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  • arbitrary typed data in django model

    - by Dmitry Shevchenko
    I have a model, say, Item. I want to store arbitrary amount of attributes on it, like title, description, release_date. And i want them to be not just strings but have python type, so string, boolean, datetime etc. What are my options here? EAV pattern with separate name-value table won't work because of the same DB type across all values. JSONField can probably help, but it doesn't know about datetime, for example. Also i was looking at PickeField, it fits perfectly, but i'm a bit concerned about performance.

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  • Can I get the stack traces of all threads in my c# app?

    - by Drew Shafer
    I'm debugging an apparent concurrency issue in a largish app that I hack on at work. The bug in question only manifests on certain lower-performance machines after running for many (12+) hours, and I have never reproduced it in the debugger. Because of this, my debugging tools are basically limited to analyzing log files. C# makes it easy to get the stack trace of the thread throwing the exception, but I'd like to additionally get the stack traces of every other thread currently executing in my AppDomain at the time the exception was thrown. Is this possible?

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  • Are C++ meta-templates required knowledge for programmers?

    - by Robert Gould
    In my experience Meta-templates are really fun (when your compilers are compliant), and can give good performance boosts, and luckily I'm surrounded by seasoned C++ programmers that also grok meta-templates, however occasionally a new developer arrives and can't make heads or tails of some of the meta-template tricks we use (mostly Andrei Alenxandrescu stuff), for a few weeks until he gets initiated appropriately. So I was wondering what's the situation for other C++ programmers out there? Should meta-template programming be something C++ programmers should be "required" to know (excluding entry level students of course), or not? Edit: Note my question is related to production code and not little samples or prototypes

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  • Are IoC containers about configuration files?

    - by Jader Dias
    Recently I developed a performance tester console application, with no UI, with the help of a IoC containter (Castle-Windsor-Microkernel). This library enabled me to let the user choose which test(s) to run, simply by changing the configuration file. Have I realized what IoC containers are about? I'm not sure. Even Joel said here on SO that IoC are difficult to understand. From my example, what do you conclude? Am I using IoC container for exactly what they were designed for? Or I am just using one of its secondary features?

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  • Opening a file from a pack URI in WPF

    - by cptmorgan
    Hi All, I am looking to open a .csv file from the application pack to do some unit testing. So what I would really love is some analog to File.ReadAllText(string path) which is instead X.ReadAllText(Uri uri). I haven't as yet been able to find this. Does anyone know if it is possible to read text / bytes (don't mind which) from a file in the pack without compiling this file to disk first? Oh and btw, File.ReadAllText(@"pack://application:,,,/SpreadSheetEngine/Tests/Example.csv") didn't work for me.. Thanks in advance.. Gav

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  • Recreation of MySQL DB using "mysql mydb < mydb.sql" is really slow when the table has tens of milli

    - by Jian Lin
    It seems that a MySQL database that has a table with tens of millions of records will get a big INSERT INTO statement when the following mysqldump some_db > some_db.sql is done to back up the database. (is it 1 insert statement that handles all the records?) So when reconstructing the DB using mysql some_db < some_db.sql then the CPU is hardly busy (about 1.8% usage by the mysql process... I don't see a mysqld either?) and also the hard disk doesn't seem to be too busy... Last time, the whole restore process took 5 hours. Is there a way to make it faster? Such as, when doing mysqldump, can it break the INSERT statement into shorter ones, so that the mysql doesn't need to parse the line so hard when restoring the DB?

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  • fd.seek() IOError: [Errno 22] Invalid argument

    - by Julian Kessel
    My Python Interpreter (v2.6.5) raises the above error in the following codepart: fd = open("some_filename", "r") fd.seek(-2, os.SEEK_END) #same happens if you exchange the second arg. w/ 2 data=fd.read(2); last call is fd.seek() Traceback (most recent call last): File "bot.py", line 250, in <module> fd.seek(iterator, os.SEEK_END); IOError: [Errno 22] Invalid argument The strange thing with this is that the exception occurs just when executing my entire code, not if only the specific part with the file opening. At the runtime of this part of code, the opened file definitely exists, disk is not full, the variable "iterator" contains a correct value like in the first codeblock. What could be my mistake? Thanks in advance

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  • New to AVL tree implementation.

