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• Datastore performance, my code or the datastore latency

  - by fredrik

  I had for the last month a bit of a problem with a quite basic datastore query. It involves 2 db.Models with one referring to the other with a db.ReferenceProperty. The problem is that according to the admin logs the request takes about 2-4 seconds to complete. I strip it down to a bare form and a list to display the results. The put works fine, but the get accumulates (in my opinion) way to much cpu time. #The get look like this: outputData['items'] = {} labelsData = Label.all() for label in labelsData: labelItem = label.item.name if labelItem not in outputData['items']: outputData['items'][labelItem] = { 'item' : labelItem, 'labels' : [] } outputData['items'][labelItem]['labels'].append(label.text) path = os.path.join(os.path.dirname(__file__), 'index.html') self.response.out.write(template.render(path, outputData)) #And the models: class Item(db.Model): name = db.StringProperty() class Label(db.Model): text = db.StringProperty() lang = db.StringProperty() item = db.ReferenceProperty(Item) I've tried to make it a number of different way ie. instead of ReferenceProperty storing all Label keys in the Item Model as a db.ListProperty. My test data is just 10 rows in Item and 40 in Label. So my questions: Is it a fools errand to try to optimize this since the high cpu usage is due to the problems with the datastore or have I just screwed up somewhere in the code? ..fredrik

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• Problem: Vectorizing Code with Intel Visual FORTRAN for X64

  - by user313209

  I'm compiling my fortran90 code using Intel Visual FORTRAN on Windows Server 2003 Enterprise X64 Edition. When I compile the code for 32 bit structure and using automatic and manual vectorizing options. The code will be compiled, vectorized. And when I run it on 8 core system the compiled code uses 70% of CPU that shows me that vectorizing is working. But when I compile the code with 64 Bit compiler, it says that the code is vectorized but when I run it it only shows CPU usage of about 12% that is full usage for one core out of 8, so it means that while the compiler says that code is vectorized, vectorization is not working. And it's strange for me because it's on a X64 Edition Windows and I was expecting to see the reverse result. I thought that it should be better to run a code that is compiled for 64 Bit architecture on a 64 bit windows. Anyone have any idea why the compiled code is not able to use the full power of multiple cores for 64 Bit Compiled version? Thanks in advance for your responses.

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• Submitting R jobs using PBS

  - by Tony

  I am submitting a job using qsub that runs parallelized R. My intention is to have R programme running on 4 different cores rather than 8 cores. Here are some of my settings in PBS file: #PBS -l nodes=1:ppn=4 .... time R --no-save < program1.R > program1.log I am issuing the command "ta job_id" and I'm seeing that 4 cores are listed. However, the job occupies a large amount of memory(31944900k used vs 32949628k total). If I were to use 8 cores, the jobs got hang due to memory limitation. top - 21:03:53 up 77 days, 11:54, 0 users, load average: 3.99, 3.75, 3.37 Tasks: 207 total, 5 running, 202 sleeping, 0 stopped, 0 zombie Cpu(s): 30.4%us, 1.6%sy, 0.0%ni, 66.8%id, 0.0%wa, 0.0%hi, 1.2%si, 0.0%st Mem: 32949628k total, 31944900k used, 1004728k free, 269812k buffers Swap: 2097136k total, 8360k used, 2088776k free, 6030856k cached Here is a snapshot when issuing command ta job_id PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1794 x 25 0 6247m 6.0g 1780 R 99.2 19.1 8:14.37 R 1795 x 25 0 6332m 6.1g 1780 R 99.2 19.4 8:14.37 R 1796 x 25 0 6242m 6.0g 1784 R 99.2 19.1 8:14.37 R 1797 x 25 0 6322m 6.1g 1780 R 99.2 19.4 8:14.33 R 1714 x 18 0 65932 1504 1248 S 0.0 0.0 0:00.00 bash 1761 x 18 0 63840 1244 1052 S 0.0 0.0 0:00.00 20016.hpc 1783 x 18 0 133m 7096 1128 S 0.0 0.0 0:00.00 python 1786 x 18 0 137m 46m 2688 S 0.0 0.1 0:02.06 R How can I prevent other users to use the other 4 cores? I like to mask somehow that my job is using 8 cores with 4 cores idling. Could anyone kindly help me out on this? Can this be solved using pbs? Many Thanks

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• What's the fastest way to bulk insert a lot of data in SQL Server (C# client)

