https://fedoraproject.org/wiki/Changes/Switch_RPMs_to_zstd_compression
= Switch RPMs to zstd compression =
== Summary ==
Binary RPMs are currently compressed with xz level 2.
Switching to zstd would increase decompression speed significantly.
== Owner ==
* Name: [[User:dmach| Daniel Mach]]
* Email: dmach@redhat.com
== Detailed Description ==
* The change requires setting a new compression algorithm in rpm
macros. Then a mass rebuild of all packages is required.
* The macro for setting the compression is: %define _binary_payload w19.zstdio
* The recommended compression level is 19. The builds will take
longer, but the additional compression time is negligible in the total
build time and it pays off in better compression ratio than xz lvl2
has.
* SRPM payload compression should stay at gzip (there's almost no
benefit in changing the compression, because SRPM's contents is
compressed already)
=== Use case: Firefox installation ===
I rebuilt firefox-66.0.5-1.fc30 with zstd level19.
Then I compared installation times with the original (xz compressed) package:
{| class="wikitable"
|-
! Compression !! Target File System !! Time
|-
| xz level 2 || tmpfs || 8s
|-
| xz level 2 || ext4 on nvme || 11s
|-
| zstd level 19 || tmpfs || 2s
|-
| zstd level 19 || ext4 on nvme || 4s
|-
|}
=== Comparison of compression algorithms and levels ===
Following table shows '''cpio''' and '''compressed cpio''' extraction
times into a tmpfs. Actual times in decompressing RPMs will differ due
to extracting on an actual disk and also some overhead in the RPM tool
(checks, scriptlets).
{| class="wikitable"
|-
! Compression !! Level !! Size B !! Size GiB
!! Compression time !! Compression time, 4 threads !!
Decompression time !! Comment
|-
| CPIO || - || 5016785692 || 4,7
|| - || - || -
||
|-
| xz || 2 || 1615017616 || 1,6
|| 9m55s || - || 1m36s
|| slow decompression
|-
| pxz || 2 || 1631869880 || 1,6
|| - || 6m11s || 1m38s
|| slow decompression
|-
| gzip || 9 || 2086354992 || 2,0
|| 10m23s || - || 31s
|| insufficient compression ratio
|-
| bzip2 || 9 || 1889161565 || 1,8
|| 8m || - || 2m50s
|| very slow decompression; compression ratio could be
better
|-
| zstd || 3 || 1913536587 || 1,8
|| 31s || 29s || 6,5s
||
|-
| zstd || 10 || 1737928978 || 1,7
|| 3m27s || 2m34s || 6,3s
||
|-
| zstd || 15 || 1717303256 || 1,7
|| 9m37s || 6m34s || 6,3s
|| identical compression speed to xz; fast decompression;
slightly worse compression ratio than xz
|-
| zstd || 17 || 1635525492 || 1,6
|| 16m16s || 11m20s || 6,7s
||
|-
| zstd || 19 || 1575843696 || 1,5
|| 24m2s || 18m55s || 7,7s
||
|-
|}
== Benefit to Fedora ==
* Faster installations/upgrades of user systems
* Faster koji builds (installations in build roots)
* Faster container builds
* Lower bandwidth on mirrors if we choose the highest compression level
== Scope ==
* Proposal owners: submit a patch to redhat-rpm-config
* Other developers: redhat-rpm-config maintainer: include the patch
and make a new build
* Release engineering: [https://pagure.io/releng/issue/8345 #8345]
mass rebuild is needed
== Upgrade/compatibility impact ==
* RPM in Fedora supports zstd compression already (from Fedora 28,
rpm-4.14.0-0.rc2.5.fc28). No impact on Fedora users is expected.
* Fedora <= 27 and some other distros will not be able to decompress
zstd-compressed RPMs.
== How To Test ==
* dnf install <package>
* rpm -q --qf "%{PAYLOADCOMPRESSOR} %{PAYLOADFLAGS}\n" <package>
* expected output: zstd 19
Also the overall system installation time should decrease significantly.
== User Experience ==
See '''Benefit to Fedora'''
== Dependencies ==
N/A
== Contingency Plan ==
* Contingency mechanism: Not needed, Fedora will stay at current compression.
* Contingency deadline: N/A
* Blocks release? No
* Blocks product? N/A
== Documentation ==
N/A
== Release Notes ==
RPMs have switched to zstd compression level 19.
Users will benefit from faster package decompression.
Users that build their packages will experience slightly longer build times.
I just want to say "Thanks Dan, for proposing and hopefully pushing this". Slow decompression speeds with xz are one of my top annoyances when working with our system. It's very sad that my SSD can write an order of magnitude faster than my CPU can decompress an rpm. And I always sadly watch the progress bars slowly crawl to the end. If we switch to a format with much faster decompression, it will not only positively impact software+updates installation speed, but also mock operations and most of our QA testing (anaconda installations, system upgrades). That's a massive improvement on many fronts. If we can do it while maintaining roughly the same repo size and compose time, even better (if we can't, a slight increase is I believe a worthy tradeoff).