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  • Load balancer - how to write one for a custom application?

    - by Poni
    Hi! I've written a simple server application which will run distributed on several machines. My question is how does a network load balancer works, in general? I've heard of round-robin and other algorithms, but what I haven't got answer to is how does the process really goes? In socket terms. The client connects to one of the load balancer machines, asks for a "free-to-connect-to" server and simply connects to it? That's the simpliest way I can think of. .. or, does it use the load balancer as a proxy (that implies that all the NBs must be always connected to the application servers, and data is transferred through them)? It's more of a general question. How would you do this? Thank you all!

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  • How to read information from .3gp and .mp4 using ffmpeg-php?

    - by Neltharian
    I have a bit of a problem with ffmpeg-php. I'm trying to get some information from video files and it works pretty fine with file formats like .avi, .mpg or .flv but when I try to use .3gp or .mp4 in: $movie = new ffmpeg_movie('path/to/file/test.3gp'); I get error like this : ffmpeg_movie::__construct() []: ISO: File Type Major Brand: 3gp5 or ffmpeg_movie::__construct() []: ISO: File Type Major Brand: mp42 I installed ffmpeg-php on WAMP using instructions found here: http://stackoverflow.com/questions/1172916/how-to-install-ffmpeg-in-wampserver-2-0-windows-xp I need those information to send them to ffmpeg using exec(). Anyone could help me with this?

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  • Python unittest (using SQLAlchemy) does not write/update database?

    - by Jerry
    Hi, I am puzzled at why my Python unittest runs perfectly fine without actually updating the database. I can even see the SQL statements from SQLAlchemy and step through the newly created user object's email -- ...INFO sqlalchemy.engine.base.Engine.0x...954c INSERT INTO users (user_id, user_name, email, ...) VALUES (%(user_id)s, %(user_name)s, %(email)s, ...) ...INFO sqlalchemy.engine.base.Engine.0x...954c {'user_id': u'4cfdafe3f46544e1b4ad0c7fccdbe24a', 'email': u'[email protected]', ...} > .../tests/unit_tests/test_signup.py(127)test_signup_success() -> user = user_q.filter_by(user_name='test').first() (Pdb) n ...INFO sqlalchemy.engine.base.Engine.0x...954c SELECT users.user_id AS users_user_id, ... FROM users WHERE users.user_name = %(user_name_1)s LIMIT 1 OFFSET 0 ...INFO sqlalchemy.engine.base.Engine.0x...954c {'user_name_1': 'test'} > .../tests/unit_tests/test_signup.py(128)test_signup_success() -> self.assertTrue(isinstance(user, model.User)) (Pdb) user <pweb.models.User object at 0x9c95b0c> (Pdb) user.email u'[email protected]' Yet at the same time when I login to the test database, I do not see the new record there. Is it some feature from Python/unittest/SQLAlchemy/Pyramid/PostgreSQL that I'm totally unaware of? Thanks. Jerry

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  • I can't read the value from a radio button.

    - by Corey
    <html> <head> <title>Tip Calculator</title> <script type="text/javascript"><!-- function calculateBill(){ var check = document.getElementById("check").value; /* I try to get the value selected */ var tipPercent = document.getElementById("tipPercent").value; /* But it always returns the value 15 */ var tip = check * (tipPercent / 100) var bill = 1 * check + tip; document.getElementById('bill').innerHTML = bill; } --></script> </head> <body> <h1 style="text-align:center">Tip Calculator</h1> <form id="f1" name="f1"> Average Sevice: 15%<input type="radio" id="tipPercent" name="tipPercent" value="15" /> <br /> Excellent Sevice: 20%<input type="radio" id="tipPercent" name="tipPercent" value="20" /> <br /><br /> <label>Check Amount</label> <input type="text" id="check" size="10" /> <input type="button" onclick="calculateBill()" value="Calculate" /> </form> <br /> Total Bill: <p id="bill"></p> </body> </html>

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  • JavaScript snippet to read and output XML file on page load?

    - by Banderdash
    Hey guys, hoping I might get some help. Have XML file here of a list of books each with unique id and numeral value for whether they are checked out or not. I need a JavaScript snippet that requests the XML file after the page loads and displays the content of the XML file. XML file looks like this: <?xml version="1.0" encoding="UTF-8" ?> <response> <library name="My Library"> <book id="1" checked-out="1"> <authors> <author>John Resig</author> </authors> <title>Pro JavaScript Techniques (Pro)</title> <isbn-10>1590597273</isbn-10> </book> <book id="2" checked-out="0"> <authors> <author>Erich Gamma</author> <author>Richard Helm</author> <author>Ralph Johnson</author> <author>John M. Vlissides</author> </authors> <title>Design Patterns: Elements of Reusable Object-Oriented Software</title> <isbn-10>0201633612</isbn-10> </book> ... </library> </response> Would LOVE any and all help!

