Replace vector with autovector

Summary: this diff only replace the cases when we need to frequently create vector with small amount of entries. This diff doesn't aim to improve performance of a specific area, but more like a small scale test for the autovector and see how it works in real life.

Test Plan:
make check

I also ran the performance tests, however there is no performance gain/loss. All performance numbers are pretty much the same before/after the change.

Reviewers: dhruba, haobo, sdong, igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D14985

db/db_impl.cc

@@ -47,6 +47,7 @@
 #include "table/block_based_table_factory.h"
 #include "table/merger.h"
 #include "table/two_level_iterator.h"
+#include "util/autovector.h"
 #include "util/auto_roll_logger.h"
 #include "util/build_version.h"
 #include "util/coding.h"
@@ -299,8 +300,7 @@ DBImpl::DBImpl(const Options& options, const std::string& dbname)
 }
 
 DBImpl::~DBImpl() {
-  std::vector<MemTable*> to_delete;
-  to_delete.reserve(options_.max_write_buffer_number);
+  autovector<MemTable*> to_delete;
 
   // Wait for background work to finish
   if (flush_on_destroy_ && mem_->GetFirstSequenceNumber() != 0) {
@@ -455,10 +455,6 @@ void DBImpl::MaybeDumpStats() {
 }
 
 // DBImpl::SuperVersion methods
-DBImpl::SuperVersion::SuperVersion(const int num_memtables) {
-  to_delete.resize(num_memtables);
-}
-
 DBImpl::SuperVersion::~SuperVersion() {
   for (auto td : to_delete) {
     delete td;
@@ -1114,7 +1110,7 @@ Status DBImpl::WriteLevel0TableForRecovery(MemTable* mem, VersionEdit* edit) {
 }
 
 
-Status DBImpl::WriteLevel0Table(std::vector<MemTable*> &mems, VersionEdit* edit,
+Status DBImpl::WriteLevel0Table(autovector<MemTable*>& mems, VersionEdit* edit,
                                 uint64_t* filenumber) {
   mutex_.AssertHeld();
   const uint64_t start_micros = env_->NowMicros();
@@ -1131,15 +1127,15 @@ Status DBImpl::WriteLevel0Table(std::vector<MemTable*> &mems, VersionEdit* edit,
   Status s;
   {
     mutex_.Unlock();
-    std::vector<Iterator*> list;
+    std::vector<Iterator*> memtables;
     for (MemTable* m : mems) {
       Log(options_.info_log,
           "Flushing memtable with log file: %lu\n",
           (unsigned long)m->GetLogNumber());
-      list.push_back(m->NewIterator());
+      memtables.push_back(m->NewIterator());
     }
-    Iterator* iter = NewMergingIterator(env_, &internal_comparator_, &list[0],
-                                        list.size());
+    Iterator* iter = NewMergingIterator(
+        env_, &internal_comparator_, &memtables[0], memtables.size());
     Log(options_.info_log,
         "Level-0 flush table #%lu: started",
         (unsigned long)meta.number);
@@ -1214,7 +1210,7 @@ Status DBImpl::FlushMemTableToOutputFile(bool* madeProgress,
 
   // Save the contents of the earliest memtable as a new Table
   uint64_t file_number;
-  std::vector<MemTable*> mems;
+  autovector<MemTable*> mems;
   imm_.PickMemtablesToFlush(&mems);
   if (mems.empty()) {
     Log(options_.info_log, "Nothing in memstore to flush");
@@ -1316,8 +1312,7 @@ void DBImpl::ReFitLevel(int level, int target_level) {
   assert(level < NumberLevels());
 
   SuperVersion* superversion_to_free = nullptr;
-  SuperVersion* new_superversion =
-      new SuperVersion(options_.max_write_buffer_number);
+  SuperVersion* new_superversion = new SuperVersion();
 
   mutex_.Lock();
 
