ZeroMq IRC Log

Wednesday June 15, 2011

[Time] Name	Message
[00:01] dhawth	nevermind, the fix was to set DYLD_LIBRARY_PATH to the location of the shared libs. I shall send mail to jzmq suggesting the add a note about this to the readme in case anyone else runs into it.
[10:04] PaowZ	hello there ! got a question about multiple socket connection, when a client connect to two servers, for instance..
[10:05] PaowZ	it concerns this piece of python code.. http://nichol.as/zeromq-an-introduction
[10:05] PaowZ	"Selecting a message pattern" section.
[10:06] PaowZ	my question is: for 10 send(), why servers both receive 5 requests and not 10 ?
[10:07] PaowZ	how is request handling done by multiple servers ?
[10:07] PaowZ	thanks :)
[10:08] guido_g	hint: load balancing
[10:10] PaowZ	load balancing ? okay.. and I guess that if we have an odd number of sends, one server shall have to handle one more request..
[10:11] guido_g	this kind of things is explained in the guide, btw
[13:06] drbobbeaty	Has anyone heard of any kind of ZMQ-over-RDMA (on 10GbE)? I'm being asked for some kind of RDMA/RoCE and wanted to know if there is anyone that has done something like this in the ZeroMQ-space.
[13:15] pieterh	drbobbeaty: what message size, any idea?
[13:16] drbobbeaty	pieterh: The messages are all in the sub-1Kb size... all are exchange feed messages. So there are a lot of them, but none are all that big. Probably 80% are below 128bytes.
[13:17] pieterh	so the only benefit of RDMA would be latency, not throughput
[13:18] drbobbeaty	That, and the exchange feed socket reading and message decoding could be done on another box where the jumps to kernel space would be paid - leaving the other box just to "use" the data.
[13:19] pieterh	so to use as a superfast interconnect between two tasks on different boxes
[13:20] pieterh	it would mean changing the libzmq TCP transport to use RDMA
[13:20] pieterh	no-one's done that to my knowledge
[13:20] pieterh	or they haven't shared...
[13:21] pieterh	the VTX layer I'm building could be another option
[13:22] pieterh	you basically build an inprocess bridge that does weird stuff at one edge, and inproc at the other
[13:22] pieterh	that then emulates a 'normal' socket
[13:22] pieterh	would be fairly doable to get SUB socket emulation over VTX and RDMA, I reckon
[13:31] drbobbeaty	OK, can you please keep me up to date (or just announce it) when you have something like this I can look at and benchmark? I'd really appreciate it.
[13:40] pieterh	drbobbeaty: highly unlikely anyone will make this unless there's a pulling client
[13:42] drbobbeaty	pieterh: Seems reasonable. The NYSE came by selling something like this, and it wasn't going to be cheap. I didn't see anything in a quick open source scan that would do this. So I think it's got to be demand-driven.
[13:43] pieterh	what we have is a plausible framework for integrating an eventual RDMA driver with 0MQ apps
[13:43] drbobbeaty	pieterh: I'll see if they are interested in being that demand.
[13:43] pieterh	sure
[13:43] pieterh	the VTX work is happening at http://zero.mq/vtx if you want details
[14:01] john	I am having trouble understanding how to divide up my program using zmq. Should I make a separate thread for every function that takes any period of time to execute?
[14:02] john	Is there any documentation that provides a guideline for when/how to spearate out each function of a complex system using zmq?
[14:05] john	Is there a guide for best coding practices for distributed systems using 0mq?
[14:07] drbobbeaty	john___: Good questions, all, but the point of ZMQ is that it's the transport layer to do all kinds of messaging things. Figuring out how to working messaging into an app is something you sort-of need to come to the party with. It's a far more general, and therefore, far more open-ended and complex topic than specifics about ZMQ.
[14:08] drbobbeaty	john___: It's like using threads, in general. You have to have some basis of understanding why you'd want to use them in the first place to then talk about the differences in the boost::thread library or the native pthreads, etc. See what I mean?
