Summary:
and remove deprecated DB::MaxMemCompactionLevel(). In the process of pushing through a relatively clean refactoring of uses of the old functions, some other minor public APIs are also migrated from raw DB pointers to unique_ptr.
Claude did pretty much all the work, but requiring dozens of prompts to actually push through relatively clean phase out of raw DB pointers from what needed to be touched, and leaving that code in better shape. (Hundreds of `DB*` still remain all over the place even outside C and Java bindings.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14335
Test Plan: existing tests; no functional changes intended
Reviewed By: xingbowang, mszeszko-meta
Differential Revision: D93523820
Pulled By: pdillinger
fbshipit-source-id: e4ca22ad81cd2cfe91122d7507d7ca34fe03d043
Summary:
... and remove some old code and tech debt in the process.
This is arguably a great milestone and precendent in RocksDB history as for the first time we are explicitly dropping support for the ability to read source-of-truth data in old formats. (We previously dropped support for reading some old bloom filters, but those are performance optimizers not source-of-truth. https://github.com/facebook/rocksdb/issues/10184) However, DBs written with default settings since release 4.6.0, which is very nearly 10 years ago, can still be read. And by using compaction with intermediate versions, there's an upgrade path going back to (AFAIK) early releases of LevelDB (from which RocksDB was forked).
Some detail:
* The magic number for LevelDB SST files (0xdb4775248b80fb57, most recently called kLegacyBlockBasedTableMagicNumber) now only exists in the code to provide a good error message and to test that good error message.
* There is some notable refactoring and renaming around format_version handling. This is a bit of a messy area of code because the footer code being shared between different table formats (block-based, plain, cuckoo) means format_version in the footer is in ways tied to all of them, but in other ways is just tied to block-based table where we have been making updates. Hopefully code comments keep this clear.
* Now that there are old format_versions we can't read (and can't write authoritatively in tests), I've needed to split out kMinSupportedFormatVersion into a constant for reads and for writes, currently the same at format_version=2. Comments describe how to update these in the future.
* The idea of versioning the compression format is basically going away, though we're keeping BuiltinV2 in places just because it's already there. There's lots of room in the BuiltinV2 schema to expand to new built-in compression types, or new ways of handling existing compression algorithms. CompressionManager with CompatibilityName gives users the power to customize compression without the need for versions tied to format_version.
Immediate follow-up:
* Clean up compression loose ends like OLD_Compress, OLD_Uncompress
Suggested follow-up:
* Update plain table builder to migrate to new footer version so that we can drop support for legacy footer. We have to be careful that the (likely untested) forward compatibility path I put in place a while back works (or fix it and wait a while) before dropping support for plain table with legacy footer.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14315
Test Plan:
* Some tests updated / added
* A couple tests are obsolete: removed
* Also updated format compatible test, which now doesn't need to dig as far back into history building RocksDB.
Reviewed By: hx235
Differential Revision: D92577766
Pulled By: pdillinger
fbshipit-source-id: a23be846189d901ce087af4ca9a99cef18445cb7
Summary:
I don't think this option was ever useful. There was no compressed secondary cache compatibility issue that needed to accommodate compression format version 1. It was needlessly imported from legacy SST file formats. Version 1 is simply an inefficient format because it requires guessing the uncompressed size on decompression.
And as far as I know, we don't have any plans to make compressed secondary cache entries persistable across RocksDB versions. I.e. if persisting, we would simply tag the persistence layer with the version (perhaps major and minor) and throw out the cache whenever that changes. Then we don't have to deal with explicit schema versioning in persistenct caches. This is a workable approach because unlike SSTs, caches are not source-of-truth that need to survive version rollback.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14302
Test Plan: existing tests
Reviewed By: anand1976
Differential Revision: D92315003
Pulled By: pdillinger
fbshipit-source-id: 0b82cfdbd92bcd2b8fbddd6586824f53c88069c4
Summary:
* Some existing commentary and motivation around my atomic wrappers in atomic.h was based on a misreading of documentation. seq_cst *is* a safe substitute for acq_rel in all cases. I still like having a distinct type for RelaxedAtomic (as folly does) and a wrapper also for other cases to avoid readability traps like implicit conversion and implicit memory order. This PR is only comment changes and renaming.
* Create a blog post about bit fields API to help with lock-free (and low-lock) programming.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14213
Test Plan: esiting tests
Reviewed By: xingbowang
Differential Revision: D89971581
Pulled By: pdillinger
fbshipit-source-id: 9bd1181d692258d668189c2da8bd0e5d98fd6230
Summary:
This change builds on https://github.com/facebook/rocksdb/issues/14027 and https://github.com/facebook/rocksdb/issues/13965 to complete migration
of the HyperClockCache implementation to using the hygienic BitFields API.
No semantic change in the implementation details is intended, just
greatly improving readability and safety of the code while maintaining
the same performance.
In more detail,
* Refactor the main metadata atomic for each slot in an HCC table into
SlotMeta using BitFields.
* Extended BitFields APIs with some additional features, and renamed
BlahTransform classes to BlahTransformer to resolve potential naming
conflicts with member functions to create them.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14154
Test Plan:
for correctness, mostly existing tests. but also added tests
for new BitFields features. I especially ran local TSAN whitebox crash
test extensively which caught a couple of refactoring errors.
For performance, I verified with release builds of cache_bench, using
default options, that there was no noticeable/consistent difference
after all these HCC migrations vs. backing them out. That test was with
GCC 11 and -O2, which is a reasonable baseline for expected compiler
optimizations.
Reviewed By: xingbowang
Differential Revision: D87960540
Pulled By: pdillinger
fbshipit-source-id: e0257b7fea8a5c7709daef18911959201ce4e0f3
Summary:
Continuing work from https://github.com/facebook/rocksdb/issues/13965. Here I'm migrating the "next with shift" kind of bit field and for that I've added an API for atomic additive transformations that can be combined into a single atomic update for multiple fields. (I implemented more features than needed, just in case they are needed someday and to demonstrate what is possible.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14027
Test Plan: BitFields unit test updated/added, existing HCC tests
Reviewed By: xingbowang
Differential Revision: D83895094
Pulled By: pdillinger
fbshipit-source-id: e4487f34f5607b20f94b85a645ca654e6401e35d
Summary:
Oversight in https://github.com/facebook/rocksdb/issues/13964. More detail:
* Applies to cache_bench and db_bench (db_stress already using it)
* Make sure those along with db_stress treat "hyper_clock_cache" as "auto_hyper_clock_cache" because this is now the blessed implementation.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14120
Test Plan: manual runs of the tools
Reviewed By: krhancoc
Differential Revision: D86913202
Pulled By: pdillinger
fbshipit-source-id: 07b425d3522103417f4b034735376b9d759af5fb
Summary:
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14024
Fix some typo found along the codebase
Reviewed By: pdillinger
Differential Revision: D83789182
fbshipit-source-id: feb24d7d47a6faaf735fcfd50dd3ecce4a6c8cd5
Summary:
In https://github.com/facebook/rocksdb/issues/13964 I changed an expensive DEBUG check in ~AutoHyperClockTable to only run in ASAN builds. It's still expensive so I'm modifying it to scan only about one page beyond what we expect to have written to the anonymous mmap, rather than scanning the whole thing.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13998
Test Plan: manually checked that lru_cache_test running time went from 5.0s to 4.0s after the change. Verified that existing unit test ClockCacheTest.Limits uses the full anonymous mmap to be sure it is sized as expected, by temporarily breaking AutoHyperClockTable::Grow() to allow slightly exceeding the anonymous mmap size.
