🛠 This is primarily a bugfix release, driven by the bugs found and fixed since LZ4 recent integration into Google's
oss-fuzz, initiated by @cmeister2 . The new capability was put to good use by @terrelln, dramatically expanding the number of scenarios covered by the profile-guided fuzzer. These scenarios were already covered by unguided fuzzers, but a few bugs require a large combinations of factors that unguided fuzzer are unable to produce in a reasonable timeframe.
⬆️ Due to these fixes, an upgrade of LZ4 to its latest version is recommended.
- 🛠 fix : out-of-bound read in exceptional circumstances when using
decompress_partial(), by @terrelln
- fix : slim opportunity for out-of-bound write with
compress_fast()with a large enough input and when providing an output smaller than recommended (
< LZ4_compressBound(inputSize)), by @terrelln
- fix : rare data corruption bug with
LZ4_compress_destSize(), by @terrelln
- 🛠 fix : data corruption bug when Streaming with an Attached Dict in HC Mode, by @felixhandte
- perf: enable
LZ4_FAST_DEC_LOOPon aarch64/GCC by default, by @prekageo
- perf: improved
lz4framestreaming API speed, by @dreambottle
- perf: speed up
lz4hcon slow patterns when using external dictionary, by @terrelln
- 👍 api: better in-place decompression and compression support
- 👍 cli :
--listsupports multi-frames files, by @gstedman
- cli : add option
--bestas an alias of
-12, by @Low-power
- misc: Integration into
oss-fuzzby @cmeister2, expanded list of scenarios by @terrelln
- 🛠 fix : out-of-bound read in exceptional circumstances when using
🚀 This is a point release, which main objective is to fix a read out-of-bound issue reported in the decoder of v1.9.0. Upgrade from this version is recommended.
🔀 A few other improvements were also merged during this time frame (listed below).
A visible user-facing one is the introduction of a new command
--list, started by @gabrielstedman, which makes it possible to peek at the internals of a
.lz4file. It will provide the block type, checksum information, compressed and decompressed sizes (if present). The command is limited to single-frame files for the time being.
- 🛠 fix : decompression functions were reading a few bytes beyond input size (introduced in v1.9.0, reported by @ppodolsky and @danlark1)
- api : fix : lz4frame initializers compatibility with c++, reported by @degski
- cli : added command
--list, based on a patch by @gabrielstedman
- 🏁 build: improved Windows build, by @JPeterMugaas
- 🏗 build: AIX, by Norman Green
Note : this release has an issue when compiling
liblz4dynamic library on Mac OS-X. This issue is fixed in : #696 .
Warning : this version has a known bug in the decompression function which makes it read a few bytes beyond input limit. Upgrade to v1.9.1 is recommended.
🚀 LZ4 v1.9.0 is a performance focused release, also offering minor API updates.
Decompression speed improvements
⚡️ Dave Watson (@djwatson) managed to carefully optimize the LZ4 decompression hot loop, offering substantial speed improvements on x86 and x64 platforms.
🐧 Here are some benchmark running on a Core i7-9700K, source compiled using
gcc v8.2.0on Ubuntu 18.10 "Cosmic Cuttlefish" (
Linux 4.18.0-17-generic) :
Version v1.8.3 v1.9.0 Improvement enwik8 4090 MB/s 4560 MB/s +12% calgary.tar 4320 MB/s 4860 MB/s +13% silesia.tar 4210 MB/s 4970 MB/s +18%
Given that decompression speed has always been a strong point of
lz4, the improvement is quite substantial.
The new decoding loop is automatically enabled on x64 and x86.
For other cpu types, since our testing capabilities are more limited, the new decoding loop is disabled by default. However, anyone can manually enable it, by using the build macro
LZ4_FAST_DEC_LOOP, which accepts values
1. The outcome will vary depending on exact target and build chains. For example, in our limited tests with ARM platforms, we found that benefits vary strongly depending on cpu manufacturer, chip model, and compiler version, making it difficult to offer a "generic" statement. ARM situation may prove extreme though, due to the proliferation of variants available. Other cpu types may prove easier to assess.
⚡️ API updates
_destSize()compression variants have been promoted to stable status.
🐧 These variants reverse the logic, by trying to fit as much input data as possible into a fixed memory budget. This is used for example in WiredTiger and EroFS, which cram as much data as possible into the size of a physical sector, for improved storage density.
When compressing small inputs, the fixed cost of clearing the compression's internal data structures can become a significant fraction of the compression cost. In
v1.8.2, new LZ4 entry points have been introduced to perform this initialization at effectively zero cost.
LZ4_resetStreamHC_fast()are now promoted into stable.
