fd3e0f43b3
6 Commits
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Peter Dillinger
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0050a73a4f |
New stable, fixed-length cache keys (#9126)
Summary: This change standardizes on a new 16-byte cache key format for block cache (incl compressed and secondary) and persistent cache (but not table cache and row cache). The goal is a really fast cache key with practically ideal stability and uniqueness properties without external dependencies (e.g. from FileSystem). A fixed key size of 16 bytes should enable future optimizations to the concurrent hash table for block cache, which is a heavy CPU user / bottleneck, but there appears to be measurable performance improvement even with no changes to LRUCache. This change replaces a lot of disjointed and ugly code handling cache keys with calls to a simple, clean new internal API (cache_key.h). (Preserving the old cache key logic under an option would be very ugly and likely negate the performance gain of the new approach. Complete replacement carries some inherent risk, but I think that's acceptable with sufficient analysis and testing.) The scheme for encoding new cache keys is complicated but explained in cache_key.cc. Also: EndianSwapValue is moved to math.h to be next to other bit operations. (Explains some new include "math.h".) ReverseBits operation added and unit tests added to hash_test for both. Fixes https://github.com/facebook/rocksdb/issues/7405 (presuming a root cause) Pull Request resolved: https://github.com/facebook/rocksdb/pull/9126 Test Plan: ### Basic correctness Several tests needed updates to work with the new functionality, mostly because we are no longer relying on filesystem for stable cache keys so table builders & readers need more context info to agree on cache keys. This functionality is so core, a huge number of existing tests exercise the cache key functionality. ### Performance Create db with `TEST_TMPDIR=/dev/shm ./db_bench -bloom_bits=10 -benchmarks=fillrandom -num=3000000 -partition_index_and_filters` And test performance with `TEST_TMPDIR=/dev/shm ./db_bench -readonly -use_existing_db -bloom_bits=10 -benchmarks=readrandom -num=3000000 -duration=30 -cache_index_and_filter_blocks -cache_size=250000 -threads=4` using DEBUG_LEVEL=0 and simultaneous before & after runs. Before ops/sec, avg over 100 runs: 121924 After ops/sec, avg over 100 runs: 125385 (+2.8%) ### Collision probability I have built a tool, ./cache_bench -stress_cache_key to broadly simulate host-wide cache activity over many months, by making some pessimistic simplifying assumptions: * Every generated file has a cache entry for every byte offset in the file (contiguous range of cache keys) * All of every file is cached for its entire lifetime We use a simple table with skewed address assignment and replacement on address collision to simulate files coming & going, with quite a variance (super-Poisson) in ages. Some output with `./cache_bench -stress_cache_key -sck_keep_bits=40`: ``` Total cache or DBs size: 32TiB Writing 925.926 MiB/s or 76.2939TiB/day Multiply by 9.22337e+18 to correct for simulation losses (but still assume whole file cached) ``` These come from default settings of 2.5M files per day of 32 MB each, and `-sck_keep_bits=40` means that to represent a single file, we are only keeping 40 bits of the 128-bit cache key. With file size of 2\*\*25 contiguous keys (pessimistic), our simulation is about 2\*\*(128-40-25) or about 9 billion billion times more prone to collision than reality. More default assumptions, relatively pessimistic: * 100 DBs in same process (doesn't matter much) * Re-open DB in same process (new session ID related to old session ID) on average every 100 files generated * Restart process (all new session IDs unrelated to old) 24 times per day After enough data, we get a result at the end: ``` (keep 40 bits) 17 collisions after 2 x 90 days, est 10.5882 days between (9.76592e+19 corrected) ``` If we believe the (pessimistic) simulation and the mathematical generalization, we would need to run a billion machines all for 97 billion days to expect a cache key collision. To help verify that our generalization ("corrected") is robust, we can make our simulation more precise with `-sck_keep_bits=41` and `42`, which takes more running time to get enough data: ``` (keep 41 bits) 16 