  - by Andrew

  I am hitting some performance bottlenecks with my C# client inserting bulk data into a SQL Server 2005 database and I'm looking for ways in which to speed up the process. I am already using the SqlClient.SqlBulkCopy (which is based on TDS) to speed up the data transfer across the wire which helped a lot, but I'm still looking for more. I have a simple table that looks like this: CREATE TABLE [BulkData]( [ContainerId] [int] NOT NULL, [BinId] [smallint] NOT NULL, [Sequence] [smallint] NOT NULL, [ItemId] [int] NOT NULL, [Left] [smallint] NOT NULL, [Top] [smallint] NOT NULL, [Right] [smallint] NOT NULL, [Bottom] [smallint] NOT NULL, CONSTRAINT [PKBulkData] PRIMARY KEY CLUSTERED ( [ContainerIdId] ASC, [BinId] ASC, [Sequence] ASC )) I'm inserting data in chunks that average about 300 rows where ContainerId and BinId are constant in each chunk and the Sequence value is 0-n and the values are pre-sorted based on the primary key. The %Disk time performance counter spends a lot of time at 100% so it is clear that disk IO is the main issue but the speeds I'm getting are several orders of magnitude below a raw file copy. Does it help any if I: Drop the Primary key while I am doing the inserting and recreate it later Do inserts into a temporary table with the same schema and periodically transfer them into the main table to keep the size of the table where insertions are happening small Anything else? -- Based on the responses I have gotten, let me clarify a little bit: Portman: I'm using a clustered index because when the data is all imported I will need to access data sequentially in that order. I don't particularly need the index to be there while importing the data. Is there any advantage to having a nonclustered PK index while doing the inserts as opposed to dropping the constraint entirely for import? Chopeen: The data is being generated remotely on many other machines (my SQL server can only handle about 10 currently, but I would love to be able to add more). It's not practical to run the entire process on the local machine because it would then have to process 50 times as much input data to generate the output. Jason: I am not doing any concurrent queries against the table during the import process, I will try dropping the primary key and see if that helps. ~ Andrew

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• Web Workers - Transferable Objects for JSON

  - by kclem06

  HTML 5 Web workers are very slow when using worker.postMessage on a large JSON object. I'm trying to figure out how to transfer a JSON Object to a web worker - using the 'Transferable Objects' types in Chrome, in order to increase the speed of this. Here is what I'm referring to and appears it should speed this up quite a bit: http://updates.html5rocks.com/2011/12/Transferable-Objects-Lightning-Fast I'm having trouble finding a good example of this (and I don't believe I want to use an ArrayBuffer). Any help would be appreciated. I'm imagining something like this: worker = new Worker('workers.js'); var large_json = {}; for(var i = 0; i < 20000; ++i){ large_json[i] = i; large_json["test" + i] = "string"; }; //How to make this call to use Transfer Objects? Takes approx 2 seconds to serialize this for me currently. worker.webkitPostMessage(large_json);

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• High performance text file parsing in .net

  - by diamandiev

  Here is the situation: I am making a small prog to parse server log files. I tested it with a log file with several thousand requests (between 10000 - 20000 don't know exactly) What i have to do is to load the log text files into memory so that i can query them. This is taking the most resources. The methods that take the most cpu time are those (worst culprits first): string.split - splits the line values into a array of values string.contains - checking if the user agent contains a specific agent string. (determine browser ID) string.tolower - various purposes streamreader.readline - to read the log file line by line. string.startswith - determine if line is a column definition line or a line with values there were some others that i was able to replace. For example the dictionary getter was taking lots of resources too. Which i had not expected since its a dictionary and should have its keys indexed. I replaced it with a multidimensional array and saved some cpu time. Now i am running on a fast dual core and the total time it takes to load the file i mentioned is about 1 sec. Now this is really bad. Imagine a site that has tens of thousands of visits a day. It's going to take minutes to load the log file. So what are my alternatives? If any, cause i think this is just a .net limitation and i can't do much about it.

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• documenting class attributes

  - by intuited

  I'm writing a lightweight class whose attributes are intended to be publicly accessible, and only sometimes overridden in specific instantiations. There's no provision in the Python language for creating docstrings for class attributes, or any sort of attributes, for that matter. What is the accepted way, should there be one, to document these attributes? Currently I'm doing this sort of thing: class Albatross(object): """A bird with a flight speed exceeding that of an unladen swallow. Attributes: """ flight_speed = 691 __doc__ += """ flight_speed (691) The maximum speed that such a bird can attain. """ nesting_grounds = "Raymond Luxury-Yacht" __doc__ += """ nesting_grounds ("Raymond Luxury-Yacht") The locale where these birds congregate to reproduce. """ def __init__(**keyargs): """Initialize the Albatross from the keyword arguments.""" self.__dict__.update(keyargs) Although this style doesn't seem to be expressly forbidden in the docstring style guidelines, it's also not mentioned as an option. The advantage here is that it provides a way to document attributes alongside their definitions, while still creating a presentable class docstring, and avoiding having to write comments that reiterate the information from the docstring. I'm still kind of annoyed that I have to actually write the attributes twice; I'm considering using the string representations of the values in the docstring to at least avoid duplication of the default values. Is this a heinous breach of the ad hoc community conventions? Is it okay? Is there a better way? For example, it's possible to create a dictionary containing values and docstrings for the attributes and then add the contents to the class __dict__ and docstring towards the end of the class declaration; this would alleviate the need to type the attribute names and values twice. edit: this last idea is, I think, not actually possible, at least not without dynamically building the class from data, which seems like a really bad idea unless there's some other reason to do that. I'm pretty new to python and still working out the details of coding style, so unrelated critiques are also welcome.

