I wrote a blog post a while back comparing MSMQ and RabbitMQ (among others):

http://mikehadlow.blogspot.co.uk/2011/04/message-queue-shootout.html

RabbitMQ gave slightly better performance than MSMQ, but both were comprehensively out performed by ZeroMQ. If performance is your main criteria, you should definitely look at ZeroMQ.

It&#39;s worth noting that RabbitMQ and MSMQ are very different beasts. MSMQ is a simple store-and-forward queue. It doesn&#39;t provide any messaging patterns, such as pub/sub, or routing. For anything beyond simple point-to-point messaging you&#39;d probably want to use a service bus library such as NServiceBus or MassTransit on top of MSMQ.

RabbitMQ is a sophisticated server product that provides complex messaging patterns, topics and routing out-of-the-box. You also get centralized management and DR, something you&#39;d have to implement yourself if you chose MSMQ.

I&#39;m trying to troubleshoot some intermittent slowdowns in our application. I&#39;ve got a separate question [here][1] with more details.  

I ran sp_who2 to and I&#39;ve noticed a few connections that have a status of SUSPENDED and high DiskIO. Can someone explain to me what that indicates?

![enter image description here][2]


  [1]: https://stackoverflow.com/questions/17816472/how-to-determine-if-the-entity-framework-is-waiting-on-a-connection-from-the-con
  [2]: http://i.stack.imgur.com/ErNeX.png

What does a Status of &quot;Suspended&quot; and high DiskIO means from sp_who2?

How can I select a class from that object `this`?

    $(&quot;.class&quot;).click(function(){
    		$(&quot;this .subclass&quot;).css(&quot;visibility&quot;,&quot;visible&quot;);
    })

I want to select a `$(this+&quot;.subclass&quot;)`. How can I do this with Jquery?

Jquery select this + class

Can I get the comparison between RabbitMQ and MSMQ. It will be helpful performance information on different factors are available.

Comparison between RabbitMQ and MSMQ

<p>Can I get the comparison between RabbitMQ and MSMQ. It will be helpful performance information on different factors are available.</p>


In C/C++, you can set up the following code:

    double a, b, c;
    ...
    c = (a + b) / 2;

This does the exact same thing as:

    c = (a + b) * 0.5;

I&#39;m wondering which is better to use. Is one operation fundamentally faster than the other?

Is multiplication faster than float division?

**Background:**

While optimizing some [Pascal][1] code with embedded assembly language, I noticed an unnecessary `MOV` instruction, and removed it.

To my surprise, removing the un-necessary instruction caused my program to *slow down*.

I found that **adding arbitrary, useless `MOV` instructions increased performance** even further.

The effect is erratic, and changes based on execution order: **the same junk instructions transposed** up or down by a single line **produce a slowdown**.

I understand that the CPU does all kinds of optimizations and streamlining, but, this seems more like black magic.

**The data:**

A version of my code conditionally compiles **three junk operations** in the middle of a loop that runs `2**20==1048576` times. (The surrounding program just calculates [SHA-256][2] hashes).

The results on my rather old machine (Intel(R) Core(TM)2 CPU 6400  @ 2.13&amp;nbsp;GHz):

    avg time (ms) with -dJUNKOPS: 1822.84 ms
    avg time (ms) without:        1836.44 ms

The programs were run 25 times in a loop, with the run order changing randomly each time.

