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• Compile and optimize for different target architectures

  - by Peter Smit

  Summary: I want to take advantage of compiler optimizations and processor instruction sets, but still have a portable application (running on different processors). Normally I could indeed compile 5 times and let the user choose the right one to run. My question is: how can I can automate this, so that the processor is detected at runtime and the right executable is executed without the user having to chose it? I have an application with a lot of low level math calculations. These calculations will typically run for a long time. I would like to take advantage of as much optimization as possible, preferably also of (not always supported) instruction sets. On the other hand I would like my application to be portable and easy to use (so I would not like to compile 5 different versions and let the user choose). Is there a possibility to compile 5 different versions of my code and run dynamically the most optimized version that's possible at execution time? With 5 different versions I mean with different instruction sets and different optimizations for processors. I don't care about the size of the application. At this moment I'm using gcc on Linux (my code is in C++), but I'm also interested in this for the Intel compiler and for the MinGW compiler for compilation to Windows. The executable doesn't have to be able to run on different OS'es, but ideally there would be something possible with automatically selecting 32 bit and 64 bit as well. Edit: Please give clear pointers how to do it, preferably with small code examples or links to explanations. From my point of view I need a super generic solution, which is applicable on any random C++ project I have later. Edit I assigned the bounty to ShuggyCoUk, he had a great number of pointers to look out for. I would have liked to split it between multiple answers but that is not possible. I'm not having this implemented yet, so the question is still 'open'! Please, still add and/or improve answers, even though there is no bounty to be given anymore. Thanks everybody!

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• Algorithm for finding the best routes for food distribution in game

  - by Tautrimas

  Hello, I'm designing a city building game and got into a problem. Imagine Sierra's Caesar III game mechanics: you have many city districts with one market each. There are several granaries over the distance connected with a directed weighted graph. The difference: people (here cars) are units that form traffic jams (here goes the graph weights). Note: in Ceasar game series, people harvested food and stockpiled it in several big granaries, whereas many markets (small shops) took food from the granaries and delivered it to the citizens. The task: tell each district where they should be getting their food from while taking least time and minimizing congestions on the city's roads. Map example Sample diagram Suppose that yellow districts need 7, 7 and 4 apples accordingly. Bluish granaries have 7 and 11 apples accordingly. Suppose edges weights to be proportional to their length. Then, the solution should be something like the gray numbers indicated on the edges. Eg, first district gets 4 apples from the 1st and 3 apples from the 2nd granary, while the last district gets 4 apples from only the 2nd granary. Here, vertical roads are first occupied to the max, and then the remaining workers are sent to the diagonal paths. Question What practical and very fast algorithm should I use? I was looking at some papers (Congestion Games: Optimization in Competition etc.) describing congestion games, but could not get the big picture. Any help is very appreciated! P. S. I can post very little links and no images because of new user restriction.

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• How can I improve the performance of this double-for print?

  - by Florenc

  I have the following static method that prints the data imported from a 40.000 lines .xls spreadsheet. Now, it takes about 27 seconds to print the data in the console and the memory consumption is huge. import org.apache.poi.hssf.usermodel.*; import org.apache.poi.ss.usermodel.*; public static void printSheetData(List<List<HSSFCell>> sheetData) { for (int i = 0; i < sheetData.size(); i++) { List<HSSFCell> list = (List<HSSFCell>) sheetData.get(i); for (int j = 0; j < list.size(); j++) { HSSFCell cell = (HSSFCell) list.get(j); System.out.print(cell.toString()); if (j < list.size() - 1) { System.out.print(", "); } } System.out.println(""); } } Disclaimer: I know, I know large data belong to a database, don't print output in the console, premature optimization is the root of all evils...

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• Coding Practices which enable the compiler/optimizer to make a faster program.