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• Advice on designing and building distributed application to track vehicles

  - by dario-g

  I'm working on application for tracking vehicles. There will be about 10k or more vehicles. Each will be sending ~250bytes in each minute. Data contains gps location and everything from CAN Bus (every data that we can read from vehicle computer and dashboard). Data are sent by GSM/GPRS (using UDP protocol). Estimated rows with this data per day is ~2000k. I see there 3 main blocks. 1. Multithreaded Socket Server (MSS) - I have it. MSS stores received data to the queue (using NServiceBus). 2. Rule Processor Server (RPS) - this is core of this system. This block is responsible for parsing received data, storing in the database, processing rules, sending messages to Notifier Server (this will be sending e-mails/sms texts). Rule example. As I said between received bytes there will be information about current speed. When speed will be above 120 then: show alert in web application for specified users, send e-mail, send sms text. (There can be more than one instance of RPS). 3. Web application - allows reporting and defining rules by users, monitoring alerts, etc. I'm looking for advice how to design communication between RPS and Web application. Some questions: - Should Web application and RPS have separated databases or one central database will be enough? I have one domain model in web application. If there will be one central database then can I use the same model (objects) on RPS? So, how to send changed rules to RPS? I try to decouple this blocks as much as possible. I'm planning to create different instance of application for each client (each client will have separated database). One client will be have 10k vehicles, others only 100 vehicles.

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• protobuf-net v2 alpha - problems with Dictionary<string,string>?

  - by Steve

  I was using a version of v2 of protobuf-net from a few weeks ago quite successfully. (I want to use V2 due to the speed of the pre-compiled serializer running on the Compact Framework.) Everything worked great until I tried to serialize an object with a property of type Dictionary. I received the following error: {"No serializer defined for type: System.Collections.Generic.KeyValuePair`2[[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]"} It looked like there were recent changes made to improve Dictionary support, so I grabbed the latest code from today. After building the CF3.5 and FF3.5 dlls, I tried again. Now I get a different error "The model cannot be changed once frozen." If I remove the ProtoMember attribute from the Dictionary property all seems to work well. Has anyone succcessfully used a Dictionary in v2 of protobuf-net? Is this still too early of a release to be using? My speed tests showed v2 being twice as fast, does that seem accurate (validating my desire to use the less stable v2 pre-alpha bits.)

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• documenting class properties

  - by intuited

  I'm writing a lightweight class whose properties are intended to be publicly accessible, and only sometimes overridden in specific instantiations. There's no provision in the Python language for creating docstrings for class properties, or any sort of properties, for that matter. What is the accepted way, should there be one, to document these properties? Currently I'm doing this sort of thing: class Albatross(object): """A bird with a flight speed exceeding that of an unladen swallow. Properties: """ flight_speed = 691 __doc__ += """ flight_speed (691) The maximum speed that such a bird can attain """ nesting_grounds = "Throatwarbler Man Grove" __doc__ += """ nesting_grounds ("Throatwarbler Man Grove") The locale where these birds congregate to reproduce. """ def __init__(**keyargs): """Initialize the Albatross from the keyword arguments.""" self.__dict__.update(keyargs) Although this style doesn't seem to be expressly forbidden in the docstring style guidelines, it's also not mentioned as an option. The advantage here is that it provides a way to document properties alongside their definitions, while still creating a presentable class docstring, and avoiding having to write comments that reiterate the information from the docstring. I'm still kind of annoyed that I have to actually write the properties twice; I'm considering using the string representations of the values in the docstring to at least avoid duplication of the default values. Is this a heinous breach of the ad hoc community conventions? Is it okay? Is there a better way? For example, it's possible to create a dictionary containing values and docstrings for the properties and then add the contents to the class __dict__ and docstring towards the end of the class declaration; this would alleviate the need to type the property names and values twice. I'm pretty new to python and still working out the details of coding style, so unrelated critiques are also welcome.

