Patch version number to 6.2.0 for downgrade compatibility S181200

Summary:
To avoid deadlock mutex_ should never be acquired before log_write_mutex_. The patch documents that and also fixes one case in ::FlushWAL that acquires mutex_ through ::WriteStatusCheck when it already holds lock on log_write_mutex_.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5437

Differential Revision: D15749722

Pulled By: maysamyabandeh

fbshipit-source-id: f57b69c44b4b80cc6d7ddf3d3fdf4a9eb5a5a45a
(cherry picked from commit c8c1a549f0cf88fa3d7c82d1f0d96d4b7dcffbf1)

db/compaction_iterator.cc

@@ -477,20 +477,6 @@ void CompactionIterator::NextFromInput() {
       // in this snapshot.
       assert(last_sequence >= current_user_key_sequence_);
 
-      // Note2: if last_snapshot < current_user_key_snapshot, it can only
-      // mean last_snapshot is released between we process last value and
-      // this value, and findEarliestVisibleSnapshot returns the next snapshot
-      // as current_user_key_snapshot. In this case last value and current
-      // value are both in current_user_key_snapshot currently.
-      // Although last_snapshot is released we might still get a definitive
-      // response when key sequence number changes, e.g., when seq is determined
-      // too old and visible in all snapshots.
-      assert(last_snapshot == current_user_key_snapshot_ ||
-             (snapshot_checker_ != nullptr &&
-              snapshot_checker_->CheckInSnapshot(current_user_key_sequence_,
-                                                 last_snapshot) !=
-                  SnapshotCheckerResult::kNotInSnapshot));
-
       ++iter_stats_.num_record_drop_hidden;  // (A)
       input_->Next();
     } else if (compaction_ != nullptr && ikey_.type == kTypeDeletion &&

db/db_impl.cc

@@ -1026,10 +1026,13 @@ int DBImpl::FindMinimumEmptyLevelFitting(
 
 Status DBImpl::FlushWAL(bool sync) {
   if (manual_wal_flush_) {
-    // We need to lock log_write_mutex_ since logs_ might change concurrently
-    InstrumentedMutexLock wl(&log_write_mutex_);
-    log::Writer* cur_log_writer = logs_.back().writer;
-    auto s = cur_log_writer->WriteBuffer();
+    Status s;
+    {
+      // We need to lock log_write_mutex_ since logs_ might change concurrently
+      InstrumentedMutexLock wl(&log_write_mutex_);
+      log::Writer* cur_log_writer = logs_.back().writer;
+      s = cur_log_writer->WriteBuffer();
+    }
     if (!s.ok()) {
       ROCKS_LOG_ERROR(immutable_db_options_.info_log, "WAL flush error %s",
                       s.ToString().c_str());

db/db_impl.h

@@ -1261,6 +1261,8 @@ class DBImpl : public DB {
   // logfile_number_. With two_write_queues it also protects alive_log_files_,
   // and log_empty_. Refer to the definition of each variable below for more
   // details.
+  // Note: to avoid dealock, if needed to acquire both log_write_mutex_ and
+  // mutex_, the order should be first mutex_ and then log_write_mutex_.
   InstrumentedMutex log_write_mutex_;
 
   std::atomic<bool> shutting_down_;

db/db_impl_write.cc

@@ -178,9 +178,6 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
   WriteThread::WriteGroup write_group;
   bool in_parallel_group = false;
   uint64_t last_sequence = kMaxSequenceNumber;
-  if (!two_write_queues_) {
-    last_sequence = versions_->LastSequence();
-  }
 
   mutex_.Lock();
 
@@ -195,6 +192,11 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
     PERF_TIMER_STOP(write_pre_and_post_process_time);
 
     status = PreprocessWrite(write_options, &need_log_sync, &write_context);
+    if (!two_write_queues_) {
+      // Assign it after ::PreprocessWrite since the sequence might advance
+      // inside it by WriteRecoverableState
+      last_sequence = versions_->LastSequence();
+    }
 
     PERF_TIMER_START(write_pre_and_post_process_time);
   }
@@ -994,8 +996,12 @@ Status DBImpl::WriteRecoverableState() {
       for (uint64_t sub_batch_seq = seq + 1;
            sub_batch_seq < next_seq && status.ok(); sub_batch_seq++) {
         uint64_t const no_log_num = 0;
+        // Unlock it since the callback might end up locking mutex. e.g.,
+        // AddCommitted -> AdvanceMaxEvictedSeq -> GetSnapshotListFromDB
+        mutex_.Unlock();
         status = recoverable_state_pre_release_callback_->Callback(
             sub_batch_seq, !DISABLE_MEMTABLE, no_log_num);
+        mutex_.Lock();
       }
     }
     if (status.ok()) {

include/rocksdb/version.h

@@ -5,8 +5,8 @@
 #pragma once
 
 #define ROCKSDB_MAJOR 6
-#define ROCKSDB_MINOR 1
-#define ROCKSDB_PATCH 1
+#define ROCKSDB_MINOR 2
+#define ROCKSDB_PATCH 0
 
 // Do not use these. We made the mistake of declaring macros starting with
 // double underscore. Now we have to live with our choice. We'll deprecate these

util/transaction_test_util.cc

@@ -205,6 +205,12 @@ bool RandomTransactionInserter::DoInsert(DB* db, Transaction* txn,
         ROCKS_LOG_DEBUG(db->GetDBOptions().info_log,
                         "Prepare of %" PRIu64 " %s (%s)", txn->GetId(),
                         s.ToString().c_str(), txn->GetName().c_str());
+        if (rand_->OneIn(20)) {
+          // This currently only tests the mechanics of writing commit time
+          // write batch so the exact values would not matter.
+          s = txn_->GetCommitTimeWriteBatch()->Put("cat", "dog");
+          assert(s.ok());
+        }
         db->GetDBOptions().env->SleepForMicroseconds(
             static_cast<int>(cmt_delay_ms_ * 1000));
       }

utilities/transactions/transaction_test.cc

@@ -5003,6 +5003,9 @@ Status TransactionStressTestInserter(
   WriteOptions write_options;
   ReadOptions read_options;
   TransactionOptions txn_options;
+  if (rand->OneIn(2)) {
+    txn_options.use_only_the_last_commit_time_batch_for_recovery = true;
+  }
   // Inside the inserter we might also retake the snapshot. We do both since two
   // separte functions are engaged for each.
   txn_options.set_snapshot = rand->OneIn(2);

utilities/transactions/transaction_test.h

@@ -466,6 +466,7 @@ class MySQLStyleTransactionTest
       // structures.
       txn_db_options.wp_snapshot_cache_bits = 1;
       txn_db_options.wp_commit_cache_bits = 10;
+      options.write_buffer_size = 1024;
       EXPECT_OK(ReOpen());
     }
   };