Reviewed By: cbi42
Differential Revision: D83178493
Pulled By: pdillinger
fbshipit-source-id: a2bf093e98bf68b540c073800be7e193021f2692
Summary:
Start the process of migrating the HCC implementation over to my new system of "bit field atomics" to clean up the code. Here I took on the simplest of the three "bit field atomic" formats in HCC, but ended up moving some things around to end up with less plumbing of definitions and values overall.
In the process, updated BitFields to use the CRTP pattern to simplify some things (see updated example, etc.)
https://en.wikipedia.org/wiki/Curiously_recurring_template_pattern
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13965
Test Plan: existing tests. ClockCacheTest.ClockEvictionEffortCapTest caught a regression during my development, and the crash test has a history of finding subtle HCC bugs.
Reviewed By: xingbowang
Differential Revision: D82669582
Pulled By: pdillinger
fbshipit-source-id: b73dd47361cbe9fbd334413dd4ce01b3c667159e
Summary:
If there's a static initialization of Options() this could now instantiate an AutoHyperClockTable before kPageSize is initialized. Break the dependency because it's a very minor optimization.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13973
Test Plan: internal CI (not able to reproduce locally)
Reviewed By: hx235
Differential Revision: D82789849
Pulled By: pdillinger
fbshipit-source-id: 3f32b5779a4f56d2071be5aadacda2bf0f4b895d
Summary:
After seeing more people hit issues with thrashing small LRUCache shards and AutoHCC running fully in production for a while on a very large service, here I make these updates:
* In the public API, mark the case of `estimated_entry_charge = 0` (which is how you select AutoHCC) as production-ready and generally preferred. That means devoting a lot less space to how to tune FixedHCC (`estimated_entry_charge > 0`) because it is not generally recommended anymore even though in theory it is the fastest (conditional on a fragile configuration).
* In the public API, add more detail about potential problems with LRUCache and explicitly endorse HCC.
* When a default block cache is created, use AutoHCC instead of LRUCache. It's still a 32MB cache but that's just one cache shard for AutoHCC so the risk of issues with small cache shards is dramatically reduced. And a single AutoHCC shard is still essentially wait-free.
* Improve the handling of the hypothetical scenario of a failed anonymous mmap. This is hardly a concern for 64-bit Linux and likely most other OSes. It would in theory be possible to fall back on LRUCache in that case but the code structure makes that annoying/challenging. Instead we crash with an appropriate message.
* Cleaned up some includes
* Fixed some previously unreported leaks (better assertions on HCC perhaps, some subtle behavior changes)
* Added a new mode to cache_bench (detailed below)
* Avoid a particularly costly sanity check in `~AutoHyperClockTable()` even in debug builds so that unit testing, etc., isn't bogged down, except keep it in ASAN build.
Planned follow-up:
* Update HCC implementation to use my new "bit field atomics" API introduced in https://github.com/facebook/rocksdb/issues/13910 to make it easier to read and maintain
Possible follow-up:
* Re-engineer table cache to use AutoHCC also, instead of LRUCache and a single mutex to ensure no duplication across threads. (a) Pad table cache key to 128 bits for AutoHCC. (b) Stripe/shard the no-duplication mutex. (HCC's consistency model is too weak for concurrent threads to use its API to agree on a winner, even if entries could be inserted in an "open in progress" state.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13964
Test Plan:
existing tests. ClockCacheTest.ClockEvictionEffortCapTest caught a regression during my development, and the crash test has a history of finding subtle HCC bugs.
## Performance
Although we've validated AutoHCC performance under high load, etc., before we haven't really considered whether there will be unacceptable overheads for small DBs and CFs, e.g. in unit tests. For this, I have added a new mode to cache_bench: with the -stress_cache_instances=n parameter, it will create and destroy n empty cache instances several times. In the debug build, this found that a particular check in `~AutoHyperClockTable()` was extremely costly for short-lived caches (fixed). Beyond that, we can answer the question of whether it is feasible for a single process to host 1000 DBs each with 1000 CFs with default block cache instances, after moving LRUCache -> AutoHCC, for example:
```
/usr/bin/time ./cache_bench -stress_
cache_instances=1000000 -cache_type=auto_hyper_clock_cache -cache_size=33554432
```
Release build:
Average 9.8 us per 32MB LRUCache creation, 2.9 us per destruction, 24.6GB max RSS (~25KB each)
->
Average 4.3 us per 32MB AutoHCC creation, 4.9 us per destruction, 4.8GB max RSS (~5KB each)
Debug build:
Average 10.9 us per 32MB LRUCache creation, 3.5 us per destruction, 28.7GB max RSS (~29KB each)
->
Average 4.5 us per 32MB AutoHCC creation, 4.9 us per destruction, 4.7GB max RSS (~5KB each)
Despite the anonymous mmaps, it's apparently more efficient for default/small/empty structures. This is likely due to the dramatically low number of cache shards at this size. If we switch to `-stress_cache_instances=10000 -cache_size=1073741824`:
Release build:
Average 10.6 us per 1GB LRUCache, 2.8 us per destruction, 2.3 GB max RSS (~230KB each)
->
Average 130 us per 1GB AutoHCC creation, 153 us per destruction, 1.5 GB max RSS (~150KB each)
Debug build:
Average 11.2 us per 1GB LRUCache, 3.6 us per destruction, 2.4 GB max RSS (~240KB each)
->
Average 130 us per 1GB AutoHCC creation, 150 us per destruction, 1.6 GB max RSS (~160KB each)
Here it's clear that we are paying a price in time for setting up all those mmaps for the good number of cache shards and potential table growth, even though the RSS is well under control. However, I am not concerned about this at all, as it's unlikely to slow down anything notably such as unit tests. Before and after full testsuite runs confirm:
3327.73user 5188.71system 3:38.88elapsed -> 3312.07user 5704.77system 3:41.61elapsed
There is increased kernel time but acceptable. With ASAN+UBSAN:
11618.70user 15671.30system 5:54.68elapsed -> 12595.81user 16159.67system 6:32.77elapsed
Acceptable given that our ASAN+UBSAN builds are not the slowest in CI
Reviewed By: hx235
Differential Revision: D82661067
Pulled By: pdillinger
fbshipit-source-id: ab25c766ca70f2b8664849c2a838b9e1b4e72d3b
Summary:
A follow-up to https://github.com/facebook/rocksdb/issues/13904 which was incomplete in updating CI jobs to support C++20 because the C++20 usage was only in tests. Here we add subtle C++20 usage in the public API ("using enum" feature in db.h) to force the issue.
