Remove path with arena==nullptr from NewInternalIterator

Summary:
Simply code by removing code path which does not use Arena
from NewInternalIterator

Test Plan:
make all check
make valgrind_check

Reviewers: sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D22395

db/db_impl.cc

@@ -1415,20 +1415,22 @@ Status DBImpl::WriteLevel0TableForRecovery(ColumnFamilyData* cfd, MemTable* mem,
   pending_outputs_[meta.fd.GetNumber()] = 0;  // path 0 for level 0 file.
   ReadOptions ro;
   ro.total_order_seek = true;
-  Iterator* iter = mem->NewIterator(ro);
+  Arena arena;
+  Status s;
+  {
+    ScopedArenaIterator iter(mem->NewIterator(ro, &arena));
     const SequenceNumber newest_snapshot = snapshots_.GetNewest();
     const SequenceNumber earliest_seqno_in_memtable =
         mem->GetFirstSequenceNumber();
     Log(options_.info_log, "[%s] Level-0 table #%" PRIu64 ": started",
         cfd->GetName().c_str(), meta.fd.GetNumber());
 
-  Status s;
     {
       mutex_.Unlock();
-    s = BuildTable(dbname_, env_, *cfd->ioptions(), env_options_,
-                   cfd->table_cache(), iter, &meta, cfd->internal_comparator(),
-                   newest_snapshot, earliest_seqno_in_memtable,
-                   GetCompressionFlush(*cfd->options()),
+      s = BuildTable(
+          dbname_, env_, *cfd->ioptions(), env_options_, cfd->table_cache(),
+          iter.get(), &meta, cfd->internal_comparator(), newest_snapshot,
+          earliest_seqno_in_memtable, GetCompressionFlush(*cfd->options()),
           cfd->options()->compression_opts, Env::IO_HIGH);
       LogFlush(options_.info_log);
       mutex_.Lock();
@@ -1438,8 +1440,7 @@ Status DBImpl::WriteLevel0TableForRecovery(ColumnFamilyData* cfd, MemTable* mem,
         "[%s] Level-0 table #%" PRIu64 ": %" PRIu64 " bytes %s",
         cfd->GetName().c_str(), meta.fd.GetNumber(), meta.fd.GetFileSize(),
         s.ToString().c_str());
-  delete iter;
-
+  }
   pending_outputs_.erase(meta.fd.GetNumber());
 
   // Note that if file_size is zero, the file has been deleted and
@@ -1485,24 +1486,27 @@ Status DBImpl::WriteLevel0Table(ColumnFamilyData* cfd,
     std::vector<Iterator*> memtables;
     ReadOptions ro;
     ro.total_order_seek = true;
+    Arena arena;
     for (MemTable* m : mems) {
       Log(options_.info_log,
           "[%s] Flushing memtable with next log file: %" PRIu64 "\n",
           cfd->GetName().c_str(), m->GetNextLogNumber());
-      memtables.push_back(m->NewIterator(ro));
+      memtables.push_back(m->NewIterator(ro, &arena));
     }
-    Iterator* iter = NewMergingIterator(&cfd->internal_comparator(),
-                                        &memtables[0], memtables.size());
+    {
+      ScopedArenaIterator iter(NewMergingIterator(&cfd->internal_comparator(),
+                                                  &memtables[0],
+                                                  memtables.size(), &arena));
       Log(options_.info_log, "[%s] Level-0 flush table #%" PRIu64 ": started",
           cfd->GetName().c_str(), meta.fd.GetNumber());
 
