REDIS327

REDIS – Advanced Key Value
Store
Rajan Bhatt

What REDIS is ?
• REDIS is an open source, BSD licensed,
advanced key-value store. It is often referred
to as data structure server since keys can
contain String, Hashes, List, Sets and Sorted
sets..
• REDIS stands for REmote DIctionary Server

REDIS - Features
• Simplicity
• Speed
• Low Footprint
• Versatility
• Predictability
• Reliability

How to Install and Start REDIS server,
REDIS client and Bindings
• Go to http://redis.io/download and download
• Start Redis server ( TCP server, Single
Threaded, Listens on default port 6379 ).
• Command – redis-server <path to conf. file )
• Bundled REDIS client – redis-cli
• Client bindings available for all popular
languages, Java, Python, Ruby, Scala, Ruby,
Eralang, Go ..( I am running out of space )

Data Structure
• Strings
• List
• Sets
• Sorted Set
• Hash
• And Publish/Subscribe Design Pattern

Strings
• Set Key “Value” ( 4 billion Keys )
• Get Key returns “Value”
• Del Key
• Fetch Multiple Keys at once … MGET
• Set EXPIRATION key, e.g. Expire Key 5
• Command TTL returns remaining time before
key expires

Use Case for Expire, TTL
• Cache – LRU
http://antirez.com/post/redis-as-LRU-
cache.html
• Storage for Session ( HTTP or others ..)

Atomic Counter
• GET Key
 Nil
• INCR Key
1
• INCR Key
2
• Get Key
 2

Usage of INCR
• Great Use case Global Counters ( Download, Hits,
Votes ..)
• INCR downloads:total
• INCR downloads:total:today
• INCR downloads:total:2011-05-10
• INCR downloads:/downloads/file1.mpg:total
• INCR downloads:/downloads/file1.mpg:today
• INCR downloads:/downloads/file1.mpg:2011-05-
10

Counters
# Total downloads for server, all time
• GET downloads:total
# Total downloads for server, today
• GET downloads:total:today
# Total downloads for file
• GET downloads:/downloads/file1.mpg:total
# Total downloads for file today
• GET downloads:/downloads/file1.mpg:today

How do you reset daily counter ?
# Expire at 2011-05-10 23:59:59
• EXPIREAT downloads:total:today 1305064799

One more Use Case – API rate Limiting
• $ curl http://api.example.com/list.json
• INCR api:<TOKEN>:hits
1
• Pseudo-Code
if INCR('api:abc123:hits') > LIMIT
return 420 Enhance Your Calm
end

One more Use case Generating unique
IDs
• INCR global:users_ids
1
• SET users:1:username "john"
• INCR global:users_ids
2
• SET users:2:username "mary”

List
• LPUSH key 1
 1
• LPUSH Key 2
 2
• LPUSH Key 3
 3
• RPOP Key
 What should I get ?
• LPOP Key
 What should I get ?
• LLEN Key ( Length if List )
• LRANGE key 0 -1
• LTRIM 0 1

Usage of List
• Indexes ( List of comments ..)
LPUSH article:comments <ID>
Timelines (of all sorts: messages, logs, ...)
LPUSH user:<ID>:inbox "message from Alice"
LPUSH user:<ID>:inbox "message from Bob"
# Limit the messages to 100
LTRIM user:<ID>:inbox 0 99
# Get last 10 messages
LRANGE user:<ID>:inbox 0 9
# Get next 10 messages
LRANGE user:<ID>:inbox 10 19

List is “Queue”
 Publisher
• RPUSH queue “task-1”
• RPUSH queue “task-2”
Worker ( blocks and waits for tasks, 0 means
waits for ever )
• BLPOP queue 0

Basic Set
• SADD key 1  1
• SMEMBERS key  “3”, “2”, “1”
• SISMEMBER key 1  “1”
• SISMEMBER key 5  “0”
• SREM key 3  1

Set Operations
• SADD A 1
• SADD A 2
• SMEMBERS A  “1”, “2”
• SADD B 1
• SADD B 3
• SMEMBERS  “1”, “3”

Set Continues..
• SUNION A B  “1”, “2”, “3”
• SINTER A B  “1”
• SDIFF A B  “2”

Set Usages - Relationship
• SADD users:A:follows B
• SADD users:B:follows C
• SADD users:B:follows D
• SADD users:C:follows A
• SADD users:C:follows D

Set Relationship
• Joint network of A & B
SUNION users:A:follows users:B:follows
“C”,”D”,”B”
• Common for A & B
 SINTER users:B:follows users:C:follows
[]
• Unique to B compared to C
 “C”

Set – Friends & Followers
# Whom “swid1” follows
• SADD swid1:follows A
• SADD swid1:follows B
# Who are friends of “swid1”
• SADD swid1:friend C
• SADD swid1:friend B
# Whom swid1 follows and he is friend
• SINTER swid1:follows swid1:friend  “B”
# Whom swid1 follows and he is not friend
• SDIFF swid1:follows swid1:friend  “A”
# Whom Swid1 is friend with but does not follow
• SDIFF swid1:friend swid1:follows  “C”

