Revision created by MOE tool push_codebase.

MOE_MIGRATION=


git-svn-id: https://leveldb.googlecode.com/svn/trunk@22 62dab493-f737-651d-591e-8d6aee1b9529

1 files changed, 1188 insertions, 0 deletions

diff --git a/leveldb/db/db_impl.cc b/leveldb/db/db_impl.cc
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+++ b/leveldb/db/db_impl.cc
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+// 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.
+
+#include "db/db_impl.h"
+
+#include <algorithm>
+#include <set>
+#include <string>
+#include <stdint.h>
+#include <stdio.h>
+#include <vector>
+#include "db/builder.h"
+#include "db/db_iter.h"
+#include "db/dbformat.h"
+#include "db/filename.h"
+#include "db/log_reader.h"
+#include "db/log_writer.h"
+#include "db/memtable.h"
+#include "db/table_cache.h"
+#include "db/version_set.h"
+#include "db/write_batch_internal.h"
+#include "leveldb/db.h"
+#include "leveldb/env.h"
+#include "leveldb/status.h"
+#include "leveldb/table.h"
+#include "leveldb/table_builder.h"
+#include "port/port.h"
+#include "table/block.h"
+#include "table/merger.h"
+#include "table/two_level_iterator.h"
+#include "util/coding.h"
+#include "util/logging.h"
+#include "util/mutexlock.h"
+
+namespace leveldb {
+
+struct DBImpl::CompactionState {
+  Compaction* const compaction;
+
+  // Sequence numbers < smallest_snapshot are not significant since we
+  // will never have to service a snapshot below smallest_snapshot.
+  // Therefore if we have seen a sequence number S <= smallest_snapshot,
+  // we can drop all entries for the same key with sequence numbers < S.
+  SequenceNumber smallest_snapshot;
+
+  // Files produced by compaction
+  struct Output {
+    uint64_t number;
+    uint64_t file_size;
+    InternalKey smallest, largest;
+  };
+  std::vector<Output> outputs;
+
+  // State kept for output being generated
+  WritableFile* outfile;
+  TableBuilder* builder;
+
+  uint64_t total_bytes;
+
+  Output* current_output() { return &outputs[outputs.size()-1]; }
+
+  explicit CompactionState(Compaction* c)
+      : compaction(c),
+        outfile(NULL),
+        builder(NULL),
+        total_bytes(0) {
+  }
+};
+
+namespace {
+class NullWritableFile : public WritableFile {
+ public:
+  virtual Status Append(const Slice& data) { return Status::OK(); }
+  virtual Status Close() { return Status::OK(); }
+  virtual Status Flush() { return Status::OK(); }
+  virtual Status Sync() { return Status::OK(); }
+};
+}
+
+// Fix user-supplied options to be reasonable
+template <class T,class V>
+static void ClipToRange(T* ptr, V minvalue, V maxvalue) {
+  if (static_cast<V>(*ptr) > maxvalue) *ptr = maxvalue;
+  if (static_cast<V>(*ptr) < minvalue) *ptr = minvalue;
+}
+Options SanitizeOptions(const std::string& dbname,
+                        const InternalKeyComparator* icmp,
+                        const Options& src) {
+  Options result = src;
+  result.comparator = icmp;
+  ClipToRange(&result.max_open_files,           20,     50000);
+  ClipToRange(&result.write_buffer_size,        64<<10, 1<<30);
+  ClipToRange(&result.block_size,               1<<10,  4<<20);
+  if (result.info_log == NULL) {
+    // Open a log file in the same directory as the db
+    src.env->CreateDir(dbname);  // In case it does not exist
+    src.env->RenameFile(InfoLogFileName(dbname), OldInfoLogFileName(dbname));
+    Status s = src.env->NewWritableFile(InfoLogFileName(dbname),
+                                        &result.info_log);
+    if (!s.ok()) {
+      // No place suitable for logging
+      result.info_log = new NullWritableFile;
+    }
+  }
+  if (result.block_cache == NULL) {
+    result.block_cache = NewLRUCache(8 << 20);
+  }
+  return result;
+}
+
+DBImpl::DBImpl(const Options& options, const std::string& dbname)
+    : env_(options.env),
+      internal_comparator_(options.comparator),
+      options_(SanitizeOptions(dbname, &internal_comparator_, options)),
+      owns_info_log_(options_.info_log != options.info_log),
+      owns_cache_(options_.block_cache != options.block_cache),
+      dbname_(dbname),
+      db_lock_(NULL),
+      shutting_down_(NULL),
+      bg_cv_(&mutex_),
+      compacting_cv_(&mutex_),
+      mem_(new MemTable(internal_comparator_)),
+      imm_(NULL),
+      logfile_(NULL),
+      log_(NULL),
+      bg_compaction_scheduled_(false),
+      compacting_(false) {
+  has_imm_.Release_Store(NULL);
+
+  // Reserve ten files or so for other uses and give the rest to TableCache.