  - by EvilTeach

  Many years ago, C compilers were not particularly smart. As a workaround K&R invented the register keyword, to hint to the compiler, that maybe it would be a good idea to keep this variable in an internal register. They also made the tertiary operator to help generate better code. As time passed, the compilers matured. They became very smart in that their flow analysis allowing them to make better decisions about what values to hold in registers than you could possibly do. The register keyword became unimportant. FORTRAN can be faster than C for some sorts of operations, due to alias issues. In theory with careful coding, one can get around this restriction to enable the optimizer to generate faster code. What coding practices are available that may enable the compiler/optimizer to generate faster code? Identifying the platform and compiler you use, would be appreciated. Why does the technique seem to work? Sample code is encouraged. Here is a related question [Edit] This question is not about the overall process to profile, and optimize. Assume that the program has been written correctly, compiled with full optimization, tested and put into production. There may be constructs in your code that prohibit the optimizer from doing the best job that it can. What can you do to refactor that will remove these prohibitions, and allow the optimizer to generate even faster code? [Edit] Offset related link

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• Efficient way to maintain a sorted list of access counts in Python

  - by David

  Let's say I have a list of objects. (All together now: "I have a list of objects.") In the web application I'm writing, each time a request comes in, I pick out up to one of these objects according to unspecified criteria and use it to handle the request. Basically like this: def handle_request(req): for h in handlers: if h.handles(req): return h return None Assuming the order of the objects in the list is unimportant, I can cut down on unnecessary iterations by keeping the list sorted such that the most frequently used (or perhaps most recently used) objects are at the front. I know this isn't something to be concerned about - it'll make only a miniscule, undetectable difference in the app's execution time - but debugging the rest of the code is driving me crazy and I need a distraction :) so I'm asking out of curiosity: what is the most efficient way to maintain the list in sorted order, descending, by the number of times each handler is chosen? The obvious solution is to make handlers a list of (count, handler) pairs, and each time a handler is chosen, increment the count and resort the list. def handle_request(req): for h in handlers[:]: if h[1].handles(req): h[0] += 1 handlers.sort(reverse=True) return h[1] return None But since there's only ever going to be at most one element out of order, and I know which one it is, it seems like some sort of optimization should be possible. Is there something in the standard library, perhaps, that is especially well-suited to this task? Or some other data structure? (Even if it's not implemented in Python) Or should/could I be doing something completely different?

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• optimize output value using a class and public member

  - by wiso

  Suppose you have a function, and you call it a lot of times, every time the function return a big object. I've optimized the problem using a functor that return void, and store the returning value in a public member: #include <vector> const int N = 100; std::vector<double> fun(const std::vector<double> & v, const int n) { std::vector<double> output = v; output[n] *= output[n]; return output; } class F { public: F() : output(N) {}; std::vector<double> output; void operator()(const std::vector<double> & v, const int n) { output = v; output[n] *= n; } }; int main() { std::vector<double> start(N,10.); std::vector<double> end(N); double a; // first solution for (unsigned long int i = 0; i != 10000000; ++i) a = fun(start, 2)[3]; // second solution F f; for (unsigned long int i = 0; i != 10000000; ++i) { f(start, 2); a = f.output[3]; } } Yes, I can use inline or optimize in an other way this problem, but here I want to stress on this problem: with the functor I declare and construct the output variable output only one time, using the function I do that every time it is called. The second solution is two time faster than the first with g++ -O1 or g++ -O2. What do you think about it, is it an ugly optimization?

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• Speed comparison - Template specialization vs. Virtual Function vs. If-Statement

  - by Person

  Just to get it out of the way... Premature optimization is the root of all evil Make use of OOP etc. I understand. Just looking for some advice regarding the speed of certain operations that I can store in my grey matter for future reference. Say you have an Animation class. An animation can be looped (plays over and over) or not looped (plays once), it may have unique frame times or not, etc. Let's say there are 3 of these "either or" attributes. Note that any method of the Animation class will at most check for one of these (i.e. this isn't a case of a giant branch of if-elseif). Here are some options. 1) Give it boolean members for the attributes given above, and use an if statement to check against them when playing the animation to perform the appropriate action. Problem: Conditional checked every single time the animation is played. 2) Make a base animation class, and derive other animations classes such as LoopedAnimation and AnimationUniqueFrames, etc. Problem: Vtable check upon every call to play the animation given that you have something like a vector<Animation>. Also, making a separate class for all of the possible combinations seems code bloaty. 3) Use template specialization, and specialize those functions that depend on those attributes. Like template<bool looped, bool uniqueFrameTimes> class Animation. Problem: The problem with this is that you couldn't just have a vector<Animation> for something's animations. Could also be bloaty. I'm wondering what kind of speed each of these options offer? I'm particularly interested in the 1st and 2nd option because the 3rd doesn't allow one to iterate through a general container of Animations. In short, what is faster - a vtable fetch or a conditional?

