Software Development at Mercari #ioi2018

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Software Development at Mercari Yuichiro Saito (@koemu) International Olympiad in Informatics Sep 7th, 2018

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● Slides are uploaded on Speaker Deck (check the pinned post my Twitter @koemu_s) ● Feel free to record and/or share this presentation on social media! ● Have questions? ○ Q&A time after presentation ○ Visit us at the Mercari booth (in the hallway between the main entrance and Capio) ○ Contact me at koemu@mercari.com 2 Before we begin

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Programming is about solving problems 3

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COMPETITIVE PROGRAMMING REAL-WORLD ENGINEERING Given a problem Find the problem Improve yourself Improve society 4

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Me ↓ 5

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Me ↓ 6

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Mercari’s Mission Create value in a global marketplace where anyone can buy & sell 7

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8 Reduce Waste, Create Value →

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9 Mercari app, similar product recommendations Product pages show related items. Problem: Loads too slow

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10 1. Identify Issue 2. Solve Issue 3. Measure Results As an engineer...

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1. Identify Issue - Used monitoring software to confirm breakdown of latency of each process - Latency of access to the database was several times higher compared to other functions - Identified that the backend application was recursively retrieving product attributes 11

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2. Solve Issue Incorporated a cache system when accessing the database - Saves product attributes to memory - Maintain memory space using Least Recently Used (LRU) algorithm 12 How memcached works. Image from: https://zenmachine.wordpress.com/2008/12/03/50/ More on the LRU algorithm: https://github.com/memcached/memcached/wiki/UserInternals

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3. Measure Results - Significantly decreased access to database (shown in purple below) - Improved latency by 30%! 13 Released at 2:35 PM ↓

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➔ Performance optimization 14 Impact

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➔ Better customer experience 15 Impact

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➔ More completed transactions 16 Impact

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➔ Less waste, more value 17 Impact

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This is the future you can create. 18

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Q&A Time Please raise your hand if you have questions! 19

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We’re hiring! For further questions, visit us at the Mercari Booth. Link to slides pinned on Twitter (@koemu_s) 20

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Credits Images from 「いらすとや」 https://www.irasutoya.com/ English Translation by Sherry Zhang 21