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  • Howto write a class where a property can be accessed without naming it.

    - by SchlaWiener
    I have a (dump) question regarding VB/C# I often use third party classes where I can access a child object with only specifying the id or key. Example: Instead of writing: DataRow row = GetAPopulatedDataRowSomeWhere(); Object result = row.Items[1]; // DataRow has no Items property Object result = row.Items["colName"]; // Also not possible I use this code to access the members: DataRow row = GetAPopulatedDataRowSomeWhere(); Object result = row[1]; Object result = row["colName"]; Can someone tell me how a class has to look like to support this syntax? My own class has a Dictionary that I want to access this way. MyClass["key"]; // <- that's what I want MyClass.SubItems["key"]; // <- that's how I use it now

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  • Bad performance with Linux software RAID5 and LUKS encryption

    - by Philipp Wendler
    I have set up a Linux software RAID5 on three hard drives and want to encrypt it with cryptsetup/LUKS. My tests showed that the encryption leads to a massive performance decrease that I cannot explain. The RAID5 is able to write 187 MB/s [1] without encryption. With encryption on top of it, write speed is down to about 40 MB/s. The RAID has a chunk size of 512K and a write intent bitmap. I used -c aes-xts-plain -s 512 --align-payload=2048 as the parameters for cryptsetup luksFormat, so the payload should be aligned to 2048 blocks of 512 bytes (i.e., 1MB). cryptsetup luksDump shows a payload offset of 4096. So I think the alignment is correct and fits to the RAID chunk size. The CPU is not the bottleneck, as it has hardware support for AES (aesni_intel). If I write on another drive (an SSD with LVM) that is also encrypted, I do have a write speed of 150 MB/s. top shows that the CPU usage is indeed very low, only the RAID5 xor takes 14%. I also tried putting a filesystem (ext4) directly on the unencrypted RAID so see if the layering is problem. The filesystem decreases the performance a little bit as expected, but by far not that much (write speed varying, but 100 MB/s). Summary: Disks + RAID5: good Disks + RAID5 + ext4: good Disks + RAID5 + encryption: bad SSD + encryption + LVM + ext4: good The read performance is not affected by the encryption, it is 207 MB/s without and 205 MB/s with encryption (also showing that CPU power is not the problem). What can I do to improve the write performance of the encrypted RAID? [1] All speed measurements were done with several runs of dd if=/dev/zero of=DEV bs=100M count=100 (i.e., writing 10G in blocks of 100M). Edit: If this helps: I'm using Ubuntu 11.04 64bit with Linux 2.6.38. Edit2: The performance stays approximately the same if I pass a block size of 4KB, 1MB or 10MB to dd.

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  • Collection wrapping a array is read-only. Possible to make it writeable without casting?

    - by Brian Triplett
    I have a Collection<T> property that wraps a array like T[] array; public Collection<T> Items { get { return new Collection<T>(array); } } When I attempt to assign to the collection via: T variable; Items[i] = variable; I get a NotSupportedException because the colleciton's IsReadOnly property is true. Turns out that this is a design choice by Microsoft. Does anyone know a workaround that does NOT involve enumeration? It could be done if the underlying data is not an array but I enjoy the performance gains because the data is fixed length.

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  • .Net Logger (Write your own vs log4net/enterprise logger/nlog etc.)

    - by Jack
    I work for an IT department with about 50+ developers. It used to be about 100+ developers but was cut because of the recession. When our department was bigger there was an ambitious effort made to set up a special architecture group. One thing this group decided to do was create our own internal logger. They thought it was such a simple task that we could spend recources and do it ourselves. Now we are having issues with performance and difficulty viewing the logs generated and some employees are frustrated that we are spending recources on infrastructure stuff like this instead of focusing on serving our business and using stuff that already exists like log4net or Enterprise Logger. Can you assist me in listing up reasons why you should not create your own .net logger. Also reasons for why you should are welcome to get a fair point of view :)

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  • Should I write more SQL to be more efficient, or less SQL to be less buggy?

    - by RenderIn
    I've been writing a lot of one-off SQL queries to return exactly what a certain page needs and no more. I could reuse existing queries and issue a number of SQL requests linear to the number of records on the page. As an example, I have a query to return People and a query to return Job Details for a person. To return a list of people with their job details I could query once for people and then once for each person to retrieve their job details. I've found that in most cases that solution returns things in a reasonable amount of time, but I don't know how well it will scale in my environment. Instead I've been writing queries to join people + job details, or people + salary history, etc. I'm looking at my models and I see how I could shave off maybe 30% of my code if I were to re-use existing queries. This is a big temptation. Is it a bad thing to go for reuse over efficiency in general or does it all come down to the specific situation? Should I first do it the easy way and then optimize later, or is it best to get the code knocked out while everything is fresh in my mind? Thoughts, experiences?

