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  • Any tips of how to handle hierarchial trees in relational model?

    - by George
    Hello all. I have a tree structure that can be n-levels deep, without restriction. That means that each node can have another n nodes. What is the best way to retrieve a tree like that without issuing thousands of queries to the database? I looked at a few other models, like flat table model, Preorder Tree Traversal Algorithm, and so. Do you guys have any tips or suggestions of how to implement a efficient tree model? My objective in the real end is to have one or two queries that would spit the whole tree for me. With enough processing i can display the tree in dot net, but that would be in client machine, so, not much of a big deal. Thanks for the attention

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  • Is NFS capable of preserving order of operations?

    - by JustJeff
    I have a diskless host 'A', that has a directory NFS mounted on server 'B'. A process on A writes to two files F1 and F2 in that directory, and a process on B monitors these files for changes. Assume that B polls for changes faster than A is expected to make them. Process A seeks the head of the files, writes data, and flushes. Process B seeks the head of the files and does reads. Are there any guarantees about how the order of the changes performed by A will be detected at B? Specifically, if A alternately writes to one file, and then the other, is it reasonable to expect that B will notice alternating changes to F1 and F2? Or could B conceivably detect a series of changes on F1 and then a series on F2? I know there are a lot of assumptions embedded in the question. For instance, I am virtually certain that, even operating on just one file, if A performs 100 operations on the file, B may see a smaller number of changes that give the same result, due to NFS caching some of the actions on A before they are communicated to B. And of course there would be issues with concurrent file access even if NFS weren't involved and both the reading and the writing process were running on the same real file system. The reason I'm even putting the question up here is that it seems like most of the time, the setup described above does detect the changes at B in the same order they are made at A, but that occasionally some events come through in transposed order. So, is it worth trying to make this work? Is there some way to tune NFS to make it work, perhaps cache settings or something? Or is fine-grained behavior like this just too much expect from NFS?

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  • Android: Touch seriously slowing my application

    - by Jason Rogers
    Hi all, I've been raking my brains on this one for a while. when I'm running my application (opengl game) eveyrthing goes fine but when I touch the screen my application slows down quite seriously (not noticeable on powerful phones like the nexus one, but on the htc magic it gets quite annoying). I did a trace and found out that the touch events seem to be handled in a different thread and even if it doesn't take so much processing time I think androids ability to switch between threads is not so good... What is the best way to handle touch when speed is an issue ? Currently I'm using : in the GLSurfaceView @Override public boolean onTouchEvent(MotionEvent event) { GameHandler.onTouchEvent(event); return true; } Any ideas are welcome

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  • Library for Dataflow in C

    - by msutherl
    How can I do dataflow (pipes and filters, stream processing, flow based) in C? And not with UNIX pipes. I recently came across stream.py. Streams are iterables with a pipelining mechanism to enable data-flow programming and easy parallelization. The idea is to take the output of a function that turns an iterable into another iterable and plug that as the input of another such function. While you can already do this using function composition, this package provides an elegant notation for it by overloading the operator. I would like to duplicate a simple version of this kind of functionality in C. I particularly like the overloading of the operator to avoid function composition mess. Wikipedia points to this hint from a Usenet post in 1990. Why C? Because I would like to be able to do this on microcontrollers and in C extensions for other high level languages (Max, Pd*, Python). * (ironic given that Max and Pd were written, in C, specifically for this purpose – I'm looking for something barebones)

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  • strsplit in R with metacharacter

    - by user1429852
    I have received a large amount of data where the delimiter is a backslash (obviously a bad choice). I'm processing it in R for computation, and having a hard time finding how to split the string since the backslash is a metacharacter. For example, a string would look like this: "1128\0019\XA5\E2R\366\00=15" and I want to split it along the "\" character, but when I run the strsplit command: strsplit(tempStr, "\") Error in strsplit(tempStr, "\") : invalid regular expression '\', reason 'Trailing backslash' When I try to used the "fixed" option, it does not run because it is expecting something after the backslash: strsplit(tempStr, "\", fixed = TRUE) Unfortunately, I can't preprocess the data with another program because the data is generated daily. Please help and thanks!

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  • Insert into ... Select *, how to ignore identity?

    - by Haoest
    I have a temp table with the exact structure of a concrete table T. It was created like this: select top 0 * into #tmp from T After processing and filling in content into #tmp, I want to copy the content back to T like this: insert into T select * from #tmp This is okay as long as T doesn't have identity column, but in my case it does. Is there anyways I can ignore the auto-increment identity column from #tmp when I copy to T? My motivation is to avoid having to spell out every column name in the Insert Into list. EDIT: toggling identity_insert wouldn't work because the pkeys in #tmp may collide with those in T if rows were inserted into T outside of my script, that's if #tmp has auto-incremented the pkey to sync with T's in the first place.