A lot of the work for this PR was in updating the Ubuntu22 docker image, for earlier compiler/runtime versions supporting C++20, and generating a new Ubuntu24 docker image, for later compiler/runtime versions. The Ubuntu22 image needed to be updated because there are incompatibilities with clang-13 + c++20 + libstdc++ for gcc 11, seen on these examples
```
#include <chrono>
int main(int argc, char *argv[]) {
std::chrono::microseconds d = {}; return 0;
}
```
and
```
#include <coroutine>
int main() { return 0; }
```
The second was causing recurring failures in build-linux-clang-13-asan-ubsan-with-folly, now fixed.
So we have to install clang's libc++ to compile with clang-13. I haven't been able to get this to work with some of the libraries like benchmark, glog, and/or gflags, but I'm able to compile core RocksDB with clang-13. On this docker image, an extra compiler parameter is needed to compile with gcc and glog because it's built from source perhaps not perfectly, because the ubuntu package transitively conflicts with libc++.
The Ubuntu24 image seems to be low-drama and generally work for testing out newer compiler versions. The mingw build uses Ubuntu24 because the mingw package on Ubuntu22 uses a gcc version that is too old.
And the mass of other code changes are trying to work around new warnings, mostly from clang-analyze, which I upgraded to clang-18 in CI.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13915
Test Plan: CI, including temporarily including the nightly jobs in the PR jobs in earlier revisions to test and stabilize
Reviewed By: archang19
Differential Revision: D81933067
Pulled By: pdillinger
fbshipit-source-id: 7e33823006a79d5f3cf5bc1d625f0a3c08a7d74c
Summary:
The assert occasionally throws off the stress test runs. We already have sufficient logging in place to collect the signal about secondary cache capacity exceeding primary cache reservation for further investigation.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13885
Reviewed By: anand1976
Differential Revision: D80355513
Pulled By: mszeszko-meta
fbshipit-source-id: b36926f0493a3aca19818a1980ef79277db9fe7e
Summary:
The main motivation for this change is to more flexibly and efficiently support compressing data without extra copies when we do not want to support saving compressed data that is LARGER than the uncompressed. We believe pretty strongly that for the various workloads served by RocksDB, it is well worth a single byte compression marker so that we have the flexibility to save compressed or uncompressed data when compression is attempted. Why? Compression algorithms can add tens of bytes in fixed overheads and percents of bytes in relative overheads. It is also an advantage for the reader when they can bypass decompression, including at least a buffer copy in most cases, after reading just one byte.
The block-based table format in RocksDB follows this model with a single-byte compression marker, and at least after https://github.com/facebook/rocksdb/pull/13797 so does CompressedSecondaryCache. (Notably, the blob file format DOES NOT. This is left to follow-up work.)
In particular, Compressor::CompressBlock now takes in a fixed size buffer for output rather than a `std::string*`. CompressBlock itself rejects the compression if the output would not fit in the provided buffer. This also works well with `max_compressed_bytes_per_kb` option to reject compression even sooner if its ratio is insufficient (implemented in this change). In the future we might use this functionality to reduce a buffer copy (in many cases) into the WritableFileWriter buffer of the block based table builder.
This is a large change because we needed to (or were compelled to)
* Update all the existing callers of CompressBlock, sometimes with substantial changes. This includes introducing GrowableBuffer to reuse between calls rather than std::string, which (at least in C++17) requires zeroing out data when allocating/growing a buffer.
* Re-implement built-in Compressors (V2; V1 is obsolete) to efficiently implement the new version of the API, no longer wrapping the `OLD_CompressData()` function. The new compressors appropriately leverage the CompressBlock virtual call required for the customization interface and no rely on `switch` on compression type for each block. The implementations are largely adaptations of the old implementations, except
* LZ4 and LZ4HC are notably upgraded to take advantage of WorkingArea (see performance tests). And for simplicity in the new implementation, we are dropping support for some super old versions of the library.
* Getting snappy to work with limited-size output buffer required using the Sink/Source interfaces, which appear to be well supported for a long time and efficient (see performance tests).
* Replace awkward old CompressionManager::GetDecompressorForCompressor with Compressor::GetOptimizedDecompressor (which is optional to implement)
* Small behavior change where we treat lack of support for compression closer to not configuring compression, such as incompatibility with block_align. This is motivated by giving CompressionManager the freedom of determining when compression can be excluded for an entire file despite the configured "compression" type, and thus only surfacing actual incompatibilities not hypothetical ones that might be irrelevant to the CompressionManager (or build configuration). Unit tests in `table_test` and `compact_files_test` required update.
* Some lingering clean up of CompressedSecondaryCache and a re-optimization made possible by compressing into an existing buffer.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13805
Test Plan:
for correctness, existing tests
## Performance Test
As I generally only modified compression paths, I'm using a db_bench write benchmark, with before & after configurations running at the same time. vc=1 means verify_compression=1
```
USE_CLANG=1 DEBUG_LEVEL=0 LIB_MODE=static make -j100 db_bench
SUFFIX=`tty | sed 's|/|_|g'`; for CT in zlib bzip2 none snappy zstd lz4 lz4hc none snappy zstd lz4 bzip2; do for VC in 0 1; do echo "$CT vc=$VC"; (for I in `seq 1 20`; do BIN=/dev/shm/dbbench${SUFFIX}.bin; rm -f $BIN; cp db_bench $BIN; $BIN -db=/dev/shm/dbbench$SUFFIX --benchmarks=fillseq -num=10000000 -compaction_style=2 -fifo_compaction_max_table_files_size_mb=1000 -fifo_compaction_allow_compaction=0 -disable_wal -write_buffer_size=12000000 -format_version=7 -compression_type=$CT -verify_compression=$VC 2>&1 | grep micros/op; done) | awk '{n++; sum += $5;} END { print int(sum / n); }'; done; done
```
zlib vc=0 524198 -> 524904 (+0.1%)
zlib vc=1 430521 -> 430699 (+0.0%)
bzip2 vc=0 61841 -> 60835 (-1.6%)
bzip2 vc=1 49232 -> 48734 (-1.0%)
none vc=0 1802375 -> 1906227 (+5.8%)
none vc=1 1837181 -> 1950308 (+6.2%)
snappy vc=0 1783266 -> 1901461 (+6.6%)
snappy vc=1 1799703 -> 1879660 (+4.4%)
zstd vc=0 1216779 -> 1230507 (+1.1%)
zstd vc=1 996370 -> 1015415 (+1.9%)
lz4 vc=0 1801473 -> 1943095 (+7.9%)
lz4 vc=1 1799155 -> 1935242 (+7.6%)
lz4hc vc=0 349719 -> 1126909 (+222.2%)
lz4hc vc=1 348099 -> 1108933 (+218.6%)
(Repeating the most important ones)
none vc=0 1816878 -> 1952221 (+7.4%)
none vc=1 1813736 -> 1904622 (+5.0%)
snappy vc=0 1794816 -> 1875062 (+4.5%)
snappy vc=1 1789363 -> 1873771 (+4.7%)
zstd vc=0 1202592 -> 1225164 (+1.9%)
zstd vc=1 994322 -> 1016688 (+2.2%)
lz4 vc=0 1786959 -> 1971518 (+10.3%)
lz4 vc=1 1829483 -> 1935871 (+5.8%)
I confirmed manually that the new WorkingArea for LZ4HC makes the huge difference on that one, but not as much difference for LZ4, presumably because LZ4HC uses much larger buffers/structures/whatever for better compression ratios.
