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5 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
Peter Dillinger
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a004c2d850 |
Add experimental embedded blob SST support (#14851)
Summary:
Add EXPERIMENTAL embedded blob SST support for SstFileWriter through
OpenWithEmbeddedBlobs(). Eligible large values are written as same-file blob
records inline in a block-based SST as values are added (interleaved with data
blocks), while table entries store same-file BlobIndex references that readers
resolve for Get, MultiGet, and iteration, including mixed embedded and
non-embedded wide-column values.
Embedded-blob handling is folded directly into BlockBasedTableBuilder rather than
living in SstFileWriter or a separate table-builder wrapper: SstFileWriter only
selects the mode (via TableBuilderOptions::embedded_blob_options), and the
builder writes blob records inline using its own file writer and running offset.
This is enabled by disabling index-value delta encoding for these SSTs — delta
encoding reconstructs a data block's offset from the previous block and so
requires byte-contiguous data blocks, which interleaved blob records would break.
With full (non-delta) index values, blob records can sit between data blocks, so
no entry buffering/replay is needed. To keep inline blob appends correctly
ordered with data-block writes, these SSTs use single-threaded (non-parallel)
compression. The mode is the only entry point today but the placement keeps it
open to generalization beyond SstFileWriter; regardless, this experimental
feature is expected only to have niche applications.
(Previous revisions of this change allowed delta-encoded index blocks by
putting all blobs at the beginning of the file, but that was a more awkward
and memory-hungry implementation due to buffering all the data blocks before
writing.)
The on-disk record format (SimpleGen2Blob: payload bytes followed by a 5-byte
trailer of a compression marker plus a builtin checksum that is context-modified
by the record's absolute file offset) lives in db/blob/blob_gen2_format.{h,cc},
which now owns both the read (ReadAndVerifySimpleGen2BlobRecord) and write
(WriteSimpleGen2BlobRecord) sides so the format is defined in one place. This is
expected to be reused for upcoming "blog file" support.
Readers need no record-layout metadata: same-file blob resolution is purely
absolute-offset keyed, and the per-record offset-modified checksum (plus a cheap
"record fits within the file" bound) is the corruption guard. The reader's only
embedded-blob metadata is presence: a best-effort auxiliary table property
(blob count and payload-byte totals, for diagnostics) whose mere presence signals
that the SST contains embedded blobs.
Reads route through the column family's BlobSource when a DB is attached, so
embedded payloads are served from / inserted into the blob value cache and
recorded in BLOB_DB_* statistics; the cache key is derived from the
SimpleGen2Blob offset scheme (the same scheme block-based SST blocks use), so
embedded blob records stay collision-free with data blocks even when the blob
cache and block cache are the same cache. Non-DB openers (SstFileReader,
sst_dump, repair, ingestion prevalidation) have no BlobSource and fall back to a
direct, uncached read.
Same-file BlobIndex references use blob file number 0 as the marker. That value
also serves as the invalid blob-file-number sentinel in broader metadata code,
but the meanings do not conflict when used carefully: only the embedded-SST
reader/writer path interprets 0 as same-file, while generic file-metadata paths
continue to reject it as invalid. Using 1 would be worse because legacy
"stackable" BlobDB can use low blob file numbers, including 1, so reserving it
would collide with real blob files.
Compression options remain in the public API as placeholders, but embedded blob
compression support is deferred. Integrating compression with
BlockBasedTableBuilder while avoiding copied CompressAndVerifyBlock-style logic
is tricky enough to deserve a separate, focused PR.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14851
Test Plan:
- Added basic feature coverage to the crash test.
- Added BlobIndexTest.SameFileBlobIndex and BlobGarbageMeterTest.SameFileBlobIndex
coverage for same-file BlobIndex encoding, display, recognition, and ignoring
same-file references in blob-garbage accounting.
- Extended FileMetaDataTest.UpdateBoundariesBlobIndex to preserve the generic
zero-file-number corruption check while keeping same-file embedded blob
semantics at the table-reader/writer layers.
- SstFileReader embedded blob coverage: round-trip Get, MultiGet, and iterator
reads; format_version gating; ignored placeholder compression options; the
2048-byte default min_blob_size; wide-column mixed embedded/non-embedded
values; and early append-error surfacing.
- Added an interleaved-layout test (small block_size with alternating
small/large values) asserting the SST property index_value_is_delta_encoded==0,
more than one data block, and that blob records are interspersed with data
blocks (not a strict front prefix), with all values read back correctly via
Get and iteration; replaces the old "ignored bytes before/after the blob record
prefix" test.
- Added an embedded-record corruption test: flipping a byte inside a blob
record's payload yields Corruption on read with verify_checksums (the
offset-keyed record checksum is the guard now that the range pre-check is gone).
- Exercised the cached read path through BlobSource, including blob-cache
hit/miss behavior and the shared blob_cache == block_cache configuration, in
db_blob_index_test.