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  • SYN receives RST,ACK very frequently

    - by user1289508
    Hi Socket Programming experts, I am writing a proxy server on Linux for SQL Database server running on Windows. The proxy is coded using bsd sockets and in C, and it is working just fine. When I use a database client (written in JAVA, and running on a Linux box) to fire queries (with a concurrency of 100 or more) directly to the Database server, not experiencing connection resets. But through my proxy I am experiencing many connection resets. Digging deeper I came to know that connection from 'DB client' to 'Proxy' always succeeds but when the 'Proxy' tries to connect to the DB server the connection fails, due to the SYN packet getting RST,ACK. That was to give some background. The question is : Why does sometimes SYN receives RST,ACK? 'DB client(linux)' to 'Server(windows)' ---- Works fine 'DB client(linux) to 'Proxy(Linux)' to 'Server(windows)' ----- problematic I am aware that this can happen in "connection refused" case but this definitely is not that one. SYN flooding might be another scenario, but that does not explain fine behavior while firing to Server directly. I am suspecting some socket option setting may be required, that the client does before connecting and my proxy does not. Please put some light on this. Any help (links or pointers) is most appreciated. Additional info: Wrote a C client that does concurrent connections, which takes concurrency as an argument. Here are my observations: - At 5000 concurrency and above, some connects failed with 'connection refused'. - Below 2000, it works fine. But the actual problem is observed even at a concurrency of 100 or more. Note: The problem is time dependent sometimes it never comes at all and sometimes it is very frequent and DB client (directly to server) works fine at all times .

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  • SQL: joining multiples tables into one.

    - by Graveen
    I have 4 tables. r1, r2, r3 and r4. The table columns are the following: rId | rName I want to have, in fine, an unique table - let's call it R. Obviously, R will have the following structure: rTableName | rId | rName I'm looking for a solution, and the more natural for me is to: add a single column to all rX insert this column the table name i'm processing generate SQLs and concatenate them all Although I see exactly how to perform 1 and 3 with batching, editing, etc... (I have only to perform it once and for all), I don't see how to do the point 2: self-getting the tablename to insert into SQL. Have you an idea / or a different way to do that could solve my problem? Note: In fact, there are 250+ rX tables. That's why i can't do this manually. Note2: Precisely, this is with MySQL.

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  • Secure xml messages being read from database into app.

    - by scope-creep
    I have an app that reads xml from a database using NHibernate Dal. The dal calls stored procedures to read and encapsulate the data from the schema into an xml message, wrap it up to a message and enqueue it on an internal queue for processing. I would to secure the channel from the database reads to the dequeue action. What would be the best way to do it. I was thinking of signing the xml using System.Security.Cryptography.Xml namespace, but is their any other techniques or approaches I need to know about? Any help would be appreciated. Bob.

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  • Python frequency detection

    - by Tsuki
    Ok what im trying to do is a kind of audio processing software that can detect a prevalent frequency an if the frequency is played for long enough (few ms) i know i got a positive match. i know i would need to use FFT or something simiral but in this field of math i suck, i did search the internet but didn not find a code that could do only this. the goal im trying to accieve is to make myself a custom protocol to send data trough sound, need very low bitrate per sec but im also very limited on the transmiting end so the recieving software will need to be able custom (cant use an actual hardware/software modem) also i want this to be software only (no additional hardware except soundcard) thanks alot for the help.

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  • Only strip commas surrounded by numbers in a string

    - by overlook77
    I am using StreamReader to read each line of a CSV file into a string. As I am processing each line, I need to strip out any commas that ONLY are surrounded by other numbers. For example, if the string was: "textfield1", "textfield2", "100.00", "1,070.00" I would need to only take the comma out of "1,070.00" from this entire string, resulting in: "textfield1", "textfield2", "100.00", "1070.00" Each string read from the CSV file can differ in number of fields, length, etc., so I need to use something (Regular Expressions maybe?) that looks at the entire string without hardcoding a location or blanket removal of all commas. Here is the approach I have been trying: StreamReader sr = new StreamReader(strInputFile); string nextLine = sr.ReadLine(); try { while ((nextLine = sr.ReadLine()) != null) { string rawtext = nextLine.Replace("[0-9]"+","+"[0-9]" , "[0-9]"+"[0-9]"); // ....rest of code } } This obviously doesn't work because I don't understand how to do this :) I am new at C# and inexperienced in Regex, so hopefully this is relatively simple.