[14:08] travlr	john___: Reading the guide may inspire certain architectures though... http://zero.mq/zg
[14:08] michelp	john___, i found that reading some erlang books helped me understand how to design applications in a message passing environment. it's not perfect but it's a good start
[14:09] drbobbeaty	michelp: very good point. Erlang forces you to think in those terms.
[14:09] michelp	lately i've been selling 0mq to my colleagues by telling them "it's like erlang for all languages"
[14:11] john	Yeah I'll have to check out some erlang books. It's just a whole nother paradigm that I haven't yet got my head around.
[14:15] john	The other issue I'm having is since zmq doesn't force you to use any particular messaging protocol, is there any common one's out there?
[14:15] john	I guess it kind of depends on what kind of data is being passed.
[14:20] michelp	well i'm using python pickles :)
[14:20] michelp	but there's protocol buffers, and others like that
[14:21] john	yeah I've been using pickles too.
[14:22] john	I suppose as long as everything is programmed in python, pickling things is okay.
[14:22] michelp	if both ends of your project are pickles then it's a very flexible approach
[14:22] michelp	er... s/pickles/python
[14:22] michelp	cuz protobuffs and stuf like that need to be declared and maintained
[14:23] john	yeah.
[14:25] pieterh	john___: here's my under-intellectualized opinion on serialization: http://unprotocols.org/blog:9
[14:32] mrmermaid	Hello all, I'm doing projects with ZMQ on Java. Can someone please tell me if there is anyway to limit a number of connection to a PULL socket, and notify when that limit is reached?
[14:33] john	so Cheap would be used to trigger a process or send small bits of information? And nasty would be for sending complex data structures in a serialized fashion like pickle?
[14:34] john	to pieterh ^
[14:34] pieterh	john___: Cheap would be for low-volume complex messages, Nasty for high-volume simple messages
[14:34] pieterh	in most distributed architectures, messages fall into these two categories
[14:35] pieterh	for example, you typically have control and data flows
[14:35] pieterh	where control is low volume and complex (e.g. logging statistics)
[14:36] pieterh	and data is high-volume and simple (e.g. market data)
[14:36] john	ok so something like streaming video would be high volume
[14:36] pieterh	yes
[14:36] pieterh	and often you'll have multiple levels of encoding
[14:39] nicolas	I am currently using C structs for pub/sub fast data flow
[14:39] nicolas	and protocol buffers for commands req/rep
[14:40] pieterh	makes sense... formats like JSON are a real pain to work with in C
[14:45] john	Protocol buffers seem interesting, and very simple
[14:47] ASY	pieterh: are you around for the next 5 min? I would like to run few questions by you. trying to figure out the best way to structure ZMQ use in my alg.
[14:47] pieterh	ASY: I was actually about to leave but shoot...
[14:47] ASY	thanks. 1 sec.
[14:48] ASY	i have a very performance sensetive application that relays data from multiple threads to multiple ZMQ clients. it needs to be stateful, i.e. each client uses dedicated push/pull pair.
[14:50] pieterh	ok...
[14:51] ASY	1st question: i receive data from multiple threads. each thread has associated zmq push socket. I am looking at doing a blocking send() from within this thread, which means I am looking at creating a dedicated context for each thread. Alternative solution is to channel everything down the single poll loop. polls are difficult because I have SENDING socket but I can not signal a poll to
[14:51] ASY	pick up data and send it the second it is ready. I could use another internal socket to cause poll loop to cycle. it would be like a "data ready" event notifier. that would cause poll to examine senders and send out data immediately.
[14:52] pieterh	what is "performance" in your case?
[14:52] pieterh	how many clients, how many msg/sec
[14:53] ASY	the last one sounds like a correct approach. just use another socket for messaging. but that channels everything down to a single thread (that does polling) and I am wondering that this may endup being not very efficient. although efficiency is always a questionable factor. I need to ensure that in my sending of data from multiple providers there is less then 1ms delay. --- I have a
[14:53] ASY	millisecond clock(s) going out on the screen. there can be let's say 10-20 data providers but one of them may be feeding clock updates every millisecond...