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  • Is There a More Efficient Way to Write Nested While Loops?

    - by Ryan
    The code below shows nested while loops, but it's not the very efficient. Suppose I wanted to extend the code to include 100 nested while loops. Is there a better way to accomplish this task? <?php $count = 1; $num = 1; $options=3; while ( $num <=$options ) { echo "(".$num . ") "; $num1 = 1; $options1=3; while ( $num1 <=$options1 ) { echo "*".$num1 . "* "; $num2 = 1; $options2=3; while ( $num2 <=$options2 ) { echo "@".$num2 . "@ "; $num3 = 1; $options3=3; while ( $num3 <=$options3 ) { echo $num3 . " "; $num3++; $count++; } echo "<br />"; $num2++; } echo "<br />"; $num1++; } echo "<br />"; $num++; } echo $count; ?>

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  • How should I write this string-prefix check so that it's idiomatic Python?

    - by Kevin Stargel
    I have a couple of lists of items: specials = ['apple', 'banana', 'cherry', ...] smoothies = ['banana-apple', 'mocha mango', ...] I want to make a new list, special_smoothies, consisting of elements in smoothies that start with the elements in specials. However, if specials is blank, special_smoothies should be identical to smoothies. What's the most Pythonic way to do this? Is there a way to do this without a separate conditional check on whether specials is blank?

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  • How can I read the value of a radio button in JavaScript?

    - by Corey
    <html> <head> <title>Tip Calculator</title> <script type="text/javascript"><!-- function calculateBill(){ var check = document.getElementById("check").value; /* I try to get the value selected */ var tipPercent = document.getElementById("tipPercent").value; /* But it always returns the value 15 */ var tip = check * (tipPercent / 100) var bill = 1 * check + tip; document.getElementById('bill').innerHTML = bill; } --></script> </head> <body> <h1 style="text-align:center">Tip Calculator</h1> <form id="f1" name="f1"> Average Service: 15% <input type="radio" id="tipPercent" name="tipPercent" value="15" /> <br /> Excellent Service: 20% <input type="radio" id="tipPercent" name="tipPercent" value="20" /> <br /><br /> <label>Check Amount</label> <input type="text" id="check" size="10" /> <input type="button" onclick="calculateBill()" value="Calculate" /> </form> <br /> Total Bill: <p id="bill"></p> </body> </html> I try to get the value selected with document.getElementById("tipPercent").value, but it always returns the value 15.

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  • Grails - How to format a value in a textfield into comma style such that it can be easily read?

    - by WaZ
    Hi there, I want to allow users enter numbers in textfield and once the textbox loses focus. The number is formatted with commas. e.g. User enters 100000 textfield looses focus value displayed: 100,000 How can I achieve this in Grails. I have looked at <g:formatNumber number="${myNumber}" format="\\$###,##0" /> But it doesnt solve my problem as the number is from a textfield. thanks Much appreciated.

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  • What languages should a microISV use to write commercial software?

    - by Wal
    I've been writing software in Java for many years now, but it was always for internal applications that would be deployed to a server. I'd like to get into writing desktop applications now but I don't know where to start. I've written a few Java/Swing applications but again they were for internal use. My understanding is that Java and other semi-compiled and interpreted languages are too easy to reverse engineer, making them unsuitable for commercial software. I am aware that there are compilers for Java and some other interpreted language, but I've also heard that they are pricey and/or unreliable. Assuming I start a microISV and wish to develop and sell applications to a broad audience, what's my best bet? I would prefer something that can be written close to once, and compiled for different operating systems but I am not opposed to .NET and a Windows-only audience if other languages would compromise the experience (installation ease & user experience) in Windows. My only issue there is that I don't have a large starting budget and paying out the wazoo for the required development tools is not really in the cards.

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  • When to alter a function vs when to just write a new one...?

    - by Andrew Heath
    /is n00b Through the gift of knowledge and expertise encoded here, I am doing my best to avoid n00b mistakes as I learn the basics of programming. I use functions when I (think I) can in PHP, and keep them somewhat sorted in different includes. The n00b problem I'm running into now is situations where perhaps 4/5th of an existing function is relevant to a new need. Maybe there are a slightly different set of inputs, or an additional calculation or two in the series, or output needs a different format/structure... but the core of the function is still applicable. Is there a good rule of thumb regarding when one should bolt-on crap to an original function and when one should (literally) copy & paste most of it into a new function and tweak to fit the situation? On the one hand I feel bad duping code, on the other I feel bad cluttering up an existing function with stuff not always needed...

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