Technique to delete unused codes

Transcript

1. コードを削除する技術
   Technique to delete unused codes
   PHP Conference Sendai 2019
   @naopr
   

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2. @naopr
   ● Backend Engineer at Mercari, Inc.
   ● Tech Lead of CSTool Team
   ● Love
   

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3. Relationship between Mercari & Sendai
   Sendai
   Reply to inquiries
   Monitor contents
   Fukuoka
   Call-center
   Tokyo
   Head Office
   Develop apps
   

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4. Relationship between Mercari & PHP
   ● Mercari app’s API is written in PHP
   ● Migrating to microservices
   ○ From PHP to Go
   ○ Break down existing API into multiple services
   ○ MTC2018 - Mercari API: from Monolithic to Microservices
   

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5. Technique to delete
   unused codes
   

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6. Agenda
   ● Why do we need to delete unused codes?
   ● Mercari’s case
   ○ How to delete unused codes
   ○ Result
   ● Conclusion
   

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7. Why do we need to delete unused codes?
   ● Reduce development costs
   ○ Reading cost
   ○ Updating cost
   ● Speed up the system
   ○ Response time
   ○ CI
   

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8. How to delete unused codes
   Detect unused APIs
   Build project team
   Delete codes
   1
   2
   3
   

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9. Detect unused APIs
   1. List APIs that haven’t been recently accessed
   a. For a month in our case
   b. Use Google BigQuery & a script written in Go
   2. Check if we may delete the API
   a. Investigate codes
   b. Use `git blame` and ask implementer
   c. Find tickets related to it
   

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10. Make API list by spreadsheet
    

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11. Build project team
    ● Collect fellows [Important]
    ○ backend engineer
    ○ QA engineer
    ● Decide the release procedure
    ○ How to do QA
    ○ JIRA ticket
    ● Hold a kick-off with
    ○ Better to hold it every month
    

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12. Delete codes
    ● Check recent access log
    ● Check methods recursively
    ○ Type and type `git grep`!
    ○ With symbol search function by PhpStorm
    ○ Controller, Service, Exception, Entity, DB table, DB schema, test, etc...
    

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13. Result
    

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14. Result summary
    ● Deleted 349 / 370 (≒94%) unused APIs
    ○ In 3 months
    ○ 7 backend engineers + 1 frontend engineers
    ○ About 80k〜100k lines
    ● Reverted 9 PRs
    ○ Other repositories were affected when tables were dropped
    ○ Forgot to check the access log
    

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15. Conclusion
    

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16. Deleting code is difficult
    ● Need to read the code steadily or ask a senior engineer
    ● Do it with fellows, NOT alone
    ● Don’t forget to check the access log
    ● Check the impact on other repositories when drop tables
    ● Let’s hold a drinking party every month
    

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17. Let’s delete codes!
    and drink
    

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