This document discusses different techniques for pagination in databases. It begins by describing the issues with using offsets for pagination, as it can lead to unstable performance. It then introduces key-set pagination as an alternative, where the next set of rows is queried based on a unique identifier from the previous set rather than an offset. This allows for faster and more consistent performance even when browsing through many pages of data. The document also notes some limitations of key-set pagination and tools needed for it to work effectively.

1. © 2015 by Markus Winand
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From Backend to Frontend
When database optimization affects the full stack
@MarkusWinand
@SQLPerfTips
@ModernSQL

2. © 2015 by Markus Winand
Full Stack, Really?

3. © 2015 by Markus Winand
Full Stack, Really?

4. © 2015 by Markus Winand
What Users Want are Used to

5. © 2015 by Markus Winand
What Users Want are Used to
Let’s
click here

6. © 2015 by Markus Winand
User Clicks on Page 2
Gimme
Page 2!
Gimme
Rows
11 to 20

7. SQL for “Gimme Rows 11 to 20”
se!e"# *
$%om news
whe%e #op&" ' 1234
o%de% b( da#e des", &d des"
o!!se" 10
#$m$" 10

8. Inside the Database: Worst Case
L&m&# (a"#ua! %ows'10)
-> So%# (a%"ua# &ows'20)
So%# Me#hod: "op-N heapso&" Memo&(: 19)B
-> B&#map Heap S"an (a"#ua! %ows'10000)
Re"he") *ond: (#op&" ' 1234)
-> B&#map Index S"an (a"#ua! %ows'10000)
Index *ond: (#op&" ' 1234)

9. Inside the Database: Worst Case
L&m&# (a"#ua! %ows'10)
-> So%# (a%"ua# &ows'30)
So%# Me#hod: "op-N heapso&" Memo&(: 20)B
-> B&#map Heap S"an (a"#ua! %ows'10000)
Re"he") *ond: (#op&" ' 1234)
-> B&#map Index S"an (a"#ua! %ows'10000)
Index *ond: (#op&" ' 1234)

10. Inside the Database: Worst Case
L&m&# (a"#ua! %ows'10)
-> So%# (a%"ua# &ows'40)
So%# Me#hod: "op-N heapso&" Memo&(: 22)B
-> B&#map Heap S"an (a"#ua! %ows'10000)
Re"he") *ond: (#op&" ' 1234)
-> B&#map Index S"an (a"#ua! %ows'10000)
Index *ond: (#op&" ' 1234)

11. Inside the Database: Worst Case
L&m&# (a"#ua! %ows'10)
-> So%# (a%"ua# &ows'10000)
So%# Me#hod: ex"e&na# me&*e D$s): 1200)B
-> B&#map Heap S"an (a"#ua! %ows'10000)
Re"he") *ond: (#op&" ' 1234)
-> B&#map Index S"an (a"#ua! %ows'10000)
Index *ond: (#op&" ' 1234)

12. Inside the Database: Worst Case
Speed depends on the number of matched rows
and the page fetched.
Fetching the last page
can take considerably
longer than fetching
the first page.

13. Improvement 1: Indexed order by
se!e"# *
$%om news
whe%e #op&" ' 1234
o%de% b( da#e des", &d des"
o$$se# 10
!&m&# 10;
%&ea"e $ndex on news ("op$%, da"e, $d)
A single index to support the whe%e and o%de% b(
clauses.

14. Improvement 1: Indexed order by
L&m&# (a%"ua# &ows'10)
-> Index S"an Ba")wa%d (a%"ua# &ows'10)
Index *ond: (#op&" ' 0)

15. Improvement 1: Indexed order by
L&m&# (a%"ua# &ows'10)
-> Index S"an Ba")wa%d (a%"ua# &ows'20)
Index *ond: (#op&" ' 0)

16. Improvement 1: Indexed order by
L&m&# (a%"ua# &ows'10)
-> Index S"an Ba")wa%d (a%"ua# &ows'30)
Index *ond: (#op&" ' 0)

17. Improvement 1: Indexed order by
L&m&# (a%"ua# &ows'10)
-> Index S"an Ba")wa%d (a%"ua# &ows'40)
Index *ond: (#op&" ' 0)

18. Improvement 1: Indexed order by
L&m&# (a"#ua! %ows'10)
-> So%# (a%"ua# &ows'10000)
So%# Me#hod: ex"e&na# me&*e D$s): 1200)B
-> B&#map Heap S"an (a"#ua! %ows'10000)
Re"he") *ond: (#op&" ' 1234)
-> B&#map Index S"an (a"#ua! %ows'10000)
Index *ond: (#op&" ' 1234)

19. Improvement 1: Indexed order by
Fetching the first page is not affected by the
Base-Set size!
Fetching the next page
is also faster.
However, the database
might revert to the other
execution plan when
browsing to the end.

20. © 2013 by Markus Winand
It’s not just about performance

21. © 2015 by Markus Winand
Offsets Yield Unstable Results

22. © 2015 by Markus Winand
Offsets Yield Unstable Results

23. © 2015 by Markus Winand
Offsets Yield Unstable Results

24. © 2013 by Markus Winand
Why don’t we ask for
the next rows after...

25. © 2015 by Markus Winand
Asking for “Next After” in SQL

26. © 2015 by Markus Winand
Asking for “Next After” in SQL

27. © 2015 by Markus Winand
Asking for “Next After” in SQL

28. © 2015 by Markus Winand
Asking for “Next After” in SQL

29. © 2015 by Markus Winand
Asking for “Next After” in SQL

30. © 2015 by Markus Winand
Asking for “Next After” in SQL

31. SQL For “Next After” (Key-Set Pagination)
se!e"# *
$%om news
whe%e #op&" ' 1234
and (da"e, $d) < (?, ?)
o%de% b( da#e des", &d des"
!&m&# 10 Look Ma,
no offset!