**Excerpt:**

    {$asmmode intel}
    procedure example_junkop_in_sha256;
      var s1, t2 : uint32;
      begin
        // Here are parts of the SHA-256 algorithm, in Pascal:
        // s0 {r10d} := ror(a, 2) xor ror(a, 13) xor ror(a, 22)
        // s1 {r11d} := ror(e, 6) xor ror(e, 11) xor ror(e, 25)
        // Here is how I translated them (side by side to show symmetry):
      asm
        MOV r8d, a                 ; MOV r9d, e
        ROR r8d, 2                 ; ROR r9d, 6
        MOV r10d, r8d              ; MOV r11d, r9d
        ROR r8d, 11    {13 total}  ; ROR r9d, 5     {11 total}
        XOR r10d, r8d              ; XOR r11d, r9d
        ROR r8d, 9     {22 total}  ; ROR r9d, 14    {25 total}
        XOR r10d, r8d              ; XOR r11d, r9d

        // Here is the extraneous operation that I removed, causing a speedup
        // s1 is the uint32 variable declared at the start of the Pascal code.
        //
        // I had cleaned up the code, so I no longer needed this variable, and 
        // could just leave the value sitting in the r11d register until I needed
        // it again later.
        //
        // Since copying to RAM seemed like a waste, I removed the instruction, 
        // only to discover that the code ran slower without it.
        {$IFDEF JUNKOPS}
        MOV s1,  r11d
        {$ENDIF}
        
        // The next part of the code just moves on to another part of SHA-256,
        // maj { r12d } := (a and b) xor (a and c) xor (b and c)
        mov r8d,  a
        mov r9d,  b
        mov r13d, r9d // Set aside a copy of b
        and r9d,  r8d

        mov r12d, c
        and r8d, r12d  { a and c }
        xor r9d, r8d

        and r12d, r13d { c and b }
        xor r12d, r9d

        // Copying the calculated value to the same s1 variable is another speedup.
        // As far as I can tell, it doesn&#39;t actually matter what register is copied,
        // but moving this line up or down makes a huge difference.
        {$IFDEF JUNKOPS}
        MOV s1,  r9d // after mov r12d, c
        {$ENDIF}

        // And here is where the two calculated values above are actually used:
        // T2 {r12d} := S0 {r10d} + Maj {r12d};
        ADD r12d, r10d
        MOV T2, r12d

      end
    end;

**Try it yourself:**

The code is online [at GitHub][3] if you want to try it out yourself.

**My questions:**

 - Why would uselessly copying a register&#39;s contents to [RAM][4] ever increase performance?
 - Why would the same useless instruction provide a speedup on some lines, and a slowdown on others?
 - Is this behavior something that could be exploited predictably by a compiler?

  [1]: http://en.wikipedia.org/wiki/Pascal_%28programming_language%29
  [2]: http://en.wikipedia.org/wiki/SHA-2
  [3]: https://github.com/tangentstorm/coinops/tree/junkops
  [4]: http://en.wikipedia.org/wiki/Random-access_memory


Why would introducing useless MOV instructions speed up a tight loop in x86_64 assembly?

I am currently writing a program in c++ which includes reading lots of large text files. Each has ~400.000 lines with in extreme cases 4000 or more characters per line. Just for testing, I read one of the files using ifstream and the implementation offered by cplusplus.com. It took around 60 seconds, which is way too long. Now I was wondering, is there a straightforward way to improve reading speed?


edit:
The code I am using is more or less this: 

    string tmpString;
    ifstream txtFile(path);
    if(txtFile.is_open())
    {
    	while(txtFile.good())
    	{
    		m_numLines++;
    		getline(txtFile, tmpString);
    	}
    	txtFile.close();
    }

edit 2: The file I read is only 82 MB big. I mainly said that it could reach 4000 because I thought it might be necessary to know in order to do buffering.

edit 3: Thank you all for your answers, but it seems like there is not much room to improve given my problem. I have to use readline, since I want to count the number of lines. Instantiating the ifstream as binary didn&#39;t make reading any faster either. I will try to parallelize it as much as I can, that should work at least.

edit 4: So apparently there are some things I can to. Big thank you to sehe for putting so much time into this, I appreciate it a lot! =) 

Fast textfile reading in c++

Consider two versions of the same loop iteration:

	for (var i = 0; i &lt; nodes.length; i++) {
		...
	}

and

	var len = nodes.length;
	for (var i = 0; i &lt; len; i++) {
		...
	}

Is the latter version anyhow faster than the former one?