-    s = BuildTable(dbname_, env_, *cfd->ioptions(), env_options_,
-                   cfd->table_cache(), iter, &meta, cfd->internal_comparator(),
-                   newest_snapshot, earliest_seqno_in_memtable,
-                   GetCompressionFlush(*cfd->options()),
+      s = BuildTable(
+          dbname_, env_, *cfd->ioptions(), env_options_, cfd->table_cache(),
+          iter.get(), &meta, cfd->internal_comparator(), newest_snapshot,
+          earliest_seqno_in_memtable, GetCompressionFlush(*cfd->options()),
           cfd->options()->compression_opts, Env::IO_HIGH);
       LogFlush(options_.info_log);
-    delete iter;
+    }
     Log(options_.info_log,
         "[%s] Level-0 flush table #%" PRIu64 ": %" PRIu64 " bytes %s",
         cfd->GetName().c_str(), meta.fd.GetNumber(), meta.fd.GetFileSize(),
@@ -3349,7 +3353,7 @@ Iterator* DBImpl::NewInternalIterator(const ReadOptions& options,
                                       SuperVersion* super_version,
                                       Arena* arena) {
   Iterator* internal_iter;
-  if (arena != nullptr) {
+  assert(arena != nullptr);
   // Need to create internal iterator from the arena.
   MergeIteratorBuilder merge_iter_builder(&cfd->internal_comparator(), arena);
   // Collect iterator for mutable mem
@@ -3361,19 +3365,6 @@ Iterator* DBImpl::NewInternalIterator(const ReadOptions& options,
   super_version->current->AddIterators(options, env_options_,
                                        &merge_iter_builder);
   internal_iter = merge_iter_builder.Finish();
-  } else {
-    // Need to create internal iterator using malloc.
-    std::vector<Iterator*> iterator_list;
-    // Collect iterator for mutable mem
-    iterator_list.push_back(super_version->mem->NewIterator(options));
-    // Collect all needed child iterators for immutable memtables
-    super_version->imm->AddIterators(options, &iterator_list);
-    // Collect iterators for files in L0 - Ln
-    super_version->current->AddIterators(options, env_options_,
-                                         &iterator_list);
-    internal_iter = NewMergingIterator(&cfd->internal_comparator(),
-                                       &iterator_list[0], iterator_list.size());
-  }
   IterState* cleanup = new IterState(this, &mutex_, super_version);
   internal_iter->RegisterCleanup(CleanupIteratorState, cleanup, nullptr);
 
@@ -3790,10 +3781,12 @@ Status DBImpl::NewIterators(
               ? reinterpret_cast<const SnapshotImpl*>(options.snapshot)->number_
               : latest_snapshot;
 
-      auto iter = NewInternalIterator(options, cfd, super_versions[i]);
-      iter = NewDBIterator(env_, *cfd->options(),
-                           cfd->user_comparator(), iter, snapshot);
-      iterators->push_back(iter);
+      ArenaWrappedDBIter* db_iter = NewArenaWrappedDbIterator(
+          env_, *cfd->options(), cfd->user_comparator(), snapshot);
+      Iterator* internal_iter = NewInternalIterator(
+          options, cfd, super_versions[i], db_iter->GetArena());
+      db_iter->SetIterUnderDBIter(internal_iter);
+      iterators->push_back(db_iter);
     }
   }
 

db/db_impl.h

@@ -30,6 +30,7 @@
 #include "util/autovector.h"
 #include "util/stop_watch.h"
 #include "util/thread_local.h"
+#include "util/scoped_arena_iterator.h"
 #include "db/internal_stats.h"
 
 namespace rocksdb {
@@ -173,8 +174,8 @@ class DBImpl : public DB {
   // Return an internal iterator over the current state of the database.
   // The keys of this iterator are internal keys (see format.h).
   // The returned iterator should be deleted when no longer needed.
-  Iterator* TEST_NewInternalIterator(ColumnFamilyHandle* column_family =
-                                         nullptr);
+  Iterator* TEST_NewInternalIterator(
+      Arena* arena, ColumnFamilyHandle* column_family = nullptr);
 
   // Return the maximum overlapping data (in bytes) at next level for any
   // file at a level >= 1.
@@ -297,8 +298,7 @@ class DBImpl : public DB {
   Statistics* stats_;
 
