Rsync algorithm - Revision history

JohnyDog: merged to rsync

2004-11-18T01:45:31Z

merged to rsync

← Previous revision		Revision as of 01:45, 18 November 2004
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	~~{{merge}}~~ [[rsync]]		#REDIRECT [[rsync]]

	The '''rsync algorithm''' is an [[algorithm]] (invented by [[Australia]]n computer programmer [[Andrew Tridgell]]) for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility.

	The recipient splits its copy of the file into fixed-size non-overlapping chunks, say of size ''S'', and computes
	two checksums of each chunk: the [[MD4]] [[hash function\|hash]], and a weaker 'rolling checksum'. It sends these checksums to the sender.

	The sender computes the rolling checksum for ''every'' chunk of size ''S'' in its own version of the file, even overlapping chunks. This can be done efficiently because of a special property of the rolling checksum:
	If the rolling checksum of bytes ''n'' through ''n+S-1''
	is ''R'', it is easy to compute the rolling checksum of bytes ''n+1'' through ''n+S'' from ''R'', byte ''n'', and byte ''n+S''; the intervening bytes need not be reexamined.

	The sender then compares its rolling checksums with the set sent by the recipient to determine if there are any matches. If there are, the match is verified by computing the MD4 checksum for the matching block and comparing it with the MD4 checksum sent by the recipient.

	The sender then sends the recipient the parts of its file that didn't match any of the recipient's blocks, and assembly instructions about how to merge these blocks into the recipient's version to create a file identical to the sender's copy.

	If the sender's and recipient's versions of the file have many sections in common, relatively little data needs to be transferred to synchronize the two files.

	== See also ==

	* [[xdelta]][http://xdelta.org/] - alternative implementation of file differencing and [[delta compression]]

	== External links ==

	* http://rsync.samba.org/tech_report/node2.html - the algorithm

	[[Category:Algorithms]]

Antaeus Feldspar: merge notice

2004-10-26T17:56:59Z

merge notice

← Previous revision		Revision as of 17:56, 26 October 2004
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			{{merge}} [[rsync]]

	The '''rsync algorithm''' is an [[algorithm]] (invented by [[Australia]]n computer programmer [[Andrew Tridgell]]) for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility.		The '''rsync algorithm''' is an [[algorithm]] (invented by [[Australia]]n computer programmer [[Andrew Tridgell]]) for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility.

Bryan Derksen: rm redundant category

2004-07-06T06:36:26Z

rm redundant category

← Previous revision		Revision as of 06:36, 6 July 2004
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⚫	[[Category:~~Computer science~~]]
	[[Category:Algorithms]]
	The '''rsync algorithm''' is an [[algorithm]] (invented by [[Australia]]n computer programmer [[Andrew Tridgell]]) for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility.		The '''rsync algorithm''' is an [[algorithm]] (invented by [[Australia]]n computer programmer [[Andrew Tridgell]]) for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility.

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	If the sender's and recipient's versions of the file have many sections in common, relatively little data needs to be transferred to synchronize the two files.		If the sender's and recipient's versions of the file have many sections in common, relatively little data needs to be transferred to synchronize the two files.

		⚫	== See also ==


⚫	== See ~~Also~~ ==

	* [[xdelta]][http://xdelta.org/] - alternative implementation of file differencing and [[delta compression]]		* [[xdelta]][http://xdelta.org/] - alternative implementation of file differencing and [[delta compression]]

	== External ~~Links~~ ==		== External links ==

	* http://rsync.samba.org/tech_report/node2.html - the algorithm		* http://rsync.samba.org/tech_report/node2.html - the algorithm

		⚫	[[Category:Algorithms]]

217.26.164.170: added link to xdelta

2004-06-22T07:18:41Z

added link to xdelta

← Previous revision		Revision as of 07:18, 22 June 2004
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			== See Also ==

			* [[xdelta]][http://xdelta.org/] - alternative implementation of file differencing and [[delta compression]]

	== External Links ==		== External Links ==

Dominus: Category:Computer science

2004-05-31T10:45:58Z

Category:Computer science

← Previous revision		Revision as of 10:45, 31 May 2004
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			[[Category:Computer science]]
			[[Category:Algorithms]]
	The '''rsync algorithm''' is an [[algorithm]] (invented by [[Australia]]n computer programmer [[Andrew Tridgell]]) for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility.		The '''rsync algorithm''' is an [[algorithm]] (invented by [[Australia]]n computer programmer [[Andrew Tridgell]]) for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility.

Cool blade at 05:09, 25 August 2003

2003-08-25T05:09:18Z

← Previous revision		Revision as of 05:09, 25 August 2003
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	The '''rsync algorithm''' is an [[algorithm]] for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility ~~invented by [[Australia]]n computer programmer [[Andrew Tridgell]]~~.		The '''rsync algorithm''' is an [[algorithm]] (invented by [[Australia]]n computer programmer [[Andrew Tridgell]]) for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility.

	The recipient splits its copy of the file into fixed-size non-overlapping chunks, say of size ''S'', and computes		The recipient splits its copy of the file into fixed-size non-overlapping chunks, say of size ''S'', and computes

Cool blade: Added link for Andrew Tridgell

2003-08-25T05:08:15Z

Added link for Andrew Tridgell

← Previous revision		Revision as of 05:08, 25 August 2003
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	The '''rsync algorithm''' is an [[algorithm]] for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility.		The '''rsync algorithm''' is an [[algorithm]] for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility invented by [[Australia]]n computer programmer [[Andrew Tridgell]].