Reviewed By: hx235
Differential Revision: D79111736
Pulled By: pdillinger
fbshipit-source-id: 1ce1b14af9f15365f1b6da49906b5073a8cecc14
Summary:
To be compatible with some upcoming compression change/refactoring where we supply a fixed size buffer to CompressBlock, we need to support CompressedSecondaryCache storing uncompressed values when the compression ratio is not suitable. It seems crazy that CompressedSecondaryCache currently stores compressed values that are *larger* than the uncompressed value, and even explicitly exercises that case (almost exclusively) in the existing unit tests. But it's true.
This change fixes that with some other nearby refactoring/improvement:
* Update the in-memory representation of these cache entries to support uncompressed entries even when compression is enabled. AFAIK this also allows us to safely get rid of "don't support custom split/merge for the tiered case".
* Use more efficient in-memory representation for non-split entries
* For CompressionType and CacheTier, which are defined as single-byte data types, use a single byte instead of varint32. (I don't know if varint32 was an attempt at future-proofing for a memory-only schema or what.) Now using lossless_cast will raise a compiler error if either of these types is made too large for a single byte.
* Don't wrap entries in a CacheAllocationPtr object; it's not necessary. We can rely on the same allocator being provided at delete time.
* Restructure serialization/deserialization logic, hopefully simpler or easier to read/understand.
* Use a RelaxedAtomic for disable_cache_ to avoid race.
Suggested follow-up on CompressedSecondaryCache:
* Refine the exact strategy for rejecting compressions
* Still have a lot of buffer copies; try to reduce
* Revisit the split-merge logic and try to make it more efficient overall, more unified with non-split case
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13797
Test Plan:
Unit tests updated to use actually compressible strings in many places and more testing around non-compressible string.
## Performance Test
There was some pre-existing issue causing decompression failures in compressed secondary cache with cache_bench that is somehow fixed in this change. This decompression failures were present before the new compression API, but since then cause assertion failures rather than being quietly ignored. For the "before" test here, they are back to quietly ignored. And the cache_bench changes here were back-ported to the "before" configuration.
### No compressed secondary (setting expectations)
```
./cache_bench --cache_type=auto_hyper_clock_cache -cache_size=8000000000 -populate_cache
```
Max key : 3906250
Before:
Complete in 12.784 s; Rough parallel ops/sec = 2503123
Thread ops/sec = 160329; Lookup hit ratio: 0.686771
After:
Complete in 12.745 s; Rough parallel ops/sec = 2510717 (in the noise)
Thread ops/sec = 159498; Lookup hit ratio: 0.68686
### Compressed secondary, no split/merge
Same max key and approximate total memory size
```
/usr/bin/time ./cache_bench --cache_type=auto_hyper_clock_cache -cache_size=4000000000 -populate_cache -resident_ratio=0.125 -compressible_to_ratio=0.4 --secondary_cache_uri=compressed_secondary_cache://capacity=4000000000
```
Before:
Complete in 18.690 s; Rough parallel ops/sec = 1712144
Thread ops/sec = 108683; Lookup hit ratio: 0.776683
Latency: P50: 4205.19 P75: 15281.76 P99: 43810.98 P99.9: 71487.41 P99.99: 165453.32
max RSS (according to /usr/bin/time): 9341856
After:
Complete in 17.878 s; Rough parallel ops/sec = 1789951 (+4.5%)
Thread ops/sec = 114957; Lookup hit ratio: 0.792998 (+0.016)
Latency: P50: 4012.70 P75: 14477.63 P99: 40039.70 P99.9: 62521.04 P99.99: 167049.18
max RSS (according to /usr/bin/time): 9235688
The improved hit ratio is probably from fixing the failed decompressions (somehow). And my modifications could have improved CPU efficiency, or it could be the small penalty the benchmark naturally imposes on most misses (generate another value and insert it).
### Compressed secondary, with split/merge
```
/usr/bin/time ./cache_bench --cache_type=auto_hyper_clock_cache -cache_size=4000000000 -populate_cache -resident_ratio=0.125 -compressible_to_ratio=0.4 --secondary_cache_uri='compressed_secondary_cache://capacity=4000000000;enable_custom_split_merge=true'
```
Before:
Complete in 20.062 s; Rough parallel ops/sec = 1595075
Thread ops/sec = 101759; Lookup hit ratio: 0.787129
Latency: P50: 5338.53 P75: 16073.46 P99: 46752.65 P99.9: 73459.11 P99.99: 201318.75
max RSS (according to /usr/bin/time): 9049852
After:
Complete in 18.564 s; Rough parallel ops/sec = 1723771 (+8.1%)
Thread ops/sec = 110724; Lookup hit ratio: 0.813414 (+0.026)
Latency: P50: 5234.75 P75: 14590.43 P99: 41401.03 P99.9: 65606.50 P99.99: 157248.04
max RSS (according to /usr/bin/time): 8917592
Looks like an improvement
Reviewed By: anand1976
Differential Revision: D78842120
Pulled By: pdillinger
fbshipit-source-id: 5f754b160c37ebee789279178ebb5e862071bdb2
Summary:
Was reading sec_cache_res_ratio_ outside of mutex and using the result for computation that needs to be synchronized
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13747
Test Plan: existing tests. Has been showing up in crash test, and there's no interesting concurrency here that would warrant a regression test based on sync points.
Reviewed By: cbi42
Differential Revision: D77607660
Pulled By: pdillinger
fbshipit-source-id: 12a71936b3558c7528d229a11c7d2e43982ad06b
Summary:
improve assertions, one apparently a previous typo in https://github.com/facebook/rocksdb/issues/13606 and one a suspected possible area of logic error
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13737
Test Plan: watch crash test
Reviewed By: anand1976
Differential Revision: D77453102
Pulled By: pdillinger
fbshipit-source-id: d4196910a9e8d59ef814130a52ff4ebf188a976d
Summary:
* Make new format_version=7 a supported setting.
* Fix a bug in compressed_secondary_cache.cc that is newly exercised by custom compression types and showing up in crash test with tiered secondary cache
* Small change to handling of disabled compression in fv=7: use empty compression manager compatibility name.
* Get rid of GetDefaultBuiltinCompressionManager() in public API because it could cause unexpected+unsafe schema change on a user's CompressionManager if built upon the default built-in manager and we add a new built-in schema. Now must be referenced by explicit compression schema version in the public API. (That notion was already exposed in compressed secondary cache API, for better or worse.)