- Normal-path CPU regression check: release (DEBUG_LEVEL=0) db_bench on a
non-embedded DB comparing this change vs upstream main, 3 interleaved reps of
fillseq, fillrandom, readrandom, and readseq (5M keys, value_size=100,
compression none, DB on /dev/shm). All deltas were within run-to-run noise
(~1%), i.e. no measurable regression from adding the embedded-mode branch to
the builder hot path.
Reviewed By: xingbowang
Differential Revision: D108564468
Pulled By: pdillinger
fbshipit-source-id: 5f01ffb1d40c6fd5b82d2451ec3342abb5040ca6
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Peter Dillinger
|
871f79d6ef |
Reformat source files (#14331)
Summary: probably something changed, maybe https://github.com/facebook/rocksdb/issues/14311 Full command: ``` git ls-files '*.cc' '*.h' | grep -v '^third-party/' | grep -v 'range_tree' | xargs clang-format -i ``` Pull Request resolved: https://github.com/facebook/rocksdb/pull/14331 Test Plan: CI Reviewed By: mszeszko-meta Differential Revision: D93246992 Pulled By: pdillinger fbshipit-source-id: 6bc5b97978fef8aee52823dadb6daa4bea57343d |
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Peter Dillinger
|
86a1e3e0e7 |
Derive cache keys from SST unique IDs (#10394)
Summary: ... so that cache keys can be derived from DB manifest data before reading the file from storage--so that every part of the file can potentially go in a persistent cache. See updated comments in cache_key.cc for technical details. Importantly, the new cache key encoding uses some fancy but efficient math to pack data into the cache key without depending on the sizes of the various pieces. This simplifies some existing code creating cache keys, like cache warming before the file size is known. This should provide us an essentially permanent mapping between SST unique IDs and base cache keys, with the ability to "upgrade" SST unique IDs (and thus cache keys) with new SST format_versions. These cache keys are of similar, perhaps indistinguishable quality to the previous generation. Before this change (see "corrected" days between collision): ``` ./cache_bench -stress_cache_key -sck_keep_bits=43 18 collisions after 2 x 90 days, est 10 days between (1.15292e+19 corrected) ``` After this change (keep 43 bits, up through 50, to validate "trajectory" is ok on "corrected" days between collision): ``` 19 collisions after 3 x 90 days, est 14.2105 days between (1.63836e+19 corrected) 16 collisions after 5 x 90 days, est 28.125 days between (1.6213e+19 corrected) 15 collisions after 7 x 90 days, est 42 days between (1.21057e+19 corrected) 15 collisions after 17 x 90 days, est 102 days between (1.46997e+19 corrected) 15 collisions after 49 x 90 days, est 294 days between (2.11849e+19 corrected) 15 collisions after 62 x 90 days, est 372 days between (1.34027e+19 corrected) 15 collisions after 53 x 90 days, est 318 days between (5.72858e+18 corrected) 15 collisions after 309 x 90 days, est 1854 days between (1.66994e+19 corrected) ``` However, the change does modify (probably weaken) the "guaranteed unique" promise from this > SST files generated in a single process are guaranteed to have unique cache keys, unless/until number session ids * max file number = 2**86 to this (see https://github.com/facebook/rocksdb/issues/10388) > With the DB id limitation, we only have nice guaranteed unique cache keys for files generated in a single process until biggest session_id_counter and offset_in_file reach combined 64 bits I don't think this is a practical concern, though. Pull Request resolved: https://github.com/facebook/rocksdb/pull/10394 Test Plan: unit tests updated, see simulation results above Reviewed By: jay-zhuang Differential Revision: D38667529 Pulled By: pdillinger fbshipit-source-id: 49af3fe7f47e5b61162809a78b76c769fd519fba |
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Guido Tagliavini Ponce
|
b52620ab0e |
Fix key size in cache_bench (#10234)
Summary: cache_bench wasn't generating 16B keys, which are necessary for FastLRUCache. Also: - Added asserts in cache_bench, which is assuming that inserts never fail. When they fail (for example, if we used keys of the wrong size), memory allocated to the values will becomes leaked, and eventually the program crashes. - Move kCacheKeySize to the right spot. Pull Request resolved: https://github.com/facebook/rocksdb/pull/10234 Test Plan: ``make -j24 check``. Also, run cache_bench with FastLRUCache and check that memory usage doesn't blow up: ``./cache_bench -cache_type=fast_lru_cache -num_shard_bits=6 -skewed=true \ -lookup_insert_percent=100 -lookup_percent=0 -insert_percent=0 -erase_percent=0 \ -populate_cache=true -cache_size=1073741824 -ops_per_thread=10000000 \ -value_bytes=8192 -resident_ratio=1 -threads=16`` Reviewed By: pdillinger Differential Revision: D37382949 Pulled By: guidotag fbshipit-source-id: b697a942ebb215de5d341f98dc8566763436ba9b |
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Peter Dillinger
|
0050a73a4f |
New stable, fixed-length cache keys (#9126)
