Dubious Database Design

Transcript

1. DUBIOUS Database DESIGN

2. Andrew Godwin Hi, I'm Author of 1.7 Django & South

   migrations Senior Software Engineer at Only hates MySQL a little

3. “Do this. Don't ask why.”

4. Learning from failure.

5. Spacelog 1

6. Spacelog 1

7. “Redis is fast!”

8. None

9. Spacelog 1

10. Read-only, forever.

11. “Redis is fast!”

12. GET chapter-1 GET chapter-2

13. GET entry-123 GET entry-124 GET entry-125

14. ZRANGEBYSCORE .... GET entry-123 GET entry-124 GET entry-125

15. Request page Look up key range Multi-get key range Get

    speaker details

16. SELECT ... JOIN ... WHERE ...

17. Ignoring JOIN 2

18. “Joins are slow!”

19. {"id": 11, "post": "abc", "author": 1} {"id": 12, "post": "def",

    "author": 2} {"id": 13, "post", "ghi", "author": 3} {"id": 1, "name": "Andrew"} {"id": 2, "name": "Brenda"} {"id": 3, "name": "Carol"}

20. n number of authors m × number of posts

21. scan all posts build dict of author -> posts scan

    all authors and emit with posts

22. HASH JOIN

23. { "id": 11, "post":"abc", "author": {"name": "Andrew"} }

24. { "id": 11, "post":"abc", "author": { "name": "Andrew", "last_seen": 120993013,

    } }

25. The server's running, it's fine! 3

26. Write new save file Write new save file Delete old

    save file

27. Write new save file Write new save file ?

28. Tell payment processor to send Mark as processing Find unpaid

    clients Mark as paid

29. Tell payment processor to send Mark as processing Find unpaid

    clients Mark as paid

30. The Fastidious Modeller 4

31. TwitterUser FacebookUser LinkedInUser EmailUser

32. SELECT ... FROM TwitterUser SELECT ... FROM EmailUser SELECT ...

    FROM LinkedInUser
33. None
34. None

35. The database isn't magic.

36. The Table Lover 5

37. “How do I make tables at runtime?”

38. None

39. Tables/columns per language Tables/columns per customer Configurable CMS columns

40. Columns per language 300 - 400 language variants x A

    couple of translated cols per table x

41. DDL is very expensive.

42. Use JSON, hstore, or EAV-style table!

43. 6 The Cold Boot

44. Decent cache hit rate Application servers mostly utilised

45. Great engineering!

46. What would happen if I deleted the entire cache?

47. None

48. The Optimist 7

49. Sharded PostgreSQL ElasticSearch Riak Redis Flat files + + +

    +

50. Don't forget redundancy. And backups.

51. What happens if just one dies?

52. n services = n points of failure

53. The Primary Optimist 8

54. “The highest value PK is the most recent”

55. “Autoincrement will work and scale forever”

56. “IDs are numbers we can do maths on”

57. The Function Lover 9

58. "Why waste time fetching columns and rendering them separately?"

59. CREATE FUNCTION

60. CREATE FUNCTION ... import jinja2

61. bit.ly/whynotpg

62. None

63. SELECT render(template, id) FROM pages WHERE %s ~ url;

64. None

65. There's a reason behind every rule.

66. Ask why, or try yourself. Don't write it off without

    context.

67. Thanks. Andrew Godwin @andrewgodwin