@@ -1750,7 +1745,7 @@ Status DBImpl::BackgroundFlush(bool* madeProgress,
 
 void DBImpl::BackgroundCallFlush() {
   bool madeProgress = false;
-  DeletionState deletion_state(options_.max_write_buffer_number, true);
+  DeletionState deletion_state(true);
   assert(bg_flush_scheduled_);
   MutexLock l(&mutex_);
 
@@ -1796,7 +1791,7 @@ void DBImpl::TEST_PurgeObsoleteteWAL() {
 
 void DBImpl::BackgroundCallCompaction() {
   bool madeProgress = false;
-  DeletionState deletion_state(options_.max_write_buffer_number, true);
+  DeletionState deletion_state(true);
 
   MaybeDumpStats();
 
@@ -2591,16 +2586,16 @@ namespace {
 struct IterState {
   port::Mutex* mu;
   Version* version;
-  std::vector<MemTable*> mem; // includes both mem_ and imm_
+  autovector<MemTable*> mem; // includes both mem_ and imm_
   DBImpl *db;
 };
 
 static void CleanupIteratorState(void* arg1, void* arg2) {
   IterState* state = reinterpret_cast<IterState*>(arg1);
-  DBImpl::DeletionState deletion_state(state->db->GetOptions().
-                                       max_write_buffer_number);
+  DBImpl::DeletionState deletion_state;
   state->mu->Lock();
-  for (unsigned int i = 0; i < state->mem.size(); i++) {
+  auto mems_size = state->mem.size();
+  for (size_t i = 0; i < mems_size; i++) {
     MemTable* m = state->mem[i]->Unref();
     if (m != nullptr) {
       deletion_state.memtables_to_free.push_back(m);
@@ -2620,7 +2615,7 @@ Iterator* DBImpl::NewInternalIterator(const ReadOptions& options,
                                       SequenceNumber* latest_snapshot) {
   IterState* cleanup = new IterState;
   MemTable* mutable_mem;
-  std::vector<MemTable*> immutables;
+  autovector<MemTable*> immutables;
   Version* version;
 
   // Collect together all needed child iterators for mem
@@ -2638,16 +2633,17 @@ Iterator* DBImpl::NewInternalIterator(const ReadOptions& options,
   version = versions_->current();
   mutex_.Unlock();
 
-  std::vector<Iterator*> list;
-  list.push_back(mutable_mem->NewIterator(options));
+  std::vector<Iterator*> memtables;
+  memtables.push_back(mutable_mem->NewIterator(options));
   cleanup->mem.push_back(mutable_mem);
   for (MemTable* m : immutables) {
-    list.push_back(m->NewIterator(options));
+    memtables.push_back(m->NewIterator(options));
     cleanup->mem.push_back(m);
   }
-  version->AddIterators(options, storage_options_, &list);
-  Iterator* internal_iter =
-      NewMergingIterator(env_, &internal_comparator_, &list[0], list.size());
+  version->AddIterators(options, storage_options_, &memtables);
+  Iterator* internal_iter = NewMergingIterator(
+      env_, &internal_comparator_, memtables.data(), memtables.size()
+  );
   cleanup->version = version;
   cleanup->mu = &mutex_;
   cleanup->db = this;
@@ -2802,7 +2798,7 @@ std::vector<Status> DBImpl::MultiGet(const ReadOptions& options,
   StartPerfTimer(&snapshot_timer);
 
   SequenceNumber snapshot;
-  std::vector<MemTable*> to_delete;
+  autovector<MemTable*> to_delete;
 
   mutex_.Lock();
   if (options.snapshot != nullptr) {
@@ -3322,7 +3318,7 @@ Status DBImpl::MakeRoomForWrite(bool force,
           lfile->SetPreallocationBlockSize(1.1 * options_.write_buffer_size);
           new_mem = new MemTable(
             internal_comparator_, mem_rep_factory_, NumberLevels(), options_);
-          new_superversion = new SuperVersion(options_.max_write_buffer_number);
+          new_superversion = new SuperVersion();
         }
       }
       mutex_.Lock();
@@ -3703,7 +3699,7 @@ Status DBImpl::DeleteFile(std::string name) {
   FileMetaData metadata;
   int maxlevel = NumberLevels();
   VersionEdit edit(maxlevel);
-  DeletionState deletion_state(0, true);
+  DeletionState deletion_state(true);
   {
     MutexLock l(&mutex_);
     status = versions_->GetMetadataForFile(number, &level, &metadata);

