A presentation about Redis main data stuctures and possible use cases, with a fully functional example of Pub/Sub Redis usage.

1. Fabrizio Farinacci

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3. 1. What is Redis?
REmote DIctionary Server
2

4. “ is an in-memory data
structure store, that
can be served as a
database, cache or
message broker
(Pub/Sub).
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6. … a ‘‘data structure server’’?
Redis is essentially a key-value database… but it’s NOT
a plain key-value database: it’s not limited to string values,
but can also hold complex data structures.
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7. 2. Supported Data Types
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8. Strings
Command line:
> set mystr foo
OK
> set myint 1
OK
> get mystr
"foo"
> append mystr foo
(integer) 6
> incr myint
(integer) 2
> mget mystr myint
1) "foofoo"
2) "2"
Are key-value pairs, to store strings or integers, with:
□Common operations on strings (APPEND, STRLEN, exc.);
□Atomic increment/decrement (INCR/DECR) on integers;
□Get multiple values at once (MGET).
Python:
>>> import redis
>>> r = redis.StrictRedis(
host='localhost',
port=6379, db=0
)
>>> r.set('mystr', 'foo')
True
>>> r.set('myint', 1)
True
>>> r.get('mystr')
'foo'
>>> r.append('mystr', 'foo')
6L
>>> r.incr('myint')
2
>>> r.mget('mystr', 'myint')
['foofoo', '2']
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9. Lists
Are linked-lists of strings:
□Index-based access to the entries;
□Insertion and deletion at head/tail,
in constant-time (push/pop);
□Trim/Range operations available.
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10. Interacting
with Lists
Command line:
> rpush mylist A
(integer) 1
> rpush mylist B
(integer) 2
> lpush mylist first
(integer) 3
> lrange mylist 0 ‐1
1) "first"
2) "A"
3) "B"
> lrange mylist 1 3
1) "A"
2) "B"
Python:
>>> import redis
>>> r = redis.StrictRedis(
host='localhost',
port=6379, db=0
)
>>> r.rpush('mylist', 'A')
1L
>>> r.rpush('mylist', 'B')
2L
>>> r.lpush('mylist', 'first')
3L
>>> r.lrange('mylist', 0, ‐1)
['first', 'A', 'B']
>>> r.lrange('mylist', 1, 3)
['A', 'B']
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11. Sets
Are sets of strings:
□Unordered collection of non-
repeating elements;
□Intersection/Union/Difference
between multiple sets;
□Membership test available.
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12. Interacting
with Sets
Command line:
> sadd myset A
(integer) 1
> sadd myset B
(integer) 1
> sadd myset2 C
(integer) 1
> sismember myset C
(integer) 0
> smembers myset
1) "A"
2) "B"
> sunion myset myset2
1) "A"
2) "B"
3) "C"
Python:
>>> import redis
>>> r = redis.StrictRedis(
host='localhost',
port=6379, db=0
)
>>> r.sadd('myset', 'A')
1
>>> r.sadd('myset', 'B')
1
>>> r.sadd('myset2', 'C')
1
>>> r.sismember('myset', 'C')
False
>>> r.smembers('myset')
set(['A', 'B'])
>>> r.sunion('myset', 'myset2')
set(['A', 'C', 'B'])
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13. Sorted Set
(ZSET)
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Are sorted sets of strings:
□Collection of non-repeating elements
sorted by floating-point numbers
(the score) and lexicographically;
□Range operations on score/lexicon;
□Intersection/Union between sets.

14. Interacting
with ZSETs
Command line:
> zadd myzset 2 C
(integer) 1
> zadd myzset 3 D
(integer) 1
> zadd myzset 1 A
(integer) 1
> zadd myzset 2 B
(integer) 1
> zrange myzset 0 ‐1
1) "A" 2) "B" 3) "C" 4) "D"
> zrangebyscore myzset 1 2
1) "A" 2) "B" 3) "C"
> zrangebylex myzset (A [D
1) "B" 2) "C" 3) "D"
Python:
>>> import redis
>>> r = redis.StrictRedis(
host='localhost',
port=6379, db=0
)
>>> r.zadd('myzset', 2, 'C')
1
>>> r.zadd('myzset', 3, 'D')
1
>>> r.zadd('myzset', A=1)
1
>>> r.zadd('myzset', B=2)
1
>>> r.zrange('myzset', 0, ‐1)
['A', 'B', 'C', 'D']
>>> r.zrangebyscore('myzset', 1, 2)
['A', 'B', 'C']
>>> r.zrangebylex('myzset', '(A', '[D')
['B', 'C', 'D']
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15. Hash
A map of field-value pairs:
□Key-based access, specifying
selected field or fields;
□To implement objects, specifying
the name of the field and its value.
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16. Interacting
with Hashes
Command line:
> hset myhash key1 A
(integer) 1
> hmset myhash key2 B key3 C
OK
> hget myhash key2
"B"
> hmget myhash key1 key3
1) "A"
2) "C"
> hgetall myhash
1) "key1"
2) "A"
3) "key2"
4) "B"
5) "key3"
6) "C"
Python:
>>> import redis
>>> r = redis.StrictRedis(
host='localhost',
port=6379, db=0
)
>>> r.hset('myhash', 'key1', 'A')
1L
>>> r.hmset('myhash',
{'key2':'B', 'key3':'C'}
)
True
>>> r.hget('myhash', 'key2')
'B'
>>> r.hmget('myhash', 'key1', 'key3')
['A', 'C']
>>> r.hgetall('myhash')
{'key3': 'C', 'key2': 'B', 'key1': 'A'}
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17. Additional
Data
Structures
Bitmap: A set of
bit-oriented
operations (e.g.
GETBIT/SETBIT)
to manipulate string
values as blobs of
size up to 512 MB.
HyperLogLog: A
probabilistic data
structure structure
to estimate size of
sets (i.e. counting
unique elements)
efficiently and in
constant-space.
Geo: Geospatial
items, stored as
geospatial
indexes (in sorted
indexes). Support
for distance based
operations (eg.
GEODIST) and
radius queries
(GEORADIUS).
Available only in
the BETA testing
version (3.2.0).
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18. 3. Personal Project
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19. Redis
Pub/Sub
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To implement the Publish/Subscribe paradigm:
□Published messages (PUBLISH) are categorized
into channels and pushed to all the subscribers
(SUBSCRIBE).
□Publisher and subscriber are completely
decoupled: advantages are high scalability and
dynamic network features.

