Summary:
Instead of existing calls to ps from gnu_parallel, call a new wrapper that does ps, looks for unit test like processes, and uses pstack or gdb to print thread stack traces. Also, using `ps -wwf` instead of `ps -wf` ensures output is not cut off.
For security, CircleCI runs with security restrictions on ptrace (/proc/sys/kernel/yama/ptrace_scope = 1), and this change adds a work-around to `InstallStackTraceHandler()` (only used by testing tools) to allow any process from the same user to debug it. (I've also touched >100 files to ensure all the unit tests call this function.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10828
Test Plan: local manual + temporary infinite loop in a unit test to observe in CircleCI
Reviewed By: hx235
Differential Revision: D40447634
Pulled By: pdillinger
fbshipit-source-id: 718a4c4a5b54fa0f9af2d01a446162b45e5e84e1
Summary:
**Context/Summary:**
Previous experience with bugs and flaky tests taught us there exist features in RocksDB vulnerable to race condition caused by acquiring db mutex at a particular timing. This PR aggressively exposes those vulnerable features by injecting spurious wakeup and sleep to cause acquiring db mutex at various timing in order to expose such race condition
**Testing:**
- `COERCE_CONTEXT_SWITCH=1 make -j56 check / make -j56 db_stress` should reveal
- flaky tests caused by db mutex related race condition
- Reverted https://github.com/facebook/rocksdb/pull/9528
- A/B testing on `COMPILE_WITH_TSAN=1 make -j56 listener_test` w/ and w/o `COERCE_CONTEXT_SWITCH=1` followed by `./listener_test --gtest_filter=EventListenerTest.MultiCF --gtest_repeat=10`
- `COERCE_CONTEXT_SWITCH=1` can cause expected test failure (i.e, expose target TSAN data race error) within 10 run while the other couldn't.
- This proves our injection can expose flaky tests caused by db mutex related race condition faster.
- known or new race-condition-type of internal bug by continuously running this PR
- Performance
- High ops-threads time: COERCE_CONTEXT_SWITCH=1 regressed by 4 times slower (2:01.16 vs 0:22.10 elapsed ). This PR will be run as a separate CI job so this regression won't affect any existing job.
```
TEST_TMPDIR=$db /usr/bin/time ./db_stress \
--ops_per_thread=100000 --expected_values_dir=$exp --clear_column_family_one_in=0 \
--write_buffer_size=524288 —target_file_size_base=524288 —ingest_external_file_one_in=100 —compact_files_one_in=1000 —compact_range_one_in=1000
```
- Start-up time: COERCE_CONTEXT_SWITCH=1 didn't regress by 25% (0:01.51 vs 0:01.29 elapsed)
```
TEST_TMPDIR=$db ./db_stress -ops_per_thread=100000000 -expected_values_dir=$exp --clear_column_family_one_in=0 & sleep 120; pkill -9 db_stress
TEST_TMPDIR=$db /usr/bin/time ./db_stress \
--ops_per_thread=1 -reopen=0 --expected_values_dir=$exp --clear_column_family_one_in=0 --destroy_db_initially=0
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10291
Reviewed By: ajkr
Differential Revision: D39231182
Pulled By: hx235
fbshipit-source-id: 7ab6695430460e0826727fd8c66679b32b3e44b6
Summary:
Delete range logic is moved from `DBIter` to `MergingIterator`, and `MergingIterator` will seek to the end of a range deletion if possible instead of scanning through each key and check with `RangeDelAggregator`.
With the invariant that a key in level L (consider memtable as the first level, each immutable and L0 as a separate level) has a larger sequence number than all keys in any level >L, a range tombstone `[start, end)` from level L covers all keys in its range in any level >L. This property motivates optimizations in iterator:
- in `Seek(target)`, if level L has a range tombstone `[start, end)` that covers `target.UserKey`, then for all levels > L, we can do Seek() on `end` instead of `target` to skip some range tombstone covered keys.
- in `Next()/Prev()`, if the current key is covered by a range tombstone `[start, end)` from level L, we can do `Seek` to `end` for all levels > L.
This PR implements the above optimizations in `MergingIterator`. As all range tombstone covered keys are now skipped in `MergingIterator`, the range tombstone logic is removed from `DBIter`. The idea in this PR is similar to https://github.com/facebook/rocksdb/issues/7317, but this PR leaves `InternalIterator` interface mostly unchanged. **Credit**: the cascading seek optimization and the sentinel key (discussed below) are inspired by [Pebble](https://github.com/cockroachdb/pebble/blob/master/merging_iter.go) and suggested by ajkr in https://github.com/facebook/rocksdb/issues/7317. The two optimizations are mostly implemented in `SeekImpl()/SeekForPrevImpl()` and `IsNextDeleted()/IsPrevDeleted()` in `merging_iterator.cc`. See comments for each method for more detail.
One notable change is that the minHeap/maxHeap used by `MergingIterator` now contains range tombstone end keys besides point key iterators. This helps to reduce the number of key comparisons. For example, for a range tombstone `[start, end)`, a `start` and an `end` `HeapItem` are inserted into the heap. When a `HeapItem` for range tombstone start key is popped from the minHeap, we know this range tombstone becomes "active" in the sense that, before the range tombstone's end key is popped from the minHeap, all the keys popped from this heap is covered by the range tombstone's internal key range `[start, end)`.
Another major change, *delete range sentinel key*, is made to `LevelIterator`. Before this PR, when all point keys in an SST file are iterated through in `MergingIterator`, a level iterator would advance to the next SST file in its level. In the case when an SST file has a range tombstone that covers keys beyond the SST file's last point key, advancing to the next SST file would lose this range tombstone. Consequently, `MergingIterator` could return keys that should have been deleted by some range tombstone. We prevent this by pretending that file boundaries in each SST file are sentinel keys. A `LevelIterator` now only advance the file iterator once the sentinel key is processed.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10449
Test Plan:
- Added many unit tests in db_range_del_test
- Stress test: `./db_stress --readpercent=5 --prefixpercent=19 --writepercent=20 -delpercent=10 --iterpercent=44 --delrangepercent=2`
- Additional iterator stress test is added to verify against iterators against expected state: https://github.com/facebook/rocksdb/issues/10538. This is based on ajkr's previous attempt https://github.com/facebook/rocksdb/pull/5506#issuecomment-506021913.