collisions after 4 x 90 days, est 22.5 days between (1.03763e+20 corrected) (keep 42 bits) 19 collisions after 10 x 90 days, est 47.3684 days between (1.09224e+20 corrected) ``` The generalized prediction still holds. With the `-sck_randomize` option, we can see that we are beating "random" cache keys (except offsets still non-randomized) by a modest amount (roughly 20x less collision prone than random), which should make us reasonably comfortable even in "degenerate" cases: ``` 197 collisions after 1 x 90 days, est 0.456853 days between (4.21372e+18 corrected) ``` I've run other tests to validate other conditions behave as expected, never behaving "worse than random" unless we start chopping off structured data. Reviewed By: zhichao-cao Differential Revision: D33171746 Pulled By: pdillinger fbshipit-source-id: f16a57e369ed37be5e7e33525ace848d0537c88f |
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Peter Dillinger
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bda8d93ba9 |
Fix and detect headers with missing dependencies (#8893)
Summary: It's always annoying to find a header does not include its own dependencies and only works when included after other includes. This change adds `make check-headers` which validates that each header can be included at the top of a file. Some headers are excluded e.g. because of platform or external dependencies. rocksdb_namespace.h had to be re-worked slightly to enable checking for failure to include it. (ROCKSDB_NAMESPACE is a valid namespace name.) Fixes mostly involve adding and cleaning up #includes, but for FileTraceWriter, a constructor was out-of-lined to make a forward declaration sufficient. This check is not currently run with `make check` but is added to CircleCI build-linux-unity since that one is already relatively fast. Pull Request resolved: https://github.com/facebook/rocksdb/pull/8893 Test Plan: existing tests and resolving issues detected by new check Reviewed By: mrambacher Differential Revision: D30823300 Pulled By: pdillinger fbshipit-source-id: 9fff223944994c83c105e2e6496d24845dc8e572 |
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Koby Kahane
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3e745053b7 |
Fix MSVC-related build issues (#7439)
Summary: This PR addresses some build and functional issues on MSVC targets, as a step towards an eventual goal of having RocksDB build successfully for Windows on ARM64. Addressed issues include: - BitsSetToOne and CountTrailingZeroBits do not compile on non-x64 MSVC targets. A fallback implementation of BitsSetToOne when Intel intrinsics are not available is added, based on the C++20 `<bit>` popcount implementation in Microsoft's STL. - The implementation of FloorLog2 for MSVC targets (including x64) gives incorrect results. The unit test easily detects this, but CircleCI is currently configured to only run a specific set of tests for Windows CMake builds, so this seems to have been unnoticed. - AsmVolatilePause does not use YieldProcessor on Windows ARM64 targets, even though it is available. - When CondVar::TimedWait calls Microsoft STL's condition_variable::wait_for, it can potentially trigger a bug (just recently fixed in the upcoming VS 16.8's STL) that deadlocks various tests that wait for a timer to execute, since `Timer::Run` doesn't get a chance to execute before being blocked by the test function acquiring the mutex. - In c_test, `GetTempDir` assumes a POSIX-style temp path. - `NormalizePath` did not eliminate consecutive POSIX-style path separators on Windows, resulting in test failures in e.g., wal_manager_test. - Various other test failures. In a followup PR I hope to modify CircleCI's config.yml to invoke all RocksDB unit tests in Windows CMake builds with CTest, instead of the current use of `run_ci_db_test.ps1` which requires individual tests to be specified and is missing many of the existing tests. Notes from peterd: FloorLog2 is not yet used in production code (it's for something in progress). I also added a few more inexpensive platform-dependent tests to Windows CircleCI runs. And included facebook/folly#1461 as requested Pull Request resolved: https://github.com/facebook/rocksdb/pull/7439 Reviewed By: jay-zhuang Differential Revision: D24021563 Pulled By: pdillinger fbshipit-source-id: 0ec2027c0d6a494d8a0fe38d9667fc2f7e29f7e7 |
