{"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":449.20876000000004,"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":409.20876000000004,"height":23.400000000000002,"fontSize":18,"fontFamily":1,"text":"SELECT ... FOR UPDATE on the Seat Row","originalText":"SELECT ... FOR UPDATE on the Seat Row","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":647.7934,"height":129.60000000000002,"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":607.7934,"height":93.60000000000001,"fontSize":18,"fontFamily":1,"text":"BEGIN;\nSELECT * FROM seats\nWHERE seat_id = 'FLOOR-A-R1-S2' AND event_id = 'evt-taylor'\nFOR UPDATE; ← row locked","originalText":"BEGIN;\nSELECT * FROM seats\nWHERE seat_id = 'FLOOR-A-R1-S2' AND event_id = 'evt-taylor'\nFOR UPDATE; ← row locked","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":277.6,"width":537.7972,"height":223.20000000000002,"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":295.6,"width":497.7972,"height":187.20000000000002,"fontSize":18,"fontFamily":1,"text":"IF status = 'available':\nUPDATE seats SET status='held',\nheld_by=user_A,\nhold_expires_at = NOW() + '7 min'\nWHERE seat_id = 'FLOOR-A-R1-S2';\nELSE:\n→ return \"seat unavailable\"\nCOMMIT;","originalText":"IF status = 'available':\nUPDATE seats SET status='held',\nheld_by=user_A,\nhold_expires_at = NOW() + '7 min'\nWHERE seat_id = 'FLOOR-A-R1-S2';\nELSE:\n→ return \"seat unavailable\"\nCOMMIT;","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":525.8000000000001,"width":588.79804,"height":82.80000000000001,"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":543.8000000000001,"width":548.79804,"height":46.800000000000004,"fontSize":18,"fontFamily":1,"text":"User A: gets lock → hold succeeds\nUser B: waits for lock → gets lock → sees \"held\" → rejected","originalText":"User A: gets lock → hold succeeds\nUser B: waits for lock → gets lock → sees \"held\" → rejected","textAlign":"left","verticalAlign":"middle","containerId":"shape-6","lineHeight":1.3,"autoResize":false,"customData":{"revealStep":4}}],"appState":{"viewBackgroundColor":"#fbfbf8","gridSize":null},"files":{}}