    - by nn
    I am writing a sliding window compression algorithm (LZ77) that searches for phrases in a "moving" dictionary. So far I have written a BST where each node is stored in an array and it's index in the array is also the value of the starting position in the window itself. I am now looking at transforming the BST to an AVL tree. I am a little confused at the sample implementations I have seen. Some only appear to store the balance factors whereas others store the height of each tree. Are there any performance advantage/disadvantages of storing the height and/or balance factor for each node? Apologies if this is a very simple question, but I'm still not visualizing how I want to restructure my BST to implement height balancing. Thanks.

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  • How to return an image in an HTTP response with CherryPy

    - by colinmarc
    I have code which generates a Cairo ImageSurface, and I expose it like so: def preview(...): surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height) ... cherrypy.response.headers['Content-Type'] = "image/png" return surface.get_data() preview.exposed = True This doesn't work (browsers report that the image has errors). I've tested that surface.write_to_png('test.png') works, but I'm not sure what to dump the data into to return it. I'm guessing some file-like object? According to the pycairo documentation, get_data() returns a buffer. I've also now tried: tempf = os.tmpfile() surface.write_to_png(tempf) return tempf Also, is it better to create and hold this image in memory (like I'm trying to do) or write it to disk as a temp file and serve it from there? I only need the image once, then it can be discarded.

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  • Writing temporary data from R

    - by Shane
    I want to write some temporary data to disk in an R package, and I want to be sure that it can run on every OS without assuming the user has admin rights. Is there an existing R function that can provide a path to a temporary directory on all major OS's? Or a way to reference a user's home directory? Otherwise, I was thinking of trying this: Sys.getenv("temp") I presume that I can't expect people to have write access to their R locations, otherwise I could reference a path within the package directory: .find.package("package.name").

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  • Using different languages in one project

    - by Tarbal
    I recently heard about the use of several different languages in a (big) project, I also read about famous services such as Twitter using Rails as frontend, mixed with some other languages, and Scala I think it was as backend. Is this common practice? Who does that? I'm sure there are disadvantages to this. I think that you will have problems with the different interpreters/compilers and seamlessly connecting the different languages. Is this true? Why is this actually done? For performance?

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  • Precompile Lambda Expression Tree conversions as constants?

    - by Nathan
    It is fairly common to take an Expression tree, and convert it to some other form, such as a string representation (for example this question and this question, and I suspect Linq2Sql does something similar). In many cases, perhaps even most cases, the Expression tree conversion will always be the same, i.e. if I have a function public string GenerateSomeSql(Expression<Func<TResult, TProperty>> expression) then any call with the same argument will always return the same result for example: GenerateSomeSql(x => x.Age) //suppose this will always return "select Age from Person" GenerateSomeSql(x => x.Ssn) //suppose this will always return "select Ssn from Person" So, in essence, the function call with a particular argument is really just a constant, except time is wasted at runtime re-computing it continuously. Assuming, for the sake of argument, that the conversion was sufficiently complex to cause a noticeable performance hit, is there any way to pre-compile the function call into an actual constant?

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  • Simple but efficient way to store a series of small changes to an image?

    - by finnw
    I have a series of images. Each one is typically (but not always) similar to the previous one, with 3 or 4 small rectangular regions updated. I need to record these changes using a minimum of disk space. The source images are not compressed, but I would like the deltas to be compressed. I need to be able to recreate the images exactly as input (so a lossy video codec is not appropriate.) I am thinking of something along the lines of: Composite the new image with a negative of the old image Save the composited image in any common format that can compress using RLE (probably PNG.) Recreate the second image by compositing the previous image with the delta. Although the images have an alpha channel, I can ignore it for the purposes of this function. Is there an easy-to-implement algorithm or free Java library with this capability?