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Peter Dillinger
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08552b19d3 |
Genericize and clean up FastRange (#7436)
Summary: A generic algorithm in progress depends on a templatized version of fastrange, so this change generalizes it and renames it to fit our style guidelines, FastRange32, FastRange64, and now FastRangeGeneric. Pull Request resolved: https://github.com/facebook/rocksdb/pull/7436 Test Plan: added a few more test cases Reviewed By: jay-zhuang Differential Revision: D23958153 Pulled By: pdillinger fbshipit-source-id: 8c3b76101653417804997e5f076623a25586f3e8 |
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Peter Dillinger
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c4d8838a2b |
New bit manipulation functions and 128-bit value library (#7338)
Summary: These new functions and 128-bit value bit operations are expected to be used in a forthcoming Bloom filter alternative. No functional changes to production code, just new code only called by unit tests, cosmetic changes to existing headers, and fix an existing function for a yet-unused template instantiation (BitsSetToOne on something signed and smaller than 32 bits). Pull Request resolved: https://github.com/facebook/rocksdb/pull/7338 Test Plan: Unit tests included. Works with and without TEST_UINT128_COMPAT=1 to check compatibility with and without __uint128_t. Also added that parameter to the CircleCI build build-linux-shared_lib-alt_namespace-status_checked. Reviewed By: jay-zhuang Differential Revision: D23494945 Pulled By: pdillinger fbshipit-source-id: 5c0dc419100d9df5d4d9abb153b2855d5aea39e8 |
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Peter Dillinger
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bae6f58696 |
Basic MultiGet support for partitioned filters (#6757)
Summary:
In MultiGet, access each applicable filter partition only once
per batch, rather than for each applicable key. Also,
* Fix Bloom stats for MultiGet
* Fix/refactor MultiGetContext::Range::KeysLeft, including
* Add efficient BitsSetToOne implementation
* Assert that MultiGetContext::Range does not go beyond shift range
Performance test: Generate db:
$ ./db_bench --benchmarks=fillrandom --num=15000000 --cache_index_and_filter_blocks -bloom_bits=10 -partition_index_and_filters=true
...
Before (middle performing run of three; note some missing Bloom stats):
$ ./db_bench --use-existing-db --benchmarks=multireadrandom --num=15000000 --cache_index_and_filter_blocks --bloom_bits=10 --threads=16 --cache_size=20000000 -partition_index_and_filters -batch_size=32 -multiread_batched -statistics --duration=20 2>&1 | egrep 'micros/op|block.cache.filter.hit|bloom.filter.(full|use)|number.multiget'
multireadrandom : 26.403 micros/op 597517 ops/sec; (548427 of 671968 found)
rocksdb.block.cache.filter.hit COUNT : 83443275
rocksdb.bloom.filter.useful COUNT : 0
rocksdb.bloom.filter.full.positive COUNT : 0
rocksdb.bloom.filter.full.true.positive COUNT : 7931450
rocksdb.number.multiget.get COUNT : 385984
rocksdb.number.multiget.keys.read COUNT : 12351488
rocksdb.number.multiget.bytes.read COUNT : 793145000
rocksdb.number.multiget.keys.found COUNT : 7931450
After (middle performing run of three):
$ ./db_bench_new --use-existing-db --benchmarks=multireadrandom --num=15000000 --cache_index_and_filter_blocks --bloom_bits=10 --threads=16 --cache_size=20000000 -partition_index_and_filters -batch_size=32 -multiread_batched -statistics --duration=20 2>&1 | egrep 'micros/op|block.cache.filter.hit|bloom.filter.(full|use)|number.multiget'
multireadrandom : 21.024 micros/op 752963 ops/sec; (705188 of 863968 found)
rocksdb.block.cache.filter.hit COUNT : 49856682
rocksdb.bloom.filter.useful COUNT : 45684579
rocksdb.bloom.filter.full.positive COUNT : 10395458
rocksdb.bloom.filter.full.true.positive COUNT : 9908456
rocksdb.number.multiget.get COUNT : 481984
rocksdb.number.multiget.keys.read COUNT : 15423488
rocksdb.number.multiget.bytes.read COUNT : 990845600
rocksdb.number.multiget.keys.found COUNT : 9908456
So that's about 25% higher throughput even for random keys
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6757
Test Plan: unit test included
Reviewed By: anand1976
Differential Revision: D21243256
Pulled By: pdillinger
fbshipit-source-id: 5644a1468d9e8c8575be02f4e04bc5d62dbbb57f
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