The document discusses using Redis hashes to store nested data and alternatives to hashes for certain use cases. It describes how Redis hashes can store nested hashes as hash values. An example shows retrieving a hash and parsing the values as JSON to access nested data. Alternatives to hashes are explored, like storing multiple integer counters as bytes in a string to reduce memory usage for certain types of data. Code is provided to implement this counter pattern using Redis strings.

1. redis
überall
Mariano Vallés!
@zucaritask

2. redis
/rədɪs/
@zucaritask

3. redis
/rədɪs/
in memory key-value cache and store
@zucaritask

4. redis
/rədɪs/
in memory key-value cache and store
Considered a data structure server since keys
can contain strings, hashes, lists, sets …
@zucaritask

5. First: Nested hashes
In redis:
[ !
] a hash has values
[ ] those values can be hashes

6. First: Nested hashes
In redis:
! ✓
[ ] a hash has values
[ ] those values can be hashes

7. First: Nested hashes
In redis:
✓
[ ] a hash has values
[ ] those values can be hashes
!
✘

8. First: Nested hashes
:001
>
$redis.hgetall(“levels:1234").
!
{
easy_10:
“{"progress":0,"goal":10,"started_at":1415278026,"finished_at":0}",
easy_20:
"{"progress":0,"goal":20,"started_at":1415278050,"finished_at":0}"
}

9. First: Nested hashes
:001
>
$redis.hgetall(“levels:1234").
!
{
easy_10:
“{"progress":0,"goal":10,"started_at":1415278026,"finished_at":0}",
easy_20:
"{"progress":0,"goal":20,"started_at":1415278050,"finished_at":0}"
}
:002
>
$redis.hgetall(“levels:1234").inject({})
do
|result,
(key,
value)|
result[key]
=
JSON.parse(value);
result
end
=>
{
easy_10:
{progress:
0,
goal:
10,
started_at:
1415278026,
finished_at:
0}
easy_20:
{progress:
0,
:goal:
20,
started_at:
1415278050,
finished_at:
0}
}

10. Redis hash
:001
>
$redis.hgetall(“levels:1234").
!
{
easy_10:
“{"progress":0,"goal":10,"started_at":1415278026,"finished_at":0}",
easy_20:
"{"progress":0,"goal":20,"started_at":1415278050,"finished_at":0}"
}
:002
>$redis.hgetall(“levels:1234").inject({})
do
|result,
(key,
value)|
result[key]
=
JSON.parse(value);
result
end
=>
{
easy_10:
{:progress
=>
0,
:goal
=>
10,
started_at:
1415278026,
finished_at:
0}
easy_20:
{:progress
=>
0,
:goal
=>
20,
started_at:
1415278050,
finished_at:
0}
}

11. Redis hash
:001
>
$redis.hgetall(“levels:1234").
!
{
!
easy_10:
“{"progress":0,"goal":10,"started_at":1415278026,"finished_at":0}",
easy_20:
"{"progress":0,"goal":20,"started_at":1415278050,"finished_at":0}"
}
deal with
le crowd
:002
>$redis.hgetall(“levels:1234").inject({})
do
|result,
(key,
value)|
result[key]
=
JSON.parse(value);
result
end
=>
{
easy_10:
{:progress
=>
0,
:goal
=>
10,
started_at:
1415278026,
finished_at:
0}
easy_20:
{:progress
=>
0,
:goal
=>
20,
started_at:
1415278050,
finished_at:
0}
}

12. First: Nested hashes
From:
{
easy_10:
“{"progress":0,"goal":10,"started_at":1415278026,"finished_at":easy_20:
"{"progress":0,"goal":20,"started_at":1415278050,"finished_at":}

13. First: Nested hashes
From:
{
easy_10:
“{"progress":0,"goal":10,"started_at":1415278026,"finished_at":easy_20:
"{"progress":0,"goal":20,"started_at":1415278050,"finished_at":}
To:

14. First: Nested hashes
From:
{
easy_10:
“{"progress":0,"goal":10,"started_at":1415278026,"finished_at":easy_20:
"{"progress":0,"goal":20,"started_at":1415278050,"finished_at":}
To:
{
easy_10:
"0,10,1415278026,0",
easy_20:
"4,20,1415278050,0"
}

15. First: Nested hashes
{
easy_10:
"0,10,1415278026,0",
easy_20:
"4,20,1415278050,0"
} To:

16. First: Nested hashes
goal
{
easy_10:
"0,10,1415278026,0",
easy_20:
"4,20,1415278050,0"
} To:
progress
started_at
finished at