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• Google App Engine - Caching generated HTML

  - by Alexander

  I have written a Google App Engine application that programatically generates a bunch of HTML code that is really the same output for each user who logs into my system, and I know that this is going to be in-efficient when the code goes into production. So, I am trying to figure out the best way to cache the generated pages. The most probable option is to generate the pages and write them into the database, and then check the time of the database put operation for a given page against the time that the code was last updated. Then, if the code is newer than the last put to the database (for a particular HTML request), new HTML will be generated and served, and cached to the database. If the code is older than the last put to the database, then I will just get the HTML direct from the database and serve it (therefore avoiding all the CPU wastage of generating the HTML). I am not only looking to minimize load times, but to minimize CPU usage. However, one issue that I am having is that I can't figure out how to programatically check when the version of code uploaded to the app engine was updated. I am open to any suggestions on this approach, or other approaches for caching generated html. Note that while memcache could help in this situation, I believe that it is not the final solution since I really only need to re-generate html when the code is updated (as opposed to every time the memcache expires). Kind Regards, and thank you in advance for any suggestions you may be able to offer. -Alex

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• Reasons for & against a Database

  - by dbemerlin

  Hi, i had a discussion with a coworker about the architecture of a program i'm writing and i'd like some more opinions. The Situation: The Program should update at near-realtime (+/- 1 Minute). It involves the movement of objects on a coordinate system. There are some events that occur at regular intervals (i.e. creation of the objects). Movements can change at any time through user input. My solution was: Build a server that runs continously and stores the data internally. The server dumps a state-of-the-program at regular intervals to protect against powerfailures and/or crashes. He argued that the program requires a Database and i should use cronjobs to update the data. I can store movement information by storing startpoint, endpoint and speed and update the position in the cronjob (and calculate collisions with other objects there) by calculating direction and speed. His reasons: Requires more CPU & Memory because it runs constantly. Powerfailures/Crashes might destroy data. Databases are faster. My reasons against this are mostly: Not very precise as events can only occur at full minutes (wouldn't be that bad though). Requires (possibly costly) transformation of data on every run from relational data to objects. RDBMS are a general solution for a specialized problem so a specialized solution should be more efficient. Powerfailures (or other crashes) can leave the Data in an undefined state with only partially updated data unless (possibly costly) precautions (like transactions) are taken. What are your opinions about that? Which arguments can you add for any side?

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• Linux USB debug connection to LuminaryMicro evaluation board

  - by mikelong

  Hi, I am trying to connect a Stellaris LM3S8962 evaluation kit to a linux host machine. I am using the CodeSourcery G++ for the development toolchain. When I try to run a helloworld example the connection fails with this message: arm-stellaris-eabi-sprite: error: E104. I/O Error communicating with USB Device. arm-stellaris-eabi-sprite: waiting for GDB connection, to pass error along warning: Remote failure reply: E.fatal.E104. I/O Error communicating with USB Device. arm-stellaris-eabi-sprite: error: E002. Not initialized When I connect the evaluation board with the USB cable it seems the device is made available to the system: Mar 24 14:37:16 n6-ws2 kernel: usb 5-2: USB disconnect, address 5 Mar 24 14:37:18 n6-ws2 kernel: usb 5-2: new full speed USB device using uhci_hcd and address 6 Mar 24 14:37:19 n6-ws2 kernel: usb 5-2: configuration #1 chosen from 1 choice Also, it seems that I can connect in some way via the command line tool (but I do get some strange characters): [mlong@n6-ws2 bin]$ ./arm-stellaris-eabi-sprite -i CodeSourcery ARM Debug Sprite (Sourcery G++ 4.4-104) armusb: [speed=] ARMUSB device armusb:///?? - ?? (??) Does anyone have any suggestions I could try? Thanks a lot, Mike

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• How to Use Images as Navigation with innerfade Slideshow?