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• Improving File Read Performance (single file, C++, Windows)

  - by david

  I have large (hundreds of MB or more) files that I need to read blocks from using C++ on Windows. Currently the relevant functions are: errorType LargeFile::read( void* data_out, __int64 start_position, __int64 size_bytes ) const { if( !m_open ) { // return error } else { seekPosition( start_position ); DWORD bytes_read; BOOL result = ReadFile( m_file, data_out, DWORD( size_bytes ), &bytes_read, NULL ); if( size_bytes != bytes_read || result != TRUE ) { // return error } } // return no error } void LargeFile::seekPosition( __int64 position ) const { LARGE_INTEGER target; target.QuadPart = LONGLONG( position ); SetFilePointerEx( m_file, target, NULL, FILE_BEGIN ); } The performance of the above does not seem to be very good. Reads are on 4K blocks of the file. Some reads are coherent, most are not. A couple questions: Is there a good way to profile the reads? What things might improve the performance? For example, would sector-aligning the data be useful? I'm relatively new to file i/o optimization, so suggestions or pointers to articles/tutorials would be helpful.

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• Why doesn't g++ pay attention to __attribute__((pure)) for virtual functions?

  - by jchl

  According to the GCC documentation, __attribute__((pure)) tells the compiler that a function has no side-effects, and so it can be subject to common subexpression elimination. This attribute appears to work for non-virtual functions, but not for virtual functions. For example, consider the following code: extern void f( int ); class C { public: int a1(); int a2() __attribute__((pure)); virtual int b1(); virtual int b2() __attribute__((pure)); }; void test_a1( C *c ) { if( c->a1() ) { f( c->a1() ); } } void test_a2( C *c ) { if( c->a2() ) { f( c->a2() ); } } void test_b1( C *c ) { if( c->b1() ) { f( c->b1() ); } } void test_b2( C *c ) { if( c->b2() ) { f( c->b2() ); } } When compiled with optimization enabled (either -O2 or -Os), test_a2() only calls C::a2() once, but test_b2() calls b2() twice. Is there a reason for this? Is it because, even though the implementation in class C is pure, g++ can't assume that the implementation in every subclass will also be pure? If so, is there a way to tell g++ that this virtual function and every subclass's implementation will be pure?

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• Optimize Duplicate Detection

  - by Dave Jarvis

  Background This is an optimization problem. Oracle Forms XML files have elements such as: <Trigger TriggerName="name" TriggerText="SELECT * FROM DUAL" ... /> Where the TriggerText is arbitrary SQL code. Each SQL statement has been extracted into uniquely named files such as: sql/module=DIAL_ACCESS+trigger=KEY-LISTVAL+filename=d_access.fmb.sql sql/module=REP_PAT_SEEN+trigger=KEY-LISTVAL+filename=rep_pat_seen.fmb.sql I wrote a script to generate a list of exact duplicates using a brute force approach. Problem There are 37,497 files to compare against each other; it takes 8 minutes to compare one file against all the others. Logically, if A = B and A = C, then there is no need to check if B = C. So the problem is: how do you eliminate the redundant comparisons? The script will complete in approximately 208 days. Script Source Code The comparison script is as follows: #!/bin/bash echo Loading directory ... for i in $(find sql/ -type f -name \*.sql); do echo Comparing $i ... for j in $(find sql/ -type f -name \*.sql); do if [ "$i" = "$j" ]; then continue; fi # Case insensitive compare, ignore spaces diff -IEbwBaq $i $j > /dev/null # 0 = no difference (i.e., duplicate code) if [ $? = 0 ]; then echo $i :: $j >> clones.txt fi done done Question How would you optimize the script so that checking for cloned code is a few orders of magnitude faster? System Constraints Using a quad-core CPU with an SSD; trying to avoid using cloud services if possible. The system is a Windows-based machine with Cygwin installed -- algorithms or solutions in other languages are welcome. Thank you!