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  • How to find root cause for "too many connections" error in MySQL/PHP

    - by Nir
    I'm running a web service which runs algorithms that serve millions of calls daily and run some background processing as well. Every now and than I see "Too many connections" error in attempts to connect to the MySQL box" for a few seconds. However this is not necessarily attributed to high traffic times or anything I can put my finger on. I want to find the bottleneck causing it. Other than in the specific times this happens the server isn't too loaded in terms of CPU and Memory, and has 2-3 connections (threads) open and everything works smoothly. (I use Zabbix for monitoring) Any creative ideas on how to trace it?

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  • Erlang Question - Time order of messages

    - by Aiden Bell
    Read (skimmed enough to get coding) through Erlang Programming and Programming Erlang. One question, which is as simple as it sounds: If you have a process Pid1 on machine m1 and a billion million messages are sent to Pid1, are messages handled in parallel by that process (I get the impression no) and(answered below) is there any guarantee of order when processing messages? ie. Received in order sent? If so, how is clock skew handled in high traffic situations for ordering? Coming from the whole C/Thread pools/Shared State background ... I want to get this concrete. I understand distributing an application, but want to ensure the 'raw bones' are what I expect before building processes and distributing workload. Also, am I right in thinking the whole world is currently flicking through Erlang texts ;)

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  • List with non-null elements ends up containing null. A synchronization issue?

    - by Alix
    Hi. First of all, sorry about the title -- I couldn't figure out one that was short and clear enough. Here's the issue: I have a list List<MyClass> list to which I always add newly-created instances of MyClass, like this: list.Add(new MyClass()). I don't add elements any other way. However, then I iterate over the list with foreach and find that there are some null entries. That is, the following code: foreach (MyClass entry in list) if (entry == null) throw new Exception("null entry!"); will sometimes throw an exception. I should point out that the list.Add(new MyClass()) are performed from different threads running concurrently. The only thing I can think of to account for the null entries is the concurrent accesses. List<> isn't thread-safe, after all. Though I still find it strange that it ends up containing null entries, instead of just not offering any guarantees on ordering. Can you think of any other reason? Also, I don't care in which order the items are added, and I don't want the calling threads to block waiting to add their items. If synchronization is truly the issue, can you recommend a simple way to call the Add method asynchronously, i.e., create a delegate that takes care of that while my thread keeps running its code? I know I can create a delegate for Add and call BeginInvoke on it. Does that seem appropriate? Thanks.

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  • I'm getting reports that my app is draining the battery, but only on HTC Incredible.

    - by BenTobin
    Has anyone else noticed behavior specific to the HTC Incredible that might result in an app keeping the device awake and busy? I've received reports that my app is responsible for keeping the device awake and draining the battery, but only from HTC Incredible users. My app responds to a number of Intents that might be related. It has a service that starts on boot, and it also responds to changes in network connectivity. I do use a WakeLock, but I'm careful to release it when I'm done processing, and the WakeLock times out after a couple minutes whether I'm done or not. I've heard that the Incredible may have some connectivity problems, or that some of them do. Could it be that the network is going up and down frequently, triggering my app? Any other ideas? I've asked a user to send me their logs with aLogCat. If they're willing, that may help narrow down the cause.

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  • Persistent SQL Table lock from C#

    - by Chris
    I'm trying to create a persistent SQL (SQL Server 2005) lock on a table level. I'm not updating/querying the specified table, but I need to prevent a third party application from updating the locked table as a means to prevent transactions from being posted (the table I wish to lock is the key on their transaction that interferes with my processing). From my experience the table is only locked for the time a specific transaction is taking place. Any ideas? The 3rd party developer has logged this feature as an enhancement, but since they are in the middle of rolling out a major release I can expect to wait at least 6 months for this. I know that this isn't a great solution, since their software will fall over but it is of a critical enough nature that we're willing to live with the consequences.

