commercialhaskell/stack

Optionally cache Git object files in Pantry directory

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#4,758 opened on Apr 21, 2019

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help wantednewcomer friendlytype: discusstype: enhancementtype: performance

Description

Setting milestone to P1 to ensure we decide on this before the Stack 2.0 release.

I was unaware until recently of the GIT_OBJECT_DIRECTORY environment variable, described at https://git-scm.com/book/en/v2/Git-Internals-Environment-Variables. IIUC, we can set this environment variable to a shared directory inside the pantry directory, and cache repository information across usages.

Advantages:

  • Don't need to reclone the entire history of a repo when switching to a slightly later commit
  • The current inefficiency of using multiple subdirectories from a single repo will mostly disappear

Disadvantages:

  • Adds lots of additional storage

The disadvantage can be addressed with a future feature of some gc command to Stack, which is actually the topic of a likely GSoC project.

CC @borsboom and @qrilka for feedback.

Contributor guide

Tech stack
None
Domain
build systemperformance
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.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Familiarity with Git internalsKnowledge of Stack's pantry directory
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate the use of GIT OBJECT DIRECTORY in Stack's git operations. Look at the pantry module (e.g., src/Pantry/...) and how repos are cloned and cached. Review the comments from @borsboom and @qrilka for additional context. Consider implementing a config option to enable this caching behavior.