{"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":"Scheduled & Timezone-Aware Delivery","originalText":"Scheduled & Timezone-Aware Delivery","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":420,"height":68,"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":145.3,"width":380,"height":23.400000000000002,"fontSize":18,"fontFamily":1,"text":"Scheduling Service:","originalText":"Scheduling Service:","textAlign":"left","verticalAlign":"middle","containerId":"shape-2","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":2}},{"angle":0,"strokeColor":"#9180ac","backgroundColor":"#f4effb","fillStyle":"solid","strokeWidth":1.5,"strokeStyle":"solid","roughness":0.7,"opacity":100,"version":1,"versionNonce":1,"isDeleted":false,"groupIds":["step-3"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-5"}],"updated":0,"link":null,"locked":false,"id":"shape-4","type":"rectangle","seed":333,"x":30,"y":216,"width":420,"height":106.2,"customData":{"revealStep":3}},{"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-3"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-5","type":"text","seed":406,"x":50,"y":234,"width":380,"height":70.2,"fontSize":18,"fontFamily":1,"text":"Notifications with schedule_at are\nstored in a scheduled queue, not sent\nimmediately.","originalText":"Notifications with schedule_at are\nstored in a scheduled queue, not sent\nimmediately.","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":420,"height":68,"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":369.5,"width":380,"height":23.400000000000002,"fontSize":18,"fontFamily":1,"text":"Implementation options:","originalText":"Implementation options:","textAlign":"left","verticalAlign":"middle","containerId":"shape-6","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":4}},{"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-5"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-9"}],"updated":0,"link":null,"locked":false,"id":"shape-8","type":"rectangle","seed":625,"x":30,"y":440.2,"width":516.67564,"height":153,"customData":{"revealStep":5}},{"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-5"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-9","type":"text","seed":698,"x":50,"y":458.2,"width":476.67564000000004,"height":117,"fontSize":18,"fontFamily":1,"text":"Option A: Database polling\nStore in scheduled_notifications table\nCron job queries every 30s:\nWHERE send_at <= NOW() AND status=PENDING\nSimple but polling = wasteful","originalText":"Option A: Database polling\nStore in scheduled_notifications table\nCron job queries every 30s:\nWHERE send_at <= NOW() AND status=PENDING\nSimple but polling = wasteful","textAlign":"left","verticalAlign":"middle","containerId":"shape-8","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":5}},{"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-6"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-11"}],"updated":0,"link":null,"locked":false,"id":"shape-10","type":"rectangle","seed":771,"x":30,"y":618.2,"width":458.806,"height":153,"customData":{"revealStep":6}},{"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-6"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-11","type":"text","seed":844,"x":50,"y":636.2,"width":418.806,"height":117,"fontSize":18,"fontFamily":1,"text":"Option B: Redis sorted set ⭐\nZADD scheduled:{shard} send_time notif_id\nWorker: ZRANGEBYSCORE 0 {now}\nO(log N) operations, no polling waste\nShard by user_id % 64 for scale","originalText":"Option B: Redis sorted set ⭐\nZADD scheduled:{shard} send_time notif_id\nWorker: ZRANGEBYSCORE 0 {now}\nO(log N) operations, no polling waste\nShard by user_id % 64 for scale","textAlign":"left","verticalAlign":"middle","containerId":"shape-10","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":6}},{"angle":0,"strokeColor":"#9180ac","backgroundColor":"#f4effb","fillStyle":"solid","strokeWidth":1.5,"strokeStyle":"solid","roughness":0.7,"opacity":100,"version":1,"versionNonce":1,"isDeleted":false,"groupIds":["step-7"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-13"}],"updated":0,"link":null,"locked":false,"id":"shape-12","type":"rectangle","seed":917,"x":30,"y":796.2,"width":420,"height":129.60000000000002,"customData":{"revealStep":7}},{"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-7"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-13","type":"text","seed":990,"x":50,"y":814.2,"width":380,"height":93.60000000000001,"fontSize":18,"fontFamily":1,"text":"Option C: Kafka delayed topics\nNot natively supported\nCan simulate with consumer that holds\nmessages until send_time","originalText":"Option C: Kafka delayed topics\nNot natively supported\nCan simulate with consumer that holds\nmessages until