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  • SDK for writing DVD's

    - by Matt Warren
    I need to add DVD writing functionality to an application I'm working on. However it needs to be able to write out files that are being grabbed "live" from a camera, over a long period of time. I can't wait until all the files are captured before I start writing them to the DVD, I need to write them out in chunks as I go along. I've looked at IMAPI v2, but the main problems seems to be that you need to point it to all the files you plan to write out to disk before you start the burning process. I know it has to concept of "sessions", which means you can write to the DVD in several parts, before you finally "close" it. But I was wondering if there were any other DVD writing SDK's that allow you to be constantly writing files to a DVD and in particular files that are only in memory. It would be more efficient if I didn't have to write the captured images out to hard before they are burned to DVD. The solution needs to work under .NET on Windows XP and vista

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  • How to draw a rectangle in WinForm app in the correct location

    - by TooFat
    I have a WinForm app that has an image displayed in a PictureBox that has the added functionality of allowing a user to draw a rectangle on the image by clicking and dragging. The Location, Height and Width of the rectangle are saved to disk. When the image is viewed again I would like to automatically redraw that rectangle in the same position on the image. When I redraw it, however, the Height and Width are fine but the location is always off. The location is being captured in the MouseDown Event like so private void pbSample_MouseDown(object Sender, MouseEventArgs e) { if (SelectMode) { StartLocation.X = e.X; StartLocation.Y = e.Y; //later on these are saved as the location of the rectangle } } And I am redrawing it like so public void DrawSelectedArea(Rectangle rect) { Graphics g = this.PictureBox1.CreateGraphics(); Pen p = new Pen(Brushes.Black); g.DrawRectangle(p, rect); } Given the location from the MouseEventArgs captured during the MouseDown Event how can I calculate the correct location to redraw my rectangle?

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  • I want to version control my entire slice

    - by Tom
    I'm renting a slice (i.e., a VPS) from Slicehost. I've a spent a day or two filling up /usr with my favorite packages, /etc with configs and init scripts, and so on. Now I want to: save this whole setup somewhere (e.g., to load onto another machine). see what changes I've made to which files revert changes, tag revisions, and all that other good version control stuff Saving a disk image gives me (1), but not (2) and (3). Using Subversion (svn import / svn://someotherhost) might give me all three, but I expect problems if I actually try to check a project out into / and maintain .svn directories in root-owned areas. And to load my setup onto a fresh slice, I'd need to install an svn client on it first. Is there a good way to do what I want to do?

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  • ZIPLIB problem on opening zip files