```
python3 ./tools/db_crashtest.py blackbox --simple --write_buffer_size=524288 --target_file_size_base=524288 --max_bytes_for_level_base=2097152 --compression_type=none --max_background_compactions=8 --value_size_mult=33 --max_key=5000000 --interval=10 --duration=7200 --delrangepercent=3 --delpercent=9 --iterpercent=25 --writepercent=60 --readpercent=3 --prefixpercent=0 --num_iterations=1000 --range_deletion_width=100 --verify_iterator_with_expected_state_one_in=1
```
- Performance benchmark: I used a similar setup as in the blog [post](http://rocksdb.org/blog/2018/11/21/delete-range.html) that introduced DeleteRange, "a database with 5 million data keys, and 10000 range tombstones (ignoring those dropped during compaction) that were written in regular intervals after 4.5 million data keys were written". As expected, the performance with this PR depends on the range tombstone width.
```
# Setup:
TEST_TMPDIR=/dev/shm ./db_bench_main --benchmarks=fillrandom --writes=4500000 --num=5000000
TEST_TMPDIR=/dev/shm ./db_bench_main --benchmarks=overwrite --writes=500000 --num=5000000 --use_existing_db=true --writes_per_range_tombstone=50
# Scan entire DB
TEST_TMPDIR=/dev/shm ./db_bench_main --benchmarks=readseq[-X5] --use_existing_db=true --num=5000000 --disable_auto_compactions=true
# Short range scan (10 Next())
TEST_TMPDIR=/dev/shm/width-100/ ./db_bench_main --benchmarks=seekrandom[-X5] --use_existing_db=true --num=500000 --reads=100000 --seek_nexts=10 --disable_auto_compactions=true
# Long range scan(1000 Next())
TEST_TMPDIR=/dev/shm/width-100/ ./db_bench_main --benchmarks=seekrandom[-X5] --use_existing_db=true --num=500000 --reads=2500 --seek_nexts=1000 --disable_auto_compactions=true
```
Avg over of 10 runs (some slower tests had fews runs):
For the first column (tombstone), 0 means no range tombstone, 100-10000 means width of the 10k range tombstones, and 1 means there is a single range tombstone in the entire DB (width is 1000). The 1 tombstone case is to test regression when there's very few range tombstones in the DB, as no range tombstone is likely to take a different code path than with range tombstones.
- Scan entire DB
| tombstone width | Pre-PR ops/sec | Post-PR ops/sec | ±% |
| ------------- | ------------- | ------------- | ------------- |
| 0 range tombstone |2525600 (± 43564) |2486917 (± 33698) |-1.53% |
| 100 |1853835 (± 24736) |2073884 (± 32176) |+11.87% |
| 1000 |422415 (± 7466) |1115801 (± 22781) |+164.15% |
| 10000 |22384 (± 227) |227919 (± 6647) |+918.22% |
| 1 range tombstone |2176540 (± 39050) |2434954 (± 24563) |+11.87% |
- Short range scan
| tombstone width | Pre-PR ops/sec | Post-PR ops/sec | ±% |
| ------------- | ------------- | ------------- | ------------- |
| 0 range tombstone |35398 (± 533) |35338 (± 569) |-0.17% |
| 100 |28276 (± 664) |31684 (± 331) |+12.05% |
| 1000 |7637 (± 77) |25422 (± 277) |+232.88% |
| 10000 |1367 |28667 |+1997.07% |
| 1 range tombstone |32618 (± 581) |32748 (± 506) |+0.4% |
- Long range scan
| tombstone width | Pre-PR ops/sec | Post-PR ops/sec | ±% |
| ------------- | ------------- | ------------- | ------------- |
| 0 range tombstone |2262 (± 33) |2353 (± 20) |+4.02% |
| 100 |1696 (± 26) |1926 (± 18) |+13.56% |
| 1000 |410 (± 6) |1255 (± 29) |+206.1% |
| 10000 |25 |414 |+1556.0% |
| 1 range tombstone |1957 (± 30) |2185 (± 44) |+11.65% |
- Microbench does not show significant regression: https://gist.github.com/cbi42/59f280f85a59b678e7e5d8561e693b61
Reviewed By: ajkr
Differential Revision: D38450331
Pulled By: cbi42
fbshipit-source-id: b5ef12e8d8c289ed2e163ccdf277f5039b511fca
Summary:
Appears possible after 5de98f2 introduced possible lost
updates. Could be related to 2af132c also. Simply ensure no sqrt of
negative.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10586
Test Plan: test added
Reviewed By: ajkr
Differential Revision: D39068391
Pulled By: pdillinger
fbshipit-source-id: 230b214a41e6c9ae91a1ef3e8b2a17b46bbb17c2
Summary:
Imported a fix to "rocksdb.prefetched.bytes.discarded" stat from https://github.com/facebook/rocksdb/issues/10561, and added a new stat "rocksdb.async.prefetch.abort.micros" to measure time spent waiting for async reads to abort.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10585
Reviewed By: akankshamahajan15
Differential Revision: D39067000
Pulled By: anand1976
fbshipit-source-id: d7cda71abb48017239bd5fd832345a16c7024faf
Summary:
Timer has a limitation that it cannot re-register a task with the same name,
because the cancel only mark the task as invalid and wait for the Timer thread
to clean it up later, before the task is cleaned up, the same task name cannot
be added. Which makes the task option update likely to fail, which basically
cancel and re-register the same task name. Change the periodic task name to a
random unique id and store it in periodic_task_scheduler.
