Redis database

Redis in short

1. Redis Database

2. Introduction  Redis is a data-structure server store.  Store data in the form of key/value pair.  Consistency is guaranteed  by supporting "append-only file" and the availability of data is guaranteed through cluster and master-slave replication.  And it also has very cool value types:    Lists   Sets and  Sorted sets   Hash tables

3. Redis Datatypes (String)  Starting Redis is   ve ry easy, you just need to install the desired redis package and write $ redis-server to run the in memory redis server. Key-value simple example: $   SET fb www.facebook.com $ GET fb $ www.facebook.com

4. Compl ex Datatypes (Hash)  Hashes are like nested Redis Objects  that can take any number of key-value pairs. $ HMSET user:eric name "Eric Redmond" password s3cret  Single redis key can be used to retrieve all values of the hash.

5. Compl ex   Datatypes (List) Lists contain multiple ordered values that can act as both queues (FIFO) and stacks (FILO). Can exceute actions such as adding element in the middle, deleting values, ...

6. Compl ex   Datatypes (Set)  Sets are unordered collections that does not allow for duplication.  Accepts set operations such as UNION and INTERSECTION

7. Data Expiry  One of the best uses of Redis key-value store is fast-access cache for data that's more expensive to retrieve or compute.  As we know cache should be expired and get updated periodically.  Using Redis you can mark a key for expiration by using EXPIRE command and give the key time to live in seconds

8. Durability  With Redis you can choose between no persistent or save your data.  No persistent will keep the values in the main-memory.   No persistent is best choice if you run a caching server because durability will increase the latency. You can also force storing data to disk by using SAVE  command  (or BGSAVE for asynchronous save)

9. Durability (Cont.)  Redis also provides append-only file that keeps a record of all write commands.  That ensures correct value even if the server craches before value saved.  The Redis server executes the commands on the startup.  By append-only file we can be sure that the data is eventually consistent.

10. Master-Slave Replication  Redis supports master-slave replication (one server is master by defualt)  The replication feature allows Redis to ensure the availability.  Even if the main server is down, slave servers already have the replicated data and ready to serve clients.

11. Redis Cluster  Clustering is the advanced mode of replication  In this mode the servers are master servers and are connected to each other. Clustering makes Redis suitable for distributed systems.   The clus tering gives you the ability to automatically split your dataset among multiple nodes .   The op eration will continue even if some nodes are failed without having to expire most keys.

12. B loom   Filter s  A Bloom filter is a data structure designed to tell you, rapidly and memory-efficie n tly, whe t her an el ement is pres ent in a set.  Despite of being very fast, but bloom filters have probabilistic datastructure.   with bloom filters we can know that the element either  definitely is not  in the set or  may be  in the set.  Bloom filters are excellent choice to reduce the unnecessary traffic to a slower underlying system.