20. Place your screenshot here
□ Redis Pub/Sub channels are exploited as thematic channels
(EG. Sport, Tv Shows, exc.).
□ Users subscribe to the channels they’re interested in.
□ Once the web-chat session is started the user can:
■ Receive messages published on the channels of interest;
■ Publish messages onto selected channels.
Redis SubsChat:
A multi-thematic
web-chat
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21. How it has
been done?
import redis
# At the beginning, to setup the Redis interface object
r = redis.StrictRedis(host='localhost', port=6379, db=0)
...
# When start is pressed, the session starts
def on_start():
pubsub = r.pubsub()
# Disable Widgets and manage subscriptions
...
ui.checkBox.setEnabled(False)
if ui.checkBox.isChecked():
# Setup the the handler for the subscriber tasks
pubsub.subscribe(**{str(ui.checkBox.text()):
mess_handler}) ...
# This is done for all the checklists
...
# Run the receiver tasks into a parallel thread ...
thread = pubsub.run_in_thread(sleep_time=0.001)
...
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22. How it has
been done? (2)
...
# Handler that pushes the received message onto the web‐chat
def mess_handler(message):
QtCore.QMetaObject.invokeMethod(ui.textEdit,
"append",QtCore.Q_ARG(str, str(message['data'])+'n'))
...
# To send a message when send is pressed
def on_send():
# Get the info about the message from the UI
msg = str(ui.textEdit_2.toPlainText())
if len(msg) > 0:
usrname = str(ui.lineEdit.text())
if len(usrname) == 0:
usrname = '<Anonymous>'
channel = str(ui.comboBox.currentText())
ui.textEdit_2.clear()
message = ‘%s [%s]: %s' % (usrname, channel, msg)
# Publish the message onto the specified channel
r.publish(channel, message)
...
21

23. How it has
been done? (3)
...
def on_stop():
# Re‐enable the disabled widgets
...
ui.checkBox_2.setEnabled(True)
...
# This is done for all the checklists
...
pubsub.close()
...
if __name__ == "__main__":
# To setup the UI and make the application run
import sys
app = QtGui.QApplication(sys.argv)
MainWindow = QtGui.QMainWindow()
ui = Ui_MainWindow() ui.setupUi(MainWindow)
MainWindow.show()
sys.exit(app.exec_())
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24. Live Demo
Let’s see how it works!!
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25. 4. Use cases
When should we use it?
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26. Performances
and usability
Redis is an in-memory database, persistent on disk.
PROs:
□Faster reads and writes: all
happens in memory. A
transaction is considered
committed without the need of
writing on the disk.
□Simple complex data
structure manipulation: all
is in memory; lower complexity.
□Efficient persistency
management: snapshotting or
journal mode.
CONs:
□Suitable for small datasets,
of size up to memory capacity.
□Not suitable for application
where durability is a crucial
aspect.
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27. When it
should be
used? We Should use it if:
□Small datasets that
fits in memory: very
high performance,
similar to a cache.
□Assumptions on
data structures and
queries: to take
advantage of the
supported data types.
□Realize a cache
layer: for example, to
speedup a conventional
RDBMS.
We Shouldn’t use it if:
□Frequent schema
changes: a traditional
key-value approach, with
the schema managed by
the application, would be
preferred.
□Prototyping: don’t
want to waste loads of
time in the design of the
database and have the
application soon ready.
□Durability critical
applications: like seat
booking mechanism.
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28. Who’s using
Redis?
And many others!
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29. thanks!
Any questions?
You can find me at:
https://it.linkedin.com/in/fabrizio-farinacci-496679116
https://github.com/FabFari/redis-subschat
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