  - by Katie

  I am very new to JavaScript and only have the most basic understanding of how it works, so please bear with me. :) I'm using the jquery.innerfade.js script to create a slideshow with fade transitions for a website I'm developing, and I have added navigation buttons (which are set as background-images) that navigate between the “slides”. The navigation buttons have three states: default/off, hover, and on (each state is a separate image). I created a separate JavaScript document to set the buttons to “on” when they are clicked. The “hover” state is achieved through the CSS. Both the slideshow and the navigation buttons work well. There is just one thing I want to add: I would like the appropriate navigation button to display as “on” while the related “slide” is “playing”. Here's the HTML: <div id="mainFeature"> <ul id="theFeature"> <li id="the1feature"><a href="#" name="#promo1"><img src="_images/carousel/promo1.jpg" /></a></li> <li id="the2feature"><a href="#" name="#promo2"><img src="_images/carousel/promo2.jpg" /></a></li> <li id="the3feature"><a href="#" name="#promo3"><img src="_images/carousel/promo3.jpg" /></a></li> </ul> <div id="promonav-con"> <div id="primarypromonav"> <ul class="links"> <li id="the1title" class="promotop"><a rel="1" href="#promo1" class="promo1" id="promo1" onMouseDown="promo1on()"><strong>Botox Cosmetic</strong></a></li> <li id="the2title" class="promotop"><a rel="2" href="#promo2" class="promo2" id="promo2" onMouseDown="promo2on()"><strong>Promo 2</strong></a></li> <li id="the3title" class="promotop"><a rel="3" href="#promo3" class="promo3" id="promo3" onMouseDown="promo3on()"><strong>Promo 3</strong></a></li> </ul> </div> </div> And here is the jquery.innerfade.js, with my changes: (function($) { $.fn.innerfade = function(options) { return this.each(function() { $.innerfade(this, options); }); }; $.innerfade = function(container, options) { var settings = { 'speed': 'normal', 'timeout': 2000, 'containerheight': 'auto', 'runningclass': 'innerfade', 'children': null }; if (options) $.extend(settings, options); if (settings.children === null) var elements = $(container).children(); else var elements = $(container).children(settings.children); if (elements.length > 1) { $(container).css('position', 'relative').css('height', settings.containerheight).addClass(settings.runningclass); for (var i = 0; i < elements.length; i++) { $(elements[i]).css('z-index', String(elements.length-i)).css('position', 'absolute').hide(); }; this.ifchanger = setTimeout(function() { $.innerfade.next(elements, settings, 1, 0); }, settings.timeout); $(elements[0]).show(); } }; $.innerfade.next = function(elements, settings, current, last) { $(elements[last]).fadeOut(settings.speed); $(elements[current]).fadeIn(settings.speed, function() { removeFilter($(this)[0]); }); if ((current + 1) < elements.length) { current = current + 1; last = current - 1; } else { current = 0; last = elements.length - 1; } this.ifchanger = setTimeout((function() { $.innerfade.next(elements, settings, current, last); }), settings.timeout); }; })(jQuery); // **** remove Opacity-Filter in ie **** function removeFilter(element) { if(element.style.removeAttribute){ element.style.removeAttribute('filter'); } } jQuery(document).ready(function() { jQuery('ul#theFeature').innerfade({ speed: 1000, timeout: 7000, containerheight: '291px' }); // jQuery('#mainFeature .links').children('li').children('a').attr('href', 'javascript:void(0);'); jQuery('#mainFeature .links').children('li').children('a').click(function() { clearTimeout(jQuery.innerfade.ifchanger); for(i=1;i<5;i++) { jQuery('#the'+i+'feature').css("display", "none"); //jQuery('#the'+i+'title').children('a').css("background-color","#226478"); } // if(the_widths[(jQuery(this).attr('rel')-1)]==960) { // jQuery("#vic").hide(); // } else { // jQuery("#vic").show(); // } // jQuery('#the'+(jQuery(this).attr('rel'))+'title').css("background-color", "#286a7f"); jQuery('#the'+(jQuery(this).attr('rel'))+'feature').css("display", "block"); clearTimeout(jQuery.innerfade.ifchanger); }); }); And the separate JavaScript that I created: function promo1on() {document.getElementById("promo1").className="promo1on"; document.getElementById("promo2").className="promo2"; document.getElementById("promo2").className="promo2"; } function promo2on() {document.getElementById("promo2").className="promo2on"; document.getElementById("promo1").className="promo1"; document.getElementById("promo3").className="promo3"; } function promo3on() {document.getElementById("promo3").className="promo3on"; document.getElementById("promo1").className="promo1"; document.getElementById("promo2").className="promo2"; } And, finally, the CSS: #mainFeature {float: left; width: 672px; height: 290px; margin: 0 0 9px 0; list-style: none;} #mainFeature li {list-style: none;} #mainFeature #theFeature {margin: 0; padding: 0; position: relative;} #mainFeature #theFeature li {position: absolute; top: 0; left: 0;} #promonav-con {width: 463px; height: 26px; padding: 0; margin: 0; position: absolute; z-index: 900; top: 407px; left: 283px;} #primarypromonav {padding: 0; margin: 0;} #mainFeature .links {padding: 0; margin: 0; list-style: none; position: relative; font-family: arial, verdana, sans-serif; width: 463px; height: 26px;} #mainFeature .links li.promotop {list-style: none; display: block; float: left; display: inline; margin: 0; padding: 0;} #mainFeature .links li a {display: block; float: left; display: inline; height: 26px; text-decoration: none; margin: 0; padding: 0; cursor: pointer;} #mainFeature .links li a strong {margin-left: -9999px;} #mainFeature .links li a.promo1 {background: url(../_images/carouselnav/promo1.gif); width: 155px;} #mainFeature .links li:hover a.promo1 {background: url(../_images/carouselnav/promo1_hover.gif); width: 155px;} #mainFeature .links li a.promo1:hover {background: url(../_images/carouselnav/promo1_hover.gif); width: 155px;} .promo1on {background: url(../_images/carouselnav/promo1_on.gif); width: 155px;} #mainFeature .links li a.promo2 {background: url(../_images/carouselnav/promo2.gif); width: 153px;} #mainFeature .links li:hover a.promo2 {background: url(../_images/carouselnav/promo2_hover.gif); width: 153px;} #mainFeature .links li a.promo2:hover {background: url(../_images/carouselnav/promo2_hover.gif); width: 153px;} .promo2on {background: url(../_images/carouselnav/promo2_on.gif); width: 153px;} #mainFeature .links li a.promo3 {background: url(../_images/carouselnav/promo3.gif); width: 155px;} #mainFeature .links li:hover a.promo3 {background: url(../_images/carouselnav/promo3_hover.gif); width: 155px;} #mainFeature .links li a.promo3:hover {background: url(../_images/carouselnav/promo3_hover.gif); width: 155px;} .promo3on {background: url(../_images/carouselnav/promo3_on.gif); width: 155px;} Hopefully this makes sense! Again, I'm very new to JavaScript/JQuery, so I apologize if this is a mess. I'm very grateful for any suggestions. Thanks!

