rocksdb/include/utilities/utility_db.h

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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.
#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_