WritePrepared: Fix deadlock in WriteRecoverableState (#5306)

Summary:
The recent improvement in https://github.com/facebook/rocksdb/pull/3661 could cause a deadlock: When writing recoverable state, we also commit its sequence number to commit table, which could result into evicting existing commit entry, which could result into advancing max_evicted_seq_, which would need to get snapshots from database, which requires obtaining db mutex. The patch releases db_mutex before calling the callback in WriteRecoverableState to avoid the potential deadlock. It also improves the stress tests to let the issue be manifested in the tests.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5306

Differential Revision: D15341458

Pulled By: maysamyabandeh

fbshipit-source-id: 05dcbed7e21b789fd1e5fd5ee8eea08077162323

db/compaction_iterator.cc

@@ -493,20 +493,6 @@ 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_write.cc

@@ -214,9 +214,6 @@ 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();
 
@@ -231,6 +228,11 @@ 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);
   }
@@ -1113,8 +1115,12 @@ 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()) {

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

@@ -5096,6 +5096,9 @@ 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

@@ -477,6 +477,7 @@ 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());
     }
   };