rfc9659v2.txt		rfc9659.txt
	Internet Engineering Task Force (IETF) N. Jaju, Ed.		Internet Engineering Task Force (IETF) N. Jaju, Ed.
	Request for Comments: 9659 Google		Request for Comments: 9659 Google
	Updates: 8878 F. Handte, Ed.		Updates: 8878 W. F. Handte, Ed.
	Category: Informational Meta Platforms, Inc.		Category: Informational Meta Platforms, Inc.
	ISSN: 2070-1721 September 2024		ISSN: 2070-1721 September 2024
	Window Sizing for Zstandard Content Encoding		Window Sizing for Zstandard Content Encoding
	Abstract		Abstract
	Deployments of Zstandard, or "zstd", can use different window sizes		Deployments of Zstandard, or "zstd", can use different window sizes
	to limit memory usage during compression and decompression. Some		to limit memory usage during compression and decompression. Some
	browsers and user agents limit window sizes to mitigate memory usage		browsers and user agents limit window sizes to mitigate memory usage
	skipping to change at line 75 ¶		skipping to change at line 75 ¶
	compression mechanism similar to gzip. When used with HTTP, the		compression mechanism similar to gzip. When used with HTTP, the
	"zstd" content coding token signals to the decoder that the content		"zstd" content coding token signals to the decoder that the content
	is Zstandard-compressed.		is Zstandard-compressed.
	An important property of Zstandard-compressed content is its		An important property of Zstandard-compressed content is its
	Window_Size ([RFC8878], Section 3.1.1.1.2), which describes the		Window_Size ([RFC8878], Section 3.1.1.1.2), which describes the
	maximum distance for back-references and therefore how much of the		maximum distance for back-references and therefore how much of the
	content must be kept in memory during decompression.		content must be kept in memory during decompression.
	The minimum Window_Size is 1 KB. The maximum Window_Size is (1<<41)		The minimum Window_Size is 1 KB. The maximum Window_Size is (1<<41)
	+ 7*(1<<38) bytes, which is 3.75 TB. Larger Window_Size values tend		+ 7*(1<<38) bytes, where "<<" denotes a bitwise left shift, which is
	to improve the compression ratio but at the cost of increased memory		3.75 TB. Larger Window_Size values tend to improve the compression
	usage.		ratio but at the cost of increased memory usage.
	To protect against unreasonable memory usage, some browsers and user		To protect against unreasonable memory usage, some browsers and user
	agents limit the maximum Window_Size they will handle. This causes		agents limit the maximum Window_Size they will handle. This causes
	failures to decode responses when the content is compressed with a		failures to decode responses when the content is compressed with a
	larger Window_Size than the recipient allows, leading to decreased		larger Window_Size than the recipient allows, leading to decreased
	interoperability.		interoperability.
	[RFC8878], Section 3.1.1.1.2 recommends that decoders support a		[RFC8878], Section 3.1.1.1.2 recommends that decoders support a
	Window_Size of up to 8 MB, and that encoders not generate frames		Window_Size of up to 8 MB, and that encoders not generate frames
	using a Window_Size larger than 8 MB. However, it imposes no		using a Window_Size larger than 8 MB. However, it imposes no
End of changes. 2 change blocks.
	4 lines changed or deleted		4 lines changed or added
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