector<VersionEdit*>>& edit_lists) {
+  assert(vset != nullptr);
+  assert(!cfds_to_flush.empty());
+  assert(cfds_to_flush.size() == edit_lists.size());
+
+  uint64_t min_log_number_to_keep = port::kMaxUint64;
+  for (const auto& edit_list : edit_lists) {
+    uint64_t log = 0;
+    for (const auto& e : edit_list) {
+      if (e->HasLogNumber()) {
+        log = std::max(log, e->GetLogNumber());
+      }
+    }
+    if (log != 0) {
+      min_log_number_to_keep = std::min(min_log_number_to_keep, log);
+    }
+  }
+  if (min_log_number_to_keep == port::kMaxUint64) {
+    min_log_number_to_keep = cfds_to_flush[0]->GetLogNumber();
+    for (size_t i = 1; i < cfds_to_flush.size(); i++) {
+      min_log_number_to_keep =
+          std::min(min_log_number_to_keep, cfds_to_flush[i]->GetLogNumber());
+    }
+  }
+
+  std::unordered_set<const ColumnFamilyData*> flushed_cfds(
+      cfds_to_flush.begin(), cfds_to_flush.end());
+  min_log_number_to_keep =
+      std::min(min_log_number_to_keep,
+               vset->PreComputeMinLogNumberWithUnflushedData(flushed_cfds));
+
+  return min_log_number_to_keep;
+}
+
 uint64_t PrecomputeMinLogNumberToKeep2PC(
     VersionSet* vset, const ColumnFamilyData& cfd_to_flush,
     const autovector<VersionEdit*>& edit_list,

db/memtable_list.cc

@@ -757,12 +757,7 @@ Status InstallMemtableAtomicFlushResults(
   std::unique_ptr<VersionEdit> wal_deletion;
   if (vset->db_options()->track_and_verify_wals_in_manifest) {
     uint64_t min_wal_number_to_keep =
-        PrecomputeMinLogNumberToKeepNon2PC(vset, *cfds[0], edit_lists[0]);
-    for (size_t i = 1; i < cfds.size(); i++) {
-      min_wal_number_to_keep = std::min(
-          min_wal_number_to_keep,
-          PrecomputeMinLogNumberToKeepNon2PC(vset, *cfds[i], edit_lists[i]));
-    }
+        PrecomputeMinLogNumberToKeepNon2PC(vset, cfds, edit_lists);
     const auto& wals = vset->GetWalSet().GetWals();
     if (!wals.empty() && min_wal_number_to_keep > wals.begin()->first) {
       wal_deletion.reset(new VersionEdit);

db/version_set.h

@@ -26,6 +26,7 @@
 #include <memory>
 #include <set>
 #include <string>
+#include <unordered_set>
 #include <utility>
 #include <vector>
 
@@ -1136,6 +1137,23 @@ class VersionSet {
     }
     return min_log_num;
   }
+  // Returns the minimum log number which still has data not flushed to any SST
+  // file, except data from `cfds_to_skip`.
+  uint64_t PreComputeMinLogNumberWithUnflushedData(
+      const std::unordered_set<const ColumnFamilyData*>& cfds_to_skip) const {
+    uint64_t min_log_num = port::kMaxUint64;
+    for (auto cfd : *column_family_set_) {
+      if (cfds_to_skip.count(cfd)) {
+        continue;
+      }
+      // It's safe to ignore dropped column families here:
+      // cfd->IsDropped() becomes true after the drop is persisted in MANIFEST.
+      if (min_log_num > cfd->GetLogNumber() && !cfd->IsDropped()) {
+        min_log_num = cfd->GetLogNumber();
+      }
+    }
+    return min_log_num;
+  }
 
   // Create an iterator that reads over the compaction inputs for "*c".
   // The caller should delete the iterator when no longer needed.