* Improve some error messages for compression misconfiguration
* Improve testing with ObjectLibrary and CompressionManagers
* Improve testing of compression_name table property in BlockBasedTableTest.BlockBasedTableProperties2
* Improve some comments
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13713
Test Plan: existing and updated tests. Notably, the crash test has already been running with (unpublished) format_version=7
Reviewed By: mszeszko-meta, hx235
Differential Revision: D77035482
Pulled By: pdillinger
fbshipit-source-id: 95278de8734a79706a22361bff2184b1edb230ca
Summary:
Adds new classes etc. in internal compression.h that are intended to become public APIs for supporting custom/pluggable compression. Some steps remain to allow for pluggable compression and to remove a lot of legacy code (e.g. now called `OLD_CompressData` and `OLD_UncompressData`), but this change refactors the key integration points of SST building and reading and compressed secondary cache over to the new APIs.
Compared with the proposed https://github.com/facebook/rocksdb/issues/7650, this fixes a number of issues including
* Making a clean divide between public and internal APIs (currently just indicated with comments)
* Enough generality that built-in compressions generally fit into the framework rather than needing special treatment
* Avoid exposing obnoxious idioms like `compress_format_version` to the user.
* Enough generality that a compressor mixing algorithms/strategies from other compressors is pretty well supported without an extra schema layer
* Explicit thread-safety contracts (carefully considered)
* Contract details around schema compatibility and extension with code changes (more detail in next PR)
* Customizable "working areas" (e.g. for ZSTD "context")
* Decompression into an arbitrary memory location (rather than involving the decompressor in memory allocation; should facilitate reducing number of objects in block cache)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13540
Test Plan:
This is currently an internal refactor. More testing will come when the new API is migrated to the public API. A test in db_block_cache_test is updated to meaningfully cover a case (cache warming compression dictionary block) that was previously only covered in the crash test.
SST write performance test, like https://github.com/facebook/rocksdb/issues/13583. Compile with CLANG, run before & after simultaneously:
```
SUFFIX=`tty | sed 's|/|_|g'`; for ARGS in "-compression_parallel_threads=1 -compression_type=none" "-compression_parallel_threads=1 -compression_type=snappy" "-compression_parallel_threads=1 -compression_type=zstd" "-compression_parallel_threads=1 -compression_type=zstd -verify_compression=1" "-compression_parallel_threads=1 -compression_type=zstd -compression_max_dict_bytes=8180" "-compression_parallel_threads=4 -compression_type=snappy"; do echo $ARGS; (for I in `seq 1 20`; do ./db_bench -db=/dev/shm/dbbench$SUFFIX --benchmarks=fillseq -num=10000000 -compaction_style=2 -fifo_compaction_max_table_files_size_mb=1000 -fifo_compaction_allow_compaction=0 -disable_wal -write_buffer_size=12000000 $ARGS 2>&1 | grep micros/op; done) | awk '{n++; sum += $5;} END { print int(sum / n); }'; done
```
Before (this PR and with https://github.com/facebook/rocksdb/issues/13583 reverted):
-compression_parallel_threads=1 -compression_type=none
1908372
-compression_parallel_threads=1 -compression_type=snappy
1926093
-compression_parallel_threads=1 -compression_type=zstd
1208259
-compression_parallel_threads=1 -compression_type=zstd -verify_compression=1
997583
-compression_parallel_threads=1 -compression_type=zstd -compression_max_dict_bytes=8180
934246
-compression_parallel_threads=4 -compression_type=snappy
1644849
After:
-compression_parallel_threads=1 -compression_type=none
1956054 (+2.5%)
-compression_parallel_threads=1 -compression_type=snappy
1911433 (-0.8%)
-compression_parallel_threads=1 -compression_type=zstd
1205668 (-0.3%)
-compression_parallel_threads=1 -compression_type=zstd -verify_compression=1
999263 (+0.2%)
-compression_parallel_threads=1 -compression_type=zstd -compression_max_dict_bytes=8180
934322 (+0.0%)
-compression_parallel_threads=4 -compression_type=snappy
1642519 (-0.2%)
Pretty neutral change(s) overall.
SST read performance test (related to https://github.com/facebook/rocksdb/issues/13583). Set up:
```
for COMP in none snappy zstd; do echo $ARGS; ./db_bench -db=/dev/shm/dbbench-$COMP --benchmarks=fillseq,flush -num=10000000 -compaction_style=2 -fifo_compaction_max_table_files_size_mb=1000 -fifo_compaction_allow_compaction=0 -disable_wal -write_buffer_size=12000000 -compression_type=$COMP; done
```
Test (compile with CLANG, run before & after simultaneously):
```
for COMP in none snappy zstd; do echo $COMP; (for I in `seq 1 5`; do ./db_bench -readonly -db=/dev/shm/dbbench-$COMP --benchmarks=readrandom -num=10000000 -duration=20 -threads=8 2>&1 | grep micros/op; done) | awk '{n++; sum += $5;} END { print int(sum / n); }'; done
```
Before (this PR and with https://github.com/facebook/rocksdb/issues/13583 reverted):
none
1495646
snappy
1172443
zstd
706036
zstd (after constructing with -compression_max_dict_bytes=8180)
656182
After:
none
1494981 (-0.0%)
snappy
1171846 (-0.1%)
zstd
696363 (-1.4%)
zstd (after constructing with -compression_max_dict_bytes=8180)
667585 (+1.7%)
Pretty neutral.
Reviewed By: hx235
Differential Revision: D74626863
Pulled By: pdillinger
fbshipit-source-id: dc8ff3178da9b4eaa7c16aa1bb910c872afaf14a
Summary:
* Mostly, remove `sample_for_compression` from CompressionInfo because it's not used by the core function it serves, `CompressData()`. Confusing (and inefficient), especially in db_bench where it appears to use `FLAGS_sample_for_compression` in places where it is actually ignored.
* Various clarifying comments, clean-ups, and tiny optimizations
* Prepare some structures like `CompressionDict` for more usage
* Some TODOs and FIXMEs about some things I've noticed are amiss, confusing, or excessive
* A notable optimization opportunity that might become a "pay as you go" improvement for the potential indirection costs of customizable compression: use C++23's resize_and_overwrite() in compress functions to avoid zeroing the string buffer contents before populating it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13539
Test Plan: existing tests / CI
Reviewed By: hx235
Differential Revision: D73451273
Pulled By: pdillinger
fbshipit-source-id: 0373627466d695043d21146ce34d52f189ae9432
Summary:
... which is the default for CentOS 9 and Ubuntu 24, the latter of which is now available in GitHub Actions. Relevant CI job updated.
Re-formatted all cc|c|h files except in third-party/, using
```
clang-format -i `git ls-files | grep -E '[.](cc|c|h)$' | grep -v third-party/`
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13233
Test Plan: CI
Reviewed By: jaykorean, archang19
Differential Revision: D67461638
Pulled By: pdillinger
fbshipit-source-id: 0c9ac21a3f5eea6f5ade68bb6af7b6ba16c8b301
Summary:
This is a follow up to https://github.com/facebook/rocksdb/issues/13189. As mentioned in the description in the previous PR, to guard against similar bugs in the future, we should update our test implementations to reflect the real-world assumptions that we can make about `fs_scratch` when we issue reads with the filesystem buffer reuse optimization. The current test implementations reinforce the misconception that `fs_scratch` points to the same place as `result.data()` (i.e. to the start of the valid data buffer for the read result). `fs_scratch` can point to any arbitrary data structure, but for our purposes, I think we achieve what we want if we just have it point to a `Slice` which wraps the underlying result buffer inside one of its class variables.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13195
Test Plan: Existing unit tests test the same functionality but in an improved way with this change.