+  const int table_cache_size = options.max_open_files - 10;
+  table_cache_ = new TableCache(dbname_, &options_, table_cache_size);
+
+  versions_ = new VersionSet(dbname_, &options_, table_cache_,
+                             &internal_comparator_);
+}
+
+DBImpl::~DBImpl() {
+  // Wait for background work to finish
+  mutex_.Lock();
+  shutting_down_.Release_Store(this);  // Any non-NULL value is ok
+  if (bg_compaction_scheduled_) {
+    while (bg_compaction_scheduled_) {
+      bg_cv_.Wait();
+    }
+  }
+  mutex_.Unlock();
+
+  if (db_lock_ != NULL) {
+    env_->UnlockFile(db_lock_);
+  }
+
+  delete versions_;
+  delete mem_;
+  delete imm_;
+  delete log_;
+  delete logfile_;
+  delete table_cache_;
+
+  if (owns_info_log_) {
+    delete options_.info_log;
+  }
+  if (owns_cache_) {
+    delete options_.block_cache;
+  }
+}
+
+Status DBImpl::NewDB() {
+  VersionEdit new_db;
+  new_db.SetComparatorName(user_comparator()->Name());
+  new_db.SetLogNumber(0);
+  new_db.SetNextFile(2);
+  new_db.SetLastSequence(0);
+
+  const std::string manifest = DescriptorFileName(dbname_, 1);
+  WritableFile* file;
+  Status s = env_->NewWritableFile(manifest, &file);
+  if (!s.ok()) {
+    return s;
+  }
+  {
+    log::Writer log(file);
+    std::string record;
+    new_db.EncodeTo(&record);
+    s = log.AddRecord(record);
+    if (s.ok()) {
+      s = file->Close();
+    }
+  }
+  delete file;
+  if (s.ok()) {
+    // Make "CURRENT" file that points to the new manifest file.
+    s = SetCurrentFile(env_, dbname_, 1);
+  } else {
+    env_->DeleteFile(manifest);
+  }
+  return s;
+}
+
+void DBImpl::MaybeIgnoreError(Status* s) const {
+  if (s->ok() || options_.paranoid_checks) {
+    // No change needed
+  } else {
+    Log(env_, options_.info_log, "Ignoring error %s", s->ToString().c_str());
+    *s = Status::OK();
+  }
+}
+
+void DBImpl::DeleteObsoleteFiles() {
+  // Make a set of all of the live files
+  std::set<uint64_t> live = pending_outputs_;
+  versions_->AddLiveFiles(&live);
+
+  std::vector<std::string> filenames;
+  env_->GetChildren(dbname_, &filenames); // Ignoring errors on purpose
+  uint64_t number;
+  FileType type;
+  for (size_t i = 0; i < filenames.size(); i++) {
+    if (ParseFileName(filenames[i], &number, &type)) {
+      bool keep = true;
+      switch (type) {
+        case kLogFile:
+          keep = ((number == versions_->LogNumber()) ||
+                  (number == versions_->PrevLogNumber()));
+          break;
+        case kDescriptorFile:
+          // Keep my manifest file, and any newer incarnations'
+          // (in case there is a race that allows other incarnations)
+          keep = (number >= versions_->ManifestFileNumber());
+          break;
+        case kTableFile:
+          keep = (live.find(number) != live.end());
+          break;
+        case kTempFile:
+          // Any temp files that are currently being written to must
+          // be recorded in pending_outputs_, which is inserted into "live"
+          keep = (live.find(number) != live.end());
+          break;
+        case kCurrentFile:
+        case kDBLockFile:
+        case kInfoLogFile:
+          keep = true;
+          break;
+      }
+
+      if (!keep) {
+        if (type == kTableFile) {
+          table_cache_->Evict(number);
+        }
+        Log(env_, options_.info_log, "Delete type=%d #%lld\n",
+            int(type),
+            static_cast<unsigned long long>(number));
+        env_->DeleteFile(dbname_ + "/" + filenames[i]);
+      }
+    }
+  }
+}
+
+Status DBImpl::Recover(VersionEdit* edit) {
+  mutex_.AssertHeld();
+
+  // Ignore error from CreateDir since the creation of the DB is
+  // committed only when the descriptor is created, and this directory
+  // may already exist from a previous failed creation attempt.
+  env_->CreateDir(dbname_);
+  assert(db_lock_ == NULL);
+  Status s = env_->LockFile(LockFileName(dbname_), &db_lock_);
+  if (!s.ok()) {
+    return s;
+  }
+
+  if (!env_->FileExists(CurrentFileName(dbname_))) {
+    if (options_.create_if_missing) {
+      s = NewDB();
+      if (!s.ok()) {
+        return s;
+      }
+    } else {
+      return Status::InvalidArgument(
+          dbname_, "does not exist (create_if_missing is false)");
+    }
+  } else {
+    if (options_.error_if_exists) {
+      return Status::InvalidArgument(
+          dbname_, "exists (error_if_exists is true)");
+    }
+  }
+
+  s = versions_->Recover();
+  if (s.ok()) {
+    // Recover from the log files named in the descriptor
+    SequenceNumber max_sequence(0);
+    if (versions_->PrevLogNumber() != 0) { // log#==0 means no prev log
+      s = RecoverLogFile(versions_->PrevLogNumber(), edit, &max_sequence);
+    }
+    if (s.ok() && versions_->LogNumber() != 0) { // log#==0 for initial state
+      s = RecoverLogFile(versions_->LogNumber(), edit, &max_sequence);
+    }
+    if (s.ok()) {
+      if (versions_->LastSequence() < max_sequence) {
+        versions_->SetLastSequence(max_sequence);
+      }
+    }
+  }
+
+  return s;
+}
+
+Status DBImpl::RecoverLogFile(uint64_t log_number,
+                              VersionEdit* edit,
+                              SequenceNumber* max_sequence) {
+  struct LogReporter : public log::Reader::Reporter {
+    Env* env;
+    WritableFile* info_log;
+    const char* fname;
+    Status* status;  // NULL if options_.paranoid_checks==false
+    virtual void Corruption(size_t bytes, const Status& s) {
+      Log(env, info_log, "%s%s: dropping %d bytes; %s",
+          (this->status == NULL ? "(ignoring error) " : ""),
+          fname, static_cast<int>(bytes), s.ToString().c_str());
+      if (this->status != NULL && this->status->ok()) *this->status = s;
+    }
+  };
+
+  mutex_.AssertHeld();
+
+  // Open the log file
+  std::string fname = LogFileName(dbname_, log_number);
+  SequentialFile* file;
+  Status status = env_->NewSequentialFile(fname, &file);
+  if (!status.ok()) {
+    MaybeIgnoreError(&status);
+    return status;
+  }
+
+  // Create the log reader.