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• What does flushing thread local memory to global memory mean?

  - by Jack Griffith

  Hi, I am aware that the purpose of volatile variables in Java is that writes to such variables are immediately visible to other threads. I am also aware that one of the effects of a synchronized block is to flush thread-local memory to global memory. I have never fully understood the references to 'thread-local' memory in this context. I understand that data which only exists on the stack is thread-local, but when talking about objects on the heap my understanding becomes hazy. I was hoping that to get comments on the following points: When executing on a machine with multiple processors, does flushing thread-local memory simply refer to the flushing of the CPU cache into RAM? When executing on a uniprocessor machine, does this mean anything at all? If it is possible for the heap to have the same variable at two different memory locations (each accessed by a different thread), under what circumstances would this arise? What implications does this have to garbage collection? How aggressively do VMs do this kind of thing? Overall, I think am trying to understand whether thread-local means memory that is physically accessible by only one CPU or if there is logical thread-local heap partitioning done by the VM? Any links to presentations or documentation would be immensely helpful. I have spent time researching this, and although I have found lots of nice literature, I haven't been able to satisfy my curiosity regarding the different situations & definitions of thread-local memory. Thanks very much.

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• Performance degrades for more than 2 threads on Xeon X5355

  - by zoolii

  Hi All, I am writing an application using boost threads and using boost barriers to synchronize the threads. I have two machines to test the application. Machine 1 is a core2 duo (T8300) cpu machine (windows XP professional - 4GB RAM) where I am getting following performance figures : Number of threads :1 , TPS :21 Number of threads :2 , TPS :35 (66 % improvement) further increase in number of threads decreases the TPS but that is understandable as the machine has only two cores. Machine 2 is a 2 quad core ( Xeon X5355) cpu machine (windows 2003 server with 4GB RAM) and has 8 effective cores. Number of threads :1 , TPS :21 Number of threads :2 , TPS :27 (28 % improvement) Number of threads :4 , TPS :25 Number of threads :8 , TPS :24 As you can see, performance is degrading after 2 threads (though it has 8 cores). If the program has some bottle neck , then for 2 thread also it should have degraded. Any idea? , Explanations ? , Does the OS has some role in performance ? - It seems like the Core2duo (2.4GHz) scales better than Xeon X5355 (2.66GHz) though it has better clock speed. Thank you -Zoolii

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• Axis2 Webservice -> php

  - by Peter Hagström

  Hi! If I have understood Axis2 correct i can construct a WebService and then access it with any SOAP compatible client. I have a java class with a couple of methods that I have written in Eclipse, and then automatically constructed a service with the Axis2 plugin from WTP. This is the methods of my class. public int test(int i){ return i+2; } public Car CarTest(int speed){ return new Car("Biltest", speed); } public CarFactoryAdapter getCarFactory(){ carFact.getCars().add(new Car("Bmw", 250)); carFact.getCars().add(new Car("seat", 350)); carFact.getCars().add(new Car("saab", 150)); carFact.getCars().add(new Car("volv", 50)); return new CarFactoryAdapter(carFact); } The code seems to work when I try it with soapUI and the Axis2-web interface has recognized the methods of my service. But when Iam trying the methods that receives parameters with PHP´s built in soapClient i get a Unknown exception. The getCarFactory methods works at least as expected, but it seems kind of crippled if I can´t send parameters. Example of non working method invocation. ini_set('soap.wsdl_cache_ttl',0); $client = new SoapClient("http://192.168.128.162:8080/ComplexWebService/services/CarService?wsdl", array('soap_version' => SOAP_1_2, 'trace' => 1)); $ar['i'] = (int)100; print_r($client->__soapCall("test",$ar)); I need to make sure that the SOA framework i choose will be able to comunicate with many platforms, there will be clients in at least PHP and Java, but it would be good if it will work in for example .NET to.

