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• How to optimize an asp.net spawning a new process for each request ?

  - by Recycle Bin

  I have an asp.net mvc application that spawns a Process as follows: Process p = new Process(); p.EnableRaisingEvents = true; p.Exited += new EventHandler(p_Exited); p.StartInfo.Arguments = "-interaction=nonstopmode " + inputpath; p.StartInfo.WorkingDirectory = dir; p.StartInfo.UseShellExecute = false; p.StartInfo.FileName = "pdflatex.exe"; p.StartInfo.LoadUserProfile = true; p.Start(); p.WaitForExit(); Before going further, I need to know whether, e.g., pdflatex.exe is a managed code or a native code? Edit I need to consider this because: (Hopely I am not wrong...) Each Asp.net application runs in an separate/isolated AppDomain as opposed to a separate/isolated process. A native executable cannot live in an AppDomain. to be continued... Shortly speaking, I hope my site does not spawn a new process for each request. Because a process is more expensive than an application domain.

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• Python: circular imports needed for type checking

  - by phild

  First of all: I do know that there are already many questions and answers to the topic of the circular imports. The answer is more or less: "Design your Module/Class structure properly and you will not need circular imports". That is true. I tried very hard to make a proper design for my current project, I in my opinion I was successful with this. But my specific problem is the following: I need a type check in a module that is already imported by the module containing the class to check against. But this throws an import error. Like so: foo.py: from bar import Bar class Foo(object): def __init__(self): self.__bar = Bar(self) bar.py: from foo import Foo class Bar(object): def __init__(self, arg_instance_of_foo): if not isinstance(arg_instance_of_foo, Foo): raise TypeError() Solution 1: If I modified it to check the type by a string comparison, it will work. But I dont really like this solution (string comparsion is rather expensive for a simple type check, and could get a problem when it comes to refactoring). bar_modified.py: from foo import Foo class Bar(object): def __init__(self, arg_instance_of_foo): if not arg_instance_of_foo.__class__.__name__ == "Foo": raise TypeError() Solution 2: I could also pack the two classes into one module. But my project has lots of different classes like the "Bar" example, and I want to seperate them into different module files. After my own 2 solutions are no option for me: Has anyone a nicer solution for this problem?

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• Modeling complex hierarchies

  - by jdn

  To gain some experience, I am trying to make an expert system that can answer queries about the animal kingdom. However, I have run into a problem modeling the domain. I originally considered the animal kingdom hierarchy to be drawn like -animal -bird -carnivore -hawk -herbivore -bluejay -mammals -carnivores -herbivores This I figured would allow me to make queries easily like "give me all birds", but would be much more expensive to say "give me all carnivores", so I rewrote the hierarchy to look like: -animal -carnivore -birds -hawk -mammals -xyz -herbivores -birds -bluejay -mammals But now it will be much slower to query "give me all birds." This is of course a simple example, but it got me thinking that I don't really know how to model complex relationships that are not so strictly hierarchical in nature in the context of writing an expert system to answer queries as stated above. A directed, cyclic graph seems like it could mathematically solve the problem, but storing this in a relational database and maintaining it (updates) would seem like a nightmare to me. I would like to know how people typically model such things. Explanations or pointers to resources to read further would be acceptable and appreciated.

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• Microsoft products such as Visual Studio 2010 does not require to enter serial number

  - by MainMa

  Hi, I am member of WebsiteSpark and was member of DreamSpark. Both programs enable to download software and provide serial keys to use. Some software like Windows Server has an ISO file to download and a serial number displayed on the website which I must enter during installation. Some other software does not have any serial key. For example, when I downloaded Visual Studio 2010, there was just a link to an ISO file. During installation, there was no such a field as serial number (whereas Visual Studio 2008 had this field at the beginning of installation process). There is the same thing with SQL Server 2008 and Microsoft Expression Studio 3. Even when I've downloaded the public trial RTM version of Windows Seven Enterprise, there were no serial number to enter. I don't think that such expensive products as SQL Server 2008 Enterprise are delivered without serials and online validation, so I suppose that the serial is embedded into the product itself, either in installation binaries or in a separate config file, so is already in the ISO I download so I do not have to enter it. So my question is, how it is done technically? Is each 2 GBs ISO generated on-demand on the server to embed a serial each time this ISO is requested? I suppose that if it is done, it has a huge impact on servers performance (no caching, no streaming...), so what may be the techniques used behind? I want to implement the same feature in a product I intend to ship (to simplify installation by avoiding to ask to enter serial number), but I really don't see how to do it with low impact on server performance.

