cockroachdb/cockroach

kv: expose byte limits through kv.Txn API

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#63,661 opened on Apr 14, 2021

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A-kv-clientC-enhancementT-kvhelp wanted

Description

Currently, the kv.Txn API exposes key limits through the maxRows arg (which is poorly named) of its Scan and ReverseScan methods, but it does not expose an ability to impose a byte limit. Byte limits were introduced into the kv proto API in https://github.com/cockroachdb/cockroach/commit/417aa0843dbc1b816d7326cf223e141aa817bd30. However, because of this limitation in the kv.Txn API, users who want byte limits need to construct raw roachpb protos to be able to use them.

We should add byte limits to the kv.Txn and kv.DB API.

Jira issue: CRDB-6709

Contributor guide

Tech stack
go
Domain
backenddatabase
Issue type
feature
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.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Go programmingdistributed systems basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
The issue requests adding byte limits to the `kv.Txn` and `kv.DB` API. Begin by examining the existing implementation of key limits via `maxRows` in the `Scan` and `ReverseScan` methods. Review the referenced commit (417aa0843dbc1b816d7326cf223e141aa817bd30) which introduced byte limits in the kv proto API. Understand how byte limits are currently used at the proto level, then design an analogous interface at the `kv.Txn` level. Check the `roachpb` package for the proto definitions. There are no linked PRs, so the work is still open.