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• Is it a bad practice to store large files (10 MB) in a database?

  - by B Seven

  I am currently creating a web application that allows users to store and share files, 1 MB - 10 MB in size. It seems to me that storing the files in a database will significantly slow down database access. Is this a valid concern? Is it better to store the files in the file system and save the file name and path in the database? Are there any best practices related to storing files when working with a database? I am working in PHP and MySQL for this project, but is the issue the same for most environments (Ruby on Rails, PHP, .NET) and databases (MySQL, PostgreSQL).

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• Handling changes to data types and entries in a database migration

  - by jandjorgensen

  I'm fully redesigning a site that indexes a number of articles with basic search functionality. The previous site was written about a decade ago, and I'm salvaging about 30,000 entries with data stored in less-than-ideal formats. While I'm moving from MSSQL to MySQL, I don't need to make any "live" changes, so this is not a production-level migration issue so much as a redesign. For instance, dates are stored the same as tags/subjects about the articles, but in strings as "YYYYMMDDd" (the lowercase d stands for "date" in the string). Essentially, before or after I move from the previous database format to a new one, I'm going to need to do a lot of replacement of individual entries. While I understand how to do operations with regular expressions in non-database issues, my database experience isn't robust enough to know the best way to handle this. What is the best (or standard) way to handle major changes like this? Is there an SQL operation I should be looking into? Please let me know if the problem isn't clear--I'm not entirely sure what kind of answer I'm looking for.

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• ERROR in Installing a Theme in ubuntu 13.10

  - by Badar 'Prince' Ismail

  I just upgraded to Ubuntu 13.10 3 days ago and since then I've been trying to install a couple of themes for example i tried MOKA theme and many more.whenever i try to install a theme when ever i add the PPA: and after that i type sudo apt-get update its shows this: W: Failed to fetch http://ppa.launchpad.net/jolicloud-team/ppa/ubuntu/dists/saucy/main/binary-i386/Packages 404 Not Found W: Failed to fetch http://ppa.launchpad.net/webupd8team/jupiter/ubuntu/dists/saucy/main/binary-i386/Packages 404 Not Found E: Some index files failed to download. They have been ignored, or old ones used instead.

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• Is catching general exceptions really a bad thing?

  - by Bob Horn

  I typically agree with most code analysis warnings, and I try to adhere to them. However, I'm having a harder time with this one: CA1031: Do not catch general exception types I understand the rationale for this rule. But, in practice, if I want to take the same action regardless of the exception thrown, why would I handle each one specifically? Furthermore, if I handle specific exceptions, what if the code I'm calling changes to throw a new exception in the future? Now I have to change my code to handle that new exception. Whereas if I simply caught Exception my code doesn't have to change. For example, if Foo calls Bar, and Foo needs to stop processing regardless of the type of exception thrown by Bar, is there any advantage in being specific about the type of exception I'm catching?

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• Storing lots of large strings with frequent "appends" and few reads

  - by Thiago Moraes

  In my current project, I need to store a very long ASCII string to each instance of a given object. This string will receive an 2 appends per minute and will not be retrieved so frequently. The worst case scenario is a 5-10MB string. I'll have thousands of instances of my object and I'm worried that storing all those strings in the filesystem would not be optimal, but I can't think of a better solution. Can anyone suggest an alternative? Maybe a key-value store? In this case, which one? Any other thoughts?

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• Is Error Recovery Control or TLER necessary for software RAID5 using LVM

  - by Vincent Davis

  I ave been told that for RAID configurations you don't what to use standard desktop drives because they when/if they enter a error recovery mode they might time out and get dropped from the raid. Is this true for LVM software RAID or this this a hardware RAID issue primarily?. We are running this server primarily as a backup server and would like to take advantage of the lower price of the desktop drives.

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• Handling SEO for Infinite pages that cause external slow API calls

  - by Noam

  I have an 'infinite' amount of pages in my site which rely on an external API. Generating each page takes time (1 minute). Links in the site point to such pages, and when a users clicks them they are generated and he waits. Considering I cannot pre-create them all, I am trying to figure out the best SEO approach to handle these pages. Options: Create really simple pages for the web spiders and only real users will fetch the data and generate the page. A little bit 'afraid' google will see this as low quality content, which might also feel duplicated. Put them under a directory in my site (e.g. /non-generated/) and put a disallow in robots.txt. Problem here is I don't want users to have to deal with a different URL when wanting to share this page or make sense of it. Thought about maybe redirecting real users from this URL back to the regular hierarchy and that way 'fooling' google not to get to them. Again not sure he will like me for that. Letting him crawl these pages. Main problem is I can't control to rate of the API calls and also my site seems slower than it should from a spider's perspective (if he only crawled the generated pages, he'd think it's much faster). Which approach would you suggest?