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• I am trying to have a wall follow robot but there are errors on the names not being declared in my s

  - by Sam

  #include <iostream> #include <libplayerc++/playerc++.h> using namespace std; int main(int argc, char *argv[]) { using namespace PlayerCc; PlayerClient robot("localhost"); BumperProxy bp(&robot,0); Position2dProxy pp(&robot,0); pp.SetMotorEnable(true); for(;;) double turnrate, speed; double error; bool wall; motor_a_speed(0); motor_c_speed(0); while(1) { front_bumper = SENSOR_2; left_bumper = SENSOR_3; if (front_bumper > 2) { if (left_bumper < 3) { motor_a_speed(5); motor_c_speed(drive_speed); motor_a_dir(fwd); motor_c_dir(fwd); } else { motor_a_speed(drive_speed); motor_c_speed(5); motor_a_dir(rev); motor_c_dir(rev); } } else { motor_a_speed(drive_speed); motor_c_speed(drive_speed); motor_a_dir(brake); motor_c_dir(brake); mrest(100); cputs("bump"); motor_a_dir(fwd); motor_c_dir(rev); msleep(450); cputs("right"); motor_a_speed(10); motor_a_dir(fwd); motor_c_dir(fwd); mrest(1300); } pp.SetSpeed(speed, turnrate); } }

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• Optimizing MySQL for ALTER TABLE of InnoDB

  - by schuilr

  Sometime soon we will need to make schema changes to our production database. We need to minimize downtime for this effort, however, the ALTER TABLE statements are going to run for quite a while. Our largest tables have 150 million records, largest table file is 50G. All tables are InnoDB, and it was set up as one big data file (instead of a file-per-table). We're running MySQL 5.0.46 on an 8 core machine, 16G memory and a RAID10 config. I have some experience with MySQL tuning, but this usually focusses on reads or writes from multiple clients. There is lots of info to be found on the Internet on this subject, however, there seems to be very little information available on best practices for (temporarily) tuning your MySQL server to speed up ALTER TABLE on InnoDB tables, or for INSERT INTO .. SELECT FROM (we will probably use this instead of ALTER TABLE to have some more opportunities to speed things up a bit). The schema changes we are planning to do is adding a integer column to all tables and make it the primary key, instead of the current primary key. We need to keep the 'old' column as well so overwriting the existing values is not an option. What would be the ideal settings to get this task done as quick as possible?

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• Serial: write() throttling?

  - by damian

  Hi everyone, I'm working on a project sending serial data to control animation of LED lights, which need to stay in sync with a sound engine. There seems to be a large serial write buffer (OSX (POSIX) + FTDI chipset usb serial device), so without manually restricting the transmission rate, the animation system can get several seconds ahead of the serial transmission. Currently I'm manually restricting the serial write speed to the baudrate (8N1 = 10 bytes serial frame per 8 bytes data, 19200 bps serial - 1920 bytes per second max), but I am having a problem with the sound drifting out of sync over time - it starts fine, but after 10 minutes there's a noticeable (100ms+) lag between the sound and the lights. This is the code that's restricting the serial write speed (called once per animation frame, 'elapsed' is the duration of the current frame, 'baudrate' is the bps (19200)): void BufferedSerial::update( float elapsed ) { baud_timer += elapsed; if ( bytes_written > 1024 ) { // maintain baudrate float time_should_have_taken = (float(bytes_written)*10)/float(baudrate); float time_actually_took = baud_timer; // sleep if we have > 20ms lag between serial transmit and our write calls if ( time_should_have_taken-time_actually_took > 0.02f ) { float sleep_time = time_should_have_taken - time_actually_took; int sleep_time_us = sleep_time*1000.0f*1000.0f; //printf("BufferedSerial::update sleeping %i ms\n", sleep_time_us/1000 ); delayUs( sleep_time_us ); // subtract 128 bytes bytes_written -= 128; // subtract the time it should have taken to write 128 bytes baud_timer -= (float(128)*10)/float(baudrate); } } } Clearly there's something wrong, somewhere. A much better approach would be to be able to determine the number of bytes currently in the transmit queue, and try and keep that below a fixed threshold. Any advice appreciated.

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• Java runs out of memory, even though I give it plenty!

  - by spitzanator

  Hey, folks. So, I'm running a java server (specifically Winstone: http://winstone.sourceforge.net/ ) Like this: java -server -Xmx12288M -jar /usr/share/java/winstone-0.9.10.jar --useSavedSessions=false --webappsDir=/var/servlets --commonLibFolder=/usr/share/java This has worked fine in the past, but now it needs to load a bunch more stuff into memory than it has before. The odd part is that, according to 'top', it has 15.0g of VIRT(ual memory) and it's RES(ident set) is 8.4g. Once it hits 8.4g, the CPU hangs at 100% (even though it's loading from disk), and eventually, I get Java's OutOfMemoryError. Presumably, the CPU hanging at 100% is Java doing garbage collection. So, my question is, what gives? I gave it 12 gigs of memory! And it's only using 8.2 gigs before it throws in the towel. What am I doing wrong? Oh, and I'm using java version "1.6.0_07" Java(TM) SE Runtime Environment (build 1.6.0_07-b06) Java HotSpot(TM) 64-Bit Server VM (build 10.0-b23, mixed mode) on Linux. Thanks, Matt