    - by Ahmet vardar
    I am using this class to create zip <?php // vim: expandtab sw=4 ts=4 sts=4: class zipfile { var $datasec = array(); var $ctrl_dir = array(); var $eof_ctrl_dir = "\x50\x4b\x05\x06\x00\x00\x00\x00"; var $old_offset = 0; function unix2DosTime($unixtime = 0) { $timearray = ($unixtime == 0) ? getdate() : getdate($unixtime); if ($timearray['year'] < 1980) { $timearray['year'] = 1980; $timearray['mon'] = 1; $timearray['mday'] = 1; $timearray['hours'] = 0; $timearray['minutes'] = 0; $timearray['seconds'] = 0; } // end if return (($timearray['year'] - 1980) << 25) | ($timearray['mon'] << 21) | ($timearray['mday'] << 16) | ($timearray['hours'] << 11) | ($timearray['minutes'] << 5) | ($timearray['seconds'] >> 1); } // end of the 'unix2DosTime()' method function addFile($data, $name, $time = 0) { $name = str_replace('\\', '/', $name); $dtime = dechex($this->unix2DosTime($time)); $hexdtime = '\x' . $dtime[6] . $dtime[7] . '\x' . $dtime[4] . $dtime[5] . '\x' . $dtime[2] . $dtime[3] . '\x' . $dtime[0] . $dtime[1]; eval('$hexdtime = "' . $hexdtime . '";'); $fr = "\x50\x4b\x03\x04"; $fr .= "\x14\x00"; // ver needed to extract $fr .= "\x00\x00"; // gen purpose bit flag $fr .= "\x08\x00"; // compression method $fr .= $hexdtime; // last mod time and date // "local file header" segment $unc_len = strlen($data); $crc = crc32($data); $zdata = gzcompress($data); $zdata = substr(substr($zdata, 0, strlen($zdata) - 4), 2); // fix crc bug $c_len = strlen($zdata); $fr .= pack('V', $crc); // crc32 $fr .= pack('V', $c_len); // compressed filesize $fr .= pack('V', $unc_len); // uncompressed filesize $fr .= pack('v', strlen($name)); // length of filename $fr .= pack('v', 0); // extra field length $fr .= $name; // "file data" segment $fr .= $zdata; // "data descriptor" segment (optional but necessary if archive is not // served as file) $fr .= pack('V', $crc); // crc32 $fr .= pack('V', $c_len); // compressed filesize $fr .= pack('V', $unc_len); // uncompressed filesize // add this entry to array $this -> datasec[] = $fr; // now add to central directory record $cdrec = "\x50\x4b\x01\x02"; $cdrec .= "\x00\x00"; // version made by $cdrec .= "\x14\x00"; // version needed to extract $cdrec .= "\x00\x00"; // gen purpose bit flag $cdrec .= "\x08\x00"; // compression method $cdrec .= $hexdtime; // last mod time & date $cdrec .= pack('V', $crc); // crc32 $cdrec .= pack('V', $c_len); // compressed filesize $cdrec .= pack('V', $unc_len); // uncompressed filesize $cdrec .= pack('v', strlen($name) ); // length of filename $cdrec .= pack('v', 0 ); // extra field length $cdrec .= pack('v', 0 ); // file comment length $cdrec .= pack('v', 0 ); // disk number start $cdrec .= pack('v', 0 ); // internal file attributes $cdrec .= pack('V', 32 ); // external file attributes - 'archive' bit set $cdrec .= pack('V', $this -> old_offset ); // relative offset of local header $this -> old_offset += strlen($fr); $cdrec .= $name; // optional extra field, file comment goes here // save to central directory $this -> ctrl_dir[] = $cdrec; } // end of the 'addFile()' method function file() { $data = implode('', $this -> datasec); $ctrldir = implode('', $this -> ctrl_dir); return $data . $ctrldir . $this -> eof_ctrl_dir . pack('v', sizeof($this -> ctrl_dir)) . // total # of entries "on this disk" pack('v', sizeof($this -> ctrl_dir)) . // total # of entries overall pack('V', strlen($ctrldir)) . // size of central dir pack('V', strlen($data)) . // offset to start of central dir "\x00\x00"; // .zip file comment length } // end of the 'file()' method function addFiles($files ) { foreach($files as $file) { if (is_file($file)) //directory check { $data = implode("",file($file)); $this->addFile($data,$file); } } } function output($file) { $fp=fopen($file,"w"); fwrite($fp,$this->file()); fclose($fp); } } // end of the 'zipfile' class ?> It creates zip file but when i try to open it on Mac os x snow leopard and windows 7, it doesnt open. on mac i had this error: Error 1: operation not permitted Any idea ? thanks

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  • ASP.Net Web Site Project vs. Web Application Project

    - by user144612
    I'm trying to convince my co-workers to switch from a web site project to a web application project, because I want the use of the project file. However I can't diffuse this argument against: The web site project allows each page to be compiled into a single dll. Their argument is this enables easy fixing of errors found after publishing. This is contrast to how the web application project compiles all code behind into a single dll. Is updating a single page's dll essentially different to updating the entire site's dll? Is there some way to compile each page's code behind into a seperate dll in the web application project? Are there some prohibitive (performance,memory?) costs to compiling each page's code behind into seperate dll's that we are unaware of? Why is the feature(?) to compile each page to separate dlls in web site projects and not web app projects?