[14:54] pieterh	just use poll
[14:54] pieterh	it sounds like you're making it much too complex
[14:55] pieterh	to solve performance problems you don't have
[14:55] ASY	so whenever data is ready on the thread, send it to an event socket, that causes poll rotation and upon rotation if will see that data is ready and send it when POLL_OUT state is available.
[14:55] pieterh	also, it'd help a lot if you start by explaining your use case
[14:55] pieterh	rather than the solution
[14:55] pieterh	since your solution is most likely wrong
[14:55] ASY	lol
[14:55] pieterh	and I can't read your mind about what your design process was :)
[14:56] ASY	well, i have different data providers
[14:56] ASY	that send property updates from multiple directions/devices/sockets/pipes/threads you name it.
[14:56] pieterh	that's it?
[14:56] ASY	all of this goes into a single in-memory hash.
[14:56] pieterh	ah
[14:57] ASY	and needs to be distributed to clients
[14:57] pieterh	have you read the Guideclone pattern?
[14:57] pieterh	*Guide clone pattern
[14:58] ASY	i am sure i did at some point.
[14:58] pieterh	it covers exactly this, property distribution to multiple clients
[14:58] ASY	my problem is state
[14:58] pieterh	ASY, I have to go, so please send an email to the list, with background and maybe a diagram
[14:58] ASY	when client connects, he and only he because he connected needs a full state flush so that he can establish the state since further messages are only deltas
[14:58] pieterh	cyl
[14:59] ASY	k
[14:59] ASY	cheers
[15:05] john	is there a simple way of keeping track of how many subscribers are currently connected?
[15:11] mrmermaid	I lost the connection, but can anyone please point me to the right direction to limit the number of connections to a PULL socket ?
[15:15] mrmermaid	What I'm trying to do is having a server with a Pull socket, and client with push socket
[15:18] PaowZ	hello there! just entered the word of 0MQ and saw that the archive contains what one needs to build from MSVC under windows.. but what if I wish to build the lib using mingw32 ?
[16:41] john	I am getting a weird error when I try to start 100 threads each with it's own zmq.SUB connection. It says "Too many open files"
[16:41] john	any ideas?
[16:41] ssi	ulimit -n
[16:41] john	ssi, is that to allow unlimited number of threads?
[16:41] ssi	no, set a limit
[16:42] ssi	ulimit -n 256, or something
[16:42] ssi	is number of open files allowed
[16:47] john	I bumped it up to 512 and I still have the same problem. :(
[16:48] john	I did ulimit -a and it says it is set to 512 now.
[16:49] john	ah, I have some permission problems it looks like I will have to add my user to a group or something.
[17:45] cremes	PaowZ: take a look at the FAQ: http://www.zeromq.org/area:faq
[17:45] cremes	PaowZ: there are instructions for building 0mq under mingw there
[17:49] magarwal	how do i filter a multipart message at the subscriber end
[17:59] cremes	magarwal: the filtering happens on the bytes of the first message part
[18:00] cremes	use setsockopt and ZM_FILTER to set the byte string to use as the filter
[18:00] magarwal	cremes, i am sending a multipart message, how can i filter the message on one of the parts of the message
[18:01] cremes	magarwal: if you want to use the built-in filtering, then you can only filter on the first message part
[18:01] cremes	if you want to filter on some other part, then that's just plain 'ol application logic and has
[18:01] magarwal	thanks
[18:01] cremes	nothing to do with 0mq
[18:02] magarwal	is it possible to extract a part of the multipart message instead of getting the compete data/message
[18:03] cremes	magarwal: no, all parts are delivered atomically
[18:04] magarwal	once i received the complete the data message, is it possible to look/extract a part of the message
[18:04] magarwal	without parsing the whole message string
[18:04] cremes	magarwal: yes
[18:04] cremes	if your message has 3 parts
[18:05] cremes	and the 3rd part is all you want
[18:05] cremes	your app can skip decoding the first two (make sure to dealloc them) and just decode the final one
[18:05] cremes	this is all application logic though and has little to do with 0mq
[18:05] cremes	0mq just ships bytes around
[18:05] cremes	what you do with them on the receiving end is up to you
[18:07] magarwal	cremes, got it thanks
[18:07] magarwal	i am doing this to subscribe only to SPY subscriber.setsockopt( ZMQ_SUBSCRIBE,"SPY" , 3);
[18:08] magarwal	but this would also match "SPY1" for example... rt?