Also refactor the `periodic_work` to `periodic_task` to make each job function
as a `task`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10379
Test Plan: unittests
Reviewed By: ajkr
Differential Revision: D38000615
Pulled By: jay-zhuang
fbshipit-source-id: e4135f9422e3b53aaec8eda54f4e18ce633a279e
Summary:
EnvLogger was built to replace PosixLogger that supports multiple Envs. Make FileSystem use EnvLogger by default, remove Posix FS specific implementation and remove PosixLogger code,
Some hacky changes are made to make sure iostats are not polluted by logging, in order to pass existing unit tests.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10436
Test Plan: Run db_bench and watch info log files.
Reviewed By: anand1976
Differential Revision: D38259855
fbshipit-source-id: 67d65874bfba7a33535b6d0dd0ed92cbbc9888b8
Summary:
Which will be used for tiered storage to preclude hot data from
compacting to the cold tier (the last level).
Internally, adding seqno to time mapping. A periodic_task is scheduled
to record the current_seqno -> current_time in certain cadence. When
memtable flush, the mapping informaiton is stored in sstable property.
During compaction, the mapping information are merged and get the
approximate time of sequence number, which is used to determine if a key
is recently inserted or not and preclude it from the last level if it's
recently inserted (within the `preclude_last_level_data_seconds`).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10338
Test Plan: CI
Reviewed By: siying
Differential Revision: D37810187
Pulled By: jay-zhuang
fbshipit-source-id: 6953be7a18a99de8b1cb3b162d712f79c2b4899f
Summary:
Add a couple of stats to help users estimate the impact of potential MultiGet perf improvements -
1. NUM_LEVEL_READ_PER_MULTIGET - A histogram stat for number of levels that required MultiGet to read from a file
2. MULTIGET_COROUTINE_COUNT - A ticker stat to count the number of times the coroutine version of MultiGetFromSST was used
The NUM_DATA_BLOCKS_READ_PER_LEVEL stat is obsoleted as it doesn't provide useful information for MultiGet optimization.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10182
Reviewed By: akankshamahajan15
Differential Revision: D37213296
Pulled By: anand1976
fbshipit-source-id: 5d2b7708017c0e278578ae4bffac3926f6530efb
Summary:
There was an overflow bug when computing the variance in the HistogramStat class.
This manifests, for instance, when running cache_bench with default arguments. This executes 32M lookups/inserts/deletes in a block cache, and then computes (among other things) the variance of the latencies. The variance is computed as ``variance = (cur_sum_squares * cur_num - cur_sum * cur_sum) / (cur_num * cur_num)``, where ``cum_sum_squares`` is the sum of the squares of the samples, ``cur_num`` is the number of samples, and ``cur_sum`` is the sum of the samples. Because the median latency in a typical run is around 3800 nanoseconds, both the ``cur_sum_squares * cur_num`` and ``cur_sum * cur_sum`` terms overflow as uint64_t.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10100
Test Plan: Added a unit test. Run ``make -j24 histogram_test && ./histogram_test``.
Reviewed By: pdillinger
Differential Revision: D36942738
Pulled By: guidotag
fbshipit-source-id: 0af5fb9e2a297a284e8e74c24e604d302906006e
Summary:
In case of non-TransactionDB and avoid_flush_during_recovery = true, RocksDB won't
flush the data from WAL to L0 for all column families if possible. As a
result, not all column families can increase their log_numbers, and
min_log_number_to_keep won't change.
For transaction DB (.allow_2pc), even with the flush, there may be old WAL files that it must not delete because they can contain data of uncommitted transactions and min_log_number_to_keep won't change.
If we persist a new MANIFEST with
advanced log_numbers for some column families, then during a second
crash after persisting the MANIFEST, RocksDB will see some column
families' log_numbers larger than the corrupted wal, and the "column family inconsistency" error will be hit, causing recovery to fail.
As a solution, RocksDB will persist the new MANIFEST after successfully syncing the new WAL.
If a future recovery starts from the new MANIFEST, then it means the new WAL is successfully synced. Due to the sentinel empty write batch at the beginning, kPointInTimeRecovery of WAL is guaranteed to go after this point.
If future recovery starts from the old MANIFEST, it means the writing the new MANIFEST failed. We won't have the "SST ahead of WAL" error.
Currently, RocksDB DB::Open() may creates and writes to two new MANIFEST files even before recovery succeeds. This PR buffers the edits in a structure and writes to a new MANIFEST after recovery is successful
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9922
Test Plan:
1. Update unit tests to fail without this change
2. make crast_test -j
Branch with unit test and no fix https://github.com/facebook/rocksdb/pull/9942 to keep track of unit test (without fix)
Reviewed By: riversand963
Differential Revision: D36043701
Pulled By: akankshamahajan15
fbshipit-source-id: 5760970db0a0920fb73d3c054a4155733500acd9
Summary:
The RocksDB iterator is a hierarchy of iterators. MergingIterator maintains a heap of LevelIterators, one for each L0 file and for each non-zero level. The Seek() operation naturally lends itself to parallelization, as it involves positioning every LevelIterator on the correct data block in the correct SST file. It lookups a level for a target key, to find the first key that's >= the target key. This typically involves reading one data block that is likely to contain the target key, and scan forward to find the first valid key. The forward scan may read more data blocks. In order to find the right data block, the iterator may read some metadata blocks (required for opening a file and searching the index).
This flow can be parallelized.
Design: Seek will be called two times under async_io option. First seek will send asynchronous request to prefetch the data blocks at each level and second seek will follow the normal flow and in FilePrefetchBuffer::TryReadFromCacheAsync it will wait for the Poll() to get the results and add the iterator to min_heap.
- Status::TryAgain is passed down from FilePrefetchBuffer::PrefetchAsync to block_iter_.Status indicating asynchronous request has been submitted.
