1 //  Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
2 //  This source code is licensed under both the GPLv2 (found in the
3 //  COPYING file in the root directory) and Apache 2.0 License
4 //  (found in the LICENSE.Apache file in the root directory).
5 
6 #pragma once
7 
8 #include <array>
9 
10 #include "rocksdb/unique_id.h"
11 
12 namespace ROCKSDB_NAMESPACE {
13 
14 using UniqueId64x3 = std::array<uint64_t, 3>;
15 
16 // Helper for GetUniqueIdFromTableProperties. This function can also be used
17 // for temporary ids for files without sufficient information in table
18 // properties. The internal unique id is more structured than the public
19 // unique id, so can be manipulated in more ways but very carefully.
20 // These must be long term stable to ensure GetUniqueIdFromTableProperties
21 // is long term stable.
22 Status GetSstInternalUniqueId(const std::string &db_id,
23                               const std::string &db_session_id,
24                               uint64_t file_number, UniqueId64x3 *out);
25 
26 // Helper for GetUniqueIdFromTableProperties. External unique ids go through
27 // this extra hashing layer so that prefixes of the unique id have predictable
28 // "full" entropy. This hashing layer is 1-to-1 on the first 128 bits and on
29 // the full 192 bits.
30 // This transformation must be long term stable to ensure
31 // GetUniqueIdFromTableProperties is long term stable.
32 void InternalUniqueIdToExternal(UniqueId64x3 *in_out);
33 
34 // Reverse of InternalUniqueIdToExternal mostly for testing purposes
35 // (demonstrably 1-to-1 on the first 128 bits and on the full 192 bits).
36 void ExternalUniqueIdToInternal(UniqueId64x3 *in_out);
37 
38 // Convert numerical format to byte format for public API
39 std::string EncodeUniqueIdBytes(const UniqueId64x3 &in);
40 
41 // Reformat a random value down to our "DB session id" format,
42 // which is intended to be compact and friendly for use in file names.
43 // `lower` is fully preserved and data is lost from `upper`.
44 //
45 // Detail: Encoded into 20 chars in base-36 ([0-9A-Z]), which is ~103 bits of
46 // entropy, which is enough to expect no collisions across a billion servers
47 // each opening DBs a million times (~2^50). Benefits vs. RFC-4122 unique id:
48 // * Save ~ dozen bytes per SST file
49 // * Shorter shared backup file names (some platforms have low limits)
50 // * Visually distinct from DB id format (usually RFC-4122)
51 std::string EncodeSessionId(uint64_t upper, uint64_t lower);
52 
53 // Reverse of EncodeSessionId. Returns NotSupported on error rather than
54 // Corruption because non-standard session IDs should be allowed with degraded
55 // functionality.
56 Status DecodeSessionId(const std::string &db_session_id, uint64_t *upper,
57                        uint64_t *lower);
58 
59 }  // namespace ROCKSDB_NAMESPACE
60