Menu
So if for example I am trying to implement something that looks like Facebook's Graph API that needs to be very quick and support millions of users, what is the disadvantage of just using Redis instead of a RDBMS?
Thanks! Jonathan
318
Redis is essentially a data structure server. It supports commands and doesn't support a query language, so there is no case of using ad-hoc queries. Data access paths have to be designed, and this results in a loss of flexibility.
Redis stores everything in primary memory. RDBMS stores everything in secondary memory. In Redis, Read and Write operations are extremely fast because of storing data in primary memory. In RDBMS, Read and Write operations are slow because of storing data in secondary memory.
As Redis is an in-memory storage, you cannot store large data that won't fit you machine's memory size. Redis usually work very bad when the data it stores is larger than 1/3 of the RAM size. So, this is the fatal limitation of using Redis as a database.
There are plenty of potential benefits and potential drawbacks of using Redis instead of a classical RDBMS. They are very different beasts indeed.
Focusing only on the potential drawbacks:
Redis is an in-memory store: all your data must fit in memory. RDBMS usually stores the data on disks, and cache part of the data in memory. With a RDBMS, you can manage more data than you have memory. With Redis, you cannot.
Redis is a data structure server. There is no query language (only commands) and no support for a relational algebra. You cannot submit ad-hoc queries (like you can using SQL on a RDBMS). All data accesses should be anticipated by the developer, and proper data access paths must be designed. A lot of flexibility is lost.
Redis offers 2 options for persistency: regular snapshotting and append-only files. None of them is as secure as a real transactional server providing redo/undo logging, block checksuming, point-in-time recovery, flashback capabilities, etc ...
Redis only offers basic security (in term of access rights) at the instance level. RDBMS all provide fine grained per-object access control lists (or role management).
A unique Redis instance is not scalable. It only runs on one CPU core in single-threaded mode. To get scalability, several Redis instances must be deployed and started. Distribution and sharding are done on client-side (i.e. the developer has to take care of them). If you compare them to a unique Redis instance, most RDBMS provide more scalability (typically providing parallelism at the connection level). They are multi-processed (Oracle, PostgreSQL, ...) or multi-threaded (MySQL, Microsoft SQL Server, ... ), taking benefits of multi-cores machines.
Here, I have only described the main drawbacks, but keep in mind there are also plenty of benefits in using Redis (very fast, good concurrency support, low latency, protocol pipelining, good to easily implement optimistic concurrent patterns, good usability/complexity ratio, excellent support from Salvatore and Pieter, pragmatic no-nonsense approach, ...)
For your specific problem (graph), I would suggest to have a look at neo4J or OrientDB which are specifically designed to store graph-oriented data.
137
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
