ACR Storage - ACR Supports Large-Scale Repositories and Artifacts without Data Plane API Issues

# Overview

### Description
This roadmap item tracks ACR's work to ensure that a single ACR registry can support a large number of repositories with a large number of artifacts in each repository, without degradation in Data Plane API List and GET operations.

As part of this work, ACR will be publishing supported limits for:
- **Number of repositories** per registry
- **Number of artifacts** (manifests) per repository
- **Number of tags** per repository
- **Number of referrers** per artifact

### Context
As customers store more container images, Helm charts, and OCI artifacts in their registries, the number of repositories, artifacts, tags, and referrers per artifact continues to grow. Some customers manage registries with tens of thousands of repositories and hundreds of thousands of artifacts per repository.

### Problem Statement
Currently:
- Data Plane API operations such as listing repositories, listing tags, listing referrers, and GET operations on manifests and blobs can experience performance issues or timeouts when a registry contains a very large number of repositories or when individual repositories contain a very large number of artifacts, tags, or referrers.
- Customers with large-scale registries may encounter API errors, slow responses, or incomplete results when querying their registries.
- There are no published limits for the number of repositories, artifacts, tags, or referrers that a single registry can reliably support.
- This limits the practical usability of ACR for customers with large-scale artifact storage needs.

### Proposal
ACR will improve the scalability and performance of Data Plane API List and GET operations to ensure reliable and performant behavior even for registries with very large numbers of repositories, artifacts, tags, and referrers. ACR will also publish supported limits so that customers can plan their registry usage accordingly.

This work complements ACR's ongoing storage scale improvements.

### Related Issues
- ACR registries support PiB-scale storage limits: https://github.com/Azure/acr/issues/853

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# Milestones

### 🚧 In Progress
- [ ] Improvements to Data Plane API List/GET performance at large scale
- [ ] Validation at target scale thresholds
- [ ] Published limits for repositories, artifacts, tags, and referrers

### ⏳ GA
- [ ] General Availability of large-scale repository support with published limits

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# Status
**Active development** — follow this issue for milestone updates.