32. Key-Set Pagination: Worst Case

33. Key-Set Pagination: Worst Case
L&m&# (a%"ua# &ows'10)
-> So%# (a%"ua# &ows'10)
So%# Me#hod: "op-N heapso&" Memo&(: 18)B
-> B&#map Heap S"an (&ows'10000)
Re"he") *ond: (#op&" ' 1234)
-> B&#map Index S"an (&ows'10000)
Index *ond: (#op&" ' 1234)

34. Key-Set Pagination: Worst Case
L&m&# (a"#ua! %ows'10)
-> So%# (a%"ua# &ows'10)
So%# Me#hod: "op-N heapso&" Memo&(: 18)B
-> B&#map Heap S"an (a%"ua# &ows'9990)
Rows Remo+ed b( F$#"e&: 10 (new &n 9.2)
-> B&#map Index S"an (a%"ua# &ows'10000)
Index *ond: (#op&" ' 1234)

35. Key-Set Pagination: Worst Case
L&m&# (a"#ua! %ows'10)
-> So%# (a%"ua# &ows'10)
So%# Me#hod: "op-N heapso&" Memo&(: 18)B
-> B&#map Heap S"an (a%"ua# &ows'9980)
Rows Remo+ed b( F$#"e&: 20 (new &n 9.2)
-> B&#map Index S"an (a%"ua# &ows'10000)
Index *ond: (#op&" ' 1234)

36. Key-Set Pagination: Worst Case
L&m&# (a"#ua! %ows'10)
-> So%# (a%"ua# &ows'10)
So%# Me#hod: "op-N heapso&" Memo&(: 18)B
-> B&#map Heap S"an (a%"ua# &ows'9970)
Rows Remo+ed b( F$#"e&: 30 (new &n 9.2)
-> B&#map Index S"an (a%"ua# &ows'10000)
Index *ond: (#op&" ' 1234)

37. Key-Set Pagination: Worst Case
L&m&# (a"#ua! %ows'10)
-> So%# (a%"ua# &ows'10)
So%# Me#hod: "op-N heapso&" Memo&(: 18)B
-> B&#map Heap S"an (a%"ua# &ows'10)
Rows Remo+ed b( F$#"e&: 9990 (new &n 9.2)
-> B&#map Index S"an (a%"ua# &ows'10000)
Index *ond: (#op&" ' 1234)

38. Key-Set Pagination w/o Index for order by
Always needs to retrieve the full base set, but the
top-n sort buffer needs
to hold only 10 rows.
The response time remains
the same even when
browsing to the last page.
And the memory footprint
is very low!

39. Key-Set Pagination: Best Case
se!e"# *
$%om news
whe%e #op&" ' 1234
and (da#e, &d) < (?, ?)
o%de% b( da#e des", &d des"
!&m&# 10;
%&ea"e $ndex on news ("op$%, da"e, $d)

40. Key-Set Pagination: Best Case
L&m&# (a%"ua# &ows'10)
-> Index S"an Ba")wa%d (a%"ua# &ows'10)
Index *ond: (#op&" ' 1234)

41. Key-Set Pagination: Best Case
L&m&# (a%"ua# &ows'10)
-> Index S"an Ba")wa%d (a%"ua# &ows'10)
Index *ond: ((#op&" ' 1234)
AND (ROW(d#, &d) < ROW(‘...’, 23456)))

42. Key-Set Pagination: Best Case
L&m&# (a%"ua# &ows'10)
-> Index S"an Ba")wa%d (a%"ua# &ows'10)
Index *ond: ((#op&" ' 1234)
AND (ROW(d#, &d) < ROW(‘...’, 34567)))

43. Key-Set Pagination: Best Case
L&m&# (a%"ua# &ows'10)
-> Index S"an Ba")wa%d (a%"ua# &ows'10)
Index *ond: ((#op&" ' 1234)
AND (ROW(d#, &d) < ROW(‘...’, 45678)))

44. Key-Set Pagination: Best Case
L&m&# (a%"ua# &ows'10)
-> Index S"an Ba")wa%d (a%"ua# &ows'10)
Index *ond: ((#op&" ' 1234)
AND (ROW(d#, &d) < ROW(‘...’, 56789)))

45. Key-Set Pagination: Best Case
Successively browsing back doesn’t slow down.
Neither the size of the
base set(*) nor the fetched
page number affects the
response time.
(*) the index tree depth still affects the response time.

46. ComparisonOffsetKey-Set
Worst Case Best Case

47. © 2015 by Markus Winand
Too good to be true?
Key-Set Pagination has serious limitations:
‣You cannot directly navigate to arbitrary pages
‣because you need the values from the previous page
‣Bi-directional navigation is possible but tedious
‣you need to reverse the o%de% b( direction and RV comparison
‣Tooling...???

48. © 2015 by Markus Winand
Required Tooling for Key-Set Pagination

49. © 2015 by Markus Winand
Required Tooling for Key-Set Pagination
Proper Row-
Values Support.
Don’t use
OFFSET.NoSQL is
also
Also for
NoSQL

50. © 2015 by Markus Winand
Required Tooling for Key-Set Pagination
Proper Row-
Values Support.
Don’t use
OFFSET.
Offer
Infinite Scrolling.
Don’t think in
pages.
Ask the right
question.

51. OFFSET is EVIL
http://use-the-index-luke.com/no-offset

52. © 2015 by Markus Winand
About Markus Winand
Tuning developers for
high SQL performance
Training & co (one-man show):
winand.at
Geeky blog:
use-the-index-luke.com
Author of:
SQL Performance Explained