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• memcached: which is faster, doing an add (and checking result), or doing a get (and set when returni

  - by Mike Sherov

  The title of this question isn't so clear, but the code and question is straightforward. Let's say I want to show my users an ad once per day. To accomplish this, every time they visit a page on my site, I check to see if a certain memcache key has any data stored on it. If so, don't show an ad. If not, store the value '1' in that key with an expiration of 86400. I can do this 2 ways: //version a $key='OPD_'.date('Ymd').'_'.$type.'_'.$user; if($memcache->get($key)===false){ $memcache->set($key,'1',false,$expire); //show ad } //version b $key='OPD_'.date('Ymd').'_'.$type.'_'.$user; if($memcache->add($key,'1',false,$expire)){ //show ad } Now, it might seem obvious that b is better, it always makes 1 memcache call. However, what is the overhead of "add" vs. "get"? These aren't the real comparisons... and I just made up these numbers, but let's say 1 add ~= 1 set ~= 5 get in terms of effort, and the average user views 5 pages a day: a: (5 get * 1 effort) + (1 set * 5 effort) = 10 units of effort b: (5 add * 5 effort) = 25 units of effort Would it make sense to always do the add call? Is this an unnecessary micro-optimization?

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• Diffence between FQL query and Graph API object access

  - by jwynveen

  What's the difference between accessing user data with the Facebook Graph API (http://graph.facebook.com/btaylor) and using the Graph API to make a FQL query of the same user (https://api.facebook.com/method/fql.query?query=QUERY). Also, does anyone know which of them the Facebook Developer Toolkit (for ASP.NET) uses? The reason I ask is because I'm trying to access the logged in user's birthday after they begin a Facebook Connect session on my site, but when I use the toolkit it doesn't return it. However, if I make a manual call to the Graph API for that user object, it does return it. It's possible I might have something wrong with my call from the toolkit. I think I may need to include the session key, but I'm not sure how to get it. Here's the code I'm using: _connectSession = new ConnectSession(APPLICATION_KEY, SECRET_KEY); try { if (!_connectSession.IsConnected()) { // Not authenticated, proceed as usual. statusResponse = "Please sign-in with Facebook."; } else { // Authenticated, create API instance _facebookAPI = new Api(_connectSession); // Load user user user = _facebookAPI.Users.GetInfo(); statusResponse = user.ToString(); ViewData["fb_user"] = user; } } catch (Exception ex) { //An error happened, so disconnect session _connectSession.Logout(); statusResponse = "Please sign-in with Facebook."; }

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• NHibernate Query across multiple tables

  - by Dai Bok

  I am using NHibernate, and am trying to figure out how to write a query, that searchs all the names of my entities, and lists the results. As a simple example, I have the following objects; public class Cat { public string name {get; set;} } public class Dog { public string name {get; set;} } public class Owner { public string firstname {get; set;} public string lastname {get; set;} } Eventaully I want to create a query , say for example, which and returns all the pet owners with an name containing "ted", OR pets with a name containing "ted". Here is an example of the SQL I want to execute: SELECT TOP 10 d.*, c.*, o.* FROM owners AS o INNER JOIN dogs AS d ON o.id = d.ownerId INNER JOIN cats AS c ON o.id = c.ownerId WHERE o.lastname like '%ted%' OR o.firstname like '%ted%' OR c.name like '%ted%' OR d.name like '%ted%' When I do it using Criteria like this: var criteria = session.CreateCriteria<Owner>() .Add( Restrictions.Disjunction() .Add(Restrictions.Like("FirstName", keyword, MatchMode.Anywhere)) .Add(Restrictions.Like("LastName", keyword, MatchMode.Anywhere)) ) .CreateCriteria("Dog").Add(Restrictions.Like("Name", keyword, MatchMode.Anywhere)) .CreateCriteria("Cat").Add(Restrictions.Like("Name", keyword, MatchMode.Anywhere)); return criteria.List<Owner>(); The following query is generated: SELECT TOP 10 d.*, c.*, o.* FROM owners AS o INNER JOIN dogs AS d ON o.id = d.ownerId INNER JOIN cats AS c ON o.id = c.ownerId WHERE o.lastname like '%ted%' OR o.firstname like '%ted%' AND d.name like '%ted%' AND c.name like '%ted%' How can I adjust my query so that the .CreateCriteria("Dog") and .CreateCriteria("Cat") generate an OR instead of the AND? thanks for your help.