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  • improving conversions to binary and back in C#

    - by Saad Imran.
    I'm trying to write a general purpose socket server for a game I'm working on. I know I could very well use already built servers like SmartFox and Photon, but I wan't to go through the pain of creating one myself for learning purposes. I've come up with a BSON inspired protocol to convert the the basic data types, their arrays, and a special GSObject to binary and arrange them in a way so that it can be put back together into object form on the client end. At the core, the conversion methods utilize the .Net BitConverter class to convert the basic data types to binary. Anyways, the problem is performance, if I loop 50,000 times and convert my GSObject to binary each time it takes about 5500ms (the resulting byte[] is just 192 bytes per conversion). I think think this would be way too slow for an MMO that sends 5-10 position updates per second with a 1000 concurrent users. Yes, I know it's unlikely that a game will have a 1000 users on at the same time, but like I said earlier this is supposed to be a learning process for me, I want to go out of my way and build something that scales well and can handle at least a few thousand users. So yea, if anyone's aware of other conversion techniques or sees where I'm loosing performance I would appreciate the help. GSBitConverter.cs This is the main conversion class, it adds extension methods to main datatypes to convert to the binary format. It uses the BitConverter class to convert the base types. I've shown only the code to convert integer and integer arrays, but the rest of the method are pretty much replicas of those two, they just overload the type. public static class GSBitConverter { public static byte[] ToGSBinary(this short value) { return BitConverter.GetBytes(value); } public static byte[] ToGSBinary(this IEnumerable<short> value) { List<byte> bytes = new List<byte>(); short length = (short)value.Count(); bytes.AddRange(length.ToGSBinary()); for (int i = 0; i < length; i++) bytes.AddRange(value.ElementAt(i).ToGSBinary()); return bytes.ToArray(); } public static byte[] ToGSBinary(this bool value); public static byte[] ToGSBinary(this IEnumerable<bool> value); public static byte[] ToGSBinary(this IEnumerable<byte> value); public static byte[] ToGSBinary(this int value); public static byte[] ToGSBinary(this IEnumerable<int> value); public static byte[] ToGSBinary(this long value); public static byte[] ToGSBinary(this IEnumerable<long> value); public static byte[] ToGSBinary(this float value); public static byte[] ToGSBinary(this IEnumerable<float> value); public static byte[] ToGSBinary(this double value); public static byte[] ToGSBinary(this IEnumerable<double> value); public static byte[] ToGSBinary(this string value); public static byte[] ToGSBinary(this IEnumerable<string> value); public static string GetHexDump(this IEnumerable<byte> value); } Program.cs Here's the the object that I'm converting to binary in a loop. class Program { static void Main(string[] args) { GSObject obj = new GSObject(); obj.AttachShort("smallInt", 15); obj.AttachInt("medInt", 120700); obj.AttachLong("bigInt", 10900800700); obj.AttachDouble("doubleVal", Math.PI); obj.AttachStringArray("muppetNames", new string[] { "Kermit", "Fozzy", "Piggy", "Animal", "Gonzo" }); GSObject apple = new GSObject(); apple.AttachString("name", "Apple"); apple.AttachString("color", "red"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)1.5); GSObject lemon = new GSObject(); apple.AttachString("name", "Lemon"); apple.AttachString("color", "yellow"); apple.AttachBool("inStock", false); apple.AttachFloat("price", (float)0.8); GSObject apricoat = new GSObject(); apple.AttachString("name", "Apricoat"); apple.AttachString("color", "orange"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)1.9); GSObject kiwi = new GSObject(); apple.AttachString("name", "Kiwi"); apple.AttachString("color", "green"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)2.3); GSArray fruits = new GSArray(); fruits.AddGSObject(apple); fruits.AddGSObject(lemon); fruits.AddGSObject(apricoat); fruits.AddGSObject(kiwi); obj.AttachGSArray("fruits", fruits); Stopwatch w1 = Stopwatch.StartNew(); for (int i = 0; i < 50000; i++) { byte[] b = obj.ToGSBinary(); } w1.Stop(); Console.WriteLine(BitConverter.IsLittleEndian ? "Little Endian" : "Big Endian"); Console.WriteLine(w1.ElapsedMilliseconds + "ms"); } Here's the code for some of my other classes that are used in the code above. Most of it is repetitive. GSObject GSArray GSWrappedObject

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  • Tokenizer for full-text

    - by user72185
    This should be an ideal case of not re-inventing the wheel, but so far my search has been in vain. Instead of writing one myself, I would like to use an existing C++ tokenizer. The tokens are to be used in an index for full text searching. Performance is very important, I will parse many gigabytes of text. Edit: Please note that the tokens are to be used in a search index. Creating such tokens is not an exact science (afaik) and requires some heuristics. This has been done a thousand time before, and probably in a thousand different ways, but I can't even find one of them :) Any good pointers? Thanks!

