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SDIFF used an algorithm that was O(N) where N is the total number of elements of all the sets involved in the operation. The algorithm worked like that: ALGORITHM 1: 1) For the first set, add all the members to an auxiliary set. 2) For all the other sets, remove all the members of the set from the auxiliary set. So it is an O(N) algorithm where N is the total number of elements in all the sets involved in the diff operation. Cristobal Viedma suggested to modify the algorithm to the following: ALGORITHM 2: 1) Iterate all the elements of the first set. 2) For every element, check if the element also exists in all the other remaining sets. 3) Add the element to the auxiliary set only if it does not exist in any of the other sets. The complexity of this algorithm on the worst case is O(N*M) where N is the size of the first set and M the total number of sets involved in the operation. However when there are elements in common, with this algorithm we stop the computation for a given element as long as we find a duplicated element into another set. I (antirez) added an additional step to algorithm 2 to make it faster, that is to sort the set to subtract from the biggest to the smallest, so that it is more likely to find a duplicate in a larger sets that are checked before the smaller ones. WHAT IS BETTER? None of course, for instance if the first set is much larger than the other sets the second algorithm does a lot more work compared to the first algorithm. Similarly if the first set is much smaller than the other sets, the original algorithm will less work. So this commit makes Redis able to guess the number of operations required by each algorithm, and select the best at runtime according to the input received. However, since the second algorithm has better constant times and can do less work if there are duplicated elements, an advantage is given to the second algorithm.
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.
Code contributions
---
Note: by contributing code to the Redis project in any form, including sending
a pull request via Github, a code fragment or patch via private email or
public discussion groups, you agree to release your code under the terms
of the BSD license that you can find in the COPYING file included in the Redis
source distribution.
Please see the CONTRIBUTING file in this source distribution for more
information.
Enjoy!
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