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• SQLiteQueryBuilder.buildQuery not using selectArgs?

  - by user297468

  Alright, I'm trying to query a sqlite database. I was trying to be good and use the query method of SQLiteDatabase and pass in the values in the selectArgs parameter to ensure everything got properly escaped, but it wouldn't work. I never got any rows returned (no errors, either). I started getting curious about the SQL that this generated so I did some more poking around and found SQLiteQueryBuilder (and apparently Stack Overflow doesn't handle links with parentheses in them well, so I can't link to the anchor for the buildQuery method), which I assume uses the same logic to generate the SQL statement. I did this: SQLiteQueryBuilder builder = new SQLiteQueryBuilder(); builder.setTables(BarcodeDb.Barcodes.TABLE_NAME); String sql = builder.buildQuery(new String[] { BarcodeDb.Barcodes.ID, BarcodeDb.Barcodes.TIMESTAMP, BarcodeDb.Barcodes.TYPE, BarcodeDb.Barcodes.VALUE }, "? = '?' AND ? = '?'", new String[] { BarcodeDb.Barcodes.VALUE, barcode.getValue(), BarcodeDb.Barcodes.TYPE, barcode.getType()}, null, null, null, null); Log.d(tag, "Query is: " + sql); The SQL that gets logged at this point is: SELECT _id, timestamp, type, value FROM barcodes WHERE (? = '?' AND ? = '?') However, here's what the documentation for SQLiteQueryBuilder.buildQuery says about the selectAgs parameter: You may include ?s in selection, which will be replaced by the values from selectionArgs, in order that they appear in the selection. ...but it isn't working. Any ideas?

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• PHP, ImageMagick, Google's Page Speed, & JPG File Size Optimization

  - by Sonny

  I have photo gallery code that does image re-sizing and thumbnail creation. I use ImageMagick to do this. I ran a gallery page through Google's Page Speed tool and it revealed that the re-sized images and thumbnails both have about an extra 10KB of data (JPEG files specifically). What can I add to my scripts to optimize the file size? ADDITIONAL INFORMATION I am using the imagick::FILTER_LANCZOS filter with a blur setting of 0.9 when calling the resizeImage() function. JPEGs have a quality setting of 80.

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• Lost connection to MySQL server during query

  - by Otavio

  I have a huge table and I need to process all rows in it. I'm always getting this Lost connection message and I'm not able to reconnect and restore the cursor to the last position it was. This is basically the code I have here: # import MySQLdb class DB: conn = None def connect(self): self.conn = MySQLdb.connect('hostname', 'user', '*****', 'some_table', cursorclass=MySQLdb.cursors.SSCursor) def query(self, sql): try: cursor = self.conn.cursor() cursor.execute(sql) except (AttributeError, MySQLdb.OperationalError): self.connect() cursor = self.conn.cursor() cursor.execute(sql) return cursor # # db = DB() sql = "SELECT bla FROM foo" data = db.query(sql) for row in data: do_something(row) # But I'm always getting this: # Traceback (most recent call last): File "teste.py", line 124, in <module> run() File "teste.py", line 109, in run for row in data: File "/usr/lib64/python2.5/site-packages/MySQLdb/cursors.py", line 417, in next row = self.fetchone() File "/usr/lib64/python2.5/site-packages/MySQLdb/cursors.py", line 388, in fetchone r = self._fetch_row(1) File "/usr/lib64/python2.5/site-packages/MySQLdb/cursors.py", line 285, in _fetch_row return self._result.fetch_row(size, self._fetch_type) _mysql_exceptions.OperationalError: (2013, 'Lost connection to MySQL server during query') Exception _mysql_exceptions.OperationalError: (2013, 'Lost connection to MySQL server during query') in <bound method SSCursor.__del__ of <MySQLdb.cursors.SSCursor object at 0x7f7e3c8da410>> ignored # Do you have any idea?