+  LogReporter reporter;
+  reporter.env = env_;
+  reporter.info_log = options_.info_log;
+  reporter.fname = fname.c_str();
+  reporter.status = (options_.paranoid_checks ? &status : NULL);
+  // We intentially make log::Reader do checksumming even if
+  // paranoid_checks==false so that corruptions cause entire commits
+  // to be skipped instead of propagating bad information (like overly
+  // large sequence numbers).
+  log::Reader reader(file, &reporter, true/*checksum*/);
+  Log(env_, options_.info_log, "Recovering log #%llu",
+      (unsigned long long) log_number);
+
+  // Read all the records and add to a memtable
+  std::string scratch;
+  Slice record;
+  WriteBatch batch;
+  MemTable* mem = NULL;
+  while (reader.ReadRecord(&record, &scratch) &&
+         status.ok()) {
+    if (record.size() < 12) {
+      reporter.Corruption(
+          record.size(), Status::Corruption("log record too small"));
+      continue;
+    }
+    WriteBatchInternal::SetContents(&batch, record);
+
+    if (mem == NULL) {
+      mem = new MemTable(internal_comparator_);
+    }
+    status = WriteBatchInternal::InsertInto(&batch, mem);
+    MaybeIgnoreError(&status);
+    if (!status.ok()) {
+      break;
+    }
+    const SequenceNumber last_seq =
+        WriteBatchInternal::Sequence(&batch) +
+        WriteBatchInternal::Count(&batch) - 1;
+    if (last_seq > *max_sequence) {
+      *max_sequence = last_seq;
+    }
+
+    if (mem->ApproximateMemoryUsage() > options_.write_buffer_size) {
+      status = WriteLevel0Table(mem, edit);
+      if (!status.ok()) {
+        // Reflect errors immediately so that conditions like full
+        // file-systems cause the DB::Open() to fail.
+        break;
+      }
+      delete mem;
+      mem = NULL;
+    }
+  }
+
+  if (status.ok() && mem != NULL) {
+    status = WriteLevel0Table(mem, edit);
+    // Reflect errors immediately so that conditions like full
+    // file-systems cause the DB::Open() to fail.
+  }
+
+  delete mem;
+  delete file;
+  return status;
+}
+
+Status DBImpl::WriteLevel0Table(MemTable* mem, VersionEdit* edit) {
+  mutex_.AssertHeld();
+  const uint64_t start_micros = env_->NowMicros();
+  FileMetaData meta;
+  meta.number = versions_->NewFileNumber();
+  pending_outputs_.insert(meta.number);
+  Iterator* iter = mem->NewIterator();
+  Log(env_, options_.info_log, "Level-0 table #%llu: started",
+      (unsigned long long) meta.number);
+
+  Status s;
+  {
+    mutex_.Unlock();
+    s = BuildTable(dbname_, env_, options_, table_cache_, iter, &meta, edit);
+    mutex_.Lock();
+  }
+
+  Log(env_, options_.info_log, "Level-0 table #%llu: %lld bytes %s",
+      (unsigned long long) meta.number,
+      (unsigned long long) meta.file_size,
+      s.ToString().c_str());
+  delete iter;
+  pending_outputs_.erase(meta.number);
+
+  CompactionStats stats;
+  stats.micros = env_->NowMicros() - start_micros;
+  stats.bytes_written = meta.file_size;
+  stats_[0].Add(stats);
+  return s;
+}
+
+Status DBImpl::CompactMemTable() {
+  mutex_.AssertHeld();
+  assert(imm_ != NULL);
+  assert(compacting_);
+
+  // Save the contents of the memtable as a new Table
+  VersionEdit edit;
+  Status s = WriteLevel0Table(imm_, &edit);
+
+  // Replace immutable memtable with the generated Table
+  if (s.ok()) {
+    edit.SetPrevLogNumber(0);
+    s = versions_->LogAndApply(&edit, imm_);
+  }
+
+  if (s.ok()) {
+    // Commit to the new state
+    imm_ = NULL;
+    has_imm_.Release_Store(NULL);
+    DeleteObsoleteFiles();
+  }
+
+  compacting_cv_.SignalAll();  // Wake up waiter even if there was an error
+  return s;
+}
+
+void DBImpl::TEST_CompactRange(
+    int level,
+    const std::string& begin,
+    const std::string& end) {
+  MutexLock l(&mutex_);
+  while (compacting_) {
+    compacting_cv_.Wait();
+  }
+  Compaction* c = versions_->CompactRange(
+      level,
+      InternalKey(begin, kMaxSequenceNumber, kValueTypeForSeek),
+      InternalKey(end, 0, static_cast<ValueType>(0)));
+
+  if (c != NULL) {
+    CompactionState* compact = new CompactionState(c);
+    DoCompactionWork(compact);  // Ignore error in test compaction
+    CleanupCompaction(compact);
+  }
+
+  // Start any background compaction that may have been delayed by this thread
+  MaybeScheduleCompaction();
+}
+
+Status DBImpl::TEST_CompactMemTable() {
+  MutexLock l(&mutex_);
+  Status s = MakeRoomForWrite(true /* force compaction */);
+  if (s.ok()) {