db/db_impl.h

@@ -7,6 +7,7 @@
 // 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 <atomic>
 #include <deque>
 #include <set>
@@ -16,13 +17,14 @@
 #include "db/log_writer.h"
 #include "db/snapshot.h"
 #include "db/version_edit.h"
+#include "memtable_list.h"
+#include "port/port.h"
 #include "rocksdb/db.h"
 #include "rocksdb/env.h"
 #include "rocksdb/memtablerep.h"
 #include "rocksdb/transaction_log.h"
-#include "port/port.h"
+#include "util/autovector.h"
 #include "util/stats_logger.h"
-#include "memtable_list.h"
 
 namespace rocksdb {
 
@@ -138,10 +140,10 @@ class DBImpl : public DB {
     // We need to_delete because during Cleanup(), imm.UnrefAll() returns
     // all memtables that we need to free through this vector. We then
     // delete all those memtables outside of mutex, during destruction
-    std::vector<MemTable*> to_delete;
+    autovector<MemTable*> to_delete;
 
     // should be called outside the mutex
-    explicit SuperVersion(const int num_memtables = 0);
+    SuperVersion() = default;
     ~SuperVersion();
     SuperVersion* Ref();
     // Returns true if this was the last reference and caller should
@@ -180,7 +182,7 @@ class DBImpl : public DB {
     std::vector<uint64_t> log_delete_files;
 
     // a list of memtables to be free
-    std::vector<MemTable *> memtables_to_free;
+    autovector<MemTable*> memtables_to_free;
 
     SuperVersion* superversion_to_free; // if nullptr nothing to free
 
@@ -190,15 +192,13 @@ class DBImpl : public DB {
     // that corresponds to the set of files in 'live'.
     uint64_t manifest_file_number, log_number, prev_log_number;
 
-    explicit DeletionState(const int num_memtables = 0,
-                           bool create_superversion = false) {
+    explicit DeletionState(bool create_superversion = false) {
       manifest_file_number = 0;
       log_number = 0;
       prev_log_number = 0;
-      memtables_to_free.reserve(num_memtables);
       superversion_to_free = nullptr;
       new_superversion =
-          create_superversion ? new SuperVersion(num_memtables) : nullptr;
+          create_superversion ? new SuperVersion() : nullptr;
     }
 
     ~DeletionState() {
@@ -283,7 +283,7 @@ class DBImpl : public DB {
   // for the entire period. The second method WriteLevel0Table supports
   // concurrent flush memtables to storage.
   Status WriteLevel0TableForRecovery(MemTable* mem, VersionEdit* edit);
-  Status WriteLevel0Table(std::vector<MemTable*> &mems, VersionEdit* edit,
+  Status WriteLevel0Table(autovector<MemTable*>& mems, VersionEdit* edit,
                                 uint64_t* filenumber);
 
   uint64_t SlowdownAmount(int n, int top, int bottom);

db/memtable_list.cc

@@ -31,7 +31,7 @@ void MemTableList::RefAll() {
 // Drop reference count on all underling memtables. If the
 // refcount of an underlying memtable drops to zero, then
 // return it in to_delete vector.
-void MemTableList::UnrefAll(std::vector<MemTable*>* to_delete) {
+void MemTableList::UnrefAll(autovector<MemTable*>* to_delete) {
   for (auto &memtable : memlist_) {
     MemTable* m = memtable->Unref();
     if (m != nullptr) {
@@ -58,7 +58,7 @@ bool MemTableList::IsFlushPending(int min_write_buffer_number_to_merge) {
 }
 