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• Enumerate all paths in a weighted graph from A to B where path length is between C1 and C2

  - by awmross

  Given two points A and B in a weighted graph, find all paths from A to B where the length of the path is between C1 and C2. Ideally, each vertex should only be visited once, although this is not a hard requirement. I supose I could use a heuristic to sort the results of the algorithm to weed out "silly" paths (e.g. a path that just visits the same two nodes over and over again) I can think of simple brute force algorithms, but are there any more sophisticed algorithms that will make this more efficient? I can imagine as the graph grows this could become expensive. In the application I am developing, A & B are actually the same point (i.e. the path must return to the start), if that makes any difference. Note that this is an engineering problem, not a computer science problem, so I can use an algorithm that is fast but not necessarily 100% accurate. i.e. it is ok if it returns most of the possible paths, or if most of the paths returned are within the given length range.

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• Full complete MySQL database replication? Ideas? What do people do?

  - by mauriciopastrana

  Currently I have two Linux servers running MySQL, one sitting on a rack right next to me under a 10 Mbit/s upload pipe (main server) and another some couple of miles away on a 3 Mbit/s upload pipe (mirror). I want to be able to replicate data on both servers continuously, but have run into several roadblocks. One of them being, under MySQL master/slave configurations, every now and then, some statements drop (!), meaning; some people logging on to the mirror URL don't see data that I know is on the main server and vice versa. Let's say this happens on a meaningful block of data once every month, so I can live with it and assume it's a "lost packet" issue (i.e., god knows, but we'll compensate). The other most important (and annoying) recurring issue is that, when for some reason we do a major upload or update (or reboot) on one end and have to sever the link, then LOAD DATA FROM MASTER doesn't work and I have to manually dump on one end and upload on the other, quite a task nowadays moving some .5 TB worth of data. Is there software for this? I know MySQL (the "corporation") offers this as a VERY expensive service (full database replication). I am just wondering what people out there do. The way it's structured, we run an automatic failover where if one server is not up, then the main URL just resolves to the other server.

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• Automated Legal Processing

  - by Chris S

  Will it ever be possible to make legal systems quantifiable enough to process with computer algorithms? What technologies would have to be in place before this is possible? Are there any existing technologies that are already trying to accomplish this? Out of curiosity, I downloaded the text for laws in my local municipality, and tried applying some simple NLP tricks to extract rules from sentences. I had mixed results. Some sentences were very explicit (e.g. "Cars may not be left in the park overnight"), but other sentences seemed hopelessly vague (e.g. "The council's purpose is to ensure the well-being of the community"). I apologize if this is too open-ended a topic, but I've often wondered what society would look like if legal systems were based on less ambiguous language. Lawyers, and the legal process in general, are so expensive because they have to manually process a complex set of rules codified in ambiguous legal texts. If this system could be represented in software, this huge expense could potentially be eliminated, making the legal system more accessible for everyone.

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• Performance: float to int cast and clipping result to range

  - by durandai

  I'm doing some audio processing with float. The result needs to be converted back to PCM samples, and I noticed that the cast from float to int is surprisingly expensive. Whats furthermore frustrating that I need to clip the result to the range of a short (-32768 to 32767). While I would normally instictively assume that this could be assured by simply casting float to short, this fails miserably in Java, since on the bytecode level it results in F2I followed by I2S. So instead of a simple: int sample = (short) flotVal; I needed to resort to this ugly sequence: int sample = (int) floatVal; if (sample > 32767) { sample = 32767; } else if (sample < -32768) { sample = -32768; } Is there a faster way to do this? (about ~6% of the total runtime seems to be spent on casting, while 6% seem to be not that much at first glance, its astounding when I consider that the processing part involves a good chunk of matrix multiplications and IDCT) EDIT The cast/clipping code above is (not surprisingly) in the body of a loop that reads float values from a float[] and puts them into a byte[]. I have a test suite that measures total runtime on several test cases (processing about 200MB of raw audio data). The 6% were concluded from the runtime difference when the cast assignment "int sample = (int) floatVal" was replaced by assigning the loop index to sample. EDIT @leopoldkot: I'm aware of the truncation in Java, as stated in the original question (F2I, I2S bytecode sequence). I only tried the cast to short because I assumed that Java had an F2S bytecode, which it unfortunately does not (comming originally from an 68K assembly background, where a simple "fmove.w FP0, D0" would have done exactly what I wanted).