Reviewed By: hx235
Differential Revision: D66896380
Pulled By: archang19
fbshipit-source-id: 377e67ec70427716f2b7b7388d99b78003c01eb0
Summary:
In theory, there should be no danger in mutability, as table
builders and readers work from copies of BlockBasedTableOptions.
However, there is currently an unresolved read-write race that
affecting SetOptions on BBTO fields. This should be generally
acceptable for non-pointer options of 64 bits or less, but a fix
is needed to make it mutability general here. See
https://github.com/facebook/rocksdb/issues/10079
This change systematically sets all of those "simple" options (and future
such options) as mutable. (Resurrecting this PR perhaps preferable to
proposed https://github.com/facebook/rocksdb/issues/13063)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10021
Test Plan: Some unit test updates. XXX comment added to stress test code
Reviewed By: cbi42
Differential Revision: D64360967
Pulled By: pdillinger
fbshipit-source-id: ff220fa778331852fe331b42b76ac4adfcd2d760
Summary:
When an item is inserted into the compressed secondary cache, this PR calculates the charge using the malloc_usable_size of the allocated memory, as well as the unique pointer allocation.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13032
Test Plan: New unit test
Reviewed By: pdillinger
Differential Revision: D63418493
Pulled By: anand1976
fbshipit-source-id: 1db2835af6867442bb8cf6d9bf412e120ddd3824
Summary:
If the lowest_used_cache_tier DB option is set to kVolatileTier, skip insertion of compressed blocks into the secondary cache. Previously, these were always inserted into the secondary cache via the InsertSaved() method, leading to pollution of the secondary cache with blocks that would never be read.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13030
Test Plan: Add a new unit test
Reviewed By: pdillinger
Differential Revision: D63329841
Pulled By: anand1976
fbshipit-source-id: 14d2fce2ed309401d9ad4d2e7c356218b6673f7b
Summary:
This PR allows a Cache object to be created using the object registry.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13024
Reviewed By: pdillinger
Differential Revision: D63043233
Pulled By: anand1976
fbshipit-source-id: 5bc3f7c29b35ad62638ff8205451303e2cecea9d
Summary:
Add the `ApplyToHandle` method to the `Cache` interface to allow a caller to request the invocation of a callback on the given cache handle. The goal here is to allow a cache that manages multiple cache instances to use a callback on a handle to determine which instance it belongs to. For example, the callback can hash the key and use that to pick the correct target instance. This is useful to redirect methods like `Ref` and `Release`, which don't know the cache key.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12987
Reviewed By: pdillinger
Differential Revision: D62151907
Pulled By: anand1976
fbshipit-source-id: e4ffbbb96eac9061d2ab0e7e1739eea5ebb1cd58
Summary:
It appears the arm testsuite is failing because it is building without snappy, which is causing the SST files not to be compressed, which somehow causes these tests to fail. Manually setting LZ4 which is already required.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12993
Test Plan: reproduced and verified fix on ARM laptop
Reviewed By: anand1976
Differential Revision: D62216451
Pulled By: pdillinger
fbshipit-source-id: 3f21fcd9be0edaa66c7eca0cb7d56b998171e263
Summary:
Currently, when files become obsolete, the block cache entries associated with them just age out naturally. With pure LRU, this is not too bad, as once you "use" enough cache entries to (re-)fill the cache, you are guranteed to have purged the obsolete entries. However, HyperClockCache is a counting clock cache with a somewhat longer memory, so could be more negatively impacted by previously-hot cache entries becoming obsolete, and taking longer to age out than newer single-hit entries.
Part of the reason we still have this natural aging-out is that there's almost no connection between block cache entries and the file they are associated with. Everything is hashed into the same pool(s) of entries with nothing like a secondary index based on file. Keeping track of such an index could be expensive.
This change adds a new, mutable CF option `uncache_aggressiveness` for erasing obsolete block cache entries. The process can be speculative, lossy, or unproductive because not all potential block cache entries associated with files will be resident in memory, and attempting to remove them all could be wasted CPU time. Rather than a simple on/off switch, `uncache_aggressiveness` basically tells RocksDB how much CPU you're willing to burn trying to purge obsolete block cache entries. When such efforts are not sufficiently productive for a file, we stop and move on.
The option is in ColumnFamilyOptions so that it is dynamically changeable for already-open files, and customizeable by CF.
Note that this block cache removal happens as part of the process of purging obsolete files, which is often in a background thread (depending on `background_purge_on_iterator_cleanup` and `avoid_unnecessary_blocking_io` options) rather than along CPU critical paths.
Notable auxiliary code details:
* Possibly fixing some issues with trivial moves with `only_delete_metadata`: unnecessary TableCache::Evict in that case and missing from the ObsoleteFileInfo move operator. (Not able to reproduce an current failure.)
* Remove suspicious TableCache::Erase() from VersionSet::AddObsoleteBlobFile() (TODO follow-up item)
Marked EXPERIMENTAL until more thorough validation is complete.
Direct stats of this functionality are omitted because they could be misleading. Block cache hit rate is a better indicator of benefit, and CPU profiling a better indicator of cost.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12694
Test Plan:
* Unit tests added, including refactoring an existing test to make better use of parameterized tests.
* Added to crash test.
* Performance, sample command:
```
for I in `seq 1 10`; do for UA in 300; do for CT in lru_cache fixed_hyper_clock_cache auto_hyper_clock_cache; do rm -rf /dev/shm/test3; TEST_TMPDIR=/dev/shm/test3 /usr/bin/time ./db_bench -benchmarks=readwhilewriting -num=13000000 -read_random_exp_range=6 -write_buffer_size=10000000 -bloom_bits=10 -cache_type=$CT -cache_size=390000000 -cache_index_and_filter_blocks=1 -disable_wal=1 -duration=60 -statistics -uncache_aggressiveness=$UA 2>&1 | grep -E 'micros/op|rocksdb.block.cache.data.(hit|miss)|rocksdb.number.keys.(read|written)|maxresident' | awk '/rocksdb.block.cache.data.miss/ { miss = $4 } /rocksdb.block.cache.data.hit/ { hit = $4 } { print } END { print "hit rate = " ((hit * 1.0) / (miss + hit)) }' | tee -a results-$CT-$UA; done; done; done
```
Averaging 10 runs each case, block cache data block hit rates
```
lru_cache
UA=0 -> hit rate = 0.327, ops/s = 87668, user CPU sec = 139.0
UA=300 -> hit rate = 0.336, ops/s = 87960, user CPU sec = 139.0
fixed_hyper_clock_cache
UA=0 -> hit rate = 0.336, ops/s = 100069, user CPU sec = 139.9
UA=300 -> hit rate = 0.343, ops/s = 100104, user CPU sec = 140.2
auto_hyper_clock_cache
UA=0 -> hit rate = 0.336, ops/s = 97580, user CPU sec = 140.5
UA=300 -> hit rate = 0.345, ops/s = 97972, user CPU sec = 139.8
```
Conclusion: up to roughly 1 percentage point of improved block cache hit rate, likely leading to overall improved efficiency (because the foreground CPU cost of cache misses likely outweighs the background CPU cost of erasure, let alone I/O savings).