 // Returns the memtables that need to be flushed.
-void MemTableList::PickMemtablesToFlush(std::vector<MemTable*>* ret) {
+void MemTableList::PickMemtablesToFlush(autovector<MemTable*>* ret) {
   for (auto it = memlist_.rbegin(); it != memlist_.rend(); it++) {
     MemTable* m = *it;
     if (!m->flush_in_progress_) {
@@ -76,12 +76,12 @@ void MemTableList::PickMemtablesToFlush(std::vector<MemTable*>* ret) {
 
 // Record a successful flush in the manifest file
 Status MemTableList::InstallMemtableFlushResults(
-                      const std::vector<MemTable*> &mems,
+                      const autovector<MemTable*> &mems,
                       VersionSet* vset, Status flushStatus,
                       port::Mutex* mu, Logger* info_log,
                       uint64_t file_number,
                       std::set<uint64_t>& pending_outputs,
-                      std::vector<MemTable*>* to_delete) {
+                      autovector<MemTable*>* to_delete) {
   mu->AssertHeld();
 
   // If the flush was not successful, then just reset state.
@@ -213,7 +213,7 @@ bool MemTableList::Get(const LookupKey& key, std::string* value, Status* s,
   return false;
 }
 
-void MemTableList::GetMemTables(std::vector<MemTable*>* output) {
+void MemTableList::GetMemTables(autovector<MemTable*>* output) {
   for (auto &memtable : memlist_) {
     output->push_back(memtable);
   }

db/memtable_list.h

@@ -3,15 +3,17 @@
 //  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.
 //
-
 #pragma once
+
 #include <string>
 #include <list>
 #include <deque>
-#include "rocksdb/db.h"
+
 #include "db/dbformat.h"
+#include "db/memtable.h"
 #include "db/skiplist.h"
-#include "memtable.h"
+#include "rocksdb/db.h"
+#include "util/autovector.h"
 
 namespace rocksdb {
 
@@ -47,7 +49,7 @@ class MemTableList {
   // Drop reference count on all underling memtables. If the refcount
   // on an underlying memtable drops to zero, then return it in
   // to_delete vector.
-  void UnrefAll(std::vector<MemTable*>* to_delete);
+  void UnrefAll(autovector<MemTable*>* to_delete);
 
   // Returns the total number of memtables in the list
   int size();
@@ -58,15 +60,15 @@ class MemTableList {
 
   // Returns the earliest memtables that needs to be flushed. The returned
   // memtables are guaranteed to be in the ascending order of created time.
-  void PickMemtablesToFlush(std::vector<MemTable*>* mems);
+  void PickMemtablesToFlush(autovector<MemTable*>* mems);
 
   // Commit a successful flush in the manifest file
-  Status InstallMemtableFlushResults(const std::vector<MemTable*> &m,
+  Status InstallMemtableFlushResults(const autovector<MemTable*> &m,
                       VersionSet* vset, Status flushStatus,
                       port::Mutex* mu, Logger* info_log,
                       uint64_t file_number,
                       std::set<uint64_t>& pending_outputs,
-                      std::vector<MemTable*>* to_delete);
+                      autovector<MemTable*>* to_delete);
 
   // New memtables are inserted at the front of the list.
   // Takes ownership of the referenced held on *m by the caller of Add().
@@ -81,7 +83,7 @@ class MemTableList {
            MergeContext& merge_context, const Options& options);
 
   // Returns the list of underlying memtables.
-  void GetMemTables(std::vector<MemTable*>* list);
+  void GetMemTables(autovector<MemTable*>* list);
 
   // Request a flush of all existing memtables to storage
   void FlushRequested() { flush_requested_ = true; }

util/autovector.h

@@ -57,11 +57,9 @@ class autovector {
     typedef std::random_access_iterator_tag iterator_category;
 
     iterator_impl(TAutoVector* vect, size_t index)
-      : vect_(vect)
-      , index_(index) {
-    };
+        : vect_(vect), index_(index) {};
     iterator_impl(const iterator_impl&) = default;
-    ~iterator_impl() { }
+    ~iterator_impl() {}
     iterator_impl& operator=(const iterator_impl&) = default;
 