+    // Wait until the compaction completes
+    while (imm_ != NULL && bg_error_.ok()) {
+      compacting_cv_.Wait();
+    }
+    if (imm_ != NULL) {
+      s = bg_error_;
+    }
+  }
+  return s;
+}
+
+void DBImpl::MaybeScheduleCompaction() {
+  mutex_.AssertHeld();
+  if (bg_compaction_scheduled_) {
+    // Already scheduled
+  } else if (compacting_) {
+    // Some other thread is running a compaction.  Do not conflict with it.
+  } else if (shutting_down_.Acquire_Load()) {
+    // DB is being deleted; no more background compactions
+  } else if (imm_ == NULL && !versions_->NeedsCompaction()) {
+    // No work to be done
+  } else {
+    bg_compaction_scheduled_ = true;
+    env_->Schedule(&DBImpl::BGWork, this);
+  }
+}
+
+void DBImpl::BGWork(void* db) {
+  reinterpret_cast<DBImpl*>(db)->BackgroundCall();
+}
+
+void DBImpl::BackgroundCall() {
+  MutexLock l(&mutex_);
+  assert(bg_compaction_scheduled_);
+  if (!shutting_down_.Acquire_Load() &&
+      !compacting_) {
+    BackgroundCompaction();
+  }
+  bg_compaction_scheduled_ = false;
+  bg_cv_.SignalAll();
+
+  // Previous compaction may have produced too many files in a level,
+  // so reschedule another compaction if needed.
+  MaybeScheduleCompaction();
+}
+
+void DBImpl::BackgroundCompaction() {
+  mutex_.AssertHeld();
+  assert(!compacting_);
+
+  if (imm_ != NULL) {
+    compacting_ = true;
+    CompactMemTable();
+    compacting_ = false;
+    compacting_cv_.SignalAll();
+    return;
+  }
+
+  Compaction* c = versions_->PickCompaction();
+  if (c == NULL) {
+    // Nothing to do
+    return;
+  }
+
+  Status status;
+  if (c->IsTrivialMove()) {
+    // Move file to next level
+    assert(c->num_input_files(0) == 1);
+    FileMetaData* f = c->input(0, 0);
+    c->edit()->DeleteFile(c->level(), f->number);
+    c->edit()->AddFile(c->level() + 1, f->number, f->file_size,
+                       f->smallest, f->largest);
+    status = versions_->LogAndApply(c->edit(), NULL);
+    Log(env_, options_.info_log, "Moved #%lld to level-%d %lld bytes %s\n",
+        static_cast<unsigned long long>(f->number),
+        c->level() + 1,
+        static_cast<unsigned long long>(f->file_size),
+        status.ToString().c_str());
+  } else {
+    CompactionState* compact = new CompactionState(c);
+    status = DoCompactionWork(compact);
+    CleanupCompaction(compact);
+  }
+  delete c;
+
+  if (status.ok()) {
+    // Done
+  } else if (shutting_down_.Acquire_Load()) {
+    // Ignore compaction errors found during shutting down
+  } else {
+    Log(env_, options_.info_log,
+        "Compaction error: %s", status.ToString().c_str());
+    if (options_.paranoid_checks && bg_error_.ok()) {
+      bg_error_ = status;
+    }
+  }
+}
+
+void DBImpl::CleanupCompaction(CompactionState* compact) {
+  mutex_.AssertHeld();
+  if (compact->builder != NULL) {
+    // May happen if we get a shutdown call in the middle of compaction
+    compact->builder->Abandon();
+    delete compact->builder;
+  } else {
+    assert(compact->outfile == NULL);
+  }
+  delete compact->outfile;
+  for (size_t i = 0; i < compact->outputs.size(); i++) {
+    const CompactionState::Output& out = compact->outputs[i];
+    pending_outputs_.erase(out.number);
+  }
+  delete compact;
+}
+
+Status DBImpl::OpenCompactionOutputFile(CompactionState* compact) {
+  assert(compact != NULL);
+  assert(compact->builder == NULL);
+  uint64_t file_number;
+  {
+    mutex_.Lock();
+    file_number = versions_->NewFileNumber();
+    pending_outputs_.insert(file_number);
+    CompactionState::Output out;
+    out.number = file_number;
+    out.smallest.Clear();
+    out.largest.Clear();
+    compact->outputs.push_back(out);
+    mutex_.Unlock();
+  }
+
+  // Make the output file
+  std::string fname = TableFileName(dbname_, file_number);
+  Status s = env_->NewWritableFile(fname, &compact->outfile);
+  if (s.ok()) {
+    compact->builder = new TableBuilder(options_, compact->outfile);
+  }
+  return s;
+}
+
+Status DBImpl::FinishCompactionOutputFile(CompactionState* compact,
+                                          Iterator* input) {
+  assert(compact != NULL);
+  assert(compact->outfile != NULL);
+  assert(compact->builder != NULL);
+
+  const uint64_t output_number = compact->current_output()->number;
+  assert(output_number != 0);
+
+  // Check for iterator errors
+  Status s = input->status();
+  const uint64_t current_entries = compact->builder->NumEntries();