- If for some reason asynchronous request returns error in submitting the request, it will fallback to sequential reading of blocks in one pass.
- If the data already exists in prefetch_buffer, it will return the data without prefetching further and it will be treated as single pass of seek.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9994
Test Plan:
- **Run Regressions.**
```
./db_bench -db=/tmp/prefix_scan_prefetch_main -benchmarks="fillseq" -key_size=32 -value_size=512 -num=5000000 -use_direct_io_for_flush_and_compaction=true -target_file_size_base=16777216
```
i) Previous release 7.0 run for normal prefetching with async_io disabled:
```
./db_bench -use_existing_db=true -db=/tmp/prefix_scan_prefetch_main -benchmarks="seekrandom" -key_size=32 -value_size=512 -num=5000000 -use_direct_reads=true -seek_nexts=327680 -duration=120 -ops_between_duration_checks=1
Initializing RocksDB Options from the specified file
Initializing RocksDB Options from command-line flags
RocksDB: version 7.0
Date: Thu Mar 17 13:11:34 2022
CPU: 24 * Intel Core Processor (Broadwell)
CPUCache: 16384 KB
Keys: 32 bytes each (+ 0 bytes user-defined timestamp)
Values: 512 bytes each (256 bytes after compression)
Entries: 5000000
Prefix: 0 bytes
Keys per prefix: 0
RawSize: 2594.0 MB (estimated)
FileSize: 1373.3 MB (estimated)
Write rate: 0 bytes/second
Read rate: 0 ops/second
Compression: Snappy
Compression sampling rate: 0
Memtablerep: SkipListFactory
Perf Level: 1
------------------------------------------------
DB path: [/tmp/prefix_scan_prefetch_main]
seekrandom : 483618.390 micros/op 2 ops/sec; 338.9 MB/s (249 of 249 found)
```
ii) normal prefetching after changes with async_io disable:
```
./db_bench -use_existing_db=true -db=/tmp/prefix_scan_prefetch_main -benchmarks="seekrandom" -key_size=32 -value_size=512 -num=5000000 -use_direct_reads=true -seek_nexts=327680 -duration=120 -ops_between_duration_checks=1
Set seed to 1652922591315307 because --seed was 0
Initializing RocksDB Options from the specified file
Initializing RocksDB Options from command-line flags
RocksDB: version 7.3
Date: Wed May 18 18:09:51 2022
CPU: 32 * Intel Xeon Processor (Skylake)
CPUCache: 16384 KB
Keys: 32 bytes each (+ 0 bytes user-defined timestamp)
Values: 512 bytes each (256 bytes after compression)
Entries: 5000000
Prefix: 0 bytes
Keys per prefix: 0
RawSize: 2594.0 MB (estimated)
FileSize: 1373.3 MB (estimated)
Write rate: 0 bytes/second
Read rate: 0 ops/second
Compression: Snappy
Compression sampling rate: 0
Memtablerep: SkipListFactory
Perf Level: 1
------------------------------------------------
DB path: [/tmp/prefix_scan_prefetch_main]
seekrandom : 483080.466 micros/op 2 ops/sec 120.287 seconds 249 operations; 340.8 MB/s (249 of 249 found)
```
iii) db_bench with async_io enabled completed succesfully
```
./db_bench -use_existing_db=true -db=/tmp/prefix_scan_prefetch_main -benchmarks="seekrandom" -key_size=32 -value_size=512 -num=5000000 -use_direct_reads=true -seek_nexts=327680 -duration=120 -ops_between_duration_checks=1 -async_io=1 -adaptive_readahead=1
Set seed to 1652924062021732 because --seed was 0
Initializing RocksDB Options from the specified file
Initializing RocksDB Options from command-line flags
RocksDB: version 7.3
Date: Wed May 18 18:34:22 2022
CPU: 32 * Intel Xeon Processor (Skylake)
CPUCache: 16384 KB
Keys: 32 bytes each (+ 0 bytes user-defined timestamp)
Values: 512 bytes each (256 bytes after compression)
Entries: 5000000
Prefix: 0 bytes
Keys per prefix: 0
RawSize: 2594.0 MB (estimated)
FileSize: 1373.3 MB (estimated)
Write rate: 0 bytes/second
Read rate: 0 ops/second
Compression: Snappy
Compression sampling rate: 0
Memtablerep: SkipListFactory
Perf Level: 1
------------------------------------------------
DB path: [/tmp/prefix_scan_prefetch_main]
seekrandom : 553913.576 micros/op 1 ops/sec 120.199 seconds 217 operations; 293.6 MB/s (217 of 217 found)
```
- db_stress with async_io disabled completed succesfully
```
export CRASH_TEST_EXT_ARGS=" --async_io=0"
make crash_test -j
```
I**n Progress**: db_stress with async_io is failing and working on debugging/fixing it.
Reviewed By: anand1976
Differential Revision: D36459323
Pulled By: akankshamahajan15
fbshipit-source-id: abb1cd944abe712bae3986ae5b16704b3338917c
Summary:
This PR implements a coroutine version of batched MultiGet in order to concurrently read from multiple SST files in a level using async IO, thus reducing the latency of the MultiGet. The API from the user perspective is still synchronous and single threaded, with the RocksDB part of the processing happening in the context of the caller's thread. In Version::MultiGet, the decision is made whether to call synchronous or coroutine code.
A good way to review this PR is to review the first 4 commits in order - de773b3, 70c2f70, 10b50e1, and 377a597 - before reviewing the rest.
