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SRANDMEMBER called with just the key argument can just return a single random element from a Redis Set. However many users need to return multiple unique elements from a Set, this is not a trivial problem to handle in the client side, and for truly good performance a C implementation was required. After many requests for this feature it was finally implemented. The problem implementing this command is the strategy to follow when the number of elements the user asks for is near to the number of elements that are already inside the set. In this case asking random elements to the dictionary API, and trying to add it to a temporary set, may result into an extremely poor performance, as most add operations will be wasted on duplicated elements. For this reason this implementation uses a different strategy in this case: the Set is copied, and random elements are returned to reach the specified count. The code actually uses 4 different algorithms optimized for the different cases. If the count is negative, the command changes behavior and allows for duplicated elements in the returned subset.
Where to find complete Redis documentation? ------------------------------------------- This README is just a fast "quick start" document. You can find more detailed documentation at http://redis.io Building Redis -------------- Redis can be compiled and used on Linux, OSX, OpenBSD, NetBSD, FreeBSD. We support big endian and little endian architectures. It may compile on Solaris derived systems (for instance SmartOS) but our support for this platform is "best effort" and Redis is not guaranteed to work as well as in Linux, OSX, and *BSD there. It is as simple as: % make You can run a 32 bit Redis binary using: % make 32bit After building Redis is a good idea to test it, using: % make test NOTE: if after building Redis with a 32 bit target you need to rebuild it with a 64 bit target you need to perform a "make clean" in the root directory of the Redis distribution. Allocator --------- Selecting a non-default memory allocator when building Redis is done by setting the `MALLOC` environment variable. Redis is compiled and linked against libc malloc by default, with the exception of jemalloc being the default on Linux systems. This default was picked because jemalloc has proven to have fewer fragmentation problems than libc malloc. To force compiling against libc malloc, use: % make MALLOC=libc To compile against jemalloc on Mac OS X systems, use: % make MALLOC=jemalloc Verbose build ------------- Redis will build with a user friendly colorized output by default. If you want to see a more verbose output use the following: % make V=1 Running Redis ------------- To run Redis with the default configuration just type: % cd src % ./redis-server If you want to provide your redis.conf, you have to run it using an additional parameter (the path of the configuration file): % cd src % ./redis-server /path/to/redis.conf It is possible to alter the Redis configuration passing parameters directly as options using the command line. Examples: % ./redis-server --port 9999 --slaveof 127.0.0.1 6379 % ./redis-server /etc/redis/6379.conf --loglevel debug All the options in redis.conf are also supported as options using the command line, with exactly the same name. Playing with Redis ------------------ You can use redis-cli to play with Redis. Start a redis-server instance, then in another terminal try the following: % cd src % ./redis-cli redis> ping PONG redis> set foo bar OK redis> get foo "bar" redis> incr mycounter (integer) 1 redis> incr mycounter (integer) 2 redis> You can find the list of all the available commands here: http://redis.io/commands Installing Redis ----------------- In order to install Redis binaries into /usr/local/bin just use: % make install You can use "make PREFIX=/some/other/directory install" if you wish to use a different destination. Make install will just install binaries in your system, but will not configure init scripts and configuration files in the appropriate place. This is not needed if you want just to play a bit with Redis, but if you are installing it the proper way for a production system, we have a script doing this for Ubuntu and Debian systems: % cd utils % ./install_server The script will ask you a few questions and will setup everything you need to run Redis properly as a background daemon that will start again on system reboots. You'll be able to stop and start Redis using the script named /etc/init.d/redis_<portnumber>, for instance /etc/init.d/redis_6379. Enjoy!
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