   Iterator* NewInternalIterator(const ReadOptions&, ColumnFamilyData* cfd,
-                                SuperVersion* super_version,
-                                Arena* arena = nullptr);
+                                SuperVersion* super_version, Arena* arena);
 
  private:
   friend class DB;

db/db_impl_debug.cc

@@ -20,7 +20,8 @@ uint64_t DBImpl::TEST_GetLevel0TotalSize() {
   return default_cf_handle_->cfd()->current()->NumLevelBytes(0);
 }
 
-Iterator* DBImpl::TEST_NewInternalIterator(ColumnFamilyHandle* column_family) {
+Iterator* DBImpl::TEST_NewInternalIterator(Arena* arena,
+                                           ColumnFamilyHandle* column_family) {
   ColumnFamilyData* cfd;
   if (column_family == nullptr) {
     cfd = default_cf_handle_->cfd();
@@ -33,7 +34,7 @@ Iterator* DBImpl::TEST_NewInternalIterator(ColumnFamilyHandle* column_family) {
   SuperVersion* super_version = cfd->GetSuperVersion()->Ref();
   mutex_.Unlock();
   ReadOptions roptions;
-  return NewInternalIterator(roptions, cfd, super_version);
+  return NewInternalIterator(roptions, cfd, super_version, arena);
 }
 
 int64_t DBImpl::TEST_MaxNextLevelOverlappingBytes(

db/db_test.cc

@@ -41,6 +41,7 @@
 #include "util/rate_limiter.h"
 #include "util/statistics.h"
 #include "util/testharness.h"
+#include "util/scoped_arena_iterator.h"
 #include "util/sync_point.h"
 #include "util/testutil.h"
 
@@ -755,11 +756,12 @@ class DBTest {
   }
 
   std::string AllEntriesFor(const Slice& user_key, int cf = 0) {
-    Iterator* iter;
+    ScopedArenaIterator iter;
+    Arena arena;
     if (cf == 0) {
-      iter = dbfull()->TEST_NewInternalIterator();
+      iter.set(dbfull()->TEST_NewInternalIterator(&arena));
     } else {
-      iter = dbfull()->TEST_NewInternalIterator(handles_[cf]);
+      iter.set(dbfull()->TEST_NewInternalIterator(&arena, handles_[cf]));
     }
     InternalKey target(user_key, kMaxSequenceNumber, kTypeValue);
     iter->Seek(target.Encode());
@@ -804,7 +806,6 @@ class DBTest {
       }
       result += "]";
     }
-    delete iter;
     return result;
   }
 
@@ -1042,11 +1043,12 @@ class DBTest {
 
   // Utility method to test InplaceUpdate
   void validateNumberOfEntries(int numValues, int cf = 0) {
-    Iterator* iter;
+    ScopedArenaIterator iter;
+    Arena arena;
     if (cf != 0) {
-      iter = dbfull()->TEST_NewInternalIterator(handles_[cf]);
+      iter.set(dbfull()->TEST_NewInternalIterator(&arena, handles_[cf]));
     } else {
-      iter = dbfull()->TEST_NewInternalIterator();
+      iter.set(dbfull()->TEST_NewInternalIterator(&arena));
     }
     iter->SeekToFirst();
     ASSERT_EQ(iter->status().ok(), true);
@@ -1060,7 +1062,6 @@ class DBTest {
       ASSERT_EQ(ikey.sequence, (unsigned)seq--);
       iter->Next();
     }
-    delete iter;
     ASSERT_EQ(0, seq);
   }
 
@@ -4210,7 +4211,10 @@ TEST(DBTest, CompactionFilter) {
   // TODO: figure out sequence number squashtoo
   int count = 0;
   int total = 0;
-  Iterator* iter = dbfull()->TEST_NewInternalIterator(handles_[1]);
+  Arena arena;
+  {
+    ScopedArenaIterator iter(
+        dbfull()->TEST_NewInternalIterator(&arena, handles_[1]));
     iter->SeekToFirst();
     ASSERT_OK(iter->status());
     while (iter->Valid()) {
@@ -4223,9 +4227,9 @@ TEST(DBTest, CompactionFilter) {
       }
       iter->Next();
     }
+  }
   ASSERT_EQ(total, 100000);
   ASSERT_EQ(count, 1);
-  delete iter;
 