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• Returning Database Blobs in TurboGears 2.x / FCGI / Lighttpd extremely slow

  - by Tom

  Hey everyone, I am running a TG2 App on lighttpd via flup/fastcgi. We are reading images (~30kb each) from BlobFields in a MySQL database and return those images with a custom mime type via a controller method. Caching these images on the hard disk makes no sense because they change with every request, the only reason we cache these in the DB is that creating these images is quite expensive and the data used to create the images is also present in plain text on the website. Now to the problem itself: When returning such an image, things get extremely slow. The code runs totally fine on paster itself with no visible delay, but as soon as its running via fcgi/lighttpd the described phenomenon happens. I profiled the method of my controller that returns my blob, and the entire method runs in a few miliseconds, but when "return" executes, the entire app hangs for roughly 10 seconds. We could not reproduce the same error with PHP on FCGI. This only seems to happen with Turbogears or Pylons. Here for your consideration the concerned piece of source code: @expose(content_type=CUSTOM_CONTENT_TYPE) def return_img(self, img_id): """ Return a DB persisted image when requested """ img = model.Images.by_id(img_id) #get image from DB response.headers['content-type'] = 'image/png' return img.data # this causes the app to hang for 10 seconds

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• Test Driven Development with C++: How to test a class which depends on other classes?

  - by Nikhil

  Suppose I have a class A which depends on 3 other classes X, Y and Z, either A uses these through a reference or a pointer or say A is templated to be instantiated with X, Y and Z doesn't matter, the key is that in order to test A, I need to have X, Y and Z. So I need to have fakes for A, B and C. Suppose I write them. Now, how do I swap real and fake objects easily? I can see that this works very easily in the case of templates. In order to make it work when A depends on X, Y and Z through a reference or a pointer, I would need to have a base class say X_Interface from which I can inherit X_Real and X_Fake. So basically, I would end up in having 3 times the number of classes for every class that would need to have a fake. I am most likely missing something. There has to be a simpler way to do this. Having a base class X_Interface is also quite expensive as I will be using more space and making virtual calls. I guess I could use CRTP as I know whether its a X_Real or X_Fake at compile time but still there must be a better way.

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• invasive vs non-invasive ref-counted pointers in C++

  - by anon

  For the past few years, I've generally accepted that if I am going to use ref-counted smart pointers invasive smart pointers is the way to go -- However, I'm starting to like non-invasive smart pointers due to the following: I only use smart pointers (so no Foo* lying around, only Ptr) I'm starting to build custom allocators for each class. (So Foo would overload operator new). Now, if Foo has a list of all Ptr (as it easily can with non-invasive smart pointers). Then, I can avoid memory fragmentation issues since class Foo move the objects around (and just update the corresponding Ptr). The only reason why this Foo moving objects around in non-invasive smart pointers being easier than invasive smart pointers is: In non-invasive smart pointers, there is only one pointer that points to each Foo. In invasive smart pointers, I have no idea how many objects point to each Foo. Now, the only cost of non-invasive smart pointers ... is the double indirection. [Perhaps this screws up the caches]. Does anyone have a good study of expensive this extra layer of indirection is?