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• NULL-keys for key/value table

  - by user72185

  (Using Oracle) I have a table with key/value pairs like this: create table MESSAGE_INDEX ( KEY VARCHAR2(256) not null, VALUE VARCHAR2(4000) not null, MESSAGE_ID NUMBER not null ) I now want to find all the messages where key = 'someKey' and value is 'val1', 'val2' or 'val3' - OR value is null in which case there will be no entry in the table at all. This is to save space; there would be a large number of keys with null values if I stored them all. I think this works: SELECT message_id FROM message_index idx WHERE ((key = 'someKey' AND value IN ('val1', 'val2', 'val3')) OR NOT EXISTS (SELECT 1 FROM message_index WHERE key = 'someKey' AND idx.message_id = message_id)) But is is extremely slow. Takes 8 seconds with 700K records in message_index and there will be many more records and more search criteria when moving outside of my test environment. Primary key is key, value, message_id: add constraint PK_KEY_VALUE primary key (KEY, VALUE, MESSAGE_ID) And I added another index for message_id, to speed up searching for missing keys: create index IDX_MESSAGE_ID on MESSAGE_INDEX (MESSAGE_ID) I will be doing several of these key/value lookups in every search, not just one as shown above. So far I am doing them nested, where output id's of one level is the input to the next. E.g.: SELECT message_id from message_index WHERE (key/value compare) AND message_id IN ( SELECT ... and so on ) What can I do to speed this up?

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• Are MEF's ComposableParts contracts instance-based?

  - by Dave

  I didn't really know how to phrase the title of my questions, so my apologies in advance. I read through parts of the MEF documentation to try to find the answer to my question, but couldn't find it. I'm using ImportMany to allow MEF to create multiple instances of a specific plugin. That plugin Imports several parts, and within calls to a specific instance, it wants these Imports to be singletons. However, what I don't want is for all instances of this plugin to use the same singleton. For example, let's say my application ImportManys Blender appliances. Every time I ask for one, I want a different Blender. However, each Blender Imports a ControlPanel. I want each Blender to have its own ControlPanel. To make things a little more interesting, each Blender can load BlendPrograms, which are also contained within their own assemblies, and MEF takes care of this loading. A BlendProgram might need to access the ControlPanel to get the speed, but I want to ensure that it is accessing the correct ControlPanel (i.e. the one that is associated with the Blender that is associated with the program!) This diagram might clear things up a little bit: As the note shows, I believe that the confusion could come from an inherently-poor design. The BlendProgram shouldn't touch the ControlPanel directly, and instead perhaps the BlendProgram should get the speed via the Blender, which will then delegate the request to its ControlPanel. If this is the case, then I assume the BlendProgram needs to have a reference to a specific Blender. In order to do this, is the right way to leverage MEF and use an ImportingConstructor for BlendProgram, i.e. [ImportingConstructor] public class BlendProgram : IBlendProgram { public BlendProgram( Blender blender) {} } And if this is the case, how do I know that MEF will use the intended Blender plugin?

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• Thoughts on GoGrid vs EC2

  - by Jason

  I am currently hosting my SaaS application at GoGrid (Microsoft stack). Here's what I have: Database Server - physical box, 12 GB RAM, 2 X Quad Core CPU (2.13 GHz Xeon E5506) 2 Web / App servers - cloud servers, 2 GB RAM, 2 VCPUs 300 GB monthly bandwidth I am paying around $900 / month for this. My web / app servers are busting at the seams and need to be upgraded to 4 GB of RAM. I also need a firewall, and GoGrid just added this service for an additional $200. After the upgrade, I will be paying around $1,400. I started looking at Amazon EC2, specifically this config: Database server - "High Memory Double Extra Large Instance" - 34 GB RAM, 13 EC2 compute units 2 Web / App servers - "Large Instance" - 7.5 GB RAM, 4 EC2 compute units If I go with 1 year reserved instances, my upfront cost would be $4,500 and my monthly would be $700. This comes to $1,075 / month when amortized. Amazon also includes a firewall for free. Here are my questions: Do any of you have experience running a database (especially SQL Server) on an EC2 instance? How did it perform compared to a dedicated machine? One of my major concerns is with disk I/O. Amazon's description of a compute unit is fairly vague. Any ideas on how the CPU performance on the database servers would compare? I am hoping that the Amazon solution will provide significantly better performance than my current or even improved GoGrid setup. Having a virtual database server would also be nice in terms of availability. Right now I would be in serious trouble if I had any hardware issues. Thanks for any insight...

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• Optimizing a shared buffer in a producer/consumer multithreaded environment

  - by Etan

  I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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