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  • A question of long-running and disruptive branches

    - by Matt Enright
    We are about to begin prototyping a new application that will share some existing infrastructure assemblies with an existing application, and also involve a significant subset of the existing domain model. Parts of the domain model will likely undergo some serious changes for this new application, and the endgame for all of this, once the new application has been fully specified and is launch-ready is that we would like to re-unify the models of the two applications (as well as share a database, link functionality, etc.), but for the duration of development, prototyping, etc, we will be using a separate database so that we can change things without worrying about impact to development or use of the existing application. Since it is a prototype, there will be a pretty long window during which serious changes or rearchitecturing can occur as product management experiments with different workflows, different customer bases are surveyed, and we try and keep up. We have already made a Subversion branch, so as to not impact concurrent development on the mature application, and are toying with 2 potential ways of moving forward with this: Use the svn branch as the sole mechanism of separation. Make our changes to the existing domain models, and evaluate their impact on the existing application (and make requisite changes to ProjectA) when we have established that our long-running side branch is stable enough for re-entry to trunk. "Fork" the shared code (temporarily): Copy ProjectA.Entities to NewProject.Entities, and treat all of the NewProject code as self-contained. When all of the perturbations around the model have died down and we feel satisfied, manually re-integrate the changes (as granular or sweeping as warranted) back into ProjectA.Entities, updating ProjectA to use the improved models at each step (this can take place either before or after the subversion merge has occurred). The subversion merge will then not handle recombination of any of the heavy changes here. Note: the "fork" method only applies to the code we see significant changes in store for, and whose modification will break ProjectA - shared infrastructure stuff for example, we would just modify in place (on our branch) and let the merge sort out. Development is hard, go shopping. Naturally, after not coming to an agreement, we're turning it over to the oracle of power that is SO. Any experience with any of these methods, pain points to watch out for, something new entirely?

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  • Can a Java HashMap's size() be out of sync with its actual entries' size ?

    - by trix
    I have a Java HashMap called statusCountMap. Calling size() results in 30. But if I count the entries manually, it's 31 This is in one of my TestNG unit tests. These results below are from Eclipse's Display window (type code - highlight - hit Display Result of Evaluating Selected Text). statusCountMap.size() (int) 30 statusCountMap.keySet().size() (int) 30 statusCountMap.values().size() (int) 30 statusCountMap (java.util.HashMap) {40534-INACTIVE=2, 40526-INACTIVE=1, 40528-INACTIVE=1, 40492-INACTIVE=3, 40492-TOTAL=4, 40513-TOTAL=6, 40532-DRAFT=4, 40524-TOTAL=7, 40526-DRAFT=2, 40528-ACTIVE=1, 40524-DRAFT=2, 40515-ACTIVE=1, 40513-DRAFT=4, 40534-DRAFT=1, 40514-TOTAL=3, 40529-DRAFT=4, 40515-TOTAL=3, 40492-ACTIVE=1, 40528-TOTAL=4, 40514-DRAFT=2, 40526-TOTAL=3, 40524-INACTIVE=2, 40515-DRAFT=2, 40514-ACTIVE=1, 40534-TOTAL=3, 40513-ACTIVE=2, 40528-DRAFT=2, 40532-TOTAL=4, 40524-ACTIVE=3, 40529-ACTIVE=1, 40529-TOTAL=5} statusCountMap.entrySet().size() (int) 30 What gives ? Anyone has experienced this ? I'm pretty sure statusCountMap is not being modified at this point. There are 2 methods (lets call them methodA and methodB) that modify statusCountMap concurrently, by repeatedly calling incrementCountInMap. private void incrementCountInMap(Map map, Long id, String qualifier) { String key = id + "-" + qualifier; if (map.get(key) == null) { map.put(key, 0); } synchronized (map) { map.put(key, map.get(key).intValue() + 1); } } methodD is where I'm getting the issue. methodD has a TestNG @dependsOnMethods = { "methodA", "methodB" } so when methodD is executing, statusCountMap is pretty much static already. I'm mentioning this because it might be a bug in TestNG. I'm using Sun JDK 1.6.0_24. TestNG is testng-5.9-jdk15.jar Hmmm ... after rereading my post, could it be because of concurrent execution of outside-of-synchronized-block map.get(key) == null & map.put(key,0) that's causing this issue ?

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  • While in a transaction, how can reads to an affected row be prevented until the transaction is done?