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• Handling Indirection and keeping layers of method calls, objects, and even xml files straight

  - by Cervo

  How do you keep everything straight as you trace deeply into a piece of software through multiple method calls, object constructors, object factories, and even spring wiring. I find that 4 or 5 method calls are easy to keep in my head, but once you are going to 8 or 9 calls deep it gets hard to keep track of everything. Are there strategies for keeping everything straight? In particular, I might be looking for how to do task x, but then as I trace down (or up) I lose track of that goal, or I find multiple layers need changes, but then I lose track of which changes as I trace all the way down. Or I have tentative plans that I find out are not valid but then during the tracing I forget that the plan is invalid and try to consider the same plan all over again killing time.... Is there software that might be able to help out? grep and even eclipse can help me to do the actual tracing from a call to the definition but I'm more worried about keeping track of everything including the de-facto plan for what has to change (which might vary as you go down/up and realize the prior plan was poor). In the past I have dealt with a few big methods that you trace and pretty much can figure out what is going on within a few calls. But now there are dozens of really tiny methods, many just a single call to another method/constructor and it is hard to keep track of them all.

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• Patterns for Handling Changing Property Sets in C++

  - by Bhargav Bhat

  I have a bunch "Property Sets" (which are simple structs containing POD members). I'd like to modify these property sets (eg: add a new member) at run time so that the definition of the property sets can be externalized and the code itself can be re-used with multiple versions/types of property sets with minimal/no changes. For example, a property set could look like this: struct PropSetA { bool activeFlag; int processingCount; /* snip few other such fields*/ }; But instead of setting its definition in stone at compile time, I'd like to create it dynamically at run time. Something like: class PropSet propSetA; propSetA("activeFlag",true); //overloading the function call operator propSetA("processingCount",0); And the code dependent on the property sets (possibly in some other library) will use the data like so: bool actvFlag = propSet["activeFlag"]; if(actvFlag == true) { //Do Stuff } The current implementation behind all of this is as follows: class PropValue { public: // Variant like class for holding multiple data-types // overloaded Conversion operator. Eg: operator bool() { return (baseType == BOOLEAN) ? this->ToBoolean() : false; } // And a method to create PropValues various base datatypes static FromBool(bool baseValue); }; class PropSet { public: // overloaded[] operator for adding properties void operator()(std::string propName, bool propVal) { propMap.insert(std::make_pair(propName, PropVal::FromBool(propVal))); } protected: // the property map std::map<std::string, PropValue> propMap; }; This problem at hand is similar to this question on SO and the current approach (described above) is based on this answer. But as noted over at SO this is more of a hack than a proper solution. The fundamental issues that I have with this approach are as follows: Extending this for supporting new types will require significant code change. At the bare minimum overloaded operators need to be extended to support the new type. Supporting complex properties (eg: struct containing struct) is tricky. Supporting a reference mechanism (needed for an optimization of not duplicating identical property sets) is tricky. This also applies to supporting pointers and multi-dimensional arrays in general. Are there any known patterns for dealing with this scenario? Essentially, I'm looking for the equivalent of the visitor pattern, but for extending class properties rather than methods. Edit: Modified problem statement for clarity and added some more code from current implementation.

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• Error message during update from 13.04 to 13.10