Summary: This change standardizes on a new 16-byte cache key format for block cache (incl compressed and secondary) and persistent cache (but not table cache and row cache). The goal is a really fast cache key with practically ideal stability and uniqueness properties without external dependencies (e.g. from FileSystem). A fixed key size of 16 bytes should enable future optimizations to the concurrent hash table for block cache, which is a heavy CPU user / bottleneck, but there appears to be measurable performance improvement even with no changes to LRUCache. This change replaces a lot of disjointed and ugly code handling cache keys with calls to a simple, clean new internal API (cache_key.h). (Preserving the old cache key logic under an option would be very ugly and likely negate the performance gain of the new approach. Complete replacement carries some inherent risk, but I think that's acceptable with sufficient analysis and testing.) The scheme for encoding new cache keys is complicated but explained in cache_key.cc. Also: EndianSwapValue is moved to math.h to be next to other bit operations. (Explains some new include "math.h".) ReverseBits operation added and unit tests added to hash_test for both. Fixes https://github.com/facebook/rocksdb/issues/7405 (presuming a root cause) Pull Request resolved: https://github.com/facebook/rocksdb/pull/9126 Test Plan: ### Basic correctness Several tests needed updates to work with the new functionality, mostly because we are no longer relying on filesystem for stable cache keys so table builders & readers need more context info to agree on cache keys. This functionality is so core, a huge number of existing tests exercise the cache key functionality. ### Performance Create db with `TEST_TMPDIR=/dev/shm ./db_bench -bloom_bits=10 -benchmarks=fillrandom -num=3000000 -partition_index_and_filters` And test performance with `TEST_TMPDIR=/dev/shm ./db_bench -readonly -use_existing_db -bloom_bits=10 -benchmarks=readrandom -num=3000000 -duration=30 -cache_index_and_filter_blocks -cache_size=250000 -threads=4` using DEBUG_LEVEL=0 and simultaneous before & after runs. Before ops/sec, avg over 100 runs: 121924 After ops/sec, avg over 100 runs: 125385 (+2.8%) ### Collision probability I have built a tool, ./cache_bench -stress_cache_key to broadly simulate host-wide cache activity over many months, by making some pessimistic simplifying assumptions: * Every generated file has a cache entry for every byte offset in the file (contiguous range of cache keys) * All of every file is cached for its entire lifetime We use a simple table with skewed address assignment and replacement on address collision to simulate files coming & going, with quite a variance (super-Poisson) in ages. Some output with `./cache_bench -stress_cache_key -sck_keep_bits=40`: ``` Total cache or DBs size: 32TiB Writing 925.926 MiB/s or 76.2939TiB/day Multiply by 9.22337e+18 to correct for simulation losses (but still assume whole file cached) ``` These come from default settings of 2.5M files per day of 32 MB each, and `-sck_keep_bits=40` means that to represent a single file, we are only keeping 40 bits of the 128-bit cache key. With file size of 2\*\*25 contiguous keys (pessimistic), our simulation is about 2\*\*(128-40-25) or about 9 billion billion times more prone to collision than reality. More default assumptions, relatively pessimistic: * 100 DBs in same process (doesn't matter much) * Re-open DB in same process (new session ID related to old session ID) on average every 100 files generated * Restart process (all new session IDs unrelated to old) 24 times per day After enough data, we get a result at the end: ``` (keep 40 bits) 17 collisions after 2 x 90 days, est 10.5882 days between (9.76592e+19 corrected) ``` If we believe the (pessimistic) simulation and the mathematical generalization, we would need to run a billion machines all for 97 billion days to expect a cache key collision. To help verify that our generalization ("corrected") is robust, we can make our simulation more precise with `-sck_keep_bits=41` and `42`, which takes more running time to get enough data: ``` (keep 41 bits) 16 collisions after 4 x 90 days, est 22.5 days between (1.03763e+20 corrected) (keep 42 bits) 19 collisions after 10 x 90 days, est 47.3684 days between (1.09224e+20 corrected) ``` The generalized prediction still holds. With the `-sck_randomize` option, we can see that we are beating "random" cache keys (except offsets still non-randomized) by a modest amount (roughly 20x less collision prone than random), which should make us reasonably comfortable even in "degenerate" cases: ``` 197 collisions after 1 x 90 days, est 0.456853 days between (4.21372e+18 corrected) ``` I've run other tests to validate other conditions behave as expected, never behaving "worse than random" unless we start chopping off structured data. Reviewed By: zhichao-cao Differential Revision: D33171746 Pulled By: pdillinger fbshipit-source-id: f16a57e369ed37be5e7e33525ace848d0537c88f |