SDCH (Shared Dictionary Compression for HTTP) is a data compression algorithm created by Google, based on VCDIFF (RFC 3284).
SDCH achieves its effectiveness by using pre-negotiated dictionaries to "warm up" its internal state prior to encoding or decoding.
[1][2] SDCH compression was removed from Google Chrome, and other Chromium products, in version 59 (2017-06-05).
This created extra effort in production to keep the dictionaries fresh and reduced its applicability.
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