They are supplemented by new entry points,
LZ4_initStream()and its corresponding
HCvariant, which must be used on any uninitialized memory segment that will be converted into an LZ4 state. After that, only
reset*_fast()is needed to start some new compression job re-using the same context. This proves especially effective when compressing a lot of small data.
decompress*_fast()variants have been moved into the deprecate section.
🔒 While they offer slightly faster decompression speed (~+5%), they are also unprotected against malicious inputs, resulting in security liability. There are some limited cases where this property could prove acceptable (perfectly controlled environment, same producer / consumer), but in most cases, the risk is not worth the benefit.
🗄 We want to discourage such usage as clearly as possible, by pushing the
_fast()variant into deprecation area.
🚀 For the time being, they will not yet generate deprecation warnings when invoked, to give time to existing applications to move towards
decompress*_safe(). But this is the next stage, and is likely to happen in a future release.
LZ4_resetStreamHC()have also been moved into the deprecate section, to emphasize the preference towards
LZ4_resetStream_fast(). Their real equivalent are actually
LZ4_initStreamHC(), which are more generic (can accept any memory area to initialize) and safer (control size and alignment). Also, the naming makes it clearer when to use
initStream()and when to use
🔄 Changes list
🚀 This release brings an assortment of small improvements and bug fixes, as detailed below :
- perf: large decompression speed improvement on x86/x64 (up to +20%) by @djwatson
- api : changed :
_destSize()compression variants are promoted to stable API
- api : new :
- 🐎 api : changed :
LZ4_resetStream(HC)as recommended reset function, for better performance on small data
- 👍 cli : support custom block sizes, by @blezsan
- 🏗 build: source code can be amalgamated, by Bing Xu
- 🏗 build: added meson build, by @lzutao
- build: new build macros :
- install: MidnightBSD, by @laffer1
- 🏁 install: msys2 on Windows 10, by @vtorri
🚀 This is maintenance release, mainly triggered by issue #560.
#560 is a data corruption that can only occur in
v1.8.2, at level 9 (only), for some "large enough" data blocks (> 64 KB), featuring a fairly specific data pattern, improbable enough that multiple cpu running various fuzzers non-stop during a period of several weeks where not able to find it. Big thanks to @Pashugan for finding and sharing a reproducible sample.
⚡️ Due to this fix,
v1.8.3is a recommended update.
🚀 A few other minor features were already merged, and are therefore bundled in this release too.
lz4prove too slow, it's now possible to invoke
--fast=#command, by @jennifermliu . This is equivalent to the
accelerationparameter in the API, in which user forfeit some compression ratio for the benefit of better speed.
🛠 The verbose CLI has been fixed, and now displays the real amount of time spent compressing (instead of cpu time). It also shows a new indicator,
cpu load %, so that users can determine if the limiting factor was cpu or I/O bandwidth.
Finally, an existing function,
LZ4_decompress_safe_partial(), has been enhanced to make it possible to decompress only the beginning of an LZ4 block, up to a specified number of bytes. Partial decoding can be useful to save CPU time and memory, when the objective is to extract a limited portion from a larger block.
🚀 LZ4 v1.8.2 is a performance focused release, featuring important improvements for small inputs, especially when coupled with dictionary compression.
General speed improvements
👍 LZ4 decompression speed has always been a strong point. In v1.8.2, this gets even better, as it improves decompression speed by about 10%, thanks in a large part to suggestion from @svpv .
💻 For example, on a Mac OS-X laptop with an Intel Core i7-5557U CPU @ 3.10GHz,
silesia.tarcompiled with default compiler
Version v1.8.1 v1.8.2 Improvement Decompression speed 2490 MB/s 2770 MB/s +11%
Compression speeds also receive a welcomed boost, though improvement is not evenly distributed, with higher levels benefiting quite a lot more.
Version v1.8.1 v1.8.2 Improvement lz4 -1 504 MB/s 516 MB/s +2% lz4 -9 23.2 MB/s 25.6 MB/s +10% lz4 -12 3.5 Mb/s 9.5 MB/s +170%
Should you aim for best possible decompression speed, it's possible to request LZ4 to actively favor decompression speed, even if it means sacrificing some compression ratio in the process. This can be requested in a variety of ways depending on interface, such as using command
--favor-decSpeedon CLI. This option must be combined with ultra compression mode (levels 10+), as it needs careful weighting of multiple solutions, which only this mode can process.
The resulting compressed object always decompresses faster, but is also larger. Your mileage will vary, depending on file content. Speed improvement can be as low as 1%, and as high as 40%. It's matched by a corresponding file size increase, which tends to be proportional. The general expectation is 10-20% faster decompression speed for 1-2% bigger files.