  - by layonhands

  The following was reported after I attempted to report the problem back to Ubuntu: The problem cannot be reported: You have some obsolete package versions installed. Please upgrade the following packages and check if the problem still occurs: ubuntu-release-upgrader-gtk, apport, apport-gtk, apport-symptoms, apt, apt-utils, at-spi2-core, binutils, dbus, gcc-4.7-base, gdb, gir1.2-atk-1.0, gir1.2-gtk-3.0, glib-networking, glib-networking-common, glib-networking-services, gnupg, gpgv, ifupdown, initramfs-tools, initramfs-tools-bin, kmod, libappindicator3-1, libapt-inst1.5, libapt-pkg4.12, libasound2, libatk-bridge2.0-0, libatk1.0-0, libatk1.0-data, libatspi2.0-0, libc-bin, libc6, libcups2, libdbus-1-3, libdbusmenu-glib4, libdbusmenu-gtk3-4, libdrm-intel1, libdrm-nouveau2, libdrm-radeon1, libdrm2, libgail-3-0, libgcc1, libgcrypt11, libglib2.0-0, libglib2.0-data, libgnutls26, libgomp1, libgstreamer-plugins-base1.0-0, libgstreamer1.0-0, libgtk-3-0, libgtk-3-bin, libgtk-3-common, libgudev-1.0-0, libicu48, libindicator3-7, libkmod2, liblcms2-2, libpci3, libplymouth2, libpolkit-agent-1-0, libpolkit-backend-1-0, libpolkit-gobject-1-0, libprocps0, libpython-stdlib, libpython2.7, libpython2.7-minimal, libpython2.7-stdlib, libpython3-stdlib, libpython3.3-minimal, libpython3.3-stdlib, libssl1.0.0, libstdc++6, libtiff5, libudev1, libx11-6, libx11-data, libx11-xcb1, libxcb-dri2-0, libxcb-glx0, libxcb-render0, libxcb-shm0, libxcb1, libxcursor1, libxext6, libxfixes3, libxi6, libxinerama1, libxml2, libxrandr2, libxrender1, libxres1, libxt6, libxtst6, libxxf86vm1, lsb-base, lsb-release, module-init-tools, multiarch-support, openssl, passwd, pciutils, perl, perl-base, perl-modules, plymouth, plymouth-theme-ubuntu-text, policykit-1, procps, python, python-gi, python-minimal, python2.7, python2.7-minimal, python3, python3-apport, python3-distupgrade, python3-gi, python3-minimal, python3-problem-report, python3-software-properties, python3-update-manager, python3.3, python3.3-minimal, rsyslog, shared-mime-info, software-properties-common, software-properties-gtk, tar, tzdata, ubuntu-release-upgrader-core, ubuntu-release-upgrader-gtk, udev, update-manager, update-manager-core, update-notifier, update-notifier-common If this question has already been answered, I'm sorry for the repost, but I would appreciate a link to the fix. Thanks. FYI: Dell Latitude D630, Intel Centrino processor. Also, the updater is currently running what seems to be the update. I will report back when it is done going through its process to let you know if it is in fact the 13.10 update. Update 2: System went through an update, but it wasn't for the OS. I think it was an update for the error message mentioned above. Now the OS update is currently running the 'distribution upgrade' portion of the update. This is further than it had gone before. Again I will report back once this is done to let you know whether or not the update was successful. Final Update: Don't know for sure what happened, but I'm almost sure that the error mentioned above was resolved in the first update prior to the 13.10 update. All set.

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• How to simulate inner join on very large files in java (without running out of memory)

