docs(redis): explain cache tag keys without TTL filling Redis

[Soner (shyim)]

Summary

Documents a real customer case: a cache Redis that kept running out of memory even though volatile-lru was configured correctly.

• Shopware's redis_tag_aware cache adapter stores a tag index in Redis (one set per cache tag) so related entries can be invalidated together. These tag-index keys have no TTL.
• When cached items expire, their entries in the tag sets are not removed, leaving orphaned members. Because volatile-lru only evicts keys with a TTL, these persistent sets accumulate and can never be evicted — under high cache churn Redis eventually has too little evictable data left and returns OOM errors.
• A full cache Redis is healthy; the real problem is having too many keys without a TTL. Symfony does not prune the tag sets automatically, so operators must do it on a schedule.

Changes:

• guides/hosting/performance/caches.md — new self-contained section "Cache tags and keys without a TTL", written for a junior dev/DevOps reader: a TTL + eviction primer, a before/after walkthrough of how orphaned tags accumulate, a redis-cli INFO keyspace self-diagnosis, and a scheduled-cleanup fix.
• guides/hosting/infrastructure/redis.md — a cross-linked warning in the ephemeral-data section where volatile-lru is recommended.
• .wordlist.txt — added evictable and OOM.

Related links

• Cleanup tooling: FroshTools (frosh:redis-tag:cleanup) and shopware-redis-cli-helper.
• Symfony RedisTagAwareAdapter.

Checklist

• I reviewed affected links, code samples, and cross-references, including PageRef references where relevant.
• I added or updated redirects in .gitbook.yaml if pages were moved, renamed, or deleted.
• I updated .wordlist.txt (and sorted it) if spellcheck flags new legitimate terms.
• Any required dependent changes in downstream modules have already been merged and published.
• This pull request is ready for review.

Notes

shopware-redis-cli-helper currently lives under a personal GitHub account. If linking a personal repo from official docs is undesirable, I can drop it and keep only the FroshTools reference.

[shopware-dev-docs-connector]

Developer Docs healthcheck

Status: Completed with success.
Repository: shopware/docs
Commit: 60ac282
Preview: https://developer-documentation-9ndekhcn3-shopware-frontends.vercel.app
Workflow run: #4329

[Copilot]

Pull request overview

Adds operational documentation to help operators diagnose and prevent Redis OOM conditions caused by persistent (no-TTL) tag-index keys created by Symfony/Shopware’s tag-aware Redis cache adapter, and cross-links the guidance from the Redis infrastructure page. Also updates the spellcheck allowlist for newly introduced terms.

Changes:

• Added a new section explaining how tag-index sets without TTL can accumulate and prevent volatile-lru from freeing memory.
• Added a warning callout in the Redis “Ephemeral data” section linking to the new cache-tag guidance.
• Added OOM and evictable to .wordlist.txt for spellcheck.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
guides/hosting/performance/caches.md	Adds a new “Cache tags and keys without a TTL” section with diagnosis and cleanup guidance.
guides/hosting/infrastructure/redis.md	Adds a warning callout about no-TTL tag-index keys and links to the cache-tag section.
.wordlist.txt	Adds OOM and evictable to the spellcheck wordlist.

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[Micha Hobert (Isengo1989)]

Thx for the PR Soner (@shyim) 👍

I believe this is very helpful for understanding the quirks of a key-value cache. Often, it is a black box to many, and we should keep documenting like this 💯