envoyproxy/envoy

redis: Send TRYAGAIN if key not found in MGET request

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#31,038 opened on Nov 24, 2023

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area/redisenhancementhelp wanted

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Description

Title: Send TRYAGAIN if key not found in MGET request

Description:

When an MGET request is issued, redis_proxy send GET request on each key and collects the response here.

As per redis cluster spec here , if a hash slot is in migrating state and if any of the keys are not found, the response to the downstream client should be TRYAGAIN.

We run redis_proxy on server side, however it seems this part of the code is common if redis_proxy is executed on client or server side. In this case the redis server needs to respond with TRYAGAIN for the MGET request but today individual GET request prohibits this behavior.

Contributor guide

Research direction
Examine the MGET handling in command splitter impl.cc (lines 278-310). Understand how individual GET responses are aggregated and how the cluster slot state is tracked. Modify the logic to detect if a key is not found due to a migrating slot and return TRYAGAIN instead of empty response.
Tech stack
cpp
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
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++
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60