For-loop performance: storing array length in a variable

As the title suggests... I&#39;m trying to figure out the fastest way with the least overhead to determine if a record exists in a table or not. 

Sample query:

    SELECT COUNT(*) FROM products WHERE products.id = ?;

        vs

    SELECT COUNT(products.id) FROM products WHERE products.id = ?;

        vs

    SELECT products.id FROM products WHERE products.id = ?;

Say the `?` is swapped with `&#39;TB100&#39;`... both the first and second queries will return the exact same result (say... `1` for this conversation). The last query will return `&#39;TB100&#39;` as expected, or nothing if the `id` is not present in the table. 

The purpose is to figure out if the `id` is in the table or not. If not, the program will next insert the record, if it is, the program will skip it or perform an UPDATE query based on other program logic outside the scope of this question.

Which is faster and has less overhead? (This will be repeated tens of thousands of times per program run, and will be run many times a day). 

(Running this query against M$ SQL Server from Java via the M$ provided JDBC driver)

Fastest way to determine if record exists

1. What are the allowed types of messages (strings, bytes, integers, etc.)?
2. What is the maximum size of a message?
3. What is the maximum number of queues and exchanges?

What are the limits of messages, queues and exchanges?

The [RabbitMQ Java client](http://www.rabbitmq.com/releases/rabbitmq-java-client/v3.1.5/rabbitmq-java-client-javadoc-3.1.5/) has the following concepts:

* `Connection` - a connection to a RabbitMQ server instance
* `Channel` - ???
* Consumer thread pool - a pool of threads that consume messages off the RabbitMQ server queues
* Queue - a structure that holds messages in FIFO order

I&#39;m trying to understand the relationship, **and more importantly**, the *associations* between them.

  1. I&#39;m still not quite sure what a `Channel` is, other than the fact that this is the structure that you publish and consume from, and that it is created from an open connection. If someone could explain to me what the &quot;Channel&quot; represents, it might help clear a few things up.
  2. What is the relationship between Channel and Queue? Can the same Channel be used to communicate to multiples Queues, or does it have to be 1:1?
  3. What is the relationship between Queue and the Consumer Pool? Can multiple Consumers be subscribed to the same Queue? Can multiple Queues be consumed by the same Consumer? Or is the relationship 1:1?

RabbitMQ and relationship between channel and connection

I just read [RabbitMQ&#39;s Java API docs](http://www.rabbitmq.com/api-guide.html), and found it very informative and straight-forward. The example for how to set up a simple `Channel` for publishing/consuming is very easy to follow and understand. But it&#39;s a very simple/basic example, and it left me with an important question: **How can I set up 1+ `Channels` to publish/consume to and from multiple queues?**

Let&#39;s say I have a RabbitMQ server with 3 queues on it: `logging`, `security_events` and `customer_orders`. So we&#39;d either need a single `Channel` to have the ability to publish/consume to all 3 queues, or more likely, have 3 separate `Channels`, each dedicated to a single queue.

On top of this, RabbitMQ&#39;s best practices dictate that we set up 1 `Channel` per consumer thread. For this example, let&#39;s say `security_events` is fine with only 1 consumer thread, but `logging` and `customer_order` both need 5 threads to handle the volume. So, if I understand correctly, does that mean we need:

* 1 `Channel` and 1 consumer thread for publishing/consuming to and from `security_events`; and
* 5 `Channels` and 5 consumer threads for publishing/consuming to and from `logging`; and
* 5 `Channels` and 5 consumer threads for publishing/consuming to and from `customer_orders`?

If my understanding is misguided here, please begin by correcting me. Either way, could some battle-weary RabbitMQ veteran **help me &quot;connect the dots&quot; with a decent code example for setting up publishers/consumers that meet my requirements here?** Thanks in advance!