Reviewed By: ajkr
Differential Revision: D57932442
Pulled By: pdillinger
fbshipit-source-id: 84a243ca5f965f731f346a4853009780a904af6c
Summary:
A `BlockBasedTable` with `TieredSecondaryCache` containing a NVM cache inserts blocks into the compressed cache and the corresponding compressed block into the NVM cache. The `BlockFetcher` is used to get the uncompressed and compressed blocks by calling `ReadBlockContents()` and `GetUncompressedBlock()` respectively. If the file system supports FSBuffer (i.e returning a FS allocated buffer rather than caller provided), that buffer gets freed between the two calls. This PR fixes it by making the FSBuffer unique pointer a member rather than local variable.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12712
Test Plan:
1. Add a unit test
2. Release validation stress test
Reviewed By: jaykorean
Differential Revision: D57974026
Pulled By: anand1976
fbshipit-source-id: cfa895914e74b4f628413b40e6e39d8d8e5286bd
Summary:
`-Wextra-semi` or `-Wextra-semi-stmt`
If the code compiles, this is safe to land.
Reviewed By: palmje
Differential Revision: D55534619
fbshipit-source-id: 26f3c35a51b38a3cbfa12a6f76a2bb783a7b4d8e
Summary:
we saw crash test fail with
```
lru_cache.cc:249: void rocksdb::lru_cache::LRUCacheShard::LRU_Remove(rocksdb::lru_cache::LRUHandle *): Assertion `high_pri_pool_usage_ >= e->total_charge' failed.
```
One cause for this is that `lru_low_pri_` pointer is not updated in `LRU_insert()` before we try to balance high pri and low pri pool in `MaintainPoolSize();`. A repro unit test is provided.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12429
Test Plan:
Not able to reproduce the failure with db_stress yet.
`./lru_cache_test --gtest_filter="*InsertAfterReducingCapacity*`. It fails the assertion before this PR.
Reviewed By: pdillinger
Differential Revision: D54908919
Pulled By: cbi42
fbshipit-source-id: f485fdbc0ea61c8092a0be5fe561a59c15c78fd3
Summary:
When internal cpp modernizer attempts to format rocksdb code, it will replace macro `ROCKSDB_NAMESPACE` with its default definition `rocksdb` when collapsing nested namespace. We filed a feedback for the tool T180254030 and the team filed a bug for this: https://github.com/llvm/llvm-project/issues/83452. At the same time, they suggested us to run the modernizer tool ourselves so future auto codemod attempts will be smaller. This diff contains:
Running
`xplat/scripts/codemod_service/cpp_modernizer.sh`
in fbcode/internal_repo_rocksdb/repo (excluding some directories in utilities/transactions/lock/range/range_tree/lib that has a non meta copyright comment)
without swapping out the namespace macro `ROCKSDB_NAMESPACE`
Followed by RocksDB's own
`make format`
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12398
Test Plan: Auto tests
Reviewed By: hx235
Differential Revision: D54382532
Pulled By: jowlyzhang
fbshipit-source-id: e7d5b40f9b113b60e5a503558c181f080b9d02fa
Summary:
`-Wextra-semi` or `-Wextra-semi-stmt`
If the code compiles, this is safe to land.
Reviewed By: palmje
Differential Revision: D54362213
fbshipit-source-id: 0bbc9e5fce917fc4f72423f0a4c8cb2c2b1759dd
Summary:
The following are risks associated with pointer-to-pointer reinterpret_cast:
* Can produce the "wrong result" (crash or memory corruption). IIRC, in theory this can happen for any up-cast or down-cast for a non-standard-layout type, though in practice would only happen for multiple inheritance cases (where the base class pointer might be "inside" the derived object). We don't use multiple inheritance a lot, but we do.
* Can mask useful compiler errors upon code change, including converting between unrelated pointer types that you are expecting to be related, and converting between pointer and scalar types unintentionally.
I can only think of some obscure cases where static_cast could be troublesome when it compiles as a replacement:
* Going through `void*` could plausibly cause unnecessary or broken pointer arithmetic. Suppose we have
`struct Derived: public Base1, public Base2`. If we have `Derived*` -> `void*` -> `Base2*` -> `Derived*` through reinterpret casts, this could plausibly work (though technical UB) assuming the `Base2*` is not dereferenced. Changing to static cast could introduce breaking pointer arithmetic.
* Unnecessary (but safe) pointer arithmetic could arise in a case like `Derived*` -> `Base2*` -> `Derived*` where before the Base2 pointer might not have been dereferenced. This could potentially affect performance.
With some light scripting, I tried replacing pointer-to-pointer reinterpret_casts with static_cast and kept the cases that still compile. Most occurrences of reinterpret_cast have successfully been changed (except for java/ and third-party/). 294 changed, 257 remain.
A couple of related interventions included here:
* Previously Cache::Handle was not actually derived from in the implementations and just used as a `void*` stand-in with reinterpret_cast. Now there is a relationship to allow static_cast. In theory, this could introduce pointer arithmetic (as described above) but is unlikely without multiple inheritance AND non-empty Cache::Handle.
* Remove some unnecessary casts to void* as this is allowed to be implicit (for better or worse).
Most of the remaining reinterpret_casts are for converting to/from raw bytes of objects. We could consider better idioms for these patterns in follow-up work.
I wish there were a way to implement a template variant of static_cast that would only compile if no pointer arithmetic is generated, but best I can tell, this is not possible. AFAIK the best you could do is a dynamic check that the void* conversion after the static cast is unchanged.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12308
Test Plan: existing tests, CI
Reviewed By: ltamasi
Differential Revision: D53204947
Pulled By: pdillinger
fbshipit-source-id: 9de23e618263b0d5b9820f4e15966876888a16e2
Summary:
Add ```CompressionOptions``` to ```CompressedSecondaryCacheOptions``` to allow users to set options such as compression level. It allows performance to be fine tuned.
Tests -
Run db_bench and verify compression options in the LOG file
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12234
Reviewed By: ajkr
Differential Revision: D52758133
Pulled By: anand1976
fbshipit-source-id: af849fbffce6f84704387c195d8edba40d9548f6
Summary:
HyperClockCache is intended to mitigate performance problems under stress conditions (as well as optimizing average-case parallel performance). In LRUCache, the biggest such problem is lock contention when one or a small number of cache entries becomes particularly hot. Regardless of cache sharding, accesses to any particular cache entry are linearized against a single mutex, which is held while each access updates the LRU list. All HCC variants are fully lock/wait-free for accessing blocks already in the cache, which fully mitigates this contention problem.