+  if (s.ok()) {
+    s = compact->builder->Finish();
+  } else {
+    compact->builder->Abandon();
+  }
+  const uint64_t current_bytes = compact->builder->FileSize();
+  compact->current_output()->file_size = current_bytes;
+  compact->total_bytes += current_bytes;
+  delete compact->builder;
+  compact->builder = NULL;
+
+  // Finish and check for file errors
+  if (s.ok()) {
+    s = compact->outfile->Sync();
+  }
+  if (s.ok()) {
+    s = compact->outfile->Close();
+  }
+  delete compact->outfile;
+  compact->outfile = NULL;
+
+  if (s.ok() && current_entries > 0) {
+    // Verify that the table is usable
+    Iterator* iter = table_cache_->NewIterator(ReadOptions(),
+                                               output_number,
+                                               current_bytes);
+    s = iter->status();
+    delete iter;
+    if (s.ok()) {
+      Log(env_, options_.info_log,
+          "Generated table #%llu: %lld keys, %lld bytes",
+          (unsigned long long) output_number,
+          (unsigned long long) current_entries,
+          (unsigned long long) current_bytes);
+    }
+  }
+  return s;
+}
+
+
+Status DBImpl::InstallCompactionResults(CompactionState* compact) {
+  mutex_.AssertHeld();
+  Log(env_, options_.info_log,  "Compacted %d@%d + %d@%d files => %lld bytes",
+      compact->compaction->num_input_files(0),
+      compact->compaction->level(),
+      compact->compaction->num_input_files(1),
+      compact->compaction->level() + 1,
+      static_cast<long long>(compact->total_bytes));
+
+  // Add compaction outputs
+  compact->compaction->AddInputDeletions(compact->compaction->edit());
+  const int level = compact->compaction->level();
+  for (size_t i = 0; i < compact->outputs.size(); i++) {
+    const CompactionState::Output& out = compact->outputs[i];
+    compact->compaction->edit()->AddFile(
+        level + 1,
+        out.number, out.file_size, out.smallest, out.largest);
+    pending_outputs_.erase(out.number);
+  }
+  compact->outputs.clear();
+
+  Status s = versions_->LogAndApply(compact->compaction->edit(), NULL);
+  if (s.ok()) {
+    compact->compaction->ReleaseInputs();
+    DeleteObsoleteFiles();
+  } else {
+    // Discard any files we may have created during this failed compaction
+    for (size_t i = 0; i < compact->outputs.size(); i++) {
+      env_->DeleteFile(TableFileName(dbname_, compact->outputs[i].number));
+    }
+  }
+  return s;
+}
+
+Status DBImpl::DoCompactionWork(CompactionState* compact) {
+  const uint64_t start_micros = env_->NowMicros();
+  int64_t imm_micros = 0;  // Micros spent doing imm_ compactions
+
+  Log(env_, options_.info_log,  "Compacting %d@%d + %d@%d files",
+      compact->compaction->num_input_files(0),
+      compact->compaction->level(),
+      compact->compaction->num_input_files(1),
+      compact->compaction->level() + 1);
+
+  assert(versions_->NumLevelFiles(compact->compaction->level()) > 0);
+  assert(compact->builder == NULL);
+  assert(compact->outfile == NULL);
+  if (snapshots_.empty()) {
+    compact->smallest_snapshot = versions_->LastSequence();
+  } else {
+    compact->smallest_snapshot = snapshots_.oldest()->number_;
+  }
+
+  // Release mutex while we're actually doing the compaction work
+  compacting_ = true;
+  mutex_.Unlock();
+
+  Iterator* input = versions_->MakeInputIterator(compact->compaction);
+  input->SeekToFirst();
+  Status status;
+  ParsedInternalKey ikey;
+  std::string current_user_key;
+  bool has_current_user_key = false;
+  SequenceNumber last_sequence_for_key = kMaxSequenceNumber;
+  for (; input->Valid() && !shutting_down_.Acquire_Load(); ) {
+    // Prioritize immutable compaction work
+    if (has_imm_.NoBarrier_Load() != NULL) {
+      const uint64_t imm_start = env_->NowMicros();
+      mutex_.Lock();
+      if (imm_ != NULL) {
+        CompactMemTable();
+        compacting_cv_.SignalAll();  // Wakeup MakeRoomForWrite() if necessary
+      }
+      mutex_.Unlock();
+      imm_micros += (env_->NowMicros() - imm_start);
+    }
+
+    Slice key = input->key();
+    InternalKey tmp_internal_key;
+    tmp_internal_key.DecodeFrom(key);
+    if (compact->compaction->ShouldStopBefore(tmp_internal_key) &&
+        compact->builder != NULL) {
+      status = FinishCompactionOutputFile(compact, input);
+      if (!status.ok()) {
+        break;
+      }
+    }
+
+    // Handle key/value, add to state, etc.