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  • Python: split a list based on a condition?

    - by Parand
    What's the best way, both aesthetically and from a performance perspective, to split a list of items into multiple lists based on a conditional? The equivalent of: good = [x for x in mylist if x in goodvals] bad = [x for x in mylist if x not in goodvals] is there a more elegant way to do this? Update: here's the actual use case, to better explain what I'm trying to do: # files looks like: [ ('file1.jpg', 33L, '.jpg'), ('file2.avi', 999L, '.avi'), ... ] IMAGE_TYPES = ('.jpg','.jpeg','.gif','.bmp','.png') images = [f for f in files if f[2].lower() in IMAGE_TYPES] anims = [f for f in files if f[2].lower() not in IMAGE_TYPES]

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  • How can I reuse my javascript code between client and server?

    - by Chris Farmer
    I have some javascript code that includes an ANTLR-generated lexer and parser, and some associated syntax tree evaluation functionality. This code runs in the browser in my web app to support users who author code snippets which process scientific data. Now I'd like to do some additional background processing on the server using the same generated parser. I would prefer not to have to re-implement this stuff in C# and have multiple bits of code that did the exact same thing. Performance isn't as critical to me as eliminating duplication, since this is a background process. So, how can I call into my javascript code from C#? And how can I format my script so that it plays nicely with my .NET web app?

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  • Writing out BMP files with DataBuffer.TYPE_FLOAT or DataBuffer.TYPE_DOUBLE in java

    - by Basil Dsouza
    Hi Guys, I had a problem working with the image classes in java. I am creating a buffered image with DataBuffer.TYPE_DOUBLE. This all works fine in memory (I think). But the problem starts when I try to write it using ImageIO.write. Initially I was getting no exception at all and instead was only getting an empty output file for my troubles.. After a bit of poking around in the code, i found out that the bmp writer doesnt support writing type_double type of files. From: BMPImageWriterSpi.canEncodeImage: if (dataType < DataBuffer.TYPE_BYTE || dataType > DataBuffer.TYPE_INT) return false; So my question is, does anyone have a way of writing out those kind of images to disk? any documentation or tutorial, or link would be helpful. Thanks, Basil Dsouza

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  • Concatenation Operator

    - by Chaitanya
    This might be a silly question but it struck me, and here i ask. <?php $x="Hi"; $y=" There"; $z = $x.$y; $a = "$x$y"; echo "$z"."<br />"."$a"; ?> $z uses the traditional concatenation operator provided by php and concatenates, conversely $a doesn't, My questions: by not using the concatenation operator, does it effect the performance? If it doesn't why at all have the concatenation operator. Why have 2 modes of implementation when one does the work?

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  • Very long strings as primary keys in a database for caching

    - by Bill Zimmerman
    Hi, I am working on a web app that allows users to create dynamic PDF files based on what they enter into a form (it is not very structured data). The idea is that User 1 enters several words (arbitrary # of words, practically capped of course), for example: A B C D E There is no such string in the database, so I was thinking: Store this string as a primary key in a MySQL database (it could be maybe around 50-100k of text, but usually probably less than 200 words) Generate the PDF file, and create a link to it in the database When the next user requests A B C D E, then I can just serve the file instead of recreating it each time. (simple cache) The PDF is cpu intensive to generate, so I am trying to cache as much as I can... My questions are: Does anyone have any alternative ideas to my approach What will the database performance be like? Is there a better way to design the schema than using the input string as the primary key?

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