Filename decompression speed
Speed Improvement Size change silesia.tar 2870 MB/s 3070 MB/s +7 % +1.45% dickens 2390 MB/s 2450 MB/s +2 % +0.21% nci 3740 MB/s 4250 MB/s +13 % +1.93% osdb 3140 MB/s 4020 MB/s +28 % +4.04% xml 3770 MB/s 4380 MB/s +16 % +2.74%
LZ4_compress_destSize()also receives a ~10% speed boost, since it now internally redirects toward primary internal implementation of LZ4 fast mode, rather than relying on a separate custom implementation. This allows it to take advantage of all the optimization work that has gone into the main implementation.
Compressing small contents
🚀 When compressing small inputs, the fixed cost of clearing the compression's internal data structures can become a significant fraction of the compression cost. This release adds a new way, under certain conditions, to perform this initialization at effectively zero cost.
🆕 New, experimental LZ4 APIs have been introduced to take advantage of this functionality in block mode:
More detail about how and when to use these functions is provided in their respective headers.
LZ4 Frame mode has been modified to use this faster reset whenever possible.
LZ4F_compressFrame_usingCDict()prototype has been modified to additionally take an
LZ4F_CCtx*context, so it can use this speed-up.
Efficient Dictionary compression
👌 Support for dictionaries has been improved in a similar way: they can now be used in-place, which avoids the expense of copying the context state from the dictionary into the working context. Users are expect to see a noticeable performance improvement for small data.
Experimental prototypes (
LZ4_attach_HC_dictionary()) have been added to LZ4 block API using a loaded dictionary in-place. LZ4 Frame API users should benefit from this optimization transparently.
🐎 The previous two changes, when taken advantage of, can provide meaningful performance improvements when compressing small data. Both changes have no impact on the produced compressed data. The only observable difference is speed.
🚀 This is a representative graphic of the sort of speed boost to expect. The red lines are the speeds seen for an input blob of the specified size, using the previous LZ4 release (v1.8.1) at compression levels 1 and 9 (those being, fast mode and default HC level). The green lines are the equivalent observations for v1.8.2. This benchmark was performed on the Silesia Corpus. Results for the
dickenstext are shown, other texts and compression levels saw similar improvements. The benchmark was compiled with GCC 7.2.0 with
-O3 -march=native -mtune=native -DNDEBUGunder Linux 4.6 and run on an
Intel Xeon CPU E5-2680 v4 @ 2.40GHz.
The content of
lz4frame_static.hhas been folded into
lz4frame.h, hidden by a macro guard "
#ifdef LZ4F_STATIC_LINKING_ONLY". This means
lz4frame_static.his retained as a shell that simply sets the guard macro and includes
🔄 Changes list
🚀 This release also brings an assortment of small improvements and bug fixes, as detailed below :
- perf: faster compression on small files, by @felixhandte
- perf: improved decompression speed and binary size, by Alexey Tourbin (@svpv)
- perf: faster HC compression, especially at max level
- perf: very small compression ratio improvement
- 🛠 fix : compression compatible with low memory addresses (
- 🛠 fix : decompression segfault when provided with
NULLinput, by @terrelln
- cli : new command
- cli : benchmark mode more accurate for small inputs
- fullbench : can bench
_destSize()variants, by @felixhandte
- 📜 doc : clarified block format parsing restrictions, by Alexey Tourbin (@svpv)
🛠 It's the same as
v1.8.1, but the version number in source code has been fixed, thanks to @sunpoet.
📚 The version number is used in cli and documentation display, to create the full name of dynamic library, and can be requested via
LZ4 v1.8.1 most visible new feature is its support for Dictionary compression.
This was already somewhat possible, but in a complex way, requiring knowledge of internal working.
👌 Support is now more formally added on the API side within
lib/lz4frame_static.h. It's early days, and this new API is tagged "experimental" for the time being.
lz4doesn't specify how to build a dictionary. All it says is that it can be any file up to 64 KB.
🏗 This approach is compatible with
zstddictionary builder, which can be instructed to create a 64 KB dictionary with this command :
zstd --train dirSamples/* -o dictName --maxdict=64KB
🐎 LZ4 v1.8.1 also offers improved performance at ultra settings (levels 10+).
