ad5325a736
Summary: * New public header unique_id.h and function GetUniqueIdFromTableProperties which computes a universally unique identifier based on table properties of table files from recent RocksDB versions. * Generation of DB session IDs is refactored so that they are guaranteed unique in the lifetime of a process running RocksDB. (SemiStructuredUniqueIdGen, new test included.) Along with file numbers, this enables SST unique IDs to be guaranteed unique among SSTs generated in a single process, and "better than random" between processes. See https://github.com/pdillinger/unique_id * In addition to public API producing 'external' unique IDs, there is a function for producing 'internal' unique IDs, with functions for converting between the two. In short, the external ID is "safe" for things people might do with it, and the internal ID enables more "power user" features for the future. Specifically, the external ID goes through a hashing layer so that any subset of bits in the external ID can be used as a hash of the full ID, while also preserving uniqueness guarantees in the first 128 bits (bijective both on first 128 bits and on full 192 bits). Intended follow-up: * Use the internal unique IDs in cache keys. (Avoid conflicts with https://github.com/facebook/rocksdb/issues/8912) (The file offset can be XORed into the third 64-bit value of the unique ID.) * Publish the external unique IDs in FileStorageInfo (https://github.com/facebook/rocksdb/issues/8968) Pull Request resolved: https://github.com/facebook/rocksdb/pull/8990 Test Plan: Unit tests added, and checking of unique ids in stress test. NOTE in stress test we do not generate nearly enough files to thoroughly stress uniqueness, but the test trims off pieces of the ID to check for uniqueness so that we can infer (with some assumptions) stronger properties in the aggregate. Reviewed By: zhichao-cao, mrambacher Differential Revision: D31582865 Pulled By: pdillinger fbshipit-source-id: 1f620c4c86af9abe2a8d177b9ccf2ad2b9f48243
47 lines
2.1 KiB
C++
47 lines
2.1 KiB
C++
// Copyright (c) Facebook, Inc. and its affiliates. 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).
|
|
|
|
#pragma once
|
|
|
|
#include "rocksdb/table_properties.h"
|
|
|
|
namespace ROCKSDB_NAMESPACE {
|
|
|
|
// EXPERIMENTAL: This API is subject to change
|
|
//
|
|
// Computes a stable, universally unique 192-bit (24 binary char) identifier
|
|
// for an SST file from TableProperties. This is supported for table (SST)
|
|
// files created with RocksDB 6.24 and later. NotSupported will be returned
|
|
// for other cases. The first 16 bytes (128 bits) is of sufficient quality
|
|
// for almost all applications, and shorter prefixes are usable as a
|
|
// hash of the full unique id.
|
|
//
|
|
// Note: .c_str() is not compatible with binary char strings, so using
|
|
// .c_str() on the result will often result in information loss and very
|
|
// poor uniqueness probability.
|
|
//
|
|
// More detail: the first 128 bits are *guaranteed* unique for SST files
|
|
// generated in the same process (even different DBs, RocksDB >= 6.26),
|
|
// and first 128 bits are guaranteed not "all zeros" (RocksDB >= 6.26)
|
|
// so that the "all zeros" value can be used reliably for a null ID.
|
|
// Assuming one generates many SST files in the lifetime of each process,
|
|
// the probability of collision between processes is "better than
|
|
// random": if processes generate n SST files on average, we expect to
|
|
// generate roughly 2^64 * sqrt(n) files before first collision in the
|
|
// first 128 bits. See https://github.com/pdillinger/unique_id
|
|
// Using the full 192 bits, we expect to generate roughly 2^96 * sqrt(n)
|
|
// files before first collision.
|
|
Status GetUniqueIdFromTableProperties(const TableProperties &props,
|
|
std::string *out_id);
|
|
|
|
// EXPERIMENTAL: This API is subject to change
|
|
//
|
|
// Converts a binary string (unique id) to hexadecimal, with each 64 bits
|
|
// separated by '-', e.g. 6474DF650323BDF0-B48E64F3039308CA-17284B32E7F7444B
|
|
// Also works on unique id prefix.
|
|
std::string UniqueIdToHumanString(const std::string &id);
|
|
|
|
} // namespace ROCKSDB_NAMESPACE
|