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• Disposing ActiveX resources owned by another thread

  - by Stefan Teitge

  I've got a problem problem with threading and disposing resources. I've got a C# Windows Forms application which runs expensive operation in a thread. This thread instantiates an ActiveX control (AxControl). This control must be disposed as it uses a high amount of memory. So I implemented a Dispose() method and even a destructor. After the thread ends the destructor is called. This is sadly called by the UI thread. So invoking activexControl.Dispose(); fails with the message "COM object that has been separated from its underlying RCW", as the object belongs to another thread. How to do this correctly or is it just a bad design I use? (I stripped the code down to the minimum including removing any safety concerns.) class Program { [STAThread] static void Main() { // do stuff here, e.g. open a form new Thread(new ThreadStart(RunStuff); // do more stuff } private void RunStuff() { DoStuff stuff = new DoStuff(); stuff.PerformStuff(); } } class DoStuff : IDisposable { private AxControl activexControl; DoStuff() { activexControl = new AxControl(); activexControl.CreateControl(); // force instance } ~DoStuff() { Dispose(); } public void Dispose() { activexControl.Dispose(); } public void PerformStuff() { // invent perpetuum mobile here, takes time } }

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• Can I get rid of this read lock?

  - by Pieter

  I have the following helper class (simplified): public static class Cache { private static readonly object _syncRoot = new object(); private static Dictionary<Type, string> _lookup = new Dictionary<Type, string>(); public static void Add(Type type, string value) { lock (_syncRoot) { _lookup.Add(type, value); } } public static string Lookup(Type type) { string result; lock (_syncRoot) { _lookup.TryGetValue(type, out result); } return result; } } Add will be called roughly 10/100 times in the application and Lookup will be called by many threads, many of thousands of times. What I would like is to get rid of the read lock. How do you normally get rid of the read lock in this situation? I have the following ideas: Require that _lookup is stable before the application starts operation. The could be build up from an Attribute. This is done automatically through the static constructor the attribute is assigned to. Requiring the above would require me to go through all types that could have the attribute and calling RuntimeHelpers.RunClassConstructor which is an expensive operation; Move to COW semantics. public static void Add(Type type, string value) { lock (_syncRoot) { var lookup = new Dictionary<Type, string>(_lookup); lookup.Add(type, value); _lookup = lookup; } } (With the lock (_syncRoot) removed in the Lookup method.) The problem with this is that this uses an unnecessary amount of memory (which might not be a problem) and I would probably make _lookup volatile, but I'm not sure how this should be applied. (John Skeets' comment here gives me pause.) Using ReaderWriterLock. I believe this would make things worse since the region being locked is small. Suggestions are very welcome.

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• iPhone: Does it ever make sense for an object to retain its delegate?

  - by randombits

  According to the rules of memory management in a non garbage collected world, one is not supposed to retain a the calling object in a delegate. Scenario goes like this: I have a class that inherits from UITableViewController and contains a search bar. I run expensive search operations in a secondary thread. This is all done with an NSOperationQueue and subclasses NSOperation instances. I pass the controller as a delegate that adheres to a callback protocol into the NSOperation. There are edge cases when the application crashes because once an item is selected from the UITableViewController, I dismiss it and thus its retain count goes to 0 and dealloc gets invoked on it. The delegate didn't get to send its message in time as the results are being passed at about the same time the dealloc happens. Should I design this differently? Should I call retain on my controller from the delegate to ensure it exists until the NSOperation itself is dealloc'd? Will this cause a memory leak? Right now if I put a retain on the controller, the crashes goes away. I don't want to leak memory though and need to understand if there are cases where retaining the delegate makes sense. Just to recap. UITableViewController creates an NSOperationQueue and NSOperation that gets embedded into the queue. The UITableViewController passes itself as a delegate to NSOperation. NSOperation calls a method on UITableViewController when it's ready. If I retain the UITableViewController, I guarantee it's there, but I'm not sure if I'm leaking memory. If I only use an assign property, edge cases occur where the UITableViewController gets dealloc'd and objc_msgSend() gets called on an object that doesn't exist in memory and a crash is imminent.

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• Most efficient method of detecting/monitoring DOM changes?