   // overwrite all the 100K keys once again.
   for (int i = 0; i < 100000; i++) {
@@ -4280,7 +4284,7 @@ TEST(DBTest, CompactionFilter) {
   ASSERT_EQ(NumTableFilesAtLevel(1, 1), 0);
 
   // Scan the entire database to ensure that nothing is left
-  iter = db_->NewIterator(ReadOptions(), handles_[1]);
+  Iterator* iter = db_->NewIterator(ReadOptions(), handles_[1]);
   iter->SeekToFirst();
   count = 0;
   while (iter->Valid()) {
@@ -4296,7 +4300,9 @@ TEST(DBTest, CompactionFilter) {
   // TODO: remove the following or design a different
   // test
   count = 0;
-  iter = dbfull()->TEST_NewInternalIterator(handles_[1]);
+  {
+    ScopedArenaIterator iter(
+        dbfull()->TEST_NewInternalIterator(&arena, handles_[1]));
     iter->SeekToFirst();
     ASSERT_OK(iter->status());
     while (iter->Valid()) {
@@ -4307,7 +4313,7 @@ TEST(DBTest, CompactionFilter) {
       iter->Next();
     }
     ASSERT_EQ(count, 0);
-  delete iter;
+  }
 }
 
 // Tests the edge case where compaction does not produce any output -- all
@@ -4429,7 +4435,9 @@ TEST(DBTest, CompactionFilterContextManual) {
   // Verify total number of keys is correct after manual compaction.
   int count = 0;
   int total = 0;
-  Iterator* iter = dbfull()->TEST_NewInternalIterator();
+  {
+    Arena arena;
+    ScopedArenaIterator iter(dbfull()->TEST_NewInternalIterator(&arena));
     iter->SeekToFirst();
     ASSERT_OK(iter->status());
     while (iter->Valid()) {
@@ -4444,7 +4452,7 @@ TEST(DBTest, CompactionFilterContextManual) {
     }
     ASSERT_EQ(total, 700);
     ASSERT_EQ(count, 1);
-  delete iter;
+  }
 }
 
 class KeepFilterV2 : public CompactionFilterV2 {
@@ -4601,7 +4609,9 @@ TEST(DBTest, CompactionFilterV2) {
   // All the files are in the lowest level.
   int count = 0;
   int total = 0;
-  Iterator* iter = dbfull()->TEST_NewInternalIterator();
+  {
+    Arena arena;
+    ScopedArenaIterator iter(dbfull()->TEST_NewInternalIterator(&arena));
     iter->SeekToFirst();
     ASSERT_OK(iter->status());
     while (iter->Valid()) {
@@ -4614,12 +4624,12 @@ TEST(DBTest, CompactionFilterV2) {
       }
       iter->Next();
     }
+  }
 
   ASSERT_EQ(total, 100000);
   // 1 snapshot only. Since we are using universal compacton,
   // the sequence no is cleared for better compression
   ASSERT_EQ(count, 1);
-  delete iter;
 
   // create a new database with the compaction
   // filter in such a way that it deletes all keys
@@ -4643,7 +4653,7 @@ TEST(DBTest, CompactionFilterV2) {
   ASSERT_EQ(NumTableFilesAtLevel(1), 0);
 
