Redis vs. Memcached: In-Memory Data Storage Systems

1

Redis

Redis’ RDB file is, to an extent, incorruptible because it performs its write operations in a new process. Upon the generation of a new RDB file, the Redis-generated subprocess will first write the data into a temporary file, and then rename the temporary file into a RDB file through the atomic rename system call, so that the RDB file is always available whenever Redis suffers a fault. At the same time, the Redis’ RDB file is also a link in the internal implementation of Redis’ master-slave synchronization. However, RDB has its deficiency in that once the database encounters some problem, the data saved in the RDB file may be not up-to-date, and data is lost during the period from last RDB file generation to Redis failure. Note that for some businesses, this is tolerable.

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2

memcached

Memcached itself does not support distributed mode. You can only achieve the distributed storage of Memcached on the client side through distributed algorithms such as Consistent Hash. The figure below demonstrates the distributed storage implementation schema of Memcached. Before the client side sends data to the Memcached cluster, it first calculates the target node of the data through the nested distributed algorithm that in turn directly sends the data to the node for storage. But when the client side queries the data, it also needs to calculate the node that serves as the location of the data queried, and then send the query request to the node directly to get the data.

#Key-Value Database #Databases #NoSQL Databases 28 social mentions