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Add compression level option #2171

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Merged
merged 5 commits into from
Mar 16, 2024
Merged

Add compression level option #2171

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31b39d8
Add compression level option
Beihao-Zhou Mar 14, 2024
57c1b11
Merge branch 'unstable' into add-compression-level-option
git-hulk Mar 15, 2024
38964dd
Add details for compression level option config
Beihao-Zhou Mar 15, 2024
c184092
remove auto-generated namespace
Beihao-Zhou Mar 15, 2024
3265e16
set default as the same with rocksdb
Beihao-Zhou Mar 15, 2024
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23 changes: 23 additions & 0 deletions kvrocks.conf
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Expand Up @@ -727,6 +727,29 @@ rocksdb.cache_index_and_filter_blocks yes
# default snappy
rocksdb.compression snappy

# Specify the compression level to use. It trades compression speed
# and ratio, might be useful when tuning for disk space.
# See details: https://github.com/facebook/rocksdb/wiki/Space-Tuning
# For zstd: valid range is from 1 (fastest) to 19 (best ratio),
# For zlib: valid range is from 1 (fastest) to 9 (best ratio),
# For lz4: adjusting the level influences the 'acceleration'.
# RocksDB sets a negative level to indicate acceleration directly,
# with more negative values indicating higher speed and less compression.
# Note: This setting is ignored for compression algorithms like Snappy that
# do not support variable compression levels.
#
# RocksDB Default:
# - zstd: 3
# - zlib: Z_DEFAULT_COMPRESSION (currently -1)
# - kLZ4: -1 (i.e., `acceleration=1`; see `CompressionOptions::level` doc)
# For all others, RocksDB does not specify a compression level.
# If the compression type doesn't support the setting, it will be a no-op.
#
# Default: 32767 (RocksDB's generic default compression level. Internally
# it'll be translated to the default compression level specific to the
# compression library as mentioned above)
rocksdb.compression_level 32767

# If non-zero, we perform bigger reads when doing compaction. If you're
# running RocksDB on spinning disks, you should set this to at least 2MB.
# That way RocksDB's compaction is doing sequential instead of random reads.
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1 change: 1 addition & 0 deletions src/config/config.cc
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Expand Up @@ -190,6 +190,7 @@ Config::Config() {
{"rocksdb.compression", false,
new EnumField<rocksdb::CompressionType>(&rocks_db.compression, compression_types,
rocksdb::CompressionType::kNoCompression)},
{"rocksdb.compression_level", true, new IntField(&rocks_db.compression_level, 32767, INT_MIN, INT_MAX)},
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🤔why compression_level can be dynamically changed?

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@Beihao-Zhou Beihao-Zhou Mar 15, 2024 •
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Seems like RocksDB just hardcode this value 32767 into their compression level logic.
exposed level option const: https://github.com/facebook/rocksdb/blob/096fb9b67d19a9a180e7c906b4a0cdb2b2d0c1f6/include/rocksdb/compression_type.h#L53
Zlib: https://github.com/facebook/rocksdb/blob/096fb9b67d19a9a180e7c906b4a0cdb2b2d0c1f6/util/compression.h#L805
Zstd: https://github.com/facebook/rocksdb/blob/096fb9b67d19a9a180e7c906b4a0cdb2b2d0c1f6/util/compression.h#L183

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aha, my bad. I mean why it's different from compression, which could be changed dynamically.

This looks ok to me

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Oh gotcha, nwnw, I did have the same question while I was working on it.

So when we change the compression type, it doesn't require re-encoding of the existing data because each block or SST file includes metadata specifying the compression algorithm used for that particular block or file. This allows RocksDB to understand how to decompress the data regardless of the global compression settings at any given time.

However, compression level, unlike compression types, which are recorded and recognized on a per-block or per-file basis, the specific level detail isn't stored with each block or file. Therefore, if we want to change it, it will require re-encoding everything, which is a huge overhead. I think that's the reason why RocksDB doesn't allow us to dynamically SetOption() for it.

Ref: https://github.com/facebook/rocksdb/wiki/Compression (The first line explains a bit about the granularity of encoding block)

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Rocksdb don't have this interface is fair enough, however, I don't think changing the level need re-encoding. And decompress block also doesn't need the level

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Besides, maybe refer to facebook/rocksdb#6615 helps.

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I see I see, thank you very much for correcting me and finding the reference!!

{"rocksdb.block_size", true, new IntField(&rocks_db.block_size, 16384, 0, INT_MAX)},
{"rocksdb.max_open_files", false, new IntField(&rocks_db.max_open_files, 8096, -1, INT_MAX)},
{"rocksdb.write_buffer_size", false, new IntField(&rocks_db.write_buffer_size, 64, 0, 4096)},
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1 change: 1 addition & 0 deletions src/config/config.h
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Expand Up @@ -199,6 +199,7 @@ struct Config {
int level0_stop_writes_trigger;
int level0_file_num_compaction_trigger;
rocksdb::CompressionType compression;
int compression_level;
bool disable_auto_compactions;
bool enable_blob_files;
int min_blob_size;
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1 change: 1 addition & 0 deletions src/storage/storage.cc
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Expand Up @@ -165,6 +165,7 @@ rocksdb::Options Storage::InitRocksDBOptions() {
options.min_write_buffer_number_to_merge = 2;
options.write_buffer_size = config_->rocks_db.write_buffer_size * MiB;
options.num_levels = 7;
options.compression_opts.level = config_->rocks_db.compression_level;
options.compression_per_level.resize(options.num_levels);
// only compress levels >= 2
for (int i = 0; i < options.num_levels; ++i) {
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1 change: 1 addition & 0 deletions tests/cppunit/config_test.cc
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Expand Up @@ -126,6 +126,7 @@ TEST(Config, GetAndSet) {
{"rocksdb.subkey_block_cache_size", "100"},
{"rocksdb.row_cache_size", "100"},
{"rocksdb.rate_limiter_auto_tuned", "yes"},
{"rocksdb.compression_level", "32767"},
};
for (const auto &iter : immutable_cases) {
s = config.Set(nullptr, iter.first, iter.second);
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