Several simple local code clean-ups (#8565)

Summary:
This PR tries to remove some unnecessary checks as well as unreachable code blocks to
improve readability. An obvious non-public API method naming typo is also corrected.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8565

Test Plan: make check

Reviewed By: lth

Differential Revision: D29963984

Pulled By: riversand963

fbshipit-source-id: cc96e8f09890e5cfe9b20eadb63bdca5484c150a

db/db_impl/db_impl_write.cc

@@ -220,7 +220,8 @@ Status DBImpl::WriteImpl(const WriteOptions& write_options,
 
   bool need_log_sync = write_options.sync;
   bool need_log_dir_sync = need_log_sync && !log_dir_synced_;
-  if (!two_write_queues_ || !disable_memtable) {
+  assert(!two_write_queues_ || !disable_memtable);
+  {
     // With concurrent writes we do preprocess only in the write thread that
     // also does write to memtable to avoid sync issue on shared data structure
     // with the other thread

db/write_batch.cc

@@ -776,7 +776,7 @@ bool WriteBatchInternal::IsLatestPersistentState(const WriteBatch* b) {
   return b->is_latest_persistent_state_;
 }
 
-void WriteBatchInternal::SetAsLastestPersistentState(WriteBatch* b) {
+void WriteBatchInternal::SetAsLatestPersistentState(WriteBatch* b) {
   b->is_latest_persistent_state_ = true;
 }
 

db/write_batch_internal.h

@@ -214,7 +214,7 @@ class WriteBatchInternal {
 
   // This write batch includes the latest state that should be persisted. Such
   // state meant to be used only during recovery.
-  static void SetAsLastestPersistentState(WriteBatch* b);
+  static void SetAsLatestPersistentState(WriteBatch* b);
   static bool IsLatestPersistentState(const WriteBatch* b);
 };
 

utilities/transactions/write_prepared_txn.cc

@@ -158,7 +158,7 @@ Status WritePreparedTxn::CommitInternal() {
     // When not writing to memtable, we can still cache the latest write batch.
     // The cached batch will be written to memtable in WriteRecoverableState
     // during FlushMemTable
-    WriteBatchInternal::SetAsLastestPersistentState(working_batch);
+    WriteBatchInternal::SetAsLatestPersistentState(working_batch);
   }
 
   auto prepare_seq = GetId();
@@ -236,14 +236,6 @@ Status WritePreparedTxn::CommitInternal() {
                           NO_REF_LOG, DISABLE_MEMTABLE, &seq_used, ONE_BATCH,
                           &update_commit_map_with_aux_batch);
   assert(!s.ok() || seq_used != kMaxSequenceNumber);
-  if (UNLIKELY(!db_impl_->immutable_db_options().two_write_queues)) {
-    if (s.ok()) {
-      // Note: RemovePrepared should be called after WriteImpl that publishsed
-      // the seq. Otherwise SmallestUnCommittedSeq optimization breaks.
-      wpt_db_->RemovePrepared(prepare_seq, prepare_batch_cnt_);
-    }
-    wpt_db_->RemovePrepared(commit_batch_seq, commit_batch_cnt);
-  }  // else RemovePrepared is called from within PreReleaseCallback
   return s;
 }
 

utilities/transactions/write_prepared_txn_db.cc

@@ -508,13 +508,10 @@ void WritePreparedTxnDB::AddCommitted(uint64_t prepare_seq, uint64_t commit_seq,
                         prev_max, max_evicted_seq);
       AdvanceMaxEvictedSeq(prev_max, max_evicted_seq);
     }
-    // After each eviction from commit cache, check if the commit entry should
-    // be kept around because it overlaps with a live snapshot.
-    CheckAgainstSnapshots(evicted);
     if (UNLIKELY(!delayed_prepared_empty_.load(std::memory_order_acquire))) {
       WriteLock wl(&prepared_mutex_);
-      for (auto dp : delayed_prepared_) {
-        if (dp == evicted.prep_seq) {
+      auto dp_iter = delayed_prepared_.find(evicted.prep_seq);
+      if (dp_iter != delayed_prepared_.end()) {
         // This is a rare case that txn is committed but prepared_txns_ is not
         // cleaned up yet. Refer to delayed_prepared_commits_ definition for
         // why it should be kept updated.
@@ -522,10 +519,11 @@ void WritePreparedTxnDB::AddCommitted(uint64_t prepare_seq, uint64_t commit_seq,
         ROCKS_LOG_DEBUG(info_log_,
                         "delayed_prepared_commits_[%" PRIu64 "]=%" PRIu64,
                         evicted.prep_seq, evicted.commit_seq);
-          break;
-        }
       }
     }
+    // After each eviction from commit cache, check if the commit entry should
+    // be kept around because it overlaps with a live snapshot.
+    CheckAgainstSnapshots(evicted);
   }
   bool succ =
       ExchangeCommitEntry(indexed_seq, evicted_64b, {prepare_seq, commit_seq});

utilities/transactions/write_prepared_txn_db.h

@@ -1080,6 +1080,8 @@ SnapshotBackup WritePreparedTxnDB::AssignMinMaxSeqs(const Snapshot* snapshot,
     *min =
         static_cast_with_check<const SnapshotImpl>(snapshot)->min_uncommitted_;
     *max = static_cast_with_check<const SnapshotImpl>(snapshot)->number_;
+    // A duplicate of the check in EnhanceSnapshot().
+    assert(*min <= *max + 1);
     return kBackedByDBSnapshot;
   } else {
     *min = SmallestUnCommittedSeq();

utilities/transactions/write_unprepared_txn.cc

@@ -553,7 +553,7 @@ Status WriteUnpreparedTxn::CommitInternal() {
     // When not writing to memtable, we can still cache the latest write batch.
     // The cached batch will be written to memtable in WriteRecoverableState
     // during FlushMemTable
-    WriteBatchInternal::SetAsLastestPersistentState(working_batch);
+    WriteBatchInternal::SetAsLatestPersistentState(working_batch);
   }
 
   const bool includes_data = !empty && !for_recovery;