Revision b55b2f45d04d95010cd1a40f2701990abe43c3de authored by Peter Dillinger on 05 September 2019, 21:57:39 UTC, committed by Facebook Github Bot on 05 September 2019, 21:59:25 UTC
Summary: Since DynamicBloom is now only used in-memory, we're free to change it without schema compatibility issues. The new implementation is drawn from (with manifest permission) https://github.com/pdillinger/wormhashing/blob/303542a767437f56d8b66cea6ebecaac0e6a61e9/bloom_simulation_tests/foo.cc#L613 This has several speed advantages over the prior implementation: * Uses fastrange instead of % * Minimum logic to determine first (and all) probed memory addresses * (Major) Two probes per 64-bit memory fetch/write. * Very fast and effective (murmur-like) hash expansion/re-mixing. (At least on recent CPUs, integer multiplication is very cheap.) While a Bloom filter with 512-bit cache locality has about a 1.15x FP rate penalty (e.g. 0.84% to 0.97%), further restricting to two probes per 64 bits incurs an additional 1.12x FP rate penalty (e.g. 0.97% to 1.09%). Nevertheless, the unit tests show no "mediocre" FP rate samples, unlike the old implementation with more erratic FP rates. Especially for the memtable, we expect speed to outweigh somewhat higher FP rates. For example, a negative table query would have to be 1000x slower than a BF query to justify doubling BF query time to shave 10% off FP rate (working assumption around 1% FP rate). While that seems likely for SSTs, my data suggests a speed factor of roughly 50x for the memtable (vs. BF; ~1.5% lower write throughput when enabling memtable Bloom filter, after this change). Thus, it's probably not worth even 5% more time in the Bloom filter to shave off 1/10th of the Bloom FP rate, or 0.1% in absolute terms, and it's probably at least 20% slower to recoup that much FP rate from this new implementation. Because of this, we do not see a need for a 'locality' option that affects the MemTable Bloom filter and have decoupled the MemTable Bloom filter from Options::bloom_locality. Note that just 3% more memory to the Bloom filter (10.3 bits per key vs. just 10) is able to make up for the ~12% FP rate drop in the new implementation: [] # Nearly "ideal" FP-wise but reasonably fast cache-local implementation [~/wormhashing/bloom_simulation_tests] ./foo_gcc_IMPL_CACHE_WORM64_FROM32_any.out 10000000 6 10 $RANDOM 100000000 ./foo_gcc_IMPL_CACHE_WORM64_FROM32_any.out time: 3.29372 sampled_fp_rate: 0.00985956 ... [] # Close match to this new implementation [~/wormhashing/bloom_simulation_tests] ./foo_gcc_IMPL_CACHE_MUL64_BLOCK_FROM32_any.out 10000000 6 10.3 $RANDOM 100000000 ./foo_gcc_IMPL_CACHE_MUL64_BLOCK_FROM32_any.out time: 2.10072 sampled_fp_rate: 0.00985655 ... [] # Old locality=1 implementation [~/wormhashing/bloom_simulation_tests] ./foo_gcc_IMPL_CACHE_ROCKSDB_DYNAMIC_any.out 10000000 6 10 $RANDOM 100000000 ./foo_gcc_IMPL_CACHE_ROCKSDB_DYNAMIC_any.out time: 3.95472 sampled_fp_rate: 0.00988943 ... Also note the dramatic speed improvement vs. alternatives. -- Performance unit test: DynamicBloomTest.concurrent_with_perf is updated to report more precise timing data. (Measure running time of each thread, not just longest running thread, etc.) Results averaged over various sizes enabled with --enable_perf and 20 runs each; old dynamic bloom refers to locality=1, the faster of the old: old dynamic bloom, avg add latency = 65.6468 new dynamic bloom, avg add latency = 44.3809 old dynamic bloom, avg query latency = 50.6485 new dynamic bloom, avg query latency = 43.2186 old avg parallel add latency = 41.678 new avg parallel add latency = 24.5238 old avg parallel hit latency = 14.6322 new avg parallel hit latency = 12.3939 old avg parallel miss latency = 16.7289 new avg parallel miss latency = 12.2134 Tested on a dedicated 64-bit production machine at Facebook. Significant improvement all around. Despite now using std::atomic<uint64_t>, quick before-and-after test on a 32-bit machine (Intel Atom N270, released 2008) shows no regression in performance, in some cases modest improvement. -- Performance integration test (synthetic): with DEBUG_LEVEL=0, used TEST_TMPDIR=/dev/shm ./db_bench --benchmarks=fillrandom,readmissing,readrandom,stats --num=2000000 and optionally with -memtable_whole_key_filtering -memtable_bloom_size_ratio=0.01 300 runs each configuration. Write throughput change by enabling memtable bloom: Old locality=0: -3.06% Old locality=1: -2.37% New: -1.50% conclusion -> seems to substantially close the gap Readmissing throughput change by enabling memtable bloom: Old locality=0: +34.47% Old locality=1: +34.80% New: +33.25% conclusion -> maybe a small new penalty from FP rate Readrandom throughput change by enabling memtable bloom: Old locality=0: +31.54% Old locality=1: +31.13% New: +30.60% conclusion -> maybe also from FP rate (after memtable flush) -- Another conclusion we can draw from this new implementation is that the existing 32-bit hash function is not inherently crippling the Bloom filter speed or accuracy, below about 5 million keys. For speed, the implementation is essentially the same whether starting with 32-bits or 64-bits of hash; it just determines whether the first multiplication after fastrange is a pseudorandom expansion or needed re-mix. Note that this multiplication can occur while memory is fetching. For accuracy, in a standard configuration, you need about 5 million keys before you have about a 1.1x FP penalty due to using a 32-bit hash vs. 64-bit: [~/wormhashing/bloom_simulation_tests] ./foo_gcc_IMPL_CACHE_MUL64_BLOCK_FROM32_any.out $((5 * 1000 * 1000 * 10)) 6 10 $RANDOM 100000000 ./foo_gcc_IMPL_CACHE_MUL64_BLOCK_FROM32_any.out time: 2.52069 sampled_fp_rate: 0.0118267 ... [~/wormhashing/bloom_simulation_tests] ./foo_gcc_IMPL_CACHE_MUL64_BLOCK_any.out $((5 * 1000 * 1000 * 10)) 6 10 $RANDOM 100000000 ./foo_gcc_IMPL_CACHE_MUL64_BLOCK_any.out time: 2.43871 sampled_fp_rate: 0.0109059 Pull Request resolved: https://github.com/facebook/rocksdb/pull/5762 Differential Revision: D17214194 Pulled By: pdillinger fbshipit-source-id: ad9da031772e985fd6b62a0e1db8e81892520595
1 parent 19e8c9b
db_options.h
// Copyright (c) 2011-present, Facebook, Inc. 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 <string>
#include <vector>
#include "rocksdb/options.h"
namespace rocksdb {
struct ImmutableDBOptions {
ImmutableDBOptions();
explicit ImmutableDBOptions(const DBOptions& options);
void Dump(Logger* log) const;
bool create_if_missing;
bool create_missing_column_families;
bool error_if_exists;
bool paranoid_checks;
Env* env;
std::shared_ptr<RateLimiter> rate_limiter;
std::shared_ptr<SstFileManager> sst_file_manager;
std::shared_ptr<Logger> info_log;
InfoLogLevel info_log_level;
int max_file_opening_threads;
std::shared_ptr<Statistics> statistics;
bool use_fsync;
std::vector<DbPath> db_paths;
std::string db_log_dir;
std::string wal_dir;
uint32_t max_subcompactions;
int max_background_flushes;
size_t max_log_file_size;
size_t log_file_time_to_roll;
size_t keep_log_file_num;
size_t recycle_log_file_num;
uint64_t max_manifest_file_size;
int table_cache_numshardbits;
uint64_t wal_ttl_seconds;
uint64_t wal_size_limit_mb;
size_t manifest_preallocation_size;
bool allow_mmap_reads;
bool allow_mmap_writes;
bool use_direct_reads;
bool use_direct_io_for_flush_and_compaction;
bool allow_fallocate;
bool is_fd_close_on_exec;
bool advise_random_on_open;
size_t db_write_buffer_size;
std::shared_ptr<WriteBufferManager> write_buffer_manager;
DBOptions::AccessHint access_hint_on_compaction_start;
bool new_table_reader_for_compaction_inputs;
size_t random_access_max_buffer_size;
bool use_adaptive_mutex;
std::vector<std::shared_ptr<EventListener>> listeners;
bool enable_thread_tracking;
bool enable_pipelined_write;
bool unordered_write;
bool allow_concurrent_memtable_write;
bool enable_write_thread_adaptive_yield;
uint64_t write_thread_max_yield_usec;
uint64_t write_thread_slow_yield_usec;
bool skip_stats_update_on_db_open;
WALRecoveryMode wal_recovery_mode;
bool allow_2pc;
std::shared_ptr<Cache> row_cache;
#ifndef ROCKSDB_LITE
WalFilter* wal_filter;
#endif // ROCKSDB_LITE
bool fail_if_options_file_error;
bool dump_malloc_stats;
bool avoid_flush_during_recovery;
bool allow_ingest_behind;
bool preserve_deletes;
bool two_write_queues;
bool manual_wal_flush;
bool atomic_flush;
bool avoid_unnecessary_blocking_io;
bool persist_stats_to_disk;
bool write_dbid_to_manifest;
size_t log_readahead_size;
};
struct MutableDBOptions {
MutableDBOptions();
explicit MutableDBOptions(const MutableDBOptions& options) = default;
explicit MutableDBOptions(const DBOptions& options);
void Dump(Logger* log) const;
int max_background_jobs;
int base_background_compactions;
int max_background_compactions;
bool avoid_flush_during_shutdown;
size_t writable_file_max_buffer_size;
uint64_t delayed_write_rate;
uint64_t max_total_wal_size;
uint64_t delete_obsolete_files_period_micros;
unsigned int stats_dump_period_sec;
unsigned int stats_persist_period_sec;
size_t stats_history_buffer_size;
int max_open_files;
uint64_t bytes_per_sync;
uint64_t wal_bytes_per_sync;
bool strict_bytes_per_sync;
size_t compaction_readahead_size;
};
} // namespace rocksdb
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