  - by Constantin

  I am trying to simulate SQL joins using java and very large text files (INNER, RIGHT OUTER and LEFT OUTER). The files have already been sorted using an external sort routine. The issue I have is I am trying to find the most efficient way to deal with the INNER join part of the algorithm. Right now I am using two Lists to store the lines that have the same key and iterate through the set of lines in the right file once for every line in the left file (provided the keys still match). In other words, the join key is not unique in each file so would need to account for the Cartesian product situations ... left_01, 1 left_02, 1 right_01, 1 right_02, 1 right_03, 1 left_01 joins to right_01 using key 1 left_01 joins to right_02 using key 1 left_01 joins to right_03 using key 1 left_02 joins to right_01 using key 1 left_02 joins to right_02 using key 1 left_02 joins to right_03 using key 1 My concern is one of memory. I will run out of memory if i use the approach below but still want the inner join part to work fairly quickly. What is the best approach to deal with the INNER join part keeping in mind that these files may potentially be huge public class Joiner { private void join(BufferedReader left, BufferedReader right, BufferedWriter output) throws Throwable { BufferedReader _left = left; BufferedReader _right = right; BufferedWriter _output = output; Record _leftRecord; Record _rightRecord; _leftRecord = read(_left); _rightRecord = read(_right); while( _leftRecord != null && _rightRecord != null ) { if( _leftRecord.getKey() < _rightRecord.getKey() ) { write(_output, _leftRecord, null); _leftRecord = read(_left); } else if( _leftRecord.getKey() > _rightRecord.getKey() ) { write(_output, null, _rightRecord); _rightRecord = read(_right); } else { List<Record> leftList = new ArrayList<Record>(); List<Record> rightList = new ArrayList<Record>(); _leftRecord = readRecords(leftList, _leftRecord, _left); _rightRecord = readRecords(rightList, _rightRecord, _right); for( Record equalKeyLeftRecord : leftList ){ for( Record equalKeyRightRecord : rightList ){ write(_output, equalKeyLeftRecord, equalKeyRightRecord); } } } } if( _leftRecord != null ) { write(_output, _leftRecord, null); _leftRecord = read(_left); while(_leftRecord != null) { write(_output, _leftRecord, null); _leftRecord = read(_left); } } else { if( _rightRecord != null ) { write(_output, null, _rightRecord); _rightRecord = read(_right); while(_rightRecord != null) { write(_output, null, _rightRecord); _rightRecord = read(_right); } } } _left.close(); _right.close(); _output.flush(); _output.close(); } private Record read(BufferedReader reader) throws Throwable { Record record = null; String data = reader.readLine(); if( data != null ) { record = new Record(data.split("\t")); } return record; } private Record readRecords(List<Record> list, Record record, BufferedReader reader) throws Throwable { int key = record.getKey(); list.add(record); record = read(reader); while( record != null && record.getKey() == key) { list.add(record); record = read(reader); } return record; } private void write(BufferedWriter writer, Record left, Record right) throws Throwable { String leftKey = (left == null ? "null" : Integer.toString(left.getKey())); String leftData = (left == null ? "null" : left.getData()); String rightKey = (right == null ? "null" : Integer.toString(right.getKey())); String rightData = (right == null ? "null" : right.getData()); writer.write("[" + leftKey + "][" + leftData + "][" + rightKey + "][" + rightData + "]\n"); } public static void main(String[] args) { try { BufferedReader leftReader = new BufferedReader(new FileReader("LEFT.DAT")); BufferedReader rightReader = new BufferedReader(new FileReader("RIGHT.DAT")); BufferedWriter output = new BufferedWriter(new FileWriter("OUTPUT.DAT")); Joiner joiner = new Joiner(); joiner.join(leftReader, rightReader, output); } catch (Throwable e) { e.printStackTrace(); } } } After applying the ideas from the proposed answer, I changed the loop to this private void join(RandomAccessFile left, RandomAccessFile right, BufferedWriter output) throws Throwable { long _pointer = 0; RandomAccessFile _left = left; RandomAccessFile _right = right; BufferedWriter _output = output; Record _leftRecord; Record _rightRecord; _leftRecord = read(_left); _rightRecord = read(_right); while( _leftRecord != null && _rightRecord != null ) { if( _leftRecord.getKey() < _rightRecord.getKey() ) { write(_output, _leftRecord, null); _leftRecord = read(_left); } else if( _leftRecord.getKey() > _rightRecord.getKey() ) { write(_output, null, _rightRecord); _pointer = _right.getFilePointer(); _rightRecord = read(_right); } else { long _tempPointer = 0; int key = _leftRecord.getKey(); while( _leftRecord != null && _leftRecord.getKey() == key ) { _right.seek(_pointer); _rightRecord = read(_right); while( _rightRecord != null && _rightRecord.getKey() == key ) { write(_output, _leftRecord, _rightRecord ); _tempPointer = _right.getFilePointer(); _rightRecord = read(_right); } _leftRecord = read(_left); } _pointer = _tempPointer; } } if( _leftRecord != null ) { write(_output, _leftRecord, null); _leftRecord = read(_left); while(_leftRecord != null) { write(_output, _leftRecord, null); _leftRecord = read(_left); } } else { if( _rightRecord != null ) { write(_output, null, _rightRecord); _rightRecord = read(_right); while(_rightRecord != null) { write(_output, null, _rightRecord); _rightRecord = read(_right); } } } _left.close(); _right.close(); _output.flush(); _output.close(); } UPDATE While this approach worked, it was terribly slow and so I have modified this to create files as buffers and this works very well. Here is the update ... private long getMaxBufferedLines(File file) throws Throwable { long freeBytes = Runtime.getRuntime().freeMemory() / 2; return (freeBytes / (file.length() / getLineCount(file))); } private void join(File left, File right, File output, JoinType