{"type":"excalidraw","version":2,"source":"https://AwesomeSystemDesign.dev","elements":[{"angle":0,"strokeColor":"#628572","backgroundColor":"#edf5ee","fillStyle":"solid","strokeWidth":1.5,"strokeStyle":"solid","roughness":0.7,"opacity":100,"version":1,"versionNonce":1,"isDeleted":false,"groupIds":["step-1"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-1"}],"updated":0,"link":null,"locked":false,"id":"shape-0","type":"rectangle","seed":41,"x":30,"y":30,"width":420,"height":68,"customData":{"revealStep":1}},{"angle":0,"strokeColor":"#394557","backgroundColor":"transparent","fillStyle":"solid","strokeWidth":1.5,"strokeStyle":"solid","roughness":0.7,"opacity":100,"version":1,"versionNonce":1,"isDeleted":false,"groupIds":["step-1"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-1","type":"text","seed":114,"x":50,"y":52.3,"width":380,"height":23.400000000000002,"fontSize":18,"fontFamily":1,"text":"Automatic Hold Release","originalText":"Automatic Hold Release","textAlign":"left","verticalAlign":"middle","containerId":"shape-0","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":1}},{"angle":0,"strokeColor":"#a68a53","backgroundColor":"#fff7e6","fillStyle":"solid","strokeWidth":1.5,"strokeStyle":"solid","roughness":0.7,"opacity":100,"version":1,"versionNonce":1,"isDeleted":false,"groupIds":["step-2"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-3"}],"updated":0,"link":null,"locked":false,"id":"shape-2","type":"rectangle","seed":187,"x":30,"y":123,"width":612.57172,"height":106.2,"customData":{"revealStep":2}},{"angle":0,"strokeColor":"#394557","backgroundColor":"transparent","fillStyle":"solid","strokeWidth":1.5,"strokeStyle":"solid","roughness":0.7,"opacity":100,"version":1,"versionNonce":1,"isDeleted":false,"groupIds":["step-2"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-3","type":"text","seed":260,"x":50,"y":141,"width":572.57172,"height":70.2,"fontSize":18,"fontFamily":1,"text":"T+0:00 User holds seat S2 (Redis SET NX EX 420)\nT+5:30 User still browsing... (2:30 left on countdown)\nT+7:00 Redis TTL fires → key \"seat_hold:evt:S2\" DELETED","originalText":"T+0:00 User holds seat S2 (Redis SET NX EX 420)\nT+5:30 User still browsing... (2:30 left on countdown)\nT+7:00 Redis TTL fires → key \"seat_hold:evt:S2\" 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+ Action:","originalText":"Detection + Action:","textAlign":"left","verticalAlign":"middle","containerId":"shape-4","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":3}},{"angle":0,"strokeColor":"#6577aa","backgroundColor":"#eef1fc","fillStyle":"solid","strokeWidth":1.5,"strokeStyle":"solid","roughness":0.7,"opacity":100,"version":1,"versionNonce":1,"isDeleted":false,"groupIds":["step-4"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-7"}],"updated":0,"link":null,"locked":false,"id":"shape-6","type":"rectangle","seed":479,"x":30,"y":347.2,"width":587.3861200000001,"height":199.8,"customData":{"revealStep":4}},{"angle":0,"strokeColor":"#394557","backgroundColor":"transparent","fillStyle":"solid","strokeWidth":1.5,"strokeStyle":"solid","roughness":0.7,"opacity":100,"version":1,"versionNonce":1,"isDeleted":false,"groupIds":["step-4"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-7","type":"text","seed":552,"x":50,"y":365.2,"width":547.3861200000001,"height":163.8,"fontSize":18,"fontFamily":1,"text":"Option A: Redis Keyspace Notifications\nCONFIG SET notify-keyspace-events Ex\nSUBSCRIBE __keyevent@0__:expired\n→ Listener receives: \"seat_hold:evt-taylor:FLOOR-A-R1-S2\"\n→ Seat Inventory Svc: UPDATE seat status = 'available'\n→ WebSocket broadcast: seat S2 now available\n→ Waitlist check: offer seat to first waitlister","originalText":"Option A: Redis Keyspace Notifications\nCONFIG SET notify-keyspace-events Ex\nSUBSCRIBE __keyevent@0__:expired\n→ Listener receives: \"seat_hold:evt-taylor:FLOOR-A-R1-S2\"\n→ Seat Inventory Svc: UPDATE seat status = 'available'\n→ WebSocket broadcast: seat S2 now available\n→ Waitlist check: offer seat to first 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B: Background Sweeper (belt +\nsuspenders)\nEvery 30 seconds:\nSELECT * FROM seats\nWHERE status = 'held'\nAND hold_expires_at < NOW();\n→ Update status to 'available'\n→ Catches any Redis notification misses","originalText":"Option B: Background Sweeper (belt +\nsuspenders)\nEvery 30 seconds:\nSELECT * FROM seats\nWHERE status = 'held'\nAND hold_expires_at < NOW();\n→ Update status to 'available'\n→ Catches any Redis notification 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BOTH: Redis notifications for speed, sweeper for safety","originalText":"Use BOTH: Redis notifications for speed, sweeper for safety","textAlign":"left","verticalAlign":"middle","containerId":"shape-10","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":6}}],"appState":{"viewBackgroundColor":"#fbfbf8","gridSize":null},"files":{}}