Setting up the Redis Server
Before we can play with Redis, you will need to get the server running locally. Luckily, that's very easy.
Building Redis is a simple matter of grabbing the code and compiling it. Once built, you can place the executables in a convenient location in your
PATH. On my box, I can do all of that with these commands:
curl -O http://redis.googlecode.com/files/redis-1.0.tar.gz
tar xzvf redis-1.0.tar.gz
sudo cp redis-server redis-cli redis-benchmark /usr/local/bin
Those commands build version 1.0 of the server, which is the current stable release as of this writing. You may need to adjust the version numbers down the road to get the latest releases though.
I also copied the executables to where I prefer to have them:
/usr/local/bin. Feel free to change that directory in the last command to whatever you prefer.
If you will be talking to Redis from Ruby, as I will show in all of my examples, you are going to need a client library. I recommend Ezra Zygmuntowicz's redis-rb. You can install that gem with:
gem install redis
Running and Configuring Redis
That's it for the install. Launching the server is even easier. The pattern is just:
The argument is the path to the configuration file that tells Redis how you want it to behave. There's a sample configuration file in the Redis source code that shows the options.
I'm not going to discuss all of the configuration options. They are already well commented in the sample file. However, I do want to mention a few things.
First, if you will only be connecting to a local Redis instance, uncomment the
bind configuration in the sample file:
That tells Redis not to listen for external connections.
If you do need to accept external connections, you may want to set a limit for the number of simultaneous connections to avoid exhausting the file descriptors on your server. You can also adjust the timeout for inactive connections to reclaim those resources:
There are some other non-network limits you may wish to fiddle with as well.
By default, Redis supports multiple databases. It even has a
move() command that allows you to transfer keys between databases. I find I usually only want one though. I'm more likely to launch multiple servers if I want more. This would allow me to control resources, like memory consumption, on a per database basis, at the cost of losing the atomic
move(). Even if I didn't just want one database though, I think it would be rare to need the 16 that are configured by default. You can easily turn that down:
Another limit you may want to consider setting is the maximum memory limit. If you plan to use Redis as a memcached replacement, you will likely wish to control how much memory it can consume. You can set the maximum number of bytes Redis can allocate, after which it will start purging volatile keys. If it cannot reclaim any more memory it will start refusing write commands. Here's a sample setting for a 100MB limit:
Note that the above setting is really only a good idea when using Redis as a cache. If you are using it as a general database, you will need to monitor its memory consumption and take action before too many resources are consumed.
The last setting I want to talk about is probably the most important for using Redis.
The server will periodically fork and asynchronously dump the current contents of the database to disk. The dump is actually made to a temporary file and then moved to replace any older dump, so the operation is atomic and won't leave you with a partially dumped database. If Redis is eventually shutdown and reloaded, it will restore from this dump file.
How often it dumps the keys is configureable by the amount of time that passes and the number of changes that have been made to the data. For example, the following settings tell Redis to dump the database after 60 seconds if 100 changes have been made or after five minutes if there has been at least 1 change:
save 300 1
save 60 100
As you can see, you can set several different conditions. As soon as any one line of conditions matches, meaning both the time and the changes much match, the database is dumped and both counts restart.
Note that the time condition can be met before the changes. This means that, using the settings above, I can launch a Redis server, let it sit for five or more minutes, and then change a single key to trigger an immediate dump. The time will have already passed and as soon as I make the changes condition true as well, that is enough. In other words, I don't have to wait five minutes after I make the change.
That covers plenty about installing and running the Redis server. You are now all set to play with it.