📜 These levels receive a new code, called optimal parser, available in
🐎 Compared with previous version, the new parser uses less memory (from 384KB to 256KB), performs faster, compresses a little bit better (not much, as it was already close to theoretical limit), and resists pathological patterns which could destroy performance (see #339),
💻 For comparison, here are some quick benchmark using LZ4 v1.8.0 on my laptop with
./lz4 -b9e12 -v ~/dev/bench/silesia.tar ***LZ4 command line interface 64-bits v1.8.0, by Yann Collet*** Benchmarking levels from 9 to 12 9#silesia.tar : 211984896 -> 77897777 (2.721), 24.2 MB/s ,2401.8 MB/s 10#silesia.tar : 211984896 -> 77852187 (2.723), 16.9 MB/s ,2413.7 MB/s 11#silesia.tar : 211984896 -> 77435086 (2.738), 7.1 MB/s ,2425.7 MB/s 12#silesia.tar : 211984896 -> 77274453 (2.743), 3.3 MB/s ,2390.0 MB/s
and now using LZ4 v1.8.1 :
./lz4 -b9e12 -v ~/dev/bench/silesia.tar ***LZ4 command line interface 64-bits v1.8.1, by Yann Collet*** Benchmarking levels from 9 to 12 9#silesia.tar : 211984896 -> 77890594 (2.722), 24.4 MB/s ,2405.2 MB/s 10#silesia.tar : 211984896 -> 77859538 (2.723), 19.3 MB/s ,2476.0 MB/s 11#silesia.tar : 211984896 -> 77369725 (2.740), 10.1 MB/s ,2478.4 MB/s 12#silesia.tar : 211984896 -> 77270146 (2.743), 3.7 MB/s ,2508.3 MB/s
📜 The new parser is also directly compatible with lower compression levels, which brings additional benefits :
- Compatibility with
LZ4_*_destSize()variant, which reverses the logic by trying to fit as much data as possible into a predefined limited size buffer.
- Compatibility with Dictionary compression, as it uses the same tables as regular HC mode
In the future, this compatibility will also allow dynamic on-the-fly change of compression level, but such feature is not implemented at this stage.
🚀 The release also provides a set of small bug fixes and improvements, listed below :
- perf : faster and stronger ultra modes (levels 10+)
- perf : slightly faster compression and decompression speed
- perf : fix bad degenerative case, reported by @c-morgenstern
- 🛠 fix : decompression failed when using a combination of extDict + low memory address (#397), reported and fixed by Julian Scheid (@jscheid)
- 👍 cli : support for dictionary compression (
-D), by Felix Handte @felixhandte
- cli : fix :
lz4 -d --rmpreserves timestamp (#441)
- cli : fix : do not modify
/dev/nullpermission as root, by @aliceatlas
- api : new dictionary api in
- 👍 api :
_destSize()variant supported for all compression levels
- 🏗 build :
make testcompatible with parallel build
-jX, reported by @mwgamera
- 🏗 build : can control
LZ4LIB_VISIBILITYmacro, by @mikir
- install: fix man page directory (#387), reported by Stuart Cardall (@itoffshore)
🛠 Note :
v126.96.36.199is the same as
v.1.8.1, with the version number fixed in source code, as notified by Po-Chuan Hsieh (@sunpoet).
- Compatibility with
cli : fix : do not modify /dev/null permissions, reported by @Maokaman1
cli : added GNU separator
--specifying that all following arguments are only files
⏪ cli : restored
-BXcommand enabling block checksum
API : added
LZ4_compress_HC_destSize(), by @remittor
API : added
API : lz4frame : negative compression levels trigger fast acceleration, request by @llchan
API : lz4frame : can control block checksum and dictionary ID
API : fix : expose obsolete decoding functions, reported by @cyfdecyf
API : experimental :
lz4frame_static.h: new dictionary compression API
🏗 build : fix : static lib installation, by @ido
🏗 build : dragonFlyBSD, OpenBSD, NetBSD supported
build : LZ4_MEMORY_USAGE can be modified at compile time, through external define
⚡️ doc : Updated LZ4 Frame format to v1.6.0, restoring Dictionary-ID field in header
doc : lz4's API manual in
.htmlformat, by @inikep
lz4hc : new high compression mode, by @inikep : levels 10-12 compress more (and slower), 12 is highest level
lz4cat : fix : works with relative path (#284) and stdin (#285) (reported by @beiDei8z)
cli : fix minor notification when using
API : lz4frame :
LZ4F_compressBound(0)provides upper bound of *flush() and *End() (#290, #280)
doc : markdown version of man page, by @t-mat (#279)
🏗 build : Makefile : fix
make -jXlib+exe concurrency (#277)
🏗 build : cmake : improvements by @mgorny (#296)
⚡️ Update : earlier versions of pre-compiled Windows binaries had a bug which made them unable to decode files > 2 GB. The new binaries available below fix this issue.