  - by Graza

  I need an efficient mechanism for detecting changes to the DOM. Preferably cross-browser, but if there's any efficient means which are not cross browser, I can implement these with a fail-safe cross browser method. In particular, I need to detect changes that would affect the text on a page, so any new, removed or modified elements, or changes to inner text (innerHTML) would be required. I don't have control over the changes being made (they could be due to 3rd party javascript includes, etc), so it can't be approached from this angle - I need to "monitor" for changes somehow. Currently I've implemented a "quick'n'dirty" method which checks body.innerHTML.length at intervals. This won't of course detect changes which result in the same length being returned, but in this case is "good enough" - the chances of this happening are extremely slim, and in this project, failing to detect a change won't result in lost data. The problem with body.innerHTML.length is that it's expensive. It can take between 1 and 5 milliseconds on a fast browser, and this can bog things down a lot - I'm also dealing with a large-ish number of iframes and it all adds up. I'm pretty sure the expensiveness of doing this is because the innerHTML text is not stored statically by browsers, and needs to be calculated from the DOM every time it is read. The types of answers I am looking for are anything from the "precise" (for example event) to the "good enough" - perhaps something as "quick'n'dirty" as the innerHTML.length method, but that executes faster.

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• (Oracle) How get total number of results when using a pagination query?

  - by BestPractices

  I am using Oracle 10g and the following paradigm to get a page of 15 results as a time (so that when the user is looking at page 2 of a search result, they see records 16-30). select * from ( select rownum rnum, a.* from (my_query) a where rownum <= 30 ) where rnum > 15; Right now I'm having to run a separate SQL statement to do a "select count" on "my_query" in order to get the total number of results for my_query (so that I can show it to the user and use it to figure out total number of pages, etc). Is there any way to get the total number of results without doing this via a second query, i.e. by getting it from above query? I've tried adding "max(rownum)", but it doesn't seem to work (I get an error [ORA-01747] that seems to indicate it doesnt like me having the keyword rownum in the group by). My rationale for wanting to get this from the original query rather than doing it in a separate SQL statement is that "my_query" is an expensive query so I'd rather not run it twice (once to get the count, and once to get the page of data) if I dont have to; but whatever solution I can come up with to get the number of results from within a single query (and at the same time get the page of data I need) should not add much if any additional overhead, if possible. Please advise. Here is exactly what I'm trying to do for which I receive an ORA-01747 error because I believe it doesnt like me having ROWNUM in the group by. Note, If there is another solution that doesnt use max(ROWNUM), but something else, that is perfectly fine too. This solution was my first thought as to what might work. SELECT * FROM (SELECT r.*, ROWNUM RNUM, max(ROWNUM) FROM (SELECT t0.ABC_SEQ_ID AS c0, t0.FIRST_NAME, t0.LAST_NAME, t1.SCORE FROM ABC t0, XYZ t1 WHERE (t0.XYZ_ID = 751) AND t0.XYZ_ID = t1.XYZ_ID ORDER BY t0.RANK ASC) r WHERE ROWNUM <= 30 GROUP BY r.*, ROWNUM) WHERE RNUM > 15

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• Thread-safety of read-only memory access

  - by Edmund

  I've implemented the Barnes-Hut gravity algorithm in C as follows: Build a tree of clustered stars. For each star, traverse the tree and apply the gravitational forces from each applicable node. Update the star velocities and positions. Stage 2 is the most expensive stage, and so is implemented in parallel by dividing the set of stars. E.g. with 1000 stars and 2 threads, I have one thread processing the first 500 stars and the second thread processing the second 500. In practice this works: it speeds the computation by about 30% with two threads on a two-core machine, compared to the non-threaded version. Additionally, it yields the same numerical results as the original non-threaded version. My concern is that the two threads are accessing the same resource (namely, the tree) simultaneously. I have not added any synchronisation to the thread workers, so it's likely they will attempt to read from the same location at some point. Although access to the tree is strictly read-only I am not 100% sure it's safe. It has worked when I've tested it but I know this is no guarantee of correctness! Questions Do I need to make a private copy of the tree for each thread? Even if it is safe, are there performance problems of accessing the same memory from multiple threads?

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• Calculate the year for ending month/day?