joinType) throws Throwable { BufferedReader leftFile = new BufferedReader(new FileReader(left)); BufferedReader rightFile = new BufferedReader(new FileReader(right)); BufferedWriter outputFile = new BufferedWriter(new FileWriter(output)); long maxBufferedLines = getMaxBufferedLines(right); Record leftRecord; Record rightRecord; leftRecord = read(leftFile); rightRecord = read(rightFile); while( leftRecord != null && rightRecord != null ) { if( leftRecord.getKey().compareTo(rightRecord.getKey()) < 0) { if( joinType == JoinType.LeftOuterJoin || joinType == JoinType.LeftExclusiveJoin || joinType == JoinType.FullExclusiveJoin || joinType == JoinType.FullOuterJoin ) { write(outputFile, leftRecord, null); } leftRecord = read(leftFile); } else if( leftRecord.getKey().compareTo(rightRecord.getKey()) > 0 ) { if( joinType == JoinType.RightOuterJoin || joinType == JoinType.RightExclusiveJoin || joinType == JoinType.FullExclusiveJoin || joinType == JoinType.FullOuterJoin ) { write(outputFile, null, rightRecord); } rightRecord = read(rightFile); } else if( leftRecord.getKey().compareTo(rightRecord.getKey()) == 0 ) { String key = leftRecord.getKey(); List<File> rightRecordFileList = new ArrayList<File>(); List<Record> rightRecordList = new ArrayList<Record>(); rightRecordList.add(rightRecord); rightRecord = consume(key, rightFile, rightRecordList, rightRecordFileList, maxBufferedLines); while( leftRecord != null && leftRecord.getKey().compareTo(key) == 0 ) { processRightRecords(outputFile, leftRecord, rightRecordFileList, rightRecordList, joinType); leftRecord = read(leftFile); } // need a dispose for deleting files in list } else { throw new Exception("DATA IS NOT SORTED"); } } if( leftRecord != null ) { if( joinType == JoinType.LeftOuterJoin || joinType == JoinType.LeftExclusiveJoin || joinType == JoinType.FullExclusiveJoin || joinType == JoinType.FullOuterJoin ) { write(outputFile, leftRecord, null); } leftRecord = read(leftFile); while(leftRecord != null) { if( joinType == JoinType.LeftOuterJoin || joinType == JoinType.LeftExclusiveJoin || joinType == JoinType.FullExclusiveJoin || joinType == JoinType.FullOuterJoin ) { write(outputFile, leftRecord, null); } leftRecord = read(leftFile); } } else { if( rightRecord != null ) { if( joinType == JoinType.RightOuterJoin || joinType == JoinType.RightExclusiveJoin || joinType == JoinType.FullExclusiveJoin || joinType == JoinType.FullOuterJoin ) { write(outputFile, null, rightRecord); } rightRecord = read(rightFile); while(rightRecord != null) { if( joinType == JoinType.RightOuterJoin || joinType == JoinType.RightExclusiveJoin || joinType == JoinType.FullExclusiveJoin || joinType == JoinType.FullOuterJoin ) { write(outputFile, null, rightRecord); } rightRecord = read(rightFile); } } } leftFile.close(); rightFile.close(); outputFile.flush(); outputFile.close(); } public void processRightRecords(BufferedWriter outputFile, Record leftRecord, List<File> rightFiles, List<Record> rightRecords, JoinType joinType) throws Throwable { for(File rightFile : rightFiles) { BufferedReader rightReader = new BufferedReader(new FileReader(rightFile)); Record rightRecord = read(rightReader); while(rightRecord != null){ if( joinType == JoinType.LeftOuterJoin || joinType == JoinType.RightOuterJoin || joinType == JoinType.FullOuterJoin || joinType == JoinType.InnerJoin ) { write(outputFile, leftRecord, rightRecord); } rightRecord = read(rightReader); } rightReader.close(); } for(Record rightRecord : rightRecords) { if( joinType == JoinType.LeftOuterJoin || joinType == JoinType.RightOuterJoin || joinType == JoinType.FullOuterJoin || joinType == JoinType.InnerJoin ) { write(outputFile, leftRecord, rightRecord); } } } /** * consume all records having key (either to a single list or multiple files) each file will * store a buffer full of data. The right record returned represents the outside flow (key is * already positioned to next one or null) so we can't use this record in below while loop or * within this block in general when comparing current key. The trick is to keep consuming * from a List. When it becomes empty, re-fill it from the next file until all files have * been consumed (and the last node in the list is read). The next outside iteration will be * ready to be processed (either it will be null or it points to the next biggest key * @throws Throwable * */ private Record consume(String key, BufferedReader reader, List<Record> records, List<File> files, long bufferMaxRecordLines ) throws Throwable { boolean processComplete = false; Record record = records.get(records.size() - 1); while(!processComplete){ long recordCount = records.size(); if( record.getKey().compareTo(key) == 0 ){ record = read(reader); while( record != null && record.getKey().compareTo(key) == 0 && recordCount < bufferMaxRecordLines ) { records.add(record); recordCount++; record = read(reader); } } processComplete = true; // if record is null, we are done if( record != null ) { // if the key has changed, we are done if( record.getKey().compareTo(key) == 0 ) { // Same key means we have exhausted the buffer. // Dump entire buffer into a file. The list of file // pointers will keep track of the files ... processComplete = false; dumpBufferToFile(records, files); records.clear(); records.add(record); } } } return record; } /** * Dump all records in List of Record objects to a file. Then, add that * file to List of File objects * * NEED TO PLACE A LIMIT ON NUMBER OF FILE POINTERS (check size of file list) * * @param records * @param files * @throws Throwable */ private void dumpBufferToFile(List<Record> records, List<File> files) throws Throwable { String prefix = "joiner_" + files.size() + 1; String suffix = ".dat"; File file = File.createTempFile(prefix, suffix, new File("cache")); BufferedWriter writer = new BufferedWriter(new FileWriter(file)); for( Record record : records ) { writer.write( record.dump() ); } files.add(file); writer.flush(); writer.close(); }

