delta update
{{Primary sources|date=August 2022}}
{{short description|Update that only requires the user to download changed code}}
A delta update is a software update that requires the user to download only those parts of the software's code that are new, or have been changed from their previous state, in contrast to having to download the entire program. The use of delta updates can save significant amounts of time and computing bandwidth. The name "delta" derives from the mathematical science use of the Greek letter delta, Δ or δ to denote change.{{cite web |url=https://sciencing.com/delta-math-6678201.html |title=What is Delta in Math? |last=Mullin |first=Sean |date=2017-04-25 |website=Sciencing |publisher=Leaf Group Media |access-date=2022-09-06 |quote=delta...means 'change' or 'the change in' in mathematics}}
Uses
= Linux =
File:Delta RPM (deltarpm) in Fedora Linux 34.png]]
Fedora Linux has supported binary delta updates by default using the yum presto plugin since June 2009. This is based on RPM Package Manager's deltarpm system (2004), which was in turn based on bsdiff.{{cite web|title=Fedora Features/Presto|url=https://fedoraproject.org/wiki/Features/Presto}} This functionality has been inherited by Fedora-derived operating systems, including RedHat Enterprise Linux and its variant, CentOS. From Fedora 40 onward, delta updates had been discontinued.{{Cite web |title=Changes/Drop Delta RPMs - Fedora Project Wiki |url=https://fedoraproject.org/wiki/Changes/Drop_Delta_RPMs |access-date=2024-06-02 |website=fedoraproject.org}} openSUSE also uses delta-rpm's with its zypper manager. This is still in use, and the standard solution for the openSUSE Leap distribution today. A more primitive system, the SUSE patchrpm, worked by replacing changed files.{{cite web |title=6.3. RPM and Patches |url=https://www.pks.mpg.de/~mueller/docs/suse10.2/html/opensuse-manual_en/manual/sec.rpm.patches.html |website=www.pks.mpg.de |access-date=2020-03-24 |archive-date=2020-03-24 |archive-url=https://web.archive.org/web/20200324103323/https://www.pks.mpg.de/~mueller/docs/suse10.2/html/opensuse-manual_en/manual/sec.rpm.patches.html |url-status=dead }}
A similar system for the dpkg-APT package manager system of Debian is debdelta (2006); despite an apparent halt on the homepage, its package repository as well as the source code remains actively maintained.{{cite web|title=debdelta at the Debian Project|url=http://debdelta.debian.net/}} (for source code, see debian "developer information" for package; for repository, see http://debdeltas.debian.net/debian-deltas/pool/.) debdelta is not installed by default and not many mirrors have been set up for it. A member of the developer team has proposed yet another format that integrates directly into the currently mirrored main repositories called patch debs in 2018. It is intended to have more integrity checks.{{cite web |title=Teams/Dpkg/Spec/DeltaDebs |url=https://wiki.debian.org/Teams/Dpkg/Spec/DeltaDebs |website=Debian Wiki}}
A descendant of Debian, Ubuntu developers have tried many times to implement delta updates for their system. During 2006 they tried to create one, but were confronted with too many options and dropped the efforts.{{cite web |title=SmallerUpdates |url=https://wiki.ubuntu.com/SmallerUpdates |website=Ubuntu Wiki |accessdate=13 January 2020}} In 2011 they tried to just set up debdelta, but once again dropped the efforts in May of the same year.{{cite web|title=UbuntuDebdeltaSupport|url=https://wiki.ubuntu.com/UbuntuDebdeltaSupport}}
The Arch Linux package manager pacman used to support a form of delta updating using VCDIFF (xdelta). It was scrapped due to an arbitrary command execution vulnerability ({{CVE|2019-18183}}) due to a lack of string escaping.{{Citation needed|reason=cited ArchWiki page is now archived and no longer exists|date=August 2022}}
= Windows =
Windows Update has supported delta updates since Windows XP which are called express installation files. On redistributing updates, Windows Server Update Services has supported delta updates since Windows Server 2003.{{cite web|title=Determine Bandwidth Options to Use for Your Deployment|date=9 April 2014 |url=https://technet.microsoft.com/en-us/library/cc708456}}
= FreeBSD =
FreeBSD has supported delta updates using portsnap{{cite web|title=Secure FreeBSD ports tree updating|url=http://www.daemonology.net/portsnap/}} since November 2005.{{cite web|title=FreeBSD 6.0-RELEASE Announcement|url=http://www.freebsd.org/releases/6.0R/announce.html}} Given FreeBSD's traditional stance of focusing on source code updates, no method of delta binary updates currently exists.
= Google =
Google refers to delta updates as "smart updates." This has been implemented in Google's Android operating system devices that run on Android 2.3 or above. Google engineers have estimated that smart updates would be only about one third the size of a full update on average.{{Citation needed|date=September 2022}}
Google's open source project Chromium requires frequent updates to narrow the window of vulnerability.{{cite web|title=Smaller is faster (and safer too)|url=https://blog.chromium.org/2009/07/smaller-is-faster-and-safer-too.html}} It uses a disassembly-based diffing algorithm called "courgette" to reduce diff size of two binary executable files, which reduces the diff patch from 6.7% (bsdiff) to 0.76% (bsdiff + courgette) for one version update.{{cite web|title=Software Updates: Courgette|url=https://dev.chromium.org/developers/design-documents/software-updates-courgette}} The technology helped Chrome to push its updates to 100% of users in less than 10 days.
App APK updates in Android's Play Store use bsdiff since 2016, a new efficient delta update algorithm introduced in 2003. [https://venturebeat.com/2016/07/22/google-plays-new-delta-algorithm-reduces-size-of-android-app-updates/ Google Play’s new delta algorithm reduces size of Android app updates]
= Apple iOS =
Apple's iOS is also capable of delta updates for operating system{{Citation needed|reason=Primary source does not indicate delta updates are used in OS updates|date=August 2022}} and application updates to reduce bandwidth usage. {{Cite web|title = Technical Q&A QA1779: Reducing Download Size for iOS App Updates|url = https://developer.apple.com/library/ios/qa/qa1779/_index.html|website = developer.apple.com|accessdate = 2015-07-07}}
Over-the-air software updates
Over-the-air (OTA) software updates have been used widely across many mobile devices; Apple iOS, Google Android, Microsoft Windows Phone 8, and BlackBerry 10.{{Citation needed|date=September 2022}}