RabbitMQ by Example: Multiple Threads, Channels and Queues

The &quot;RabbitMQ in Action&quot; book on page 19 gives these descriptions of exclusive and auto-delete:

&gt; exclusive - When set to true, your queue becomes private and can only
&gt; be consumed by your app. This is useful when you need to limit a queue
&gt; to only one consumer.
&gt; 
&gt; auto-delete - The queue is automatically deleted when the last
&gt; consumer unsubscribes. If you need a temporary queue used only by one
&gt; consumer, combine auto-delete with exclusive. When the consumer
&gt; disconnects, the queue will be removed.

But as far as I can see when using exclusive, auto-delete is redundant. Only exclusive is needed. The RabbitMQ [tutorial][1] seems to say that is the case

&gt; ...once we disconnect the consumer the queue should be deleted. There&#39;s
&gt; an exclusive flag for that:

    result = channel.queue_declare(exclusive=True)

There is no mention in that tutorial about auto-delete and `sudo rabbitmqctl list_bindings` seems to indicate that the queue is in fact deleted after the receiver goes away.

  [1]: http://www.rabbitmq.com/tutorials/tutorial-three-python.html

RabbitMQ difference between exclusive and auto-delete?

I need to choose a new Queue broker for my new project.  

This time I need a scalable queue that supports pub/sub, and keeping message ordering is a must.  

I read Alexis comment: He writes:

&gt; &quot;Indeed, we think RabbitMQ provides stronger ordering than Kafka&quot;

I read the message ordering section in rabbitmq docs:

    

&gt; &quot;Messages can be returned to the queue using AMQP methods that feature
&gt; a requeue
&gt;      parameter (basic.recover, basic.reject and basic.nack), or due to a channel 
&gt;      closing while holding unacknowledged messages...With release 2.7.0 and later 
&gt;      it is still possible for individual consumers to observe messages out of 
&gt;      order if the queue has multiple subscribers. This is due to the actions of 
&gt;      other subscribers who may requeue messages. From the perspective of the queue 
&gt;      the messages are always held in the publication order.&quot;

If I need to handle messages by their order, I can only use rabbitMQ with an exclusive queue to each consumer?  

Is RabbitMQ still considered a good solution for ordered message queuing?




RabbitMQ - Message order of delivery

This two images are from http://zguide.zeromq.org/page:all.

What is the difference between this two pattern if we ignore sink in push-pull pattern ?
Is there a difference in how a message gets transfer, if yes what is the difference ?

![](https://github.com/imatix/zguide/raw/master/images/fig4.png)
![](https://github.com/imatix/zguide/raw/master/images/fig5.png)


 

difference between pub-sub and push-pull pattern in zeroMq

I&#39;ve been getting more into the internals of the Node.js architecture, and a term I see coming up a lot is &quot;tick&quot; as in &quot;next tick of the event loop&quot; or the function [nextTick()][1].

What I haven&#39;t seen is a solid definition of what exactly a &quot;tick&quot; is. Based on various articles ([such as this one][2]), I&#39;ve been able to piece a concept together in my head, but I&#39;m not sure how accurate it is.

Can I get a precise and detailed description of a Node.js event loop tick?

  [1]: http://nodejs.org/docs/latest/api/process.html#process_process_nexttick_callback
  [2]: http://howtonode.org/understanding-process-next-tick

What exactly is a Node.js event loop tick?

What&#39;s the maximum number of queues that RabbitMQ can handle on a single server?

Does it depend on RAM? Does it depends on erlang processes?

Content Type	Original Author	Original Content on Stackoverflow
Question	N K	View Question on Stackoverflow
Solution 1 - Performance	Mike Hadlow	View Answer on Stackoverflow

Comparison between RabbitMQ and MSMQ

Performance Problem Overview

Performance Solutions

Solution 1 - Performance

Jquery select this + class

What does a Status of "Suspended" and high DiskIO means from sp_who2?

Attributions