leveldb.project/db/builder.cc

// 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/builder.h"

#include "db/dbformat.h"
#include "db/filename.h"
#include "db/table_cache.h"
#include "db/version_edit.h"
#include "leveldb/db.h"
#include "leveldb/env.h"
#include "leveldb/iterator.h"

namespace leveldb {

/**
 * description:目的，将内存中的数据写入一个新的 SSTable 文件
 * @param dbname
 * @param env
 * @param options
 * @param table_cache
 * @param iter
 * @param meta ：存储新sstable的相关元数据
 * @return
 */
Status BuildTable(const std::string& dbname, Env* env, const Options& options,
                  TableCache* table_cache, Iterator* iter, FileMetaData* meta) {
  Status s;
  meta->file_size = 0;
  iter->SeekToFirst();

  std::string fname = TableFileName(dbname, meta->number);

  if (iter->Valid()) {
    WritableFile* file;
    s = env->NewWritableFile(fname, &file);
    if (!s.ok()) {
      return s;
    }

    TableBuilder* builder = new TableBuilder(options, file);
    meta->smallest.DecodeFrom(iter->key());//这里是internal_key
    auto tmp_ts = DecodeFixed64(iter->value().data() + iter->value().size() - kTSLength);
    meta->oldest_ts = tmp_ts;
    meta->newer_ts = tmp_ts;

    Slice key;
    for (; iter->Valid(); iter->Next()) {
      key = iter->key();
      builder->Add(key, iter->value());
      tmp_ts = DecodeFixed64(iter->value().data() + iter->value().size() - kTSLength);
      meta->oldest_ts = meta->oldest_ts > tmp_ts ? tmp_ts : meta->oldest_ts;
      meta->newer_ts = meta->newer_ts > tmp_ts ? meta->newer_ts : tmp_ts;
    }
    if (!key.empty()) {
      meta->largest.DecodeFrom(key);
    }

    // Finish and check for builder errors
    s = builder->Finish();
    if (s.ok()) {
      meta->file_size = builder->FileSize();
      assert(meta->file_size > 0);
    }
    delete builder;

    // Finish and check for file errors
    if (s.ok()) {
      s = file->Sync();
    }
    if (s.ok()) {
      s = file->Close();
    }
    delete file;
    file = nullptr;

    if (s.ok()) {
      // Verify that the table is usable
      Iterator* it = table_cache->NewIterator(ReadOptions(), meta->number,
                                              meta->file_size);
      s = it->status();
      delete it;
    }
  }

  // Check for input iterator errors
  if (!iter->status().ok()) {
    s = iter->status();
  }

  if (s.ok() && meta->file_size > 0) {
    // Keep it
  } else {
    env->RemoveFile(fname);
  }
  return s;
}

}  // namespace leveldb