+    bool drop = false;
+    if (!ParseInternalKey(key, &ikey)) {
+      // Do not hide error keys
+      current_user_key.clear();
+      has_current_user_key = false;
+      last_sequence_for_key = kMaxSequenceNumber;
+    } else {
+      if (!has_current_user_key ||
+          user_comparator()->Compare(ikey.user_key,
+                                     Slice(current_user_key)) != 0) {
+        // First occurrence of this user key
+        current_user_key.assign(ikey.user_key.data(), ikey.user_key.size());
+        has_current_user_key = true;
+        last_sequence_for_key = kMaxSequenceNumber;
+      }
+
+      if (last_sequence_for_key <= compact->smallest_snapshot) {
+        // Hidden by an newer entry for same user key
+        drop = true;    // (A)
+      } else if (ikey.type == kTypeDeletion &&
+                 ikey.sequence <= compact->smallest_snapshot &&
+                 compact->compaction->IsBaseLevelForKey(ikey.user_key)) {
+        // For this user key:
+        // (1) there is no data in higher levels
+        // (2) data in lower levels will have larger sequence numbers
+        // (3) data in layers that are being compacted here and have
+        //     smaller sequence numbers will be dropped in the next
+        //     few iterations of this loop (by rule (A) above).
+        // Therefore this deletion marker is obsolete and can be dropped.
+        drop = true;
+      }
+
+      last_sequence_for_key = ikey.sequence;
+    }
+#if 0
+    Log(env_, options_.info_log,
+        "  Compact: %s, seq %d, type: %d %d, drop: %d, is_base: %d, "
+        "%d smallest_snapshot: %d",
+        ikey.user_key.ToString().c_str(),
+        (int)ikey.sequence, ikey.type, kTypeValue, drop,
+        compact->compaction->IsBaseLevelForKey(ikey.user_key),
+        (int)last_sequence_for_key, (int)compact->smallest_snapshot);
+#endif
+
+    if (!drop) {
+      // Open output file if necessary
+      if (compact->builder == NULL) {
+        status = OpenCompactionOutputFile(compact);
+        if (!status.ok()) {
+          break;
+        }
+      }
+      if (compact->builder->NumEntries() == 0) {
+        compact->current_output()->smallest.DecodeFrom(key);
+      }
+      compact->current_output()->largest.DecodeFrom(key);
+      compact->builder->Add(key, input->value());
+
+      // Close output file if it is big enough
+      if (compact->builder->FileSize() >=
+          compact->compaction->MaxOutputFileSize()) {
+        status = FinishCompactionOutputFile(compact, input);
+        if (!status.ok()) {
+          break;
+        }
+      }
+    }
+
+    input->Next();
+  }
+
+  if (status.ok() && shutting_down_.Acquire_Load()) {
+    status = Status::IOError("Deleting DB during compaction");
+  }
+  if (status.ok() && compact->builder != NULL) {
+    status = FinishCompactionOutputFile(compact, input);
+  }
+  if (status.ok()) {
+    status = input->status();
+  }
+  delete input;
+  input = NULL;
+
+  CompactionStats stats;
+  stats.micros = env_->NowMicros() - start_micros - imm_micros;
+  for (int which = 0; which < 2; which++) {
+    for (int i = 0; i < compact->compaction->num_input_files(which); i++) {
+      stats.bytes_read += compact->compaction->input(which, i)->file_size;
+    }
+  }
+  for (size_t i = 0; i < compact->outputs.size(); i++) {
+    stats.bytes_written += compact->outputs[i].file_size;
+  }
+
+  mutex_.Lock();
+  stats_[compact->compaction->level() + 1].Add(stats);
+
+  if (status.ok()) {
+    status = InstallCompactionResults(compact);
+  }
+  compacting_ = false;
+  compacting_cv_.SignalAll();
+  return status;
+}
+
+Iterator* DBImpl::NewInternalIterator(const ReadOptions& options,
+                                      SequenceNumber* latest_snapshot) {
+  mutex_.Lock();
+  *latest_snapshot = versions_->LastSequence();
+
+  // Collect together all needed child iterators
