Order of received commands

[lpinca]

When using multi or pipeline the order of the commands received by the server is not the expected one:

'use strict';

var Redis = require('ioredis')
  , redis = new Redis();

redis.multi().del('foo').del('bar').exec();
redis.get('foo');

127.0.0.1:6379> MONITOR
OK
1436173662.820473 [0 127.0.0.1:50646] "info"
1436173662.827039 [0 127.0.0.1:50646] "get" "foo"
1436173662.827608 [0 127.0.0.1:50646] "multi"
1436173662.827623 [0 127.0.0.1:50646] "del" "foo"
1436173662.827629 [0 127.0.0.1:50646] "del" "bar"
1436173662.827633 [0 127.0.0.1:50646] "exec"

With node_redis the same code executes the commands in the expected order:

127.0.0.1:6379> MONITOR
OK
1436173811.377020 [0 127.0.0.1:50651] "info"
1436173811.381943 [0 127.0.0.1:50651] "MULTI"
1436173811.382434 [0 127.0.0.1:50651] "del" "foo"
1436173811.382443 [0 127.0.0.1:50651] "del" "bar"
1436173811.382448 [0 127.0.0.1:50651] "EXEC"
1436173811.382520 [0 127.0.0.1:50651] "get" "foo"

Is this wanted?

[luin]

Typically if you want to make sure the execution order of commands, you should either using pipelining or invoking another command after the previous command returning. For instance:

redis.pipeline().multi().del('foo').del('bar').exec().get('foo').exec();

Or

redis.multi().del('foo').del('bar').exec(function () {
  redis.get('foo');
});

This is because although almost all simple commands are sent to the redis server follow the exactly same order they invoked, there are still some exceptions. For example when invoking a custom lua command:

redis.echo();
redis.get('foo');

ioredis first sends evalsha xxx to the redis server and then send get. However if redis returns a NOSCRIPT error for the evalsha command, ioredis will re-send eval xxx instead. So that outwardly echo is sent after get command.

When it comes to multi/exec, ioredis internally queues commands in the other event loop, so it's sent after the latter commands. As for me, I don't like this behaviour and I'm going to make some changes to queue commands in the same event loop. However although not endearing, the current behaviour isn't wrong.

[lpinca]

I understand, thanks for the explanation.
Unfortunately I can't use a callback or a pipeline because I have something like this:

emitter.on('foo', function () {
  redis.multi().del('bar').del('baz').exec();
});

emitter.on('foo', function () {
  redis.get.('bar', function (err, res) {
    if (res) console.log('(屮ಠ益ಠ)屮 Y U STILL HERE');
  });
});

and the two listerners can't be merged because the second one is attached later. A workaround for this particular case is to call redis.get in the next tick, but I'm a bit worried about possible race conditions in a general use case.

[luin]

I'm going to try to change this behaviour at this weekend to make multi works like other simple commands.

BTW just some random workarounds:

emitter.on('foo', function () {
  redis.multi().del('bar').del('baz').exec();
});

emitter.on('foo', function () {
  setImmediate(function () {
    redis.get.('bar', function (err, res) {
      if (res) console.log('(屮ಠ益ಠ)屮 Y U STILL HERE');
    });
  });
});

emitter.on('foo', function () {
  redis.multi().del('bar').del('baz').exec(function () {
    emitter.emit('after foo');
  });
});

emitter.on('after foo', function () {
  redis.get.('bar', function (err, res) {
    if (res) console.log('(屮ಠ益ಠ)屮 Y U STILL HERE');
  });
});

emitter.on('foo', function () {
  redis.multi({ pipeline: false });
  redis.del('bar');
  redis.del('baz');
  redis.exec();
});

emitter.on('foo', function () {
  redis.get.('bar', function (err, res) {
    if (res) console.log('(屮ಠ益ಠ)屮 Y U STILL HERE');
  });
});

[lpinca]

The last example with { pipeline: false }, works well for my use case, thanks.
Just a minor thing: it would be nice if the callback for exec was optional, right now an error is thrown if one is not provided.

'use strict';

var Redis = require('ioredis')
  , redis = new Redis();

redis.multi({ pipeline: false });
redis.del('foo');
redis.del('bar');
redis.exec();

macbook:order luigi$ node index.js 
/Users/luigi/Desktop/order/node_modules/ioredis/node_modules/bluebird/js/main/async.js:43
        fn = function () { throw arg; };
                                 ^
TypeError: undefined is not a function
    at wrapper (/Users/luigi/Desktop/order/node_modules/ioredis/lib/transaction.js:58:7)
    at tryCatcher (/Users/luigi/Desktop/order/node_modules/ioredis/node_modules/bluebird/js/main/util.js:24:31)
    at Promise.successAdapter (/Users/luigi/Desktop/order/node_modules/ioredis/node_modules/bluebird/js/main/nodeify.js:22:30)
    at Promise._settlePromiseAt (/Users/luigi/Desktop/order/node_modules/ioredis/node_modules/bluebird/js/main/promise.js:563:21)
    at Promise._settlePromises (/Users/luigi/Desktop/order/node_modules/ioredis/node_modules/bluebird/js/main/promise.js:681:14)
    at Async._drainQueue (/Users/luigi/Desktop/order/node_modules/ioredis/node_modules/bluebird/js/main/async.js:123:16)
    at Async._drainQueues (/Users/luigi/Desktop/order/node_modules/ioredis/node_modules/bluebird/js/main/async.js:133:10)
    at Immediate.Async.drainQueues [as _onImmediate] (/Users/luigi/Desktop/order/node_modules/ioredis/node_modules/bluebird/js/main/async.js:15:14)
    at processImmediate [as _immediateCallback] (timers.js:367:17)

[luin]

Fixed in 1.5.11. 😄

[lpinca]

👍