   // Scan the entire database to ensure that nothing is left
-  iter = db_->NewIterator(ReadOptions());
+  Iterator* iter = db_->NewIterator(ReadOptions());
   iter->SeekToFirst();
   count = 0;
   while (iter->Valid()) {

db/forward_iterator.cc

@@ -132,9 +132,11 @@ ForwardIterator::~ForwardIterator() {
 }
 
 void ForwardIterator::Cleanup() {
-  delete mutable_iter_;
+  if (mutable_iter_ != nullptr) {
+    mutable_iter_->~Iterator();
+  }
   for (auto* m : imm_iters_) {
-    delete m;
+    m->~Iterator();
   }
   imm_iters_.clear();
   for (auto* f : l0_iters_) {
@@ -401,8 +403,8 @@ void ForwardIterator::RebuildIterators() {
   Cleanup();
   // New
   sv_ = cfd_->GetReferencedSuperVersion(&(db_->mutex_));
-  mutable_iter_ = sv_->mem->NewIterator(read_options_);
-  sv_->imm->AddIterators(read_options_, &imm_iters_);
+  mutable_iter_ = sv_->mem->NewIterator(read_options_, &arena_);
+  sv_->imm->AddIterators(read_options_, &imm_iters_, &arena_);
   const auto& l0_files = sv_->current->files_[0];
   l0_iters_.reserve(l0_files.size());
   for (const auto* l0 : l0_files) {

db/forward_iterator.h

@@ -14,6 +14,7 @@
 #include "rocksdb/iterator.h"
 #include "rocksdb/options.h"
 #include "db/dbformat.h"
+#include "util/arena.h"
 
 namespace rocksdb {
 
@@ -100,6 +101,7 @@ class ForwardIterator : public Iterator {
 
   IterKey prev_key_;
   bool is_prev_set_;
+  Arena arena_;
 };
 
 }  // namespace rocksdb

db/memtable.cc

@@ -249,13 +249,9 @@ class MemTableIterator: public Iterator {
 };
 
 Iterator* MemTable::NewIterator(const ReadOptions& options, Arena* arena) {
-  if (arena == nullptr) {
-    return new MemTableIterator(*this, options, nullptr);
-  } else {
+  assert(arena != nullptr);
   auto mem = arena->AllocateAligned(sizeof(MemTableIterator));
-    return new (mem)
-        MemTableIterator(*this, options, arena);
-  }
+  return new (mem) MemTableIterator(*this, options, arena);
 }
 
 port::RWMutex* MemTable::GetLock(const Slice& key) {

db/memtable.h

@@ -81,8 +81,7 @@ class MemTable {
   // arena: If not null, the arena needs to be used to allocate the Iterator.
   //        Calling ~Iterator of the iterator will destroy all the states but
   //        those allocated in arena.
-  Iterator* NewIterator(const ReadOptions& options,
-                        Arena* arena = nullptr);
+  Iterator* NewIterator(const ReadOptions& options, Arena* arena);
 
   // Add an entry into memtable that maps key to value at the
   // specified sequence number and with the specified type.

db/memtable_list.cc

@@ -73,9 +73,10 @@ bool MemTableListVersion::Get(const LookupKey& key, std::string* value,
 }
 
 void MemTableListVersion::AddIterators(const ReadOptions& options,
-                                       std::vector<Iterator*>* iterator_list) {
+                                       std::vector<Iterator*>* iterator_list,
+                                       Arena* arena) {
   for (auto& m : memlist_) {
-    iterator_list->push_back(m->NewIterator(options));
+    iterator_list->push_back(m->NewIterator(options, arena));
   }
 }
 

db/memtable_list.h

@@ -49,7 +49,7 @@ class MemTableListVersion {
            MergeContext& merge_context, const Options& options);
 
   void AddIterators(const ReadOptions& options,
-                    std::vector<Iterator*>* iterator_list);
+                    std::vector<Iterator*>* iterator_list, Arena* arena);
 
   void AddIterators(const ReadOptions& options,
                     MergeIteratorBuilder* merge_iter_builder);

db/repair.cc

@@ -48,6 +48,7 @@
 #include "rocksdb/env.h"
 #include "rocksdb/options.h"
 #include "rocksdb/immutable_options.h"
+#include "util/scoped_arena_iterator.h"
 