     // -- Advancement
@@ -130,9 +128,7 @@ class autovector {
       return index_ == other.index_;
     }
 
-    bool operator!=(const self_type& other) const {
-      return !(*this == other);
-    }
+    bool operator!=(const self_type& other) const { return !(*this == other); }
 
     bool operator>(const self_type& other) const {
       assert(vect_ == other.vect_);
@@ -174,13 +170,9 @@ class autovector {
     return vect_.capacity() == 0;
   }
 
-  size_type size() const {
-    return num_stack_items_ + vect_.size();
-  }
+  size_type size() const { return num_stack_items_ + vect_.size(); }
 
-  bool empty() const {
-    return size() == 0;
-  }
+  bool empty() const { return size() == 0; }
 
   // will not check boundry
   const_reference operator[](size_type n) const {
@@ -235,11 +227,9 @@ class autovector {
     }
   }
 
-  void push_back(const T& item) {
-    push_back(value_type(item));
-  }
+  void push_back(const T& item) { push_back(value_type(item)); }
 
-  template<class... Args>
+  template <class... Args>
   void emplace_back(Args&&... args) {
     push_back(value_type(args...));
   }
@@ -261,13 +251,9 @@ class autovector {
   // -- Copy and Assignment
   autovector& assign(const autovector& other);
 
-  autovector(const autovector& other) {
-    assign(other);
-  }
+  autovector(const autovector& other) { assign(other); }
 
-  autovector& operator=(const autovector& other) {
-    return assign(other);
-  }
+  autovector& operator=(const autovector& other) { return assign(other); }
 
   // move operation are disallowed since it is very hard to make sure both
   // autovectors are allocated from the same function stack.
@@ -275,41 +261,29 @@ class autovector {
   autovector(autovector&& other) = delete;
 
   // -- Iterator Operations
-  iterator begin() {
-    return iterator(this, 0);
-  }
+  iterator begin() { return iterator(this, 0); }
 
-  const_iterator begin() const {
-    return const_iterator(this, 0);
-  }
+  const_iterator begin() const { return const_iterator(this, 0); }
 
-  iterator end() {
-    return iterator(this, this->size());
-  }
+  iterator end() { return iterator(this, this->size()); }
 
-  const_iterator end() const {
-    return const_iterator(this, this->size());
-  }
+  const_iterator end() const { return const_iterator(this, this->size()); }
 
-  reverse_iterator rbegin() {
-    return reverse_iterator(end());
-  }
+  reverse_iterator rbegin() { return reverse_iterator(end()); }
 
   const_reverse_iterator rbegin() const {
     return const_reverse_iterator(end());
   }
 
-  reverse_iterator rend() {
-    return reverse_iterator(begin());
-  }
+  reverse_iterator rend() { return reverse_iterator(begin()); }
 
   const_reverse_iterator rend() const {
     return const_reverse_iterator(begin());
   }
 
  private:
-  size_type num_stack_items_ = 0; // current number of items
-  value_type values_[kSize]; // the first `kSize` items
+  size_type num_stack_items_ = 0;  // current number of items
+  value_type values_[kSize];       // the first `kSize` items
   // used only if there are more than `kSize` items.
   std::vector<T> vect_;
 };

util/cache.cc

@@ -10,10 +10,10 @@
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <vector>
 
 #include "rocksdb/cache.h"
 #include "port/port.h"
+#include "util/autovector.h"
 #include "util/hash.h"
 #include "util/mutexlock.h"
 
@@ -264,8 +264,7 @@ Cache::Handle* LRUCache::Insert(
 
   LRUHandle* e = reinterpret_cast<LRUHandle*>(
       malloc(sizeof(LRUHandle)-1 + key.size()));
-  std::vector<LRUHandle*> last_reference_list;
-  last_reference_list.reserve(1);
+  autovector<LRUHandle*> last_reference_list;
 
   e->value = value;
   e->deleter = deleter;