+  std::vector<Iterator*> list;
+  list.push_back(mem_->NewIterator());
+  if (imm_ != NULL) {
+    list.push_back(imm_->NewIterator());
+  }
+  versions_->current()->AddIterators(options, &list);
+  Iterator* internal_iter =
+      NewMergingIterator(&internal_comparator_, &list[0], list.size());
+  versions_->current()->Ref();
+  internal_iter->RegisterCleanup(&DBImpl::Unref, this, versions_->current());
+
+  mutex_.Unlock();
+  return internal_iter;
+}
+
+Iterator* DBImpl::TEST_NewInternalIterator() {
+  SequenceNumber ignored;
+  return NewInternalIterator(ReadOptions(), &ignored);
+}
+
+int64_t DBImpl::TEST_MaxNextLevelOverlappingBytes() {
+  MutexLock l(&mutex_);
+  return versions_->MaxNextLevelOverlappingBytes();
+}
+
+Status DBImpl::Get(const ReadOptions& options,
+                   const Slice& key,
+                   std::string* value) {
+  // TODO(opt): faster implementation
+  Iterator* iter = NewIterator(options);
+  iter->Seek(key);
+  bool found = false;
+  if (iter->Valid() && user_comparator()->Compare(key, iter->key()) == 0) {
+    Slice v = iter->value();
+    value->assign(v.data(), v.size());
+    found = true;
+  }
+  // Non-OK iterator status trumps everything else
+  Status result = iter->status();
+  if (result.ok() && !found) {
+    result = Status::NotFound(Slice());  // Use an empty error message for speed
+  }
+  delete iter;
+  return result;
+}
+
+Iterator* DBImpl::NewIterator(const ReadOptions& options) {
+  SequenceNumber latest_snapshot;
+  Iterator* internal_iter = NewInternalIterator(options, &latest_snapshot);
+  SequenceNumber sequence =
+      (options.snapshot ? options.snapshot->number_ : latest_snapshot);
+  return NewDBIterator(&dbname_, env_,
+                       user_comparator(), internal_iter, sequence);
+}
+
+void DBImpl::Unref(void* arg1, void* arg2) {
+  DBImpl* impl = reinterpret_cast<DBImpl*>(arg1);
+  Version* v = reinterpret_cast<Version*>(arg2);
+  MutexLock l(&impl->mutex_);
+  v->Unref();
+}
+
+const Snapshot* DBImpl::GetSnapshot() {
+  MutexLock l(&mutex_);
+  return snapshots_.New(versions_->LastSequence());
+}
+
+void DBImpl::ReleaseSnapshot(const Snapshot* s) {
+  MutexLock l(&mutex_);
+  snapshots_.Delete(s);
+}
+
+// Convenience methods
+Status DBImpl::Put(const WriteOptions& o, const Slice& key, const Slice& val) {
+  return DB::Put(o, key, val);
+}
+
+Status DBImpl::Delete(const WriteOptions& options, const Slice& key) {
+  return DB::Delete(options, key);
+}
+
+Status DBImpl::Write(const WriteOptions& options, WriteBatch* updates) {
+  Status status;
+  MutexLock l(&mutex_);
+  status = MakeRoomForWrite(false);  // May temporarily release lock and wait
+  uint64_t last_sequence = versions_->LastSequence();
+  if (status.ok()) {
+    WriteBatchInternal::SetSequence(updates, last_sequence + 1);
+    last_sequence += WriteBatchInternal::Count(updates);
+    versions_->SetLastSequence(last_sequence);
+
+    // Add to log and apply to memtable
+    status = log_->AddRecord(WriteBatchInternal::Contents(updates));
+    if (status.ok() && options.sync) {
+      status = logfile_->Sync();
+    }
+    if (status.ok()) {
+      status = WriteBatchInternal::InsertInto(updates, mem_);
+    }
+  }
+  if (options.post_write_snapshot != NULL) {
+    *options.post_write_snapshot =
+        status.ok() ? snapshots_.New(last_sequence) : NULL;
+  }
+  return status;
+}
+
+Status DBImpl::MakeRoomForWrite(bool force) {
+  mutex_.AssertHeld();
+  Status s;
+  while (true) {
+    if (!bg_error_.ok()) {
+      // Yield previous error
+      s = bg_error_;
+      break;
+    } else if (!force &&
+               (mem_->ApproximateMemoryUsage() <= options_.write_buffer_size)) {
+      // There is room in current memtable
+      break;
+    } else if (imm_ != NULL) {
+      // We have filled up the current memtable, but the previous
+      // one is still being compacted, so we wait.
