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antirez 7eb850ef0e A reimplementation of blocking operation internals.
Redis provides support for blocking operations such as BLPOP or BRPOP.
This operations are identical to normal LPOP and RPOP operations as long
as there are elements in the target list, but if the list is empty they
block waiting for new data to arrive to the list.

All the clients blocked waiting for th same list are served in a FIFO
way, so the first that blocked is the first to be served when there is
more data pushed by another client into the list.

The previous implementation of blocking operations was conceived to
serve clients in the context of push operations. For for instance:

1) There is a client "A" blocked on list "foo".
2) The client "B" performs `LPUSH foo somevalue`.
3) The client "A" is served in the context of the "B" LPUSH,
synchronously.

Processing things in a synchronous way was useful as if "A" pushes a
value that is served by "B", from the point of view of the database is a
NOP (no operation) thing, that is, nothing is replicated, nothing is
written in the AOF file, and so forth.

However later we implemented two things:

1) Variadic LPUSH that could add multiple values to a list in the
context of a single call.
2) BRPOPLPUSH that was a version of BRPOP that also provided a "PUSH"
side effect when receiving data.

This forced us to make the synchronous implementation more complex. If
client "B" is waiting for data, and "A" pushes three elemnents in a
single call, we needed to propagate an LPUSH with a missing argument
in the AOF and replication link. We also needed to make sure to
replicate the LPUSH side of BRPOPLPUSH, but only if in turn did not
happened to serve another blocking client into another list ;)

This were complex but with a few of mutually recursive functions
everything worked as expected... until one day we introduced scripting
in Redis.

Scripting + synchronous blocking operations = Issue #614.

Basically you can't "rewrite" a script to have just a partial effect on
the replicas and AOF file if the script happened to serve a few blocked
clients.

The solution to all this problems, implemented by this commit, is to
change the way we serve blocked clients. Instead of serving the blocked
clients synchronously, in the context of the command performing the PUSH
operation, it is now an asynchronous and iterative process:

1) If a key that has clients blocked waiting for data is the subject of
a list push operation, We simply mark keys as "ready" and put it into a
queue.
2) Every command pushing stuff on lists, as a variadic LPUSH, a script,
or whatever it is, is replicated verbatim without any rewriting.
3) Every time a Redis command, a MULTI/EXEC block, or a script,
completed its execution, we run the list of keys ready to serve blocked
clients (as more data arrived), and process this list serving the
blocked clients.
4) As a result of "3" maybe more keys are ready again for other clients
(as a result of BRPOPLPUSH we may have push operations), so we iterate
back to step "3" if it's needed.

The new code has a much simpler semantics, and a simpler to understand
implementation, with the disadvantage of not being able to "optmize out"
a PUSH+BPOP as a No OP.

This commit will be tested with care before the final merge, more tests
will be added likely.
2012-09-17 10:26:46 +02:00
deps hiredis library updated. 2012-08-21 17:27:01 +02:00
src A reimplementation of blocking operation internals. 2012-09-17 10:26:46 +02:00
tests A reimplementation of blocking operation internals. 2012-09-17 10:26:46 +02:00
utils Merge pull request #494 from quiver/init-fixes 2012-05-04 04:41:02 -07:00
.gitignore First implementation of Redis Sentinel. 2012-07-23 13:14:44 +02:00
00-RELEASENOTES Fix version numbers 2012-08-02 15:10:51 +03:00
BUGS Switched issues URL to Github in BUGS 2011-10-18 14:28:23 -04:00
Changelog Make log target fixed 2010-07-01 14:45:37 +02:00
CONTRIBUTING Cleaned up redis root directory and changed links for redis.io and github issues and pull requests 2011-10-18 14:14:16 -04:00
COPYING first commit 2009-03-22 10:30:00 +01:00
INSTALL INSTALL now redirects the user to README 2012-02-05 09:38:41 +01:00
Makefile Fix install target on OSX (see #495) 2012-05-15 11:18:50 +02:00
MANIFESTO Redis Manifesto moved from src to root dir 2012-02-05 09:37:08 +01:00
README README now makes clear that our support for solaris derived systems is "best effort". 2012-04-21 12:08:26 +02:00
redis.conf Sentinel: added documentation about slave-priority in redis.conf 2012-08-28 17:53:18 +02:00
runtest A few small BSD related fixes. 2012-02-08 22:24:59 +01:00
sentinel.conf Sentinel: client reconfiguration script execution. 2012-08-02 18:40:30 +02:00

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!