TODO:
1. Figure out how to build it in CircleCI (requires some dependencies to be installed)
2. Do some stress testing with coroutines enabled
No regression in synchronous MultiGet between this branch and main -
```
./db_bench -use_existing_db=true --db=/data/mysql/rocksdb/prefix_scan -benchmarks="readseq,multireadrandom" -key_size=32 -value_size=512 -num=5000000 -batch_size=64 -multiread_batched=true -use_direct_reads=false -duration=60 -ops_between_duration_checks=1 -readonly=true -adaptive_readahead=true -threads=16 -cache_size=10485760000 -async_io=false -multiread_stride=40000 -statistics
```
Branch - ```multireadrandom : 4.025 micros/op 3975111 ops/sec 60.001 seconds 238509056 operations; 2062.3 MB/s (14767808 of 14767808 found)```
Main - ```multireadrandom : 3.987 micros/op 4013216 ops/sec 60.001 seconds 240795392 operations; 2082.1 MB/s (15231040 of 15231040 found)```
More benchmarks in various scenarios are given below. The measurements were taken with ```async_io=false``` (no coroutines) and ```async_io=true``` (use coroutines). For an IO bound workload (with every key requiring an IO), the coroutines version shows a clear benefit, being ~2.6X faster. For CPU bound workloads, the coroutines version has ~6-15% higher CPU utilization, depending on how many keys overlap an SST file.
1. Single thread IO bound workload on remote storage with sparse MultiGet batch keys (~1 key overlap/file) -
No coroutines - ```multireadrandom : 831.774 micros/op 1202 ops/sec 60.001 seconds 72136 operations; 0.6 MB/s (72136 of 72136 found)```
Using coroutines - ```multireadrandom : 318.742 micros/op 3137 ops/sec 60.003 seconds 188248 operations; 1.6 MB/s (188248 of 188248 found)```
2. Single thread CPU bound workload (all data cached) with ~1 key overlap/file -
No coroutines - ```multireadrandom : 4.127 micros/op 242322 ops/sec 60.000 seconds 14539384 operations; 125.7 MB/s (14539384 of 14539384 found)```
Using coroutines - ```multireadrandom : 4.741 micros/op 210935 ops/sec 60.000 seconds 12656176 operations; 109.4 MB/s (12656176 of 12656176 found)```
3. Single thread CPU bound workload with ~2 key overlap/file -
No coroutines - ```multireadrandom : 3.717 micros/op 269000 ops/sec 60.000 seconds 16140024 operations; 139.6 MB/s (16140024 of 16140024 found)```
Using coroutines - ```multireadrandom : 4.146 micros/op 241204 ops/sec 60.000 seconds 14472296 operations; 125.1 MB/s (14472296 of 14472296 found)```
4. CPU bound multi-threaded (16 threads) with ~4 key overlap/file -
No coroutines - ```multireadrandom : 4.534 micros/op 3528792 ops/sec 60.000 seconds 211728728 operations; 1830.7 MB/s (12737024 of 12737024 found) ```
Using coroutines - ```multireadrandom : 4.872 micros/op 3283812 ops/sec 60.000 seconds 197030096 operations; 1703.6 MB/s (12548032 of 12548032 found) ```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9968
Reviewed By: akankshamahajan15
Differential Revision: D36348563
Pulled By: anand1976
fbshipit-source-id: c0ce85a505fd26ebfbb09786cbd7f25202038696
Summary:
ROCKSDB_SUPPORT_THREAD_LOCAL definition has been removed.
`__thread`(#define) has been replaced with `thread_local`(C++ keyword) across the code base.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10015
Reviewed By: siying
Differential Revision: D36485491
Pulled By: pdillinger
fbshipit-source-id: 6522d212514ee190b90b4e2750c80c7e34013c78
Summary:
Right now we still don't fully use std::numeric_limits but use a macro, mainly for supporting VS 2013. Right now we only support VS 2017 and up so it is not a problem. The code comment claims that MinGW still needs it. We don't have a CI running MinGW so it's hard to validate. since we now require C++17, it's hard to imagine MinGW would still build RocksDB but doesn't support std::numeric_limits<>.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9954
Test Plan: See CI Runs.
Reviewed By: riversand963
Differential Revision: D36173954
fbshipit-source-id: a35a73af17cdcae20e258cdef57fcf29a50b49e0
Summary:
Left HISTORY.md and unit tests.
Added a new unit test to repro the corruption scenario that this PR fixes, and HISTORY.md line for that.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9906
Reviewed By: riversand963
Differential Revision: D35940093
Pulled By: ajkr
fbshipit-source-id: 9816f99e1ce405ba36f316beb4f6378c37c8c86b
Summary:
Add stats PREFETCHED_BYTES_DISCARDED and POLL_WAIT_MICROS.
PREFETCHED_BYTES_DISCARDED records number of prefetched bytes discarded by
FilePrefetchBuffer. POLL_WAIT_MICROS records the time taken by underling
file_system Poll API.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9845
Test Plan: Update existing tests
Reviewed By: anand1976
Differential Revision: D35909694
Pulled By: akankshamahajan15
fbshipit-source-id: e009ef940bb9ed72c9446f5529095caabb8a1e36
Summary:
1) In case of non-TransactionDB and avoid_flush_during_recovery = true, RocksDB won't
flush the data from WAL to L0 for all column families if possible. As a
result, not all column families can increase their log_numbers, and
min_log_number_to_keep won't change.
2) For transaction DB (.allow_2pc), even with the flush, there may be old WAL files that it must not delete because they can contain data of uncommitted transactions and min_log_number_to_keep won't change.
If we persist a new MANIFEST with
advanced log_numbers for some column families, then during a second
crash after persisting the MANIFEST, RocksDB will see some column
families' log_numbers larger than the corrupted wal, and the "column family inconsistency" error will be hit, causing recovery to fail.
As a solution,
1. the corrupted WALs whose numbers are larger than the
corrupted wal and smaller than the new WAL will be moved to archive folder.