  - by Dave Jarvis

  Given: Start Year Start Month & Start Day End Month & End Day What SQL statement results in TRUE if a date lands between the Start and End days? 1st example: Start Date = 11-22 End Date = 01-17 Start Year = 2009 Specific Date = 2010-01-14 TRUE 2nd example: Start Date = 11-22 End Date = 11-16 Start Year = 2009 Specific Date = 2010-11-20 FALSE 3rd example: Start Date = 02-25 End Date = 03-19 Start Year = 2004 Specific Date = 2004-02-29 TRUE I was thinking of using the MySQL functions datediff and sign plus a CASE condition to determine whether the year wraps, but it seems rather expensive. Am looking for a simple, efficient calculation. Update 1 The problem is the end date cannot simply use the year. The year must be increased if the end month/day combination happens before the start date. The start date is easy: Start Date = date( concat_ws( '-', year, Start Month, Start Day ) ) The end date is not so simple. Update 2 Here is what I was thinking about for obtaining the end year: end_year = case sign( diff( date( concat_ws( year, start_month, start_day ) ), date( concat_ws( year, end_month, end_day ) ) ) ) when -1 then Start_Year + 1 else Start_Year end case Then wrap that expression (once syntactically correct) inside of another date, followed by BETWEEN statement. Update 3 To clear up some confusion: there is no end year. The end year must be calculated. Thank you!

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• How to maintain an ordered table with Core Data (or SQL) with insertions/deletions?

  - by Jean-Denis Muys

  This question is in the context of Core Data, but if I am not mistaken, it applies equally well to a more general SQL case. I want to maintain an ordered table using Core Data, with the possibility for the user to: reorder rows insert new lines anywhere delete any existing line What's the best data model to do that? I can see two ways: 1) Model it as an array: I add an int position property to my entity 2) Model it as a linked list: I add two one-to-one relations, next and previous from my entity to itself 1) makes it easy to sort, but painful to insert or delete as you then have to update the position of all objects that come after 2) makes it easy to insert or delete, but very difficult to sort. In fact, I don't think I know how to express a Sort Descriptor (SQL ORDER BY clause) for that case. Now I can imagine a variation on 1): 3) add an int ordering property to the entity, but instead of having it count one-by-one, have it count 100 by 100 (for example). Then inserting is as simple as finding any number between the ordering of the previous and next existing objects. The expensive renumbering only has to occur when the 100 holes have been filled. Making that property a float rather than an int makes it even better: it's almost always possible to find a new float midway between two floats. Am I on the right track with solution 3), or is there something smarter?

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• Fast, Unicode-capable, cross-platform programmer's text editor that shows invisibles like ZWSP?

  - by Roger_S

  Our publishing workflow includes Windows and Linux machines (there are some Macs too, but not in the critical-path workflow). Many texts include both English and Khmer and are marked-up in XML. XML Copy Editor is the best cross-platform open-source XML editor I've discovered. It utilizes the Scintilla editing component, which is generally good with Unicode but which does not enable non-printing or invisible characters like U+200B (zero-width space) and U+200C (zero-width non-joiner) to be displayed. Khmer does not separate words with a space character as Western languages do, so ZWSP is used in electronic texts to enable applications to break lines easily. Ideally I'd edit the markup and the content in a single editor, but XML awareness is less important at times than being able to display invisibles. (OpenOffice.org Writer and Microsoft Word are the only two apps I know that will display ZWSP. They are not suitable for the markup and text manipulations that need to be done to prepare manuscripts for publication, unfortunately, although I guess they're fine for authoring.) I tried out a promising editor last week, but a search-and-replace regex operation that took under a second in TextPad 4.7.3 lasted over twenty seconds. So I want to mention that speed and the ability to handle large (up to 150mb) files is also a concern. Is there a good, fast, free or not too expensive text editor, with versions on Windows and Linux and maybe mac too, Unicode-aware and capable of displaying invisibles like ZWSP? That has syntax highlighting, can handle large files and is customizable enough that I won't tear my hair out in frustration? Thanks, Roger_S

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• How to figure out which record has been deleted in an effiecient way?

  - by janetsmith

  Hi, I am working on an in-house ETL solution, from db1 (Oracle) to db2 (Sybase). We needs to transfer data incrementally (Change Data Capture?) into db2. I have only read access to tables, so I can't create any table or trigger in Oracle db1. The challenge I am facing is, how to detect record deletion in Oracle? The solution which I can think of, is by using additional standalone/embedded db (e.g. derby, h2 etc). This db contains 2 tables, namely old_data, new_data. old_data contains primary key field from tahle of interest in Oracle. Every time ETL process runs, new_data table will be populated with primary key field from Oracle table. After that, I will run the following sql command to get the deleted rows: SELECT old_data.id FROM old_data WHERE old_data.id NOT IN (SELECT new_data.id FROM new_data) I think this will be a very expensive operation when the volume of data become very large. Do you have any better idea of doing this? Thanks.