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• HQL Query Not Running

  - by Sarang

  select new UpdateCountDataBean(count(elements(am.actionId)) as noOfUpdates, am.pname as name) from ActivityMaster am group by am.pname The UpdateCountDataBean is created by me while the second class i.e. ActivityMaster is POJO class. java.lang.NullPointerException at org.hibernate.hql.ast.tree.MethodNode.handleElements(MethodNode.java:158) at org.hibernate.hql.ast.tree.MethodNode.resolveCollectionProperty(MethodNode.java:109) at org.hibernate.hql.ast.tree.CollectionFunction.resolve(CollectionFunction.java:22) at org.hibernate.hql.ast.HqlSqlWalker.processFunction(HqlSqlWalker.java:835) at org.hibernate.hql.antlr.HqlSqlBaseWalker.collectionFunction(HqlSqlBaseWalker.java:2558) at org.hibernate.hql.antlr.HqlSqlBaseWalker.aggregateExpr(HqlSqlBaseWalker.java:2907) at org.hibernate.hql.antlr.HqlSqlBaseWalker.count(HqlSqlBaseWalker.java:2483) at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectExpr(HqlSqlBaseWalker.java:1971) at org.hibernate.hql.antlr.HqlSqlBaseWalker.aliasedSelectExpr(HqlSqlBaseWalker.java:2057) at org.hibernate.hql.antlr.HqlSqlBaseWalker.constructor(HqlSqlBaseWalker.java:2226) at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectExpr(HqlSqlBaseWalker.java:1952) at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectExprList(HqlSqlBaseWalker.java:1825) at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectClause(HqlSqlBaseWalker.java:1394) at org.hibernate.hql.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:553) at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:281) at org.hibernate.hql.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:229) at org.hibernate.hql.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:228) at org.hibernate.hql.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:160) at org.hibernate.hql.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:111) at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:77) at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:56) at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:72) at org.hibernate.impl.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:133) at org.hibernate.impl.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:112) at org.hibernate.impl.SessionImpl.createQuery(SessionImpl.java:1623)

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• JPG File Size Optimization - PHP, ImageMagick, & Google's Page Speed

  - by Sonny

  I have photo gallery code that does image re-sizing and thumbnail creation. I use ImageMagick to do this. I ran a gallery page through Google's Page Speed tool and it revealed that the re-sized images and thumbnails both have about an extra 10KB of data (JPEG files specifically). What can I add to my scripts to optimize the file size? ADDITIONAL INFORMATION I am using the imagick::FILTER_LANCZOS filter with a blur setting of 0.9 when calling the resizeImage() function. JPEGs have a quality setting of 80.

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• PHP, ImageMagick, Google's Page Speed, & Image File Size Optimization

  - by Sonny

  I have photo gallery code that does image re-sizing and thumbnail creation. I use ImageMagick to do this. I ran a gallery page through Google's Page Speed tool and it revealed that the re-sized images and thumbnails both have about an extra 10KB of data (JPEG files specifically). What can I add to my scripts to optimize the file size?

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• LINQ self referencing query

  - by Chris

  I have the following SQL query: select p1.[id], p1.[useraccountid], p1.[subject], p1.[message], p1.[views], p1.[parentid], case when p2.[created] is null then p1.[created] else p2.[created] end as LastUpdate from forumposts p1 left join ( select parentid, max(created) as [created] from forumposts group by parentid ) p2 on p2.parentid = p1.id where p1.[parentid] is null order by LastUpdate desc Using the following class: public class ForumPost : PersistedObject { public int Views { get; set; } public string Message { get; set; } public string Subject { get; set; } public ForumPost Parent { get; set; } public UserAccount UserAccount { get; set; } public IList<ForumPost> Replies { get