2. Currently, RocksDB DB::Open() may creates and writes to two new MANIFEST files even before recovery succeeds. This PR buffers the edits in a structure and writes to a new MANIFEST after recovery is successful
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9634
Test Plan:
1. Added new unit tests
2. make crast_test -j
Reviewed By: riversand963
Differential Revision: D34463666
Pulled By: akankshamahajan15
fbshipit-source-id: e233d3af0ed4e2028ca0cf051e5a334a0fdc9d19
Summary:
Update stats in random_access_file_reader for Read and
ReadAsync API to take into account the read latency for async
prefetching.
It also fixes ERROR_HANDLER_AUTORESUME_RETRY_COUNT stat whose value was
incorrect in portal.h
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9810
Test Plan: Update unit test
Reviewed By: anand1976
Differential Revision: D35433081
Pulled By: akankshamahajan15
fbshipit-source-id: aeec3901270e58a003ce6b5214bd25ddcb3a12a9
Summary:
Fixes https://github.com/facebook/rocksdb/issues/9779.
The padding at the end of a struct is added implicitly according to the
sizeof spec: "When applied to a class, the result is the
number of bytes in an object of that class including any padding
required for placing objects of that type in an array"
(https://eel.is/c++draft/expr.sizeof#2.sentence-2). We should drop the
explicit padding since it assumed support for zero-length arrays, which
is non-standard.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9809
Test Plan: rely on CI
Reviewed By: riversand963
Differential Revision: D35413496
Pulled By: ajkr
fbshipit-source-id: 25d52ca45e648ad0d5657149f26f6adecbed1cb4
Summary:
Fixes https://github.com/facebook/rocksdb/issues/9718
The verify_checksums flag of read_options should be passed to the read options used by the BlockFetcher in a couple of cases where it is not at present. It will now happen (but did not, previously) on iteration and on [multi]get, where a fetcher is created as part of the iterate/get call.
This may result in much better performance in a few workloads where the client chooses to remove verification.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9767
Reviewed By: mrambacher
Differential Revision: D35218986
Pulled By: jay-zhuang
fbshipit-source-id: 329d29764bb70fbc7f2673440bc46c107a813bc8
Summary:
We found a case of cacheline bouncing due to writers locking/unlocking `mutex_` and readers accessing `block_cache_tracer_`. We discovered it only after the issue was fixed by https://github.com/facebook/rocksdb/issues/9462 shifting the `DBImpl` members such that `mutex_` and `block_cache_tracer_` were naturally placed in separate cachelines in our regression testing setup. This PR forces the cacheline alignment of `mutex_` so we don't accidentally reintroduce the problem.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9637
Reviewed By: riversand963
Differential Revision: D34502233
Pulled By: ajkr
fbshipit-source-id: 46aa313b7fe83e80c3de254e332b6fb242434c07
Summary:
In order to support old-style regex function registration, restored the original "Register<T>(string, Factory)" method using regular expressions. The PatternEntry methods were left in place but renamed to AddFactory. The goal is to allow for the deprecation of the original regex Registry method in an upcoming release.
Added modes to the PatternEntry kMatchZeroOrMore and kMatchAtLeastOne to match * or +, respectively (kMatchAtLeastOne was the original behavior).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9362
Reviewed By: pdillinger
Differential Revision: D33432562
Pulled By: mrambacher
fbshipit-source-id: ed88ab3f9a2ad0d525c7bd1692873f9bb3209d02
Summary:
Add the 3 read bytes counter to the Statistic, which will be used by storage tiering and get the information for files with different temperature.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9123
Test Plan: added new testing cases.
Reviewed By: siying
Differential Revision: D32154745
Pulled By: zhichao-cao
fbshipit-source-id: b7905d6dae469a72428742364ec07b634b6f15da
Summary:
This PR fix wrong ticker `WRITE_WITH_WAL`.
`RecordTick(WRITE_WITH_WAL)` will be called later in `WriteToWAL` and `ConcurrentWriteToWAL`.
Fixes:
1. Delete these two extra `RecordTick(WRITE_WITH_WAL)`
2. Fix corresponding test case
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9064
Reviewed By: ajkr
Differential Revision: D31944459
Pulled By: riversand963
fbshipit-source-id: f1aa8d2a4320456bc357bc5b0902032f7dcad086
Summary:
This PR adds support for building on s390x including updating travis CI. It uses the previous work in https://github.com/facebook/rocksdb/pull/6168 and adds some more changes to get all current tests (make check and jni tests) to pass. The tests were run with snappy, lz4, bzip2 and zstd all compiled in.
There are a few pieces still needed to get the travis build working that I don't think I can do. adamretter is this something you could help with?
1. A prebuilt https://rocksdb-deps.s3-us-west-2.amazonaws.com/cmake/cmake-3.14.5-Linux-s390x.deb package
2. A https://hub.docker.com/r/evolvedbinary/rocksjava s390x image
Not sure if there is more required for travis. Happy to help in any way I can.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8962
Reviewed By: mrambacher
Differential Revision: D31802198
Pulled By: pdillinger
fbshipit-source-id: 683511466fa6b505f85ba5a9964a268c6151f0c2
Summary:
`valueIndexMap_` in histogram is redundant and search in `valueIndexMap_` is slower than search in `bucketValues_`.
this PR delete `valueIndexMap_` and search in `bucketValues_` by `std::lower_bound`
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8625
Reviewed By: zhichao-cao
Differential Revision: D31613386
Pulled By: ajkr
fbshipit-source-id: d7415d724f5c8f41f80cbe82afd7467cfad6f009
Summary:
For tiered storage project, we need to know the block read count and read bytes of files with different temperature. Add FileIOByTemperature to IOStatsContext and collect the bytes read and read count from different temperature files through the RandomAccessFileReader.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8710
Test Plan: make check, add the testing cases
Reviewed By: siying
Differential Revision: D30582400
Pulled By: zhichao-cao
fbshipit-source-id: d83173de594374fc8404af5ce93a6a9be72c7141
Summary:
IOSTATS_ADD_IF_POSITIVE() doesn't seem to a macro that aims to improve performance but does the opposite. The counter to add is almost always positive so the if is just a waste. Furthermore, adding to a thread local variable seemse to be much cheaper than an if condition if branch prediction has a possibility to be wrong. Remove the macro.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8984
Test Plan: See CI completes.