 namespace rocksdb {
 
@@ -240,13 +241,15 @@ class Repairer {
     // since ExtractMetaData() will also generate edits.
     FileMetaData meta;
     meta.fd = FileDescriptor(next_file_number_++, 0, 0);
+    {
       ReadOptions ro;
       ro.total_order_seek = true;
-    Iterator* iter = mem->NewIterator(ro);
+      Arena arena;
+      ScopedArenaIterator iter(mem->NewIterator(ro, &arena));
       status = BuildTable(dbname_, env_, ioptions_, env_options_, table_cache_,
-                        iter, &meta, icmp_, 0, 0, kNoCompression,
+                          iter.get(), &meta, icmp_, 0, 0, kNoCompression,
                           CompressionOptions());
-    delete iter;
+    }
     delete mem->Unref();
     delete cf_mems_default;
     mem = nullptr;

db/version_set.cc

@@ -596,31 +596,6 @@ uint64_t Version::GetEstimatedActiveKeys() {
   return num_non_deletions_ - num_deletions_;
 }
 
-void Version::AddIterators(const ReadOptions& read_options,
-                           const EnvOptions& soptions,
-                           std::vector<Iterator*>* iters) {
-  // Merge all level zero files together since they may overlap
-  for (size_t i = 0; i < file_levels_[0].num_files; i++) {
-    const auto& file = file_levels_[0].files[i];
-    iters->push_back(cfd_->table_cache()->NewIterator(
-        read_options, soptions, cfd_->internal_comparator(), file.fd));
-  }
-
-  // For levels > 0, we can use a concatenating iterator that sequentially
-  // walks through the non-overlapping files in the level, opening them
-  // lazily.
-  for (int level = 1; level < num_levels_; level++) {
-    if (file_levels_[level].num_files != 0) {
-      iters->push_back(NewTwoLevelIterator(new LevelFileIteratorState(
-          cfd_->table_cache(), read_options, soptions,
-          cfd_->internal_comparator(), false /* for_compaction */,
-          cfd_->options()->prefix_extractor != nullptr),
-        new LevelFileNumIterator(cfd_->internal_comparator(),
-            &file_levels_[level])));
-    }
-  }
-}
-
 void Version::AddIterators(const ReadOptions& read_options,
                            const EnvOptions& soptions,
                            MergeIteratorBuilder* merge_iter_builder) {

db/version_set.h

@@ -86,8 +86,6 @@ class Version {
   // Append to *iters a sequence of iterators that will
   // yield the contents of this Version when merged together.
   // REQUIRES: This version has been saved (see VersionSet::SaveTo)
-  void AddIterators(const ReadOptions&, const EnvOptions& soptions,
-                    std::vector<Iterator*>* iters);
 
   void AddIterators(const ReadOptions&, const EnvOptions& soptions,
                     MergeIteratorBuilder* merger_iter_builder);

db/write_batch_test.cc

@@ -18,6 +18,7 @@
 #include "rocksdb/utilities/write_batch_with_index.h"
 #include "util/logging.h"
 #include "util/testharness.h"
+#include "util/scoped_arena_iterator.h"
 
 namespace rocksdb {
 
@@ -32,7 +33,8 @@ static std::string PrintContents(WriteBatch* b) {
   ColumnFamilyMemTablesDefault cf_mems_default(mem, &options);
   Status s = WriteBatchInternal::InsertInto(b, &cf_mems_default);
   int count = 0;
-  Iterator* iter = mem->NewIterator(ReadOptions());
+  Arena arena;
+  ScopedArenaIterator iter(mem->NewIterator(ReadOptions(), &arena));
   for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
     ParsedInternalKey ikey;
     memset((void *)&ikey, 0, sizeof(ikey));
@@ -67,7 +69,6 @@ static std::string PrintContents(WriteBatch* b) {
     state.append("@");
     state.append(NumberToString(ikey.sequence));
   }
-  delete iter;
   if (!s.ok()) {
     state.append(s.ToString());
   } else if (count != WriteBatchInternal::Count(b)) {

java/rocksjni/write_batch.cc

@@ -18,6 +18,7 @@
 #include "rocksdb/env.h"
 #include "rocksdb/memtablerep.h"
 #include "util/logging.h"
+#include "util/scoped_arena_iterator.h"
 #include "util/testharness.h"
 