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• Progressively stream the output of an ASP.NET page - or render a page outside of an HTTP request

  - by Evgeny

  I have an ASP.NET 2.0 page with many repeating blocks, including a third-party server-side control (so it's not just plain HTML). Each is quite expensive to generate, in terms of both CPU and RAM. I'm currently using a standard Repeater control for this. There are two problems with this simple approach: The entire page must be rendered before any of it is returned to the client, so the user must wait a long time before they see any data. (I write progress messages using Response.Write, so there is feedback, but no actual results.) The ASP.NET worker process must hold everything in memory at the same time. There is no inherent needs for this: once one block is processed it won't be changed, so it could be returned to the client and the memory could be freed. I would like to somehow return these blocks to the client one at a time, as each is generated. I'm thinking of extracting the stuff inside the Repeater into a separate page and getting it repeatedly using AJAX, but there are some complications involved in that and I wonder if there is some simper approach. Ideally I'd like to keep it as one page (from the client's point of view), but return it incrementally. Another way would be to do something similar, but on the server: still create a separate page, but have the server access it and then Response.Write() the HTML it gets to the response stream for the real client request. Is there a way to avoid an HTTP request here, though? Is there some ASP.NET method that would render a UserControl or a Page outside of an HTTP request and simply return the HTML to me as a string? I'm open to other ideas on how to do this as well.

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• regressions with many nested categorical covariates

  - by eric

  I have a few hundred thousand measurements where the dependent variable is a probability, and would like to use logistic regression. However, the covariates I have are all categorical, and worse, are all nested. By this I mean that if a certain measurement has "city - Phoenix" then obviously it is certain to have "state - Arizona" and "country - U.S." I have four such factors - the most granular has some 20k levels, but if need be I could do without that one, I think. I also have a few non-nested categorical covariates (only four or so, with maybe three different levels each). What I am most interested in is prediction - given a new observation in some city, I would like to know the relevant probability/dependent variable. I am not interested as much in the related inferential machinery - standard deviations, etc - at least as of now. I am hoping I can afford to be sloppy. However, I would love to have that information unless it requires methods that are more computationally expensive. Does anyone have any advice on how to attack this? I have looked into mixed effects, but am not sure it is what I am looking for.

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• Conditional insert as a single database transaction in HSQLDB 1.8?

  - by Kevin Pauli

  I'm using a particular database table like a "Set" data structure, i.e., you can attempt to insert the same row several times, but it will only contain one instance. The primary key is a natural key. For example, I want the following series of operations to work fine, and result in only one row for Oklahoma: insert into states_visited (state_name) values ('Oklahoma'); insert into states_visited (state_name) values ('Texas'); insert into states_visited (state_name) values ('Oklahoma'); I am of course getting an error due to the duplicate primary key on subsequent inserts of the same value. Is there a way to make the insert conditional, so that these errors are not thrown? I.e. only do the the insert if the natural key does not already exist? I know I could do a where clause and a subquery to test for the row's existence first, but it seems that would be expensive. That's 2 physical operations for one logical "conditional insert" operation. Anything like this in SQL? FYI I am using HSQLDB 1.8

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• How can I accelerate the generation of the an MD5 Checksum within vb.net?

  - by Richard

  I'm working with some very large files residing on P2 (Panasonic) cards. Part of the process we employ is to first generate a checksum of the file we are going to copy, then copy the file, then run a checksum on the file to confirm that it copied OK. The problem is, is that files are large (70 GB+) and take a long time to complete. It's an issue since we will eventually be dealing with thousands of these files. I would like to find a faster way to generate the checksum other than using the System.Security.Cryptography.MD5CryptoServiceProvider I don't care if this means using a specialized hardware card, provided it works and is not to ungodly expensive. I would prefer to have a method of encoding that provided some feedback as to how far the process has gone along so I can display it like I do now. The application is written in vb.net. I would prefer to be able to use it as component, library, reference within my application, but I'm willing to call an outside application if there is enough improvement in the speed of generating the checksum. Needless to say, the checksum must be consistent and correct. :-) Thank you in advance for your time and efforts, Richard

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