Re: [quicwg/base-drafts] Describe QPACK Feedback mechanisms (#1410)

[afrind <[e-mail]>]

afrind commented on this pull request.



>  ~~~~~~~~~~
-{:#fig-size-sync title="Table Size Synchronize"}
+{:#fig-size-sync title="Table State Synchronize"}
+
+A decoder SHOULD emit a Table State Synchronize after receiving new dynamic
+table entries if the most recently inserted entry was not the Largest Reference

Since we are going to remove length prefix, 'entries' here is vague.  How many entries?  I think in the  common case the inserts will get processed before the references, but a blocking decoder would not want to send TSS without delaying to check for a referencing header block, so perhaps the SHOULD here is misleading?

Maybe it would help to describe the tradeoff -

A decoder chooses when to emit TSS instructions.  Emitting a TSS after adding each new dynamic table entry will provide the most timely feedback to the encoder, but could be redundant with other decoder feedback.  By delaying a TSS, a decoder might be able to coalesce multiple TSS instructions, or replace them entirely with Header Acknowledgements.  However, delaying too long may lead to compression inefficiencies if the encoder waits for an entry to be acknowledged before using it.

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