+      compacting_cv_.Wait();
+    } else {
+      // Attempt to switch to a new memtable and trigger compaction of old
+      assert(versions_->PrevLogNumber() == 0);
+      uint64_t new_log_number = versions_->NewFileNumber();
+      WritableFile* lfile = NULL;
+      s = env_->NewWritableFile(LogFileName(dbname_, new_log_number), &lfile);
+      if (!s.ok()) {
+        break;
+      }
+      VersionEdit edit;
+      edit.SetPrevLogNumber(versions_->LogNumber());
+      edit.SetLogNumber(new_log_number);
+      s = versions_->LogAndApply(&edit, NULL);
+      if (!s.ok()) {
+        delete lfile;
+        env_->DeleteFile(LogFileName(dbname_, new_log_number));
+        break;
+      }
+      delete log_;
+      delete logfile_;
+      logfile_ = lfile;
+      log_ = new log::Writer(lfile);
+      imm_ = mem_;
+      has_imm_.Release_Store(imm_);
+      mem_ = new MemTable(internal_comparator_);
+      force = false;   // Do not force another compaction if have room
+      MaybeScheduleCompaction();
+    }
+  }
+  return s;
+}
+
+bool DBImpl::GetProperty(const Slice& property, std::string* value) {
+  value->clear();
+
+  MutexLock l(&mutex_);
+  Slice in = property;
+  Slice prefix("leveldb.");
+  if (!in.starts_with(prefix)) return false;
+  in.remove_prefix(prefix.size());
+
+  if (in.starts_with("num-files-at-level")) {
+    in.remove_prefix(strlen("num-files-at-level"));
+    uint64_t level;
+    bool ok = ConsumeDecimalNumber(&in, &level) && in.empty();
+    if (!ok || level < 0 || level >= config::kNumLevels) {
+      return false;
+    } else {
+      char buf[100];
+      snprintf(buf, sizeof(buf), "%d",
+               versions_->NumLevelFiles(static_cast<int>(level)));
+      *value = buf;
+      return true;
+    }
+  } else if (in == "stats") {
+    char buf[200];
+    snprintf(buf, sizeof(buf),
+             "                               Compactions\n"
+             "Level  Files Size(MB) Time(sec) Read(MB) Write(MB)\n"
+             "--------------------------------------------------\n"
+             );
+    value->append(buf);
+    for (int level = 0; level < config::kNumLevels; level++) {
+      int files = versions_->NumLevelFiles(level);
+      if (stats_[level].micros > 0 || files > 0) {
+        snprintf(
+            buf, sizeof(buf),
+            "%3d %8d %8.0f %9.0f %8.0f %9.0f\n",
+            level,
+            files,
+            versions_->NumLevelBytes(level) / 1048576.0,
+            stats_[level].micros / 1e6,
+            stats_[level].bytes_read / 1048576.0,
+            stats_[level].bytes_written / 1048576.0);
+        value->append(buf);
+      }
+    }
+    return true;
+  }
+
+  return false;
+}
+
+void DBImpl::GetApproximateSizes(
+    const Range* range, int n,
+    uint64_t* sizes) {
+  // TODO(opt): better implementation
+  Version* v;
+  {
+    MutexLock l(&mutex_);
+    versions_->current()->Ref();
+    v = versions_->current();
+  }
+
+  for (int i = 0; i < n; i++) {
+    // Convert user_key into a corresponding internal key.
+    InternalKey k1(range[i].start, kMaxSequenceNumber, kValueTypeForSeek);
+    InternalKey k2(range[i].limit, kMaxSequenceNumber, kValueTypeForSeek);
+    uint64_t start = versions_->ApproximateOffsetOf(v, k1);
+    uint64_t limit = versions_->ApproximateOffsetOf(v, k2);
+    sizes[i] = (limit >= start ? limit - start : 0);
+  }
+
+  {
+    MutexLock l(&mutex_);
+    v->Unref();
+  }
+}
+
+// Default implementations of convenience methods that subclasses of DB
+// can call if they wish
+Status DB::Put(const WriteOptions& opt, const Slice& key, const Slice& value) {
+  WriteBatch batch;
+  batch.Put(key, value);
+  return Write(opt, &batch);
+}
+
+Status DB::Delete(const WriteOptions& opt, const Slice& key) {
+  WriteBatch batch;
+  batch.Delete(key);
+  return Write(opt, &batch);
+}
+
+DB::~DB() { }
+
+Status DB::Open(const Options& options, const std::string& dbname,
+                DB** dbptr) {
+  *dbptr = NULL;
+
+  DBImpl* impl = new DBImpl(options, dbname);
+  impl->mutex_.Lock();
+  VersionEdit edit;
+  Status s = impl->Recover(&edit); // Handles create_if_missing, error_if_exists
+  if (s.ok()) {
+    uint64_t new_log_number = impl->versions_->NewFileNumber();
+    WritableFile* lfile;
+    s = options.env->NewWritableFile(LogFileName(dbname, new_log_number),
+                                     &lfile);
+    if (s.ok()) {
+      edit.SetLogNumber(new_log_number);
+      impl->logfile_ = lfile;
+      impl->log_ = new log::Writer(lfile);
+      s = impl->versions_->LogAndApply(&edit, NULL);
+    }
+    if (s.ok()) {
+      impl->DeleteObsoleteFiles();
+    }
+  }
+  impl->mutex_.Unlock();
+  if (s.ok()) {
+    *dbptr = impl;
+  } else {
+    delete impl;
+  }
+  return s;
+}
+
+Status DestroyDB(const std::string& dbname, const Options& options) {
+  Env* env = options.env;
+  std::vector<std::string> filenames;
+  // Ignore error in case directory does not exist
+  env->GetChildren(dbname, &filenames);
+  if (filenames.empty()) {
+    return Status::OK();
+  }
+
+  FileLock* lock;
+  Status result = env->LockFile(LockFileName(dbname), &lock);
+  if (result.ok()) {
+    uint64_t number;
+    FileType type;
+    for (size_t i = 0; i < filenames.size(); i++) {
+      if (ParseFileName(filenames[i], &number, &type)) {
+        Status del = env->DeleteFile(dbname + "/" + filenames[i]);
+        if (result.ok() && !del.ok()) {
+          result = del;
+        }
+      }
+    }
+    env->UnlockFile(lock);  // Ignore error since state is already gone
+    env->DeleteFile(LockFileName(dbname));
+    env->DeleteDir(dbname);  // Ignore error in case dir contains other files
+  }
+  return result;
+}
+
+}