Reviewed By: anand1976
Differential Revision: D31348163
fbshipit-source-id: 30af6d45e1aa8bbc09b2c046206cce6f67f4777a
Summary:
Made SystemClock into a Customizable class, complete with CreateFromString.
Cleaned up some of the existing SystemClock implementations that were redundant (NoSleep was the same as the internal one for MockEnv).
Changed MockEnv construction to allow Clock to be passed to the Memory/MockFileSystem.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8636
Reviewed By: zhichao-cao
Differential Revision: D30483360
Pulled By: mrambacher
fbshipit-source-id: cd0e3a876c39f8c98fe13374c06e8edbd5b9f2a1
Summary:
This keeps the implementations/API backward compatible. Implementations of Statistics will need to override this method (and be registered with the ObjectRegistry) in order to be created via CreateFromString.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8918
Reviewed By: pdillinger
Differential Revision: D30958916
Pulled By: mrambacher
fbshipit-source-id: 75b99a84e9e11fda2a9e8eff9ee1ef69a17517b2
Summary:
Make the Statistics object into a Customizable object. Statistics can now be stored and created to/from the Options file.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8637
Reviewed By: zhichao-cao
Differential Revision: D30530550
Pulled By: mrambacher
fbshipit-source-id: 5fc7d01d8431f37b2c205bbbd8342c9f697023bd
Summary:
Gets `Statistics` from the options associated with the `DB` undergoing backup, and populates new ticker stats with the thread-local `IOContext` read/write counters for the threads doing backup work.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8819
Reviewed By: pdillinger
Differential Revision: D30779238
Pulled By: ajkr
fbshipit-source-id: 75ccafc355f90906df5cf80367f7245b985772d8
Summary:
- Clarified some comments on compatibility for adding new ticker stats
- Added read I/O stats for `VerifyChecksum()` and `VerifyFileChecksums()` APIs
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8741
Test Plan: new unit test
Reviewed By: zhichao-cao
Differential Revision: D30708578
Pulled By: ajkr
fbshipit-source-id: d06b961f7e199ae92c266b683e39870aa8f63449
Summary:
Add a stat for secondary cache hits. The ```Cache::Lookup``` API had an unused ```stats``` parameter. This PR uses that to pass the pointer to a ```Statistics``` object that ```LRUCache``` uses to record the stat.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8666
Test Plan: Update a unit test in lru_cache_test
Reviewed By: zhichao-cao
Differential Revision: D30353816
Pulled By: anand1976
fbshipit-source-id: 2046f78b460428877a26ffdd2bb914ae47dfbe77
Summary:
The PerThreadDBPath has already specified a slash. It does not need to be specified when initializing the test path.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8555
Reviewed By: ajkr
Differential Revision: D29758399
Pulled By: jay-zhuang
fbshipit-source-id: 6d2b878523e3e8580536e2829cb25489844d9011
Summary:
Fixed a stats_history_test failure on Windows
* In StatsHistoryTest.InMemoryStatsHistoryPurging test, the capping memory cost of stats_history_size on Windows increases to 15000 bytes with latest changes
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8520
Reviewed By: ajkr
Differential Revision: D29734631
Pulled By: mrambacher
fbshipit-source-id: 461698fcf22ef06acfb7f7aa86f8415aaffe7f1e
Summary:
I previously didn't notice the DB mutex was being held during
block cache entry stat scans, probably because I primarily checked for
read performance regressions, because they require the block cache and
are traditionally latency-sensitive.
This change does some refactoring to avoid holding DB mutex and to
avoid triggering and waiting for a scan in GetProperty("rocksdb.cfstats").
Some tests have to be updated because now the stats collector is
populated in the Cache aggressively on DB startup rather than lazily.
(I hope to clean up some of this added complexity in the future.)
This change also ensures proper treatment of need_out_of_mutex for
non-int DB properties.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8538
Test Plan:
Added unit test logic that uses sync points to fail if the DB mutex
is held during a scan, covering the various ways that a scan might be
triggered.
Performance test - the known impact to holding the DB mutex is on
TransactionDB, and the easiest way to see the impact is to hack the
scan code to almost always miss and take an artificially long time
scanning. Here I've injected an unconditional 5s sleep at the call to
ApplyToAllEntries.
Before (hacked):
$ TEST_TMPDIR=/dev/shm ./db_bench.base_xxx -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 433.219 micros/op 2308 ops/sec; 0.1 MB/s ( transactions:78999 aborts:0)
rocksdb.db.write.micros P50 : 16.135883 P95 : 36.622503 P99 : 66.036115 P100 : 5000614.000000 COUNT : 149677 SUM : 8364856
$ TEST_TMPDIR=/dev/shm ./db_bench.base_xxx -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 448.802 micros/op 2228 ops/sec; 0.1 MB/s ( transactions:75999 aborts:0)
rocksdb.db.write.micros P50 : 16.629221 P95 : 37.320607 P99 : 72.144341 P100 : 5000871.000000 COUNT : 143995 SUM : 13472323
Notice the 5s P100 write time.