 /*
@@ -209,7 +210,9 @@ jbyteArray Java_org_rocksdb_WriteBatchTest_getContents(
   rocksdb::Status s =
       rocksdb::WriteBatchInternal::InsertInto(b, &cf_mems_default);
   int count = 0;
-  rocksdb::Iterator* iter = mem->NewIterator(rocksdb::ReadOptions());
+  Arena arena;
+  ScopedArenaIterator iter(mem->NewIterator(
+      rocksdb::ReadOptions(), false /*don't enforce total order*/, &arena));
   for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
     rocksdb::ParsedInternalKey ikey;
     memset(reinterpret_cast<void*>(&ikey), 0, sizeof(ikey));
@@ -244,7 +247,6 @@ jbyteArray Java_org_rocksdb_WriteBatchTest_getContents(
     state.append("@");
     state.append(rocksdb::NumberToString(ikey.sequence));
   }
-  delete iter;
   if (!s.ok()) {
     state.append(s.ToString());
   } else if (count != rocksdb::WriteBatchInternal::Count(b)) {

table/table_test.cc

@@ -42,6 +42,7 @@
 #include "util/statistics.h"
 #include "util/testharness.h"
 #include "util/testutil.h"
+#include "util/scoped_arena_iterator.h"
 
 namespace rocksdb {
 
@@ -223,8 +224,12 @@ class Constructor {
 
   virtual const KVMap& data() { return data_; }
 
+  virtual bool IsArenaMode() const { return false; }
+
   virtual DB* db() const { return nullptr; }  // Overridden in DBConstructor
 
+  virtual bool AnywayDeleteIterator() const { return false; }
+
  protected:
   const InternalKeyComparator* last_internal_key_;
 
@@ -279,8 +284,15 @@ class BlockConstructor: public Constructor {
 // A helper class that converts internal format keys into user keys
 class KeyConvertingIterator: public Iterator {
  public:
-  explicit KeyConvertingIterator(Iterator* iter) : iter_(iter) { }
-  virtual ~KeyConvertingIterator() { delete iter_; }
+  KeyConvertingIterator(Iterator* iter, bool arena_mode = false)
+      : iter_(iter), arena_mode_(arena_mode) {}
+  virtual ~KeyConvertingIterator() {
+    if (arena_mode_) {
+      iter_->~Iterator();
+    } else {
+      delete iter_;
+    }
+  }
   virtual bool Valid() const { return iter_->Valid(); }
   virtual void Seek(const Slice& target) {
     ParsedInternalKey ikey(target, kMaxSequenceNumber, kTypeValue);
@@ -311,6 +323,7 @@ class KeyConvertingIterator: public Iterator {
  private:
   mutable Status status_;
   Iterator* iter_;
+  bool arena_mode_;
 
   // No copying allowed
   KeyConvertingIterator(const KeyConvertingIterator&);
@@ -391,6 +404,10 @@ class TableConstructor: public Constructor {
     return table_reader_.get();
   }
 
+  virtual bool AnywayDeleteIterator() const override {
+    return convert_to_internal_key_;
+  }
+
  private:
   void Reset() {
     uniq_id_ = 0;
@@ -398,12 +415,12 @@ class TableConstructor: public Constructor {
     sink_.reset();
     source_.reset();
   }
-  bool convert_to_internal_key_;
 
   uint64_t uniq_id_;
   unique_ptr<StringSink> sink_;
   unique_ptr<StringSource> source_;
   unique_ptr<TableReader> table_reader_;
+  bool convert_to_internal_key_;
 
   TableConstructor();
 
@@ -446,10 +463,16 @@ class MemTableConstructor: public Constructor {
     return Status::OK();
   }
   virtual Iterator* NewIterator() const {
-    return new KeyConvertingIterator(memtable_->NewIterator(ReadOptions()));
+    return new KeyConvertingIterator(
+        memtable_->NewIterator(ReadOptions(), &arena_), true);
   }
 