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• How does one handle an incorrect resource file?

  - by AedonEtLIRA

  I'm starting the parser that will handle one of the key features of my app and realizing exactly who easy it would be for me to screw up a resource file that is provided to the application. For example, a simple resource that I provide to my app is a JSON file that contains an entity layout (name, fascia, location etc...). It would be easy for me to leave out the name of the entity or misspell the JSON key. Obviously catastrophic failures during parsing are to be handled in a try/catch, but how would subtle failures (such as a dyslexic spelling of name) be handled?

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• Handling packet impersonating in client-server model online game

  - by TheDespite

  I am designing a server-client model game library/engine. How do I, and should I even bother to handle frequent update packet possible impersonating? In my current design anyone could copy a packet from someone else and modify it to execute any non-critical action for another client. I am currently compressing all datagrams so that adds just a tad of security. Edit: One way I thought about was to send a unique "key" to the verified client every x_time and then the client has to add that to all of it's update packets until a new key is sent. Edit2: I should have mentioned that I am not concerned about whether the actions described in the packet are available to the client at the time, this is all checked by the server which I thought was obvious. I am only concerned about someone sending packets for another client.

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• Handling Deployment to Multiple Environments

  - by JayGee

  How should I handle deploying web applications to multiple servers? Constraints I have a dev, test and prod environment. No build server is available. Developers can't deploy to prod. The people that do deploy to prod copy files from test to prod. They don't have VS installed. Currently The way it's handled is using web.config transform. However, to deploy to prod involves putting prod code on the test server where it's copied over. Problem Sometimes simple mistakes are made, such as forgetting to change test back to the right environment after deployment. Or the test config gets moved to prod instead of the prod config. Solution So the question is, what is the best way to prevent mistakes from happening? My first thought is let the app determine which server it's on at runtime and use the appropriate settings/connection strings/etc... However, the server names could change in the not too distant future. So if multiple apps are hard coded, that would mean updating all of them. The easiest way to handle that situation would be to place a DLL in the GAC that determines the environment. Are there any drawbacks or possible complications that this would cause? Or is there a better solution to the problem than this?

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• Handling Players, enemies and attacks in HTML5

  - by Chris Morris

  I'm building a simple (currently) game with free roaming player and monsters on a map built by a 2D grid. I've been looking at the methods for implementing characters and enemies onto the screen and I've seen two seperate methods for doing this online. Drawing the player onto the screen canvas directly and refreshing the entire screen every FPS tick. Having a separate canvas to handle the player and moving the player canvas on top of the screen canvas via absolute positioning. I can see some pros and cons of both methods but what is generally the best method for doing this? I assume the second due to not having to drain resources by refreshing the map when the user is not moving, but the type of game will generally have constant movement.

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• Component-based design: handling objects interaction

  - by Milo

  I'm not sure how exactly objects do things to other objects in a component based design. Say I have an Obj class. I do: Obj obj; obj.add(new Position()); obj.add(new Physics()); How could I then have another object not only move the ball but have those physics applied. I'm not looking for implementation details but rather abstractly how objects communicate. In an entity based design, you might just have: obj1.emitForceOn(obj2,5.0,0.0,0.0); Any article or explanation to get a better grasp on a component driven design and how to do basic things would be really helpful.

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• Quickly compute added and removed lines

  - by Philippe Marschall

  I'm trying to compare two text files. I want to compute how many lines were added and removed. Basically what git diff --stat is doing. Bonus points for not having to store the entire file contents in memory. The approach I'm currently having in mind is: read each line of the old file compute a hash (probably MD5 or SHA-1) for each line store the hashes in a set do the same for each line in the new file every hash from the old file set that's missing in the new file set was removed every hash from the new file set that's missing in the old file set was added I'll probably want to exclude empty and all white space lines. There is a small issue with duplicated lines. This can either be solved by additionally storing how often a hash appears or comparing the number of lines in the old and new file and adjust either the added or removed lines so that the numbers add up. Do you see room for improvements or a better approach?

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• Dependency not satisfiable - Offline deb package install

  - by catia

  I have a new installation that has no chance of an internet connection. Since I want to add a few development software packages, I downloaded a few *.deb files. The problem is that for every package I try to install I get the same error: "Dependency not satisfiable...." Also downloaded other versions of that software (the deb files) but it didn't work. I've researched other questions in here and Google and I haven't been able to solve this yet.