However, HCC (and CLOCK in general) can exhibit extremely degraded performance under a different stress condition: when no (or almost no) entries in a cache shard are evictable (they are pinned). Unlike LRU which can find any evictable entries immediately (at the cost of more coordination / synchronization on each access), CLOCK has to search for evictable entries. Under the right conditions (almost exclusively MB-scale caches not GB-scale), the CPU cost of each cache miss could fall off a cliff and bog down the whole system.
To effectively mitigate this problem (IMHO), I'm introducing a new default behavior and tuning parameter for HCC, `eviction_effort_cap`. See the comments on the new config parameter in the public API.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12141
Test Plan:
unit test included
## Performance test
We can use cache_bench to validate no regression (CPU and memory) in normal operation, and to measure change in behavior when cache is almost entirely pinned. (TODO: I'm not sure why I had to get the pinned ratio parameter well over 1.0 to see truly bad performance, but the behavior is there.) Build with `make DEBUG_LEVEL=0 USE_CLANG=1 PORTABLE=0 cache_bench`. We also set MALLOC_CONF="narenas:1" for all these runs to essentially remove jemalloc variances from the results, so that the max RSS given by /usr/bin/time is essentially ideal (assuming the allocator minimizes fragmentation and other memory overheads well). Base command reproducing bad behavior:
```
./cache_bench -cache_type=auto_hyper_clock_cache -threads=12 -histograms=0 -pinned_ratio=1.7
```
```
Before, LRU (alternate baseline not exhibiting bad behavior):
Rough parallel ops/sec = 2290997
1088060 maxresident
Before, AutoHCC (bad behavior):
Rough parallel ops/sec = 141011 <- Yes, more than 10x slower
1083932 maxresident
```
Now let us sample a range of values in the solution space:
```
After, AutoHCC, eviction_effort_cap = 1:
Rough parallel ops/sec = 3212586
2402216 maxresident
After, AutoHCC, eviction_effort_cap = 10:
Rough parallel ops/sec = 2371639
1248884 maxresident
After, AutoHCC, eviction_effort_cap = 30:
Rough parallel ops/sec = 1981092
1131596 maxresident
After, AutoHCC, eviction_effort_cap = 100:
Rough parallel ops/sec = 1446188
1090976 maxresident
After, AutoHCC, eviction_effort_cap = 1000:
Rough parallel ops/sec = 549568
1084064 maxresident
```
I looks like `cap=30` is a sweet spot balancing acceptable CPU and memory overheads, so is chosen as the default.
```
Change to -pinned_ratio=0.85
Before, LRU:
Rough parallel ops/sec = 2108373
1078232 maxresident
Before, AutoHCC, averaged over ~20 runs:
Rough parallel ops/sec = 2164910
1077312 maxresident
After, AutoHCC, eviction_effort_cap = 30, averaged over ~20 runs:
Rough parallel ops/sec = 2145542
1077216 maxresident
```
The slight CPU improvement above is consistent with the cap, with no measurable memory overhead under moderate stress.
```
Change to -pinned_ratio=0.25 (low stress)
Before, AutoHCC, averaged over ~20 runs:
Rough parallel ops/sec = 2221149
1076540 maxresident
After, AutoHCC, eviction_effort_cap = 30, averaged over ~20 runs:
Rough parallel ops/sec = 2224521
1076664 maxresident
```
No measurable difference under normal circumstances.
Some tests repeated with FixedHCC, with similar results.
Reviewed By: anand1976
Differential Revision: D52174755
Pulled By: pdillinger
fbshipit-source-id: d278108031b1220c1fa4c89c5a9d34b7cf4ef1b8
Summary:
Example:
```
cache/clock_cache.cc:56:7: error: fallthrough annotation in unreachable code [-Werror,-Wimplicit-fallthrough]
FALLTHROUGH_INTENDED;
^
./port/lang.h:10:30: note: expanded from macro 'FALLTHROUGH_INTENDED'
^
```
In clang < 14, this is annoyingly generated from -Wimplicit-fallthrough, but was changed to -Wunreachable-code-fallthrough (implied by -Wunreachable-code) in clang 14. See https://reviews.llvm.org/D107933 for how this nuisance pattern generated false positives similar to ours in the Linux kernel.
Just to underscore the ridiculousness of this warning, here an error is reported on the annotation, not the call to do_something(), depending on the constexpr value (https://godbolt.org/z/EvxqdPTdr):
```
#include <atomic>
void do_something();
void test(int v) {
switch (v) {
case 1:
if constexpr (std::atomic<long>::is_always_lock_free) {
return;
} else {
do_something();
[[fallthrough]];
}
case 2:
return;
}
}
```
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12144
Test Plan: Added the warning to our Makefile for USE_CLANG, which reproduced the warning-as-error as shown above, but is now fixed.
Reviewed By: jaykorean
Differential Revision: D52139615
Pulled By: pdillinger
fbshipit-source-id: ba967ae700c0916d1a478bc465cf917633e337d9
Summary:
Sanitize the `secondary_cache` field in the `cache_opts` option of `TieredCacheOptions` to `nullptr` if set by the user. The nvm secondary cache should be directly set in `TieredCacheOptions`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12137
Reviewed By: akankshamahajan15
Differential Revision: D52063817
Pulled By: anand1976
fbshipit-source-id: 255116c665a9b908c8f44109a2d331d4b73e7591
Summary:
There is a bug in the `TieredSecondaryCache` that can result in a false negative. This can happen when a MultiGet does a cache lookup that gets a hit in the `TieredSecondaryCache` local nvm cache tier, and the result is available before MultiGet calls `WaitAll` (i.e the nvm cache `SecondaryCacheResultHandle` `IsReady` returns true).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12134
Test Plan: Add a new unit test in tiered_secondary_cache_test
Reviewed By: akankshamahajan15
Differential Revision: D52023309
Pulled By: anand1976
fbshipit-source-id: e5ae681226a0f12753fecb2f6acc7e5f254ae72b
Summary:
Add some asserts in the `CacheWithSecondaryAdapter` destructor to help debug a crash test failure.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12082
Reviewed By: cbi42
Differential Revision: D51486041
Pulled By: anand1976
fbshipit-source-id: 76537beed31ba27ab9ac8b4ce6deb775629e3be5
Summary:
`CacheWithSecondaryAdapter` can distribute placeholder reservations across the primary and secondary caches. The current implementation of the accounting is quite complicated in order to avoid using a mutex. This may cause the accounting to be slightly off after changes to the cache capacity and ratio, resulting in assertion failures. There's also a bug in the unlikely event that the total reservation exceeds the cache capacity. Furthermore, the current implementation is difficult to reason about.
This PR simplifies it by doing the accounting while holding a mutex. The reservations are processed in 1MB chunks in order to avoid taking a lock too frequently. As a side effect, this also removes the restriction of not allowing to increase the compressed secondary cache capacity after decreasing it to 0.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12059
Test Plan: Existing unit tests, and a new test for capacity increase from 0
Reviewed By: pdillinger
Differential Revision: D51278686
Pulled By: anand1976
fbshipit-source-id: 7e1ad2c50694772997072dd59cab35c93c12ba4f