17. In redis:
[ ] hashes are memory efficient
[ ] millions of hashes are memory
efficient
!
Last: Avoiding hashes

18. Last: Avoiding hashes
In redis:
[ ] hashes are memory efficient
[ ] millions of hashes are memory
efficient
! ✓

19. Last: Avoiding hashes
In redis:
✓
[ ] hashes are memory efficient
[ ] millions of hashes are memory
efficient
!
✘

20. Last: Avoiding hashes

21. Last: Avoiding hashes
:01
>
$redis.hgetall(“counter:1234”)

22. Last: Avoiding hashes
:01
>
$redis.hgetall(“counter:1234”)
=>
{
popup_shown:
1,
extra_life_given:
0
}

24. the crowd
has no mercy

25. the crowd
has no mercy
de a l w i th i t

26. Last: Avoiding hashes
From:
To:
:01
>
$redis.hgetall(“counter:1234”)
=>
{
popup_shown:
1,
extra_life_given:
0
}

27. Last: Avoiding hashes
From:
To:
:01
>
$redis.hgetall(“counter:1234”)
=>
{
popup_shown:
1,
extra_life_given:
0
}
:01
>
$redis.get(“counter:1234”)
=>
"u0000u0001"

28. Last: Avoiding hashes
From:
To:
:01
>
$redis.hgetall(“counter:1234”)
=>
{
popup_shown:
1,
extra_life_given:
0
}
:01
>
$redis.get(“counter:1234”)
=>
"u0000u0001"
A sequence of binary data

29. Last: Avoiding hashes
From:
To:
:01
>
$redis.hgetall(“counter:1234”)
=>
{
popup_shown:
1,
extra_life_given:
0
}
:01
>
$redis.get(“counter:1234”)
=>
"u0000u0001"
A sequence of binary data
Less memory usage FTW!

30. Last: Avoiding hashes
class
Counter
!
COUNTERS
=
%w[
VERSION
popup_shown
extra_life_given
]
!
def
set(key,
value)
$redis.setrange(
user_id,
COUNTERS.index(key),
[value].pack("C*")
)
end
!
def
[](key)
char
=
$redis.getrange(user_id,
index,
index)
char.unpack("C*").first.to_i
end
end

31. Last: Avoiding hashes
class
Counter
!
COUNTERS
=
%w[
VERSION
popup_shown
extra_life_given
]
!
def
set(key,
value)
$redis.setrange(
user_id,
COUNTERS.index(key),
[value].pack("C*")
)
end
!
def
[](key)
char
=
$redis.getrange(user_id,
index,
index)
char.unpack("C*").first.to_i
end
end

32. Last: Avoiding hashes
class
Counter
!
COUNTERS
=
%w[
VERSION
popup_shown
extra_life_given
]
!
def
set(key,
value)
$redis.setrange(
user_id,
COUNTERS.index(key),
[value].pack("C*")
)
end
!
def
[](key)
char
=
$redis.getrange(user_id,
index,
index)
char.unpack("C*").first.to_i
end
end

33. Last: Avoiding hashes
class
Counter
!
COUNTERS
=
%w[
VERSION
popup_shown
extra_life_given
]
!
def
set(key,
value)
$redis.setrange(
user_id,
COUNTERS.index(key),
[value].pack("C*")
)
end
!
def
set the value for a part of a string
[](key)
char
=
$redis.getrange(user_id,
index,
index)
char.unpack("C*").first.to_i
end
end

34. Last: Avoiding hashes
class
Counter
!
COUNTERS
=
%w[
VERSION
popup_shown
extra_life_given
]
!
def
set(key,
value)
$redis.setrange(
user_id,
COUNTERS.index(key),
[value].pack("C*")
)
end
!
def
set the value for a part of a string
starting in this position
[](key)
char
=
$redis.getrange(user_id,
index,
index)
char.unpack("C*").first.to_i
end
end

35. Last: Avoiding hashes
class
Counter
!
COUNTERS
=
%w[
VERSION
popup_shown
extra_life_given
]
!
def
set(key,
value)
$redis.setrange(
user_id,
COUNTERS.index(key),
[value].pack("C*")
)
end
!
def
set the value for a part of a string
starting in this position
turn an integer into an 8-bit unsigned char
[](key)
char
=
$redis.getrange(user_id,
index,
index)
char.unpack("C*").first.to_i
end
end

36. Last: Avoiding hashes

37. Last: Avoiding hashes
:01
>
[0].pack(“C*”)
=>
"x00"

38. Last: Avoiding hashes
:01
>
[0].pack(“C*”)
=>
"x00"
:02
>
[256].pack(“C*”)
=>
"x00"

39. Last: Avoiding hashes
Ac h t u n g , 8 bits !
:01
>
[0].pack(“C*”)
=>
"x00"
:02
>
[256].pack(“C*”)
=>
"x00"

40. redis
überall
but
@zucaritask
use
beware of the crowds