+  virtual bool AnywayDeleteIterator() const override { return true; }
+
+  virtual bool IsArenaMode() const override { return true; }
+
  private:
+  mutable Arena arena_;
   InternalKeyComparator internal_comparator_;
   MemTable* memtable_;
   std::shared_ptr<SkipListFactory> table_factory_;
@@ -800,8 +823,12 @@ class Harness {
       iter->Next();
     }
     ASSERT_TRUE(!iter->Valid());
+    if (constructor_->IsArenaMode() && !constructor_->AnywayDeleteIterator()) {
+      iter->~Iterator();
+    } else {
       delete iter;
     }
+  }
 
   void TestBackwardScan(const std::vector<std::string>& keys,
                         const KVMap& data) {
@@ -815,8 +842,12 @@ class Harness {
       iter->Prev();
     }
     ASSERT_TRUE(!iter->Valid());
+    if (constructor_->IsArenaMode() && !constructor_->AnywayDeleteIterator()) {
+      iter->~Iterator();
+    } else {
       delete iter;
     }
+  }
 
   void TestRandomAccess(Random* rnd,
                         const std::vector<std::string>& keys,
@@ -885,8 +916,12 @@ class Harness {
         }
       }
     }
+    if (constructor_->IsArenaMode() && !constructor_->AnywayDeleteIterator()) {
+      iter->~Iterator();
+    } else {
       delete iter;
     }
+  }
 
   std::string ToString(const KVMap& data, const KVMap::const_iterator& it) {
     if (it == data.end()) {
@@ -1835,7 +1870,8 @@ TEST(MemTableTest, Simple) {
   ColumnFamilyMemTablesDefault cf_mems_default(memtable, &options);
   ASSERT_TRUE(WriteBatchInternal::InsertInto(&batch, &cf_mems_default).ok());
 
-  Iterator* iter = memtable->NewIterator(ReadOptions());
+  Arena arena;
+  ScopedArenaIterator iter(memtable->NewIterator(ReadOptions(), &arena));
   iter->SeekToFirst();
   while (iter->Valid()) {
     fprintf(stderr, "key: '%s' -> '%s'\n",
@@ -1844,7 +1880,6 @@ TEST(MemTableTest, Simple) {
     iter->Next();
   }
 
-  delete iter;
   delete memtable->Unref();
 }
 

util/ldb_cmd.cc

@@ -14,6 +14,7 @@
 #include "rocksdb/write_batch.h"
 #include "rocksdb/cache.h"
 #include "util/coding.h"
+#include "util/scoped_arena_iterator.h"
 #include "utilities/ttl/db_ttl_impl.h"
 
 #include <ctime>
@@ -739,7 +740,8 @@ void InternalDumpCommand::DoCommand() {
   uint64_t c=0;
   uint64_t s1=0,s2=0;
   // Setup internal key iterator
-  auto iter = unique_ptr<Iterator>(idb->TEST_NewInternalIterator());
+  Arena arena;
+  ScopedArenaIterator iter(idb->TEST_NewInternalIterator(&arena));
   Status st = iter->status();
   if (!st.ok()) {
     exec_state_ = LDBCommandExecuteResult::FAILED("Iterator error:"

util/scoped_arena_iterator.h

+// Copyright (c) 2013, Facebook, Inc.  All rights reserved.
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree. An additional grant
+// of patent rights can be found in the PATENTS file in the same directory.
+// 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.
+#pragma once
+
+#include "rocksdb/iterator.h"
+
+namespace rocksdb {
+class ScopedArenaIterator {
+ public:
+  explicit ScopedArenaIterator(Iterator* iter = nullptr) : iter_(iter) {}
+
+  Iterator* operator->() { return iter_; }
+
+  void set(Iterator* iter) { iter_ = iter; }
+
+  Iterator* get() { return iter_; }
+
+  ~ScopedArenaIterator() { iter_->~Iterator(); }
+
+ private:
+  Iterator* iter_;
+};
+}  // namespace rocksdb