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Design a session management system for a web application handling 100,000 concurrent users.

Redis is the perfect fit: 1) Session data: HSET session:{sessionId} userId 42 role ADMIN lastActivity 1234567890. 2) TTL: EXPIRE session:{sessionId} 1800 (30 min idle timeout). 3) Reset on activity: EXPIRE session:{sessionId} 1800 on every request. 4) Lookup: HGETALL session:{sessionId} on each request. 5) Invalidation on logout: DEL session:{sessionId}. 6) Scale: Redis Cluster with 3 masters (300

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