rocksdb/include/utilities/utility_db.h

// 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.

#ifndef LEVELDB_INCLUDE_UTILITIES_UTILITY_DB_H_
#define LEVELDB_INCLUDE_UTILITIES_UTILITY_DB_H_

#include "stackable_db.h"

namespace leveldb {

// This class contains APIs to open leveldb with specific support eg. TTL
class UtilityDB {

  public:
    // Open the database with TTL support.
    //
    // USE-CASES:
    // This API should be used to open the db when key-values inserted are
    //  meant to be removed from the db in a non-strict 'ttl' amount of time
    //  Therefore, this guarantees that key-values inserted will remain in the
    //  db for >= ttl amount of time and the db will make efforts to remove the
    //  key-values as soon as possible after ttl seconds of their insertion.
    //
    // BEHAVIOUR:
    // TTL is accepted in seconds
    // (int32_t)Timestamp(creation) is suffixed to values in Put internally
    // Expired TTL values deleted in compaction only:(Timestamp+ttl<time_now)
    // Get/Iterator may return expired entries(compaction not run on them yet)
    // Different TTL may be used during different Opens
    // Example: Open1 at t=0 with ttl=4 and insert k1,k2, close at t=2
    //          Open2 at t=3 with ttl=5. Now k1,k2 should be deleted at t>=5
    // read_only=true opens in the usual read-only mode. Compactions will not be
    //  triggered(neither manual nor automatic), so no expired entries removed
    //
    // CONSTRAINTS:
    // Not specifying/passing or non-positive TTL behaves like TTL = infinity
    //
    // !!!WARNING!!!:
    // Calling DB::Open directly to re-open a db created by this API will get
    //  corrupt values(timestamp suffixed) and no ttl effect will be there
    //  during the second Open, so use this API consistently to open the db
    // Be careful when passing ttl with a small positive value because the
    //  whole database may be deleted in a small amount of time
    static Status OpenTtlDB(const Options& options,
                            const std::string& name,
                            StackableDB** dbptr,
                            int32_t ttl = 0,
                            bool read_only = false);
};

} //  namespace leveldb

#endif  //  LEVELDB_INCLUDE_UTILITIES_UTILITY_DB_H_