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er: erlang redis

Status

er is production ready. er is feature complete with redis-2.2 as of antirez/redis@59aee5513d27fdf2d24499f35611093fa0fab3fb

Code Guide

src/er.lfe and src/erp.lfe are where redis commands get created.

er.lfe creates a module where the first parameter of all commands is the redis connection (the conenction is either a er_redis PID or er_pool name): {ok, Client} = er_redis:connect(). er:set(Client, <<"chevron">>, <<"locked">>).

erp.lfe creates a parameterized module where the redis connection is carried through all the commands: {ok, Client} = er_redis:connect(). RedisClient = erp:new(Client). RedisClient:set(<<"artist">>, <<"pallett">>).

er_pool.erl gives you a centrally managed connection pool of redis clients. Create a named pool, then use regular er commands against it. If you use a command requiring exclusive use of a client (b[lr]pop, brpoplpush, subscribe, watch, etc), the client is taken out of the general pool and reserved for your individual use. When the client is done with exclusive operations, the client is returned to the general connection pool.

Connect and use anonymous pid

    {ok, Client} = er_pool:start_link().
    er:set(Client, italian, greyhound).
    <<"greyhound">> = er:get(Client, italian).

Connect and use named pool (no need for pid tracking)

    er_pool:start_link(userdb).
    er:set(userdb, hash_value_1, erlang:md5(<<"hash this">>).
    er:lpush(userdb, updates, hash_value_1).

Blocking Pop

Blocking pop blocks the current process until Timeout (600 seconds below) or until an item becomes available. Blocking operations return the atom nil on timeout. er_pool:start_link(workqueue_pool). er:blpop(workqueue_pool, blocked_key, 600).

PubSub

    er_pool:start_link(announcements).
    % Subscribe to key `another`.  Returns a pid and subscribe validation.
    {SubClientPid, [subscribe, <<"another">>, 1]} = er:subscribe(announcements, another).

    % To receive published messages, run a blocking receive.
    % er_next blocks your current process until something is published.
    % You can run er:er_next(SubClientPid) in a loop to consume all published messages.
    [message, <<"bob">>, PublishedMessage] = er:er_next(SubClientPid).

    % Clean up when you are done to avoid leaking processes and sockets:
    SubClientPid ! shutdown.

For per-command usage examples, see test/er_tests.erl.

er_redis.erl was mainly taken from http://github.com/bmizerany/redis-erl/blob/master/src/redis.erl then heavily modified to fit my purposes better. Only 20 to 30 lines of the original file survived.

Since er and erp perform the same functions only with slightly different interfaces, most of their code is shared by directly including common files.

See files include/{utils,utils-macro,redis-cmds,redis-return-types}.lfe:

  • utils.lfe - shared utility functions
  • utils-macro.lfe - includes the macro which generates return value macros
  • redis-cmds.lfe - all redis commands and their return type handlers
  • redis-return-types.lfe - an alternate format of specifying redis return types. Contains functions for converting redis return values to native types.

Building

Download LFE: ./rebar get-deps

Build: ./rebar compile

Testing

NB: Tests run against a redis on port 6991. Running tests WILL DELETE ALL DATA on your port 6991 redis. ./rebar compile cd test erlc *.erl erl -pa ../ebin 1> er_tests:test(). 2> er_concurrency_tests:test().

Next Steps

In no specific order:

  • More comprehensive test cases for er/erp
  • More features
    • bidirectional mnesia sync?
    • redis as erlang term store vs. redis as generic store
    • generate modules for pre-defined common accessors

When to use er

Use er when you want to access redis from erlang.

er converts redis return types to erlang-friendly terms. redis 1 and 0 responses are converted to true/false atoms when appropriate. redis binary results are returned as erlang binaries. redis integer results are returned as erlang numbers.

er aims to be the most semantically correct erlang redis client with a sane translation layer between how redis views the world and how erlang views the world.

Contributions

Want to help? Patches welcome.

  • Poke around in test/er_tests.erl and add some missing tests.
  • Write something to parse include/er-cmds.lfe and output docs for return types.
  • Make a nicer interface to pubsub and blocking calls.
  • Find a bug. Fix a bug.
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