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• PHP file_put_contents File Locking

  - by hozza

  The Senario: You have a file with a string (average sentence worth) on each line. For arguments sake lets say this file is 1Mb in size (thousands of lines). You have a script that reads the file, changes some of the strings within the document (not just appending but also removing and modifying some lines) and then overwrites all the data with the new data. The Questions: Does 'the server' PHP, OS or httpd etc. already have systems in place to stop issues like this (reading/writing half way through a write)? i. If it does, please explain how it works and give examples or links to relevant documentation. ii. If not, are there things I can enable or set-up, such as locking a file until a write is completed and making all other reads and/or writes fail until the previous script has finished writing? My Assumptions and Other Information: The server in question is running PHP and Apache or Lighttpd. If the script is called by one user and is halfway through writing to the file and another user reads the file at that exact moment. The user who reads it will not get the full document, as it hasn't been written yet. (If this assumption is wrong please correct me) I'm only concerned with PHP writing and reading to a text file, and in particular, the functions "fopen"/"fwrite" and mainly "file_put_contents". I have looked at the "file_put_contents" documentation but have not found the level of detail or a good explanation of what the "LOCK_EX" flag is or does. The senario is an EXAMPLE of a worst case senario where I would assume these issues are more likely to occur, due to the large size of the file and the way the data is edited. I want to learn more about these issues and don't want or need answers or comments such as "use mysql" or "why are you doing that" because I'm not doing that, I just want to learn about file read/writing with PHP and don't seem to be looking in the right places/documentation and yes I understand PHP is not the perfect language for working with files in this way...

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• Catching multiple exceptions on the client is robust and easy

  - by Alexander Kuznetsov

  Maria Zakourdaev has just demonstrated that if our T-SQL throws multiple exceptions, ERROR_MESSAGE() in TRY..CATCH block will only expose one. When we handle errors in C#, we have a very easy access to all errors. The following procedure throws two exceptions: CREATE PROCEDURE dbo.ThrowsTwoExceptions AS BEGIN ; RAISERROR ( 'Error 1' , 16 , 1 ) ; RAISERROR ( 'Error 2' , 16 , 1 ) ; END ; GO EXEC dbo.ThrowsTwoExceptions ; Both exceptions are shown by SSMS: Msg 50000 , LEVEL 16 , State 1 , PROCEDURE...(read more)

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• Attachment handling for web application with Jackrabbit

  - by Andrea Girardi

  I need to manage attachments on my Spring web application and I thought to use an open source repository. My app it's a job approval system using J2EE / SPRING 3 Framework and Postgress DB to allow user to tracks the job,right through every step of the approval process. It is a fully managed, collaborative system that operates from a central server and is accessed by a standard internet browser. An user should be able to add an attach to a request or an approval step, so, I though to use Jackrabbit with Postgres database persistence manager. I took a look to this post: http://onjava.com/pub/a/onjava/2006/10/04/what-is-java-content-repository.html?page=1 It's really interesting but, I've some question about this kind of solution :- I seen that Jackrabbit standalone as a Derby database embedded solution for persistence, is it enough for a professional use of the repository with more than 50 request / days (with attachment) ? Is there a reason for which I should use another database manager for persistence instead of the default one ?

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• Handling "related" work within a single agile work item

  - by Tesserex

  I'm on a project team of 4 devs, myself included. We've been having a long discussion on how to handle extra work that comes up in the course of a single work item. This extra work is usually things that are slightly related to the task, but not always necessary to accomplish the goal of the item (that may be an opinion). Examples include but are not limited to: refactoring of the code changed by the work item refactoring code neighboring the code changed by the item re-architecting the larger code area around the ticket. For example if an item has you changing a single function, you realize the entire class now could be redone to better accommodate this change. improving the UI on a form you just modified When this extra work is small we don't mind. The problem is when this extra work causes a substantial extension of the item beyond the original feature point estimation. Sometimes a 5 point item will actually take 13 points of time. In one case we had a 13 point item that in retrospect could have been 80 points or more. There are two options going around in our discussion for how to handle this. We can accept the extra work in the same work item, and write it off as a mis-estimation. Arguments for this have included: We plan for "padding" at the end of the sprint to account for this sort of thing. Always leave the code in better shape than you found it. Don't check in half-assed work. If we leave refactoring for later, it's hard to schedule and may never get done. You are in the best mental "context" to handle this work now, since you're waist deep in the code already. Better to get it out of the way now and be more efficient than to lose that context when you come back later. We draw a line for the current work item, and say that the extra work goes into a separate ticket. Arguments include: Having a separate ticket allows for a new estimation, so we aren't lying to ourselves about how many points things really are, or having to admit that all of our estimations are terrible. The sprint "padding" is meant for unexpected technical challenges that are direct barriers to completing the ticket requirements. It is not intended for side items that are just "nice-to-haves". If you want to schedule refactoring, just put it at the top of the backlog. There is no way for us to properly account for this stuff in an estimation, since it seems somewhat arbitrary when it comes up. A code reviewer might say "those UI controls (which you actually didn't modify in this work item) are a bit confusing, can you fix that too?" which is like an hour, but they might say "Well if this control now inherits from the same base class as the others, why don't you move all of this (hundreds of lines of) code into the base and rewire all this stuff, the cascading changes, etc.?" And that takes a week. It "contaminates the crime scene" by adding unrelated work into the ticket, making our original feature point estimates meaningless. In some cases, the extra work postpones a check-in, causing blocking between devs. Some of us are now saying that we should decide some cut off, like if the additional stuff is less than 2 FP, it goes in the same ticket, if it's more, make it a new ticket. Since we're only a few months into using Agile, what's the opinion of all the more seasoned Agile veterans around here on how to handle this?