	The recipient splits its copy of the file into fixed-size non-overlapping chunks, say of size ''S'', and computes		The recipient splits its copy of the file into fixed-size non-overlapping chunks, say of size ''S'', and computes

Dominus: elaborated, cleaned up language

2003-08-16T20:42:08Z

elaborated, cleaned up language

← Previous revision		Revision as of 20:42, 16 August 2003
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	'''~~Rsync~~ algorithm''' - an [[algorithm]] ~~that~~ [[rsync]] file transfer protocol and utility ~~use~~.		The '''rsync algorithm''' is an [[algorithm]] for efficiently transmitting a file across a communications link when the receiving computer already has a different version of the same file. It is used by the [[rsync]] file transfer protocol and utility.

			The recipient splits its copy of the file into fixed-size non-overlapping chunks, say of size ''S'', and computes
	The destination file is split into chunks, each of which is computed two checksums: a [[cryptographic hash]] and a rolling checksum. The rolling checksum has the property that if bytes ''n'' and ''n+k'' are known, the checksum of bytes ''n+1'' to ''n+k'' can be computed from these and the checksum of bytes ''n'' to ''n+k-1'' without knowing the intermediate bytes. The rolling checksum is computed for all chunk-sized contiguous blocks of the source file; any that match a destination chunk checksum are computed the cryptographic hash. All parts of the source file which don't match any chunk in the destination are transferred, and the file is reassembled.
			two checksums of each chunk: the [[MD4]] [[hash function\|hash]], and a weaker 'rolling checksum'. It sends these checksums to the sender.

			The sender computes the rolling checksum for ''every'' chunk of size ''S'' in its own version of the file, even overlapping chunks. This can be done efficiently because of a special property of the rolling checksum:
			If the rolling checksum of bytes ''n'' through ''n+S-1''
			is ''R'', it is easy to compute the rolling checksum of bytes ''n+1'' through ''n+S'' from ''R'', byte ''n'', and byte ''n+S''; the intervening bytes need not be reexamined.

			The sender then compares its rolling checksums with the set sent by the recipient to determine if there are any matches. If there are, the match is verified by computing the MD4 checksum for the matching block and comparing it with the MD4 checksum sent by the recipient.

			The sender then sends the recipient the parts of its file that didn't match any of the recipient's blocks, and assembly instructions about how to merge these blocks into the recipient's version to create a file identical to the sender's copy.

			If the sender's and recipient's versions of the file have many sections in common, relatively little data needs to be transferred to synchronize the two files.



			== External Links ==

	See also:
	* http://rsync.samba.org/tech_report/node2.html - the algorithm		* http://rsync.samba.org/tech_report/node2.html - the algorithm

The Anome: ...from these and the...

2002-11-12T13:21:32Z

...from these and the...

← Previous revision		Revision as of 13:21, 12 November 2002
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	'''Rsync algorithm''' - an [[algorithm]] that [[rsync]] file transfer protocol and utility use.		'''Rsync algorithm''' - an [[algorithm]] that [[rsync]] file transfer protocol and utility use.

	The destination file is split into chunks, each of which is computed two checksums: a [[cryptographic hash]] and a rolling checksum. The rolling checksum has the property that if bytes ''n'' and ''n+k'' are known, the checksum of bytes ''n+1'' to ''n+k'' can be computed from the checksum of bytes ''n'' to ''n+k-1'' without knowing the intermediate bytes. The rolling checksum is computed for all chunk-sized contiguous blocks of the source file; any that match a destination chunk checksum are computed the cryptographic hash. All parts of the source file which don't match any chunk in the destination are transferred, and the file is reassembled.		The destination file is split into chunks, each of which is computed two checksums: a [[cryptographic hash]] and a rolling checksum. The rolling checksum has the property that if bytes ''n'' and ''n+k'' are known, the checksum of bytes ''n+1'' to ''n+k'' can be computed from these and the checksum of bytes ''n'' to ''n+k-1'' without knowing the intermediate bytes. The rolling checksum is computed for all chunk-sized contiguous blocks of the source file; any that match a destination chunk checksum are computed the cryptographic hash. All parts of the source file which don't match any chunk in the destination are transferred, and the file is reassembled.

	See also:		See also:

PierreAbbat: source and destination mixed up

2002-11-12T12:45:58Z

source and destination mixed up

← Previous revision		Revision as of 12:45, 12 November 2002
Line 1:		Line 1:
	'''Rsync algorithm''' - an [[algorithm]] that [[rsync]] file transfer protocol and utility use.		'''Rsync algorithm''' - an [[algorithm]] that [[rsync]] file transfer protocol and utility use.

	The ~~source~~ file is split into chunks, each of which is computed two checksums: a [[cryptographic hash]] and a rolling checksum. The rolling checksum has the property that if bytes ''n'' and ''n+k'' are known, the checksum of bytes ''n+1'' to ''n+k'' can be computed from the checksum of bytes ''n'' to ''n+k-1'' without knowing the intermediate bytes. The rolling checksum is computed for all chunk-sized contiguous blocks of the ~~destination~~ file; any that match a ~~source~~ chunk checksum are computed the cryptographic hash. All ~~chunks~~ of the source file which don't match ~~anything~~ in the destination are transferred, and the file is reassembled.		The destination file is split into chunks, each of which is computed two checksums: a [[cryptographic hash]] and a rolling checksum. The rolling checksum has the property that if bytes ''n'' and ''n+k'' are known, the checksum of bytes ''n+1'' to ''n+k'' can be computed from the checksum of bytes ''n'' to ''n+k-1'' without knowing the intermediate bytes. The rolling checksum is computed for all chunk-sized contiguous blocks of the source file; any that match a destination chunk checksum are computed the cryptographic hash. All parts of the source file which don't match any chunk in the destination are transferred, and the file is reassembled.

	See also:		See also: