mirror of https://github.com/facebook/rocksdb.git
60 lines
2.6 KiB
C++
60 lines
2.6 KiB
C++
// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#pragma once
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#include <array>
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#include "rocksdb/unique_id.h"
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namespace ROCKSDB_NAMESPACE {
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using UniqueId64x3 = std::array<uint64_t, 3>;
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// Helper for GetUniqueIdFromTableProperties. This function can also be used
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// for temporary ids for files without sufficient information in table
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// properties. The internal unique id is more structured than the public
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// unique id, so can be manipulated in more ways but very carefully.
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// These must be long term stable to ensure GetUniqueIdFromTableProperties
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// is long term stable.
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Status GetSstInternalUniqueId(const std::string &db_id,
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const std::string &db_session_id,
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uint64_t file_number, UniqueId64x3 *out);
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// Helper for GetUniqueIdFromTableProperties. External unique ids go through
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// this extra hashing layer so that prefixes of the unique id have predictable
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// "full" entropy. This hashing layer is 1-to-1 on the first 128 bits and on
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// the full 192 bits.
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// This transformation must be long term stable to ensure
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// GetUniqueIdFromTableProperties is long term stable.
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void InternalUniqueIdToExternal(UniqueId64x3 *in_out);
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// Reverse of InternalUniqueIdToExternal mostly for testing purposes
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// (demonstrably 1-to-1 on the first 128 bits and on the full 192 bits).
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void ExternalUniqueIdToInternal(UniqueId64x3 *in_out);
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// Convert numerical format to byte format for public API
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std::string EncodeUniqueIdBytes(const UniqueId64x3 &in);
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// Reformat a random value down to our "DB session id" format,
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// which is intended to be compact and friendly for use in file names.
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// `lower` is fully preserved and data is lost from `upper`.
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//
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// Detail: Encoded into 20 chars in base-36 ([0-9A-Z]), which is ~103 bits of
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// entropy, which is enough to expect no collisions across a billion servers
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// each opening DBs a million times (~2^50). Benefits vs. RFC-4122 unique id:
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// * Save ~ dozen bytes per SST file
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// * Shorter shared backup file names (some platforms have low limits)
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// * Visually distinct from DB id format (usually RFC-4122)
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std::string EncodeSessionId(uint64_t upper, uint64_t lower);
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// Reverse of EncodeSessionId. Returns NotSupported on error rather than
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// Corruption because non-standard session IDs should be allowed with degraded
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// functionality.
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Status DecodeSessionId(const std::string &db_session_id, uint64_t *upper,
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uint64_t *lower);
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} // namespace ROCKSDB_NAMESPACE
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