envoyproxy/envoy

Use per-resource version to avoid hashing protos in xDS updates

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#14,367 opened on Dec 10, 2020

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area/perfarea/xdsenhancementhelp wanted

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Description

xDS APIs today use hashes of incoming resource protos to compare against the existing resource version when determining if any updates needs to be made. This is expensive (we're measuring ~8% CPU in some workloads), since we need to flatten to text for Envoy-canonical proto hashing (protobuf doesn't do its own hashing).

It's also unnecessary when delivered resources are provided via delta xDS (or even SotW when we encapsulate in a Resource object). In these cases, we have per-resource versioning that can play the same role as the hash without any computational requirement.

Opening this issue to track potential optimization work here. I think the main value is for SotW+Resource wrapper, since delta xDS will be pushing the diffing to the server-side anyway, so there isn't a lot of saving.

FWIW, I think we had a thread on this ages ago but I can't spot it.

Contributor guide

Research direction
Understand the current hashing mechanism in xDS updates (look for hash computation in the codebase, e.g., in source/common/grpc/). Then identify where per resource version information is available (e.g., in delta xDS or Resource objects). Consider how to modify the update logic to use version instead of hash. The change likely affects the xDS subscription and config update pipeline. Start by examining how resources are compared in existing code and trace the flow from SotW and delta updates.
Tech stack
cpp
Domain
backendnetworking
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C++Protocol BuffersEnvoy xDS
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30