    - by Mahn
    I'm fairly sure this has a simple solution, but I haven't been able to find it so far. Provided an InnoDB MySQL database with the isolation level set to SERIALIZABLE, and given the following operation: BEGIN WORK; SELECT * FROM users WHERE userID=1; UPDATE users SET credits=100 WHERE userID=1; COMMIT; I would like to make sure that as soon as the select inside the transaction is issued, the row corresponding to userID=1 is locked for reads until the transaction is done. As it stands now, UPDATEs to this row will wait for the transaction to be finished if it is in process, but SELECTs simply will read the previous value. I understand this is the expected behaviour in this case, but I wonder if there is a way to lock the row in such a way that SELECTs will also wait until the transaction is finished to return the values? The reason I'm looking for that is that at some point, and with enough concurrent users, it could happen that while the previous transaction is in process someone else reads the "credits" to calculate something else. Ideally the code run by that someone else should wait for the transaction to finish to use the new value, because otherwise it could lead to irreversible desync issues. Note that I don't want to lock the entire table for reads, just the specific row. Also, I could add a boolean "locked" field to the tables and set it to 1 every time I'm starting a transaction but I don't really feel this is the most elegant solution here, unless there is absolutely no other way to handle this through mysql directly.

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  • After C++ - Python or Java?

    - by carleeto
    I'm fast approaching the point in my coding where I would like to quickly write object oriented code in languages other than C++ for a variety of reasons. After a lot of research, my choices have pretty much narrowed down to Python and Java. I'm leaning towards Python because of its relationship to C, but with Java, from what I can see, I get a good introduction to using and creating test suites with Eclipse - there is also Processing which is pulling me towards Java. I'm not the kind of guy to tackle two languages at once, so which one would you recommend and why? What I want at the end is to have an additional language I can use for rapid development. Ease of learning isn't important to me as I'm willing to put in the time regardless. Ability to use the new language widely is.

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  • What happens if the first part of an if-structure is false?

    - by djerry
    Hey guys, I was wondering what happens when a program processes an if-structure with multiple conditions. I have an idea, but i'm not sure about it. I'll give an example : List<string> myTestList = null; if (myTestList != null && myTestList.Count > 0) { //process } The list is null. When processing the if, will it go from left to right exiting the if as soon as one condition is false? I've tried it and seems to throw no errors, so i assume the above explains it, but i'm not sure. Thanks in advance.

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  • How to prevent robots from automatically filling up a form?

    - by sombe
    I'm trying to come up with a good enough anti-spamming mechanism to prevent automatically generated input. I've read that techniques like captcha, 1+1=? stuff work well, but they also present an extra step impeding the free quick use of the application. (I'm not looking for anything like that please). I've tried setting some hidden fields in all of my forms, with display: none; However, I'm almost certain a robot (which is essentially a program) can be configured to trace that form field id and simply not fill it. Do you implement/know of a good anti automatic-form-filling-robots method? Is there something that can be done seamlessly with HTML AND/OR server side processing, and be (almost) foolproof? (and please no JS, one could simply disable it, and there goes my anti-spam method). Btw I'm trying not to rely on sessions for this (like, counting how many times a button is clicked to prevent overloads).

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  • Creating files on a time (hourly) basis

    - by Yaniv
    Hi there, I experimenting with twitter streaming API, I use Phirehose to connect to twitter and fetch the data but having problems storing it in files for further processing. Basically what I want to do is to create a file named date("YmdH")."."txt" for every hour of connection. Here is how my code looks like right now (not handling the hourly change of files) public function enqueueStatus($status) $data = json_decode($status,true); if(isset($data['text'])/*more conditions here*/) { $fp = fopen("/tmp/$time.txt"); fwirte ($status,$fp); fclose($fp); } Help is as always much appreciated :)

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  • client-side vs server-side

    - by amalafrida
    In general, should one design in order to place processing load on client-side? More specifically, a search engine to locate subscriber information requires a fair amount of parsing (multiple phone numbers to sort and format, hour of day, timezone, comparisons for possible substitutions of user information, etc.). Again, in general, is it preferred that one have client-side do the work? It seems to me 'yes' in a situation in which one will have many thousands of hits per minute. Use php for quick database queries ... process retrieved data client-side. yes ... no?

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  • OpenGL game written in C with a Cocoa front-end I want to port to Windows

    - by Philip
    Hello, I'm wondering if someone could offer me some tips on how to go about this. I have a MacOS X OpenGL game that is written in very portable C with the exception of the non-game-play GUI. So in Cocoa I set up the window and OpenGL context, manage preferences, registration, listen for keystrokes etc. But all of the drawing and processing of input is handled in nice portable C. So I want to port to Windows. I figured the obvious way to go about was to use the Win32 api. Then I started to read a primer on Win32 and began to wonder if maybe life isn't too short. Can I do this in C# (without converting the backend to C#)? I'd rather devote the time to learning C# than Win32. Any suggestions would be most welcome. I really don't know a lick about Windows. The last version I regularly used was 3.1...

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