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• How are Java ByteBuffer's limit and position variable's updated?

  - by Dummy Derp

  There are two scenarios: writing and reading Writing: Whenever I write something to the ByteBuffer by calling its put(byte[]) method the position variable is incremented as: current position + size of byte[] and limit stays at the max. If, however, I put the data in a view buffer then I will have to, manually, calculate and update the position Before I call the write(ByteBuffer) method of the channel to write something, I will have to flip() the Bytebuffer so that position points to zero and limit points to the last byte that was written to the ByteBuffer. Reading: Whenever I call the read(ByteBuffer) method of a channel to read something, the position variable stays at 0 and the limit variable of the ByteBuffer points to the last byte that was read. So, if the ByteBuffer is smaller than the file being read, the limit variable is pushed to max This means that the ByteBuffer is already flipped and I can proceed to extracting the values from the ByteBuffer. Please, correct me where I am wrong :)

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• Designing status management for a file processing module

  - by bot

  The background One of the functionality of a product that I am currently working on is to process a set of compressed files ( containing XML files ) that will be made available at a fixed location periodically (local or remote location - doesn't really matter for now) and dump the contents of each XML file in a database. I have taken care of the design for a generic parsing module that should be able to accommodate the parsing of any file type as I have explained in my question linked below. There is no need to take a look at the following link to answer my question but it would definitely provide a better context to the problem Generic file parser design in Java using the Strategy pattern The Goal I want to be able to keep a track of the status of each XML file and the status of each compressed file containing the XML files. I can probably have different statuses defined for the XML files such as NEW, PROCESSING, LOADING, COMPLETE or FAILED. I can derive the status of a compressed file based on the status of the XML files within the compressed file. e.g status of the compressed file is COMPLETE if no XML file inside the compressed file is in a FAILED state or status of the compressed file is FAILED if the status of at-least one XML file inside the compressed file is FAILED. A possible solution The Model I need to maintain the status of each XML file and the compressed file. I will have to define some POJOs for holding the information about an XML file as shown below. Note that there is no need to store the status of a compressed file as the status of a compressed file can be derived from the status of its XML files. public class FileInformation { private String compressedFileName; private String xmlFileName; private long lastModifiedDate; private int status; public FileInformation(final String compressedFileName, final String xmlFileName, final long lastModified, final int status) { this.compressedFileName = compressedFileName; this.xmlFileName = xmlFileName; this.lastModifiedDate = lastModified; this.status = status; } } I can then have a class called StatusManager that aggregates a Map of FileInformation instances and provides me the status of a given file at any given time in the lifetime of the appliciation as shown below : public class StatusManager { private Map<String,FileInformation> processingMap = new HashMap<String,FileInformation>(); public void add(FileInformation fileInformation) { fileInformation.setStatus(0); // 0 will indicates that the file is in NEW state. 1 will indicate that the file is in process and so on.. processingMap.put(fileInformation.getXmlFileName(),fileInformation); } public void update(String filename,int status) { FileInformation fileInformation = processingMap.get(filename); fileInformation.setStatus(status); } } That takes care of the model for the sake of explanation. So whats my question? Edited after comments from Loki and answer from Eric : - I would like to know if there are any existing design patterns that I can refer to while coming up with a design. I would also like to know how I should go about designing the status management classes. I am more interested in understanding how I can model the status management classes. I am not interested in how other components are going to be updated about a change in status at the moment as suggested by Eric.

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• Input Handling and Game loop

  - by Bob Coder

  So, I intercept the WM_KEYDOWN and other messages. Thing is, my game can't/shouldn't react to these messages just yet, since my game might be currently drawing to the screen or in the middle of updating my game entities. So the idea is to keep a keyboardstate and mousestate, which is updated by the part of my code that intercepts the windows messages. These states just keep track of which keys/buttons are currently pressed. Then, at the start of my game's update function, I access these keyboard and mouse states and my game reacts to the user input. Now, which is the best way to access these states? I assume that windows messages can be sent whenever, so the keyboard/mouse states are constantly being edited. Accessing say a list of currently pressed keys in the keyboard state the same time another part of the code is editing the list would cause problems. Should I make a deep copy of a state and act on that? How would I deal with the garbage generated though, this would take place every frame.

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