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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
// This file demonstrates how to use the utility functions defined in
// rocksdb/utilities/options_util.h to open a rocksdb database without
// remembering all the rocksdb options.
#include <cstdio>
#include <string>
#include <vector>
#include "rocksdb/cache.h"
#include "rocksdb/compaction_filter.h"
#include "rocksdb/db.h"
#include "rocksdb/options.h"
#include "rocksdb/slice.h"
#include "rocksdb/table.h"
#include "rocksdb/utilities/options_util.h"
using namespace rocksdb;
std::string kDBPath = "/tmp/rocksdb_options_file_example";
namespace {
// A dummy compaction filter
class DummyCompactionFilter : public CompactionFilter {
virtual ~DummyCompactionFilter() {}
virtual bool Filter(int level, const Slice& key, const Slice& existing_value,
std::string* new_value, bool* value_changed) const {
return false;
virtual const char* Name() const { return "DummyCompactionFilter"; }
} // namespace
int main() {
DBOptions db_opt;
db_opt.create_if_missing = true;
std::vector<ColumnFamilyDescriptor> cf_descs;
cf_descs.push_back({kDefaultColumnFamilyName, ColumnFamilyOptions()});
cf_descs.push_back({"new_cf", ColumnFamilyOptions()});
// initialize BlockBasedTableOptions
auto cache = NewLRUCache(1 * 1024 * 1024 * 1024);
BlockBasedTableOptions bbt_opts;
bbt_opts.block_size = 32 * 1024;
bbt_opts.block_cache = cache;
// initialize column families options
std::unique_ptr<CompactionFilter> compaction_filter;
compaction_filter.reset(new DummyCompactionFilter());
cf_descs[0].options.compaction_filter = compaction_filter.get();
// destroy and open DB
DB* db;
Status s = DestroyDB(kDBPath, Options(db_opt, cf_descs[0].options));
s = DB::Open(Options(db_opt, cf_descs[0].options), kDBPath, &db);
// Create column family, and rocksdb will persist the options.
ColumnFamilyHandle* cf;
s = db->CreateColumnFamily(ColumnFamilyOptions(), "new_cf", &cf);
// close DB
delete cf;
delete db;
// In the following code, we will reopen the rocksdb instance using
// the options file stored in the db directory.
// Load the options file.
DBOptions loaded_db_opt;
std::vector<ColumnFamilyDescriptor> loaded_cf_descs;
s = LoadLatestOptions(kDBPath, Env::Default(), &loaded_db_opt,
assert(loaded_db_opt.create_if_missing == db_opt.create_if_missing);
// Initialize pointer options for each column family
for (size_t i = 0; i < loaded_cf_descs.size(); ++i) {
auto* loaded_bbt_opt = reinterpret_cast<BlockBasedTableOptions*>(
// Expect the same as BlockBasedTableOptions will be loaded form file.
assert(loaded_bbt_opt->block_size == bbt_opts.block_size);
// However, block_cache needs to be manually initialized as documented
// in rocksdb/utilities/options_util.h.
loaded_bbt_opt->block_cache = cache;
// In addition, as pointer options are initialized with default value,
// we need to properly initialized all the pointer options if non-defalut
// values are used before calling DB::Open().
assert(loaded_cf_descs[0].options.compaction_filter == nullptr);
loaded_cf_descs[0].options.compaction_filter = compaction_filter.get();
// reopen the db using the loaded options.
std::vector<ColumnFamilyHandle*> handles;
s = DB::Open(loaded_db_opt, kDBPath, loaded_cf_descs, &handles, &db);
// close DB
for (auto* handle : handles) {
delete handle;
delete db;