send_time","textAlign":"left","verticalAlign":"middle","containerId":"shape-12","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":7}},{"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-8"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-15"}],"updated":0,"link":null,"locked":false,"id":"shape-14","type":"rectangle","seed":1063,"x":30,"y":950.8000000000001,"width":420,"height":68,"customData":{"revealStep":8}},{"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-8"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-15","type":"text","seed":1136,"x":50,"y":973.1,"width":380,"height":23.400000000000002,"fontSize":18,"fontFamily":1,"text":"Timezone-Aware \"Best Time to Send\":","originalText":"Timezone-Aware \"Best Time to Send\":","textAlign":"left","verticalAlign":"middle","containerId":"shape-14","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":8}},{"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-9"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-17"}],"updated":0,"link":null,"locked":false,"id":"shape-16","type":"rectangle","seed":1209,"x":30,"y":1043.8000000000002,"width":420,"height":68,"customData":{"revealStep":9}},{"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-9"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-17","type":"text","seed":1282,"x":50,"y":1066.1000000000001,"width":380,"height":23.400000000000002,"fontSize":18,"fontFamily":1,"text":"\"Send at 9 AM user's local time\"","originalText":"\"Send at 9 AM user's local time\"","textAlign":"left","verticalAlign":"middle","containerId":"shape-16","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":9}},{"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-10"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-19"}],"updated":0,"link":null,"locked":false,"id":"shape-18","type":"rectangle","seed":1355,"x":30,"y":1136.8000000000002,"width":552.50788,"height":153,"customData":{"revealStep":10}},{"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-10"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-19","type":"text","seed":1428,"x":50,"y":1154.8000000000002,"width":512.50788,"height":117,"fontSize":18,"fontFamily":1,"text":"1. Group users by timezone\nUTC-8 (PST): 50M users → 9 AM = 5 PM UTC\nUTC-5 (EST): 80M users → 9 AM = 2 PM UTC\nUTC+0 (GMT): 30M users → 9 AM = 9 AM UTC\nUTC+5:30 (IST): 100M users → 9 AM = 3:30 AM UTC","originalText":"1. Group users by timezone\nUTC-8 (PST): 50M users → 9 AM = 5 PM UTC\nUTC-5 (EST): 80M users → 9 AM = 2 PM UTC\nUTC+0 (GMT): 30M users → 9 AM = 9 AM UTC\nUTC+5:30 (IST): 100M users → 9 AM = 3:30 AM UTC","textAlign":"left","verticalAlign":"middle","containerId":"shape-18","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":10}},{"angle":0,"strokeColor":"#9180ac","backgroundColor":"#f4effb","fillStyle":"solid","strokeWidth":1.5,"strokeStyle":"solid","roughness":0.7,"opacity":100,"version":1,"versionNonce":1,"isDeleted":false,"groupIds":["step-11"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-21"}],"updated":0,"link":null,"locked":false,"id":"shape-20","type":"rectangle","seed":1501,"x":30,"y":1314.8000000000002,"width":450.73516,"height":106.2,"customData":{"revealStep":11}},{"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-11"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-21","type":"text","seed":1574,"x":50,"y":1332.8000000000002,"width":410.73516,"height":70.2,"fontSize":18,"fontFamily":1,"text":"2. Schedule separate batch per TZ bucket\n3. Each batch enqueued at the right UTC\ntime for that timezone","originalText":"2. Schedule separate batch per TZ bucket\n3. Each batch enqueued at the right UTC\ntime for that timezone","textAlign":"left","verticalAlign":"middle","containerId":"shape-20","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":11}},{"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-12"],"frameId":null,"roundness":null,"boundElements":[{"type":"text","id":"shape-23"}],"updated":0,"link":null,"locked":false,"id":"shape-22","type":"rectangle","seed":1647,"x":30,"y":1446.0000000000002,"width":424.53832,"height":82.80000000000001,"customData":{"revealStep":12}},{"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-12"],"frameId":null,"roundness":null,"boundElements":null,"updated":0,"link":null,"locked":false,"id":"shape-23","type":"text","seed":1720,"x":50,"y":1464.0000000000002,"width":384.53832,"height":46.800000000000004,"fontSize":18,"fontFamily":1,"text":"~24 timezone buckets\nStagger slightly to avoid thundering herd","originalText":"~24 timezone buckets\nStagger slightly to avoid thundering herd","textAlign":"left","verticalAlign":"middle","containerId":"shape-22","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":12}}],"appState":{"viewBackgroundColor":"#fbfbf8","gridSize":null},"files":{}}