After (hacked):
$ TEST_TMPDIR=/dev/shm ./db_bench.new_xxx -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 303.645 micros/op 3293 ops/sec; 0.1 MB/s ( transactions:98999 aborts:0)
rocksdb.db.write.micros P50 : 16.061871 P95 : 33.978834 P99 : 60.018017 P100 : 616315.000000 COUNT : 187619 SUM : 4097407
$ TEST_TMPDIR=/dev/shm ./db_bench.new_xxx -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 310.383 micros/op 3221 ops/sec; 0.1 MB/s ( transactions:96999 aborts:0)
rocksdb.db.write.micros P50 : 16.270026 P95 : 35.786844 P99 : 64.302878 P100 : 603088.000000 COUNT : 183819 SUM : 4095918
P100 write is now ~0.6s. Not good, but it's the same even if I completely bypass all the scanning code:
$ TEST_TMPDIR=/dev/shm ./db_bench.new_skip -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 311.365 micros/op 3211 ops/sec; 0.1 MB/s ( transactions:96999 aborts:0)
rocksdb.db.write.micros P50 : 16.274362 P95 : 36.221184 P99 : 68.809783 P100 : 649808.000000 COUNT : 183819 SUM : 4156767
$ TEST_TMPDIR=/dev/shm ./db_bench.new_skip -benchmarks=randomtransaction,stats -cache_index_and_filter_blocks=1 -bloom_bits=10 -partition_index_and_filters=1 -duration=30 -stats_dump_period_sec=12 -cache_size=100000000 -statistics -transaction_db 2>&1 | egrep 'db.db.write.micros|micros/op'
randomtransaction : 308.395 micros/op 3242 ops/sec; 0.1 MB/s ( transactions:97999 aborts:0)
rocksdb.db.write.micros P50 : 16.106222 P95 : 37.202403 P99 : 67.081875 P100 : 598091.000000 COUNT : 185714 SUM : 4098832
No substantial difference.
Reviewed By: siying
Differential Revision: D29738847
Pulled By: pdillinger
fbshipit-source-id: 1c5c155f5a1b62e4fea0fd4eeb515a8b7474027b
Summary:
**Summary**:
2 new statistics counters are added to RocksDB: `MEMTABLE_PAYLOAD_BYTES_AT_FLUSH` and `MEMTABLE_GARBAGE_BYTES_AT_FLUSH`. The former tracks how many raw bytes of useful data are present on the memtable at flush time, whereas the latter is tracks how many of these raw bytes are considered garbage, meaning that they ended up not being imported on the SSTables resulting from the flush operations.
**Unit test**: run `make db_flush_test -j$(nproc); ./db_flush_test` to run the unit test.
This executable includes 3 tests, that test support and correct stat calculations for workloads with inserts, deletes, and DeleteRanges. The parameters are set such that the workloads are performed on a single memtable, and a single SSTable is created as a result of the flush operation. The flush operation is manually called in the test file. The tests verify that the values of these 2 statistics counters introduced in this PR can be exactly predicted, showing that we have a full understanding of the underlying operations.
**Performance testing**:
`./db_bench -statistics -benchmarks=fillrandom -num=10000000` repeated 10 times.
Timing done using "date" function in a bash script.
_Results_:
Original Rocksdb fork: mean 66.6 sec, std 1.18 sec.
This feature branch: mean 67.4 sec, std 1.35 sec.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8411
Reviewed By: akankshamahajan15
Differential Revision: D29150629
Pulled By: bjlemaire
fbshipit-source-id: 7b3c2e86d50c6aa34fa50fd134282eacb543a5b1
Summary:
Before this PR, `get_iostats_context()` will silently return a nullptr if no thread_local support is detected.
This can be the result of build_detect_platform's failure to compile the simple code snippet on certain platforms, as
reported in https://github.com/facebook/mysql-5.6/issues/904.
To be safe, we should fail the compilation if user does not opt out IOStatsContext and
ROCKSDB_SUPPORT_THREAD_LOCAL is not defined.
If RocksDB relies on c++11, can we just always use thread_local? It turns out there might be
performance concerns (https://github.com/facebook/rocksdb/issues/5774),
which is beyond the scope of this PR. We can revisit this later. Here, we stick to the original impl.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8117
Reviewed By: ajkr
Differential Revision: D27356847
Pulled By: riversand963
fbshipit-source-id: f7d5776842277598d8341b955febb601946801ae
Summary:
Add statistics and info log for error handler: counters for bg error, bg io error, bg retryable io error, auto resume, auto resume total retry, and auto resume sucess; Histogram for auto resume retry count in each recovery call.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8050
Test Plan: make check and add test to error_handler_fs_test
Reviewed By: anand1976
Differential Revision: D26990565
Pulled By: zhichao-cao
fbshipit-source-id: 49f71e8ea4e9db8b189943976404205b56ab883f
Summary:
For performance purposes, the lower level routines were changed to use a SystemClock* instead of a std::shared_ptr<SystemClock>. The shared ptr has some performance degradation on certain hardware classes.
For most of the system, there is no risk of the pointer being deleted/invalid because the shared_ptr will be stored elsewhere. For example, the ImmutableDBOptions stores the Env which has a std::shared_ptr<SystemClock> in it. The SystemClock* within the ImmutableDBOptions is essentially a "short cut" to gain access to this constant resource.
There were a few classes (PeriodicWorkScheduler?) where the "short cut" property did not hold. In those cases, the shared pointer was preserved.
Using db_bench readrandom perf_level=3 on my EC2 box, this change performed as well or better than 6.17:
6.17: readrandom : 28.046 micros/op 854902 ops/sec; 61.3 MB/s (355999 of 355999 found)
6.18: readrandom : 32.615 micros/op 735306 ops/sec; 52.7 MB/s (290999 of 290999 found)
PR: readrandom : 27.500 micros/op 871909 ops/sec; 62.5 MB/s (367999 of 367999 found)
(Note that the times for 6.18 are prior to revert of the SystemClock).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8033
Reviewed By: pdillinger
Differential Revision: D27014563
Pulled By: mrambacher
fbshipit-source-id: ad0459eba03182e454391b5926bf5cdd45657b67
Summary:
On x86_64, this makes the struct 8 bytes smaller, so creating a PerfStepTimer on the stack will use slightly less stack space.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/7931
Reviewed By: jay-zhuang
Differential Revision: D26529470
Pulled By: ajkr
fbshipit-source-id: bbe2e843167152ffa05a5946f1add6621c9849f7
