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* Tracker bug: | * Tracker bug: [https://bugzilla.redhat.com/show_bug.cgi?id=1720729 #1720729] | ||
* Release notes tracker: | * Release notes tracker: [https://pagure.io/fedora-docs/release-notes/issue/350 #350] | ||
== Detailed Description == | == Detailed Description == | ||
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Users that build their packages will experience slightly longer build times. | Users that build their packages will experience slightly longer build times. | ||
[[Category: | Users using older systems (even RHEL8 era) may not be able to inspect these Fedora31 RPMs with those versions of rpm / rpm2cpio. | ||
[[Category:ChangeAcceptedF31]] | |||
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Latest revision as of 18:27, 26 March 2020
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: Daniel Mach
- Email: dmach@redhat.com
Current status
- Targeted release: Fedora 31
- Last updated: 2020-03-26
- Tracker bug: #1720729
- Release notes tracker: #350
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:
| 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).
| 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: #8395 mass rebuild is needed
- Policies and guidelines: not needed for this Change
- Trademark approval: N/A (not needed for this Change)
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: Revert to the previous compression and do a new mass rebuild.
- Contingency deadline: 2019-10-01 (a week before the Final Freeze)
- Blocks release? Yes
- 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.
Users using older systems (even RHEL8 era) may not be able to inspect these Fedora31 RPMs with those versions of rpm / rpm2cpio.