[18:08] magarwal	how do i ONLY subscribe to "SPY"
[18:09] cremes	magarwal: not possible
[18:10] cremes	not possible at the 0mq level
[18:10] magarwal	hmm.. so I have to do a string comparison at the app level
[18:10] cremes	yes
[18:11] cremes	unless you want to patch the SUB socket type to have more intelligent filters
[18:11] cremes	there has been some discussion about that; look at the mailing list archives
[18:11] magarwal	ok.. i'll prbably break it
[18:11] magarwal	let the professionals implement it
[18:12] cremes	if you need it, you could probably get some professional services to have it implemented
[18:12] magarwal	cremes, i was looking at the document but couldnt find a function to skip decoding the first two (as suggested by you above) in a multi-part
[18:13] cremes	magarwal: have you read the guide yet? (see the topic)
[18:13] cremes	there are lots of code examples
[18:14] john	Is there a good way to separate a GUI frontend from the backend.
[18:15] cremes	magarwal: http://zguide.zeromq.org/page:all#Multipart-Messages
[18:15] cremes	john__: that's a pretty general design question... any answer would have little to do with 0mq itself
[18:15] nishttal2	we have been using ActiveMQ as our message middleware and looking at ZeroMQ to replace ActiveMQ. is there a web interface for ZeroMQ where we can monitor messages/publishers/subscribers etc
[18:16] cremes	nishttal2: not at this time; there has been some discussion about baking that into 0mq
[18:16] cremes	nishttal2: but for now it's something you would have to build yourself
[18:16] nishttal2	cremes, i see.. how do we monitor message traffic then?
[18:17] cremes	nishttal2: what do you mean by monitor? measure latency, measure total packets, ??
[18:18] nishttal2	cremes, that and to debug situation where something is not working.. in activemq we first see what is connected and what is not and where is the message waiting
[18:18] nishttal2	really helps a lot of debugging
[18:18] cremes	nishttal2: yeah... i'm not the best person to answer that
[18:18] cremes	you might want to ping sustrik or pieterh
[18:19] cremes	or ask on the mailing list
[18:19] nishttal2	ok will do thanks
[18:20] CIA-20	jzmq: 03Brandon Ehle 07master * r6982e0f 10/ (src/Socket.cpp test/src/org/zeromq/ZMQTest.java): Fix unittest failures with libzmq 3.x - http://bit.ly/lEVrWN
[18:20] CIA-20	jzmq: 03Gonzalo Diethelm 07master * r9454aca 10/ (src/Socket.cpp test/src/org/zeromq/ZMQTest.java): Merge pull request #52 from azverkan/master ...
[18:20] cremes	nishttal2: i also highly recommend you read the guide (http://zero.mq/zg)
[18:24] nishttal2	cremes, i read the guide (didnt read the code)
[18:24] nishttal2	cremes, i dont remember any mention of the UI
[18:25] cremes	there isn't any UI but i thought the guide talked about some "system" sockets that were used for logging
[18:25] cremes	internal behavior
[18:26] nishttal2	ok will look into that
[18:26] nishttal2	thanks
[18:30] CIA-20	jzmq: 03Gonzalo Diethelm 07master * rdd3327d 10/ README : Added more information to README file. - https://github.com/zeromq/jzmq/commit/dd3327d62021077dec66cacc2b21b01c1d46b3cf
[18:50] john	is there a way to send / recv without blocking?
[18:57] john	I want to be able to update a gui from another process but without blocking the gui. I suppose I could pickle the entire gui, send it to the other process to be modified then send it back.
[18:58] linuxfood	http://api.zeromq.org/2-1:zmq-recv
[18:58] linuxfood	it's got an extra parameter flags
[18:58] linuxfood	ZMQ_NOBLOCK
[18:58] linuxfood	as does send()
[18:59] john	thanks