Add Redis cache layer with TTL strategies

[Otaiki1]

Context

Frequently read data (active raffle list, raffle detail, leaderboard) should be cached in Redis to reduce DB load and latency. ARCHITECTURE defines TTL and invalidation per data type.

Goal

• Implement CacheService that wraps Redis (e.g. ioredis or NestJS cache module).
• Provide get/set with TTL for: active raffles (30s), raffle detail (10s), leaderboard (60s), user profile (30s), platform stats (5min).
• Invalidate on relevant events (e.g. on RaffleCreated invalidate active list; on RaffleFinalized invalidate leaderboard).

Contributor guide

1. Directory: indexer/
2. Add src/cache/cache.service.ts and cache.module.ts. Use key pattern e.g. raffle:active, raffle:{id}, leaderboard, user:{address}, stats:platform.
3. Wire invalidation in processors (after DB write) or in API layer when writing.
4. Document TTL and invalidation in code or README; add Redis to docker-compose if present.

References

• ARCHITECTURE.md — Cache TTL Strategy; cache module.

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[Enemuo-debug]

@Enemuo-debug has applied to work on this issue as part of the Stellar Wave Program's 2nd wave.

Caching is one of the popular system design patterns for faster reads, and it also makes use of either TTL or another paging system. In this wave, I'd love it if allowed to work on this

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Congratulations, @Enemuo-debug! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on February 26, 2026.

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This issue has been marked as completed by a Drips Wave moderator for @Enemuo-debug as part of the Stellar Wave Program's 2nd Wave 🥳

Moderator's reason: [Auto-assessed] The contributor implemented the Redis cache layer with the specified TTL strategies and event-driven invalidation logic in PR #59. The PR has been merged and fully addresses the requirements of the issue, including documentation and unit tests.

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ℹ️ Note: This issue was marked complete via moderation. Points were issued even though the GitHub issue remains open.