Sorted Set
• ZADD key 100 A
• ZADD key 10 C
• ZADD key 80 B
• ZRANGE key 0 -1  “C”, “B”, “A”
• ZREVANGE key 0 -1  “A”, “B”, “C”
• ZINCRBY key 10 C  “20”

Sorted Set - Continues
• ZREVRANGE key 0 -1 WITHSCORES 
1) "A" 2) "100" 3) "B" 4) "80" 5) "C" 6) "20"
• ZREVRANGEBYSCORE key 100 50 
• 1) "A"
• 2) "B"

Leaderboards
# User A got 10 points
ZINCRBY scores 10 A
# User B got 15 points
 ZINCRBY scores 15 B
# User A got another 10 points
 ZINCRBY scores 10 A
# Display scores
ZREVRANGE scores 0 -1 WITHSCORES
1) "A" 2) "20" 3) "B" 4) "15"

Hashes
• Redis Hashes are maps string filed and string
values.
• This data type is perfect to represent an
object.
• A hash with few fields ( 100s ) is stored in a
way that takes very little space so you can
store millions of object is small REDIS
instances.

REDIS Hash commands
• HMSET user:1001 username john cid 1234
dept finance eaccount 5000
• HMGET user:1001 username cid ( Multi-field
GETs )
• HINCRBY user:1001 eaccount 5 ( Incrementing
specific field )
• HGET user:1001 eaccount ( Get specific field )
• HSETNX user:1001 username

REDIS - Persistence
• All datasets are stored in Memory like
Memcached, extremely fast read/write
operations.
• Datasets can be saved to Disk, Two ways
– RDB
– AOF ( Append only File )

RDB snapshots and AOF logs
• Persistence REDIS is a matter of configuration,
balancing the trade-off between performance,
disk I/O and data durability.
– RDB is a very compact single-file point-in-time
representation of REDIS dataset.
– AOF is a simple text log of write operations.

REDIS HA
• REDIS support Master/Slave configuration for HA
• Master can have multiple Slaves and Slaves can also be
connected other slaves in Graph like structure.
• REDIS replication is non-blocking on Master and Slave side.
• Replication is used both for scalability or data redundancy.
• To configure Slave is very simple just needs to add following to
slave configuration file,
Slaveof <ip-addr-of-server> 6379
• By default slaves are read only.
• What if Master fails ? How do client behave ? What are
options ?

Redis Scalability
• Client Side Sharding – Client shards key based on number of
Redis servers. This is static partitioning. Each Server is
configured with Master/Slave for redundancy.
• Server Side Sharding – twemproxy
(https://github.com/twitter/twemproxy) by Tweeter,
Consistent Hashing implementation. Another resource
http://antirez.com/news/44.
• Redis sever Pre-Sharding strategy - e.g Pinterest
• Great resource to start - http://redis.io/topics/partitioning.
• Many options.. Roll your Own which meets needs..

How to Monitor REDIS ?
• Local Monitoring : Monitd to monitor REDIS instance locally.
Restart if process fails. AS team has prototype for this.
• Remote Monitoring and Integration with Zenoss -
https://community.zenoss.org/docs/DOC-5333.
• Accessing REDIS metrics – Start redis-cli – info command with
following options, server, clients, memory, persistence, stats,
replication, cpu, commandstats, cluster,keyspace
• Many commercial SAAS vendors, DATADOG, LIBRATO, more
analysis and statistical Metrics collection.

REDIS as a Service
• Redislabs - http://redislabs.com/
• Amazon Elastic Cache service -
http://aws.amazon.com/about-aws/whats-
new/2013/09/04/amazon-elasticache-for-
redis/

How to Measure REDIS performance ?
• Redis-benchmark is a tool which comes
bundled with Redis installation.
• Check out at
http://redis.io/topics/benchmarks.
• This tool simulates N client sending M queries.
• Let us run.. See what happens.

Other feature of REDIS
• Transactions
– MULTI,EXEC,DISCARD AND WATCH are the transactions in Redis.
– Redis transactions are atomic.
– Redis transactions are started with MULTI command and then all
commands are executed once EXEC is executed.
• LUA scripting
– Lua scripting is used to implement custom command and/or
extension. This is very similar to stored procedure in RDBMS.
– Redis Lua interpreter loads seven libraries:
base,string,table,math,debug,cjson and cmsgpack.

Summary
• Redis offers excellent caching and persistence
options along with various data structure for
applications.
• This is true Lego building block for a service
developer. Use case is only limited by
imagination.
• At least start with, replacing Memcached.
• Excellent Live Documentation..check it out
http://redis.io

REDIS327

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