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Why Use A No-SQL Database Like Redis

This entry was posted on Dec 01 2011

For the last three months I have been working on different websites that I inherited that rely heavily on Redis. Redis is another no-sql database that uses key/value pairs to store data but does not give you the flexibility to write queries like you’re used to with relational databases like MySQL and Postgres.

Interestingly, these sites also use MySQL. I never had a chance to use or learn about No-SQL databases beforehand but the idea of using two types of databases for one application sounded like a convoluted and unnecessary solution. However, the more I use Redis (especially in these applications) the more I love it.

Redis is used in these applications for caching. When a request it made, rather than PHP sending queries to MySQL, it requests the data directly from Redis, which is pulled straight from the RAM. This results is a much faster response time and requires less resources from the server.

As there are already some good tutorials on what Redis is and how to use it, I will show you some great tricks I found through my travels that I did not see in the general documentation. Start the Redis client (redis-cli) and try the following two tricks:

List All Keys In The Database:

keys *

Show Variable Type:

type <variable-name>

Monitor Queries:
Monitor the queries being sent to Redis by using telnet to login to redis on the port number it’s running (default 6379) and type monitor. This is very helpful if the queries are being sent from an application and you need to debug exactly what’s the query is.

Running Multiple Instances Of Redis:
As I am running multiple applications that require Redis, I needed to learn how to run multiple versions of Redis. This is because you don’t define separate databases like you would with MySQL for example. There is no logins and no way to clearly separate data between applications. An excellent description on how to run multiple version of Redis can be found at chrislaskey.com.

Start Learning:
To get a better understanding of Redis I recommend using the online practical guide found at try.redis-db.com. This guide explains what different types of variables are available and how to access them.

Conclusion:
Redis has shown me what’s available in no-sql databases and that relational databases may not always be the answer. I can see that as I use Redis more in my own projects I will find that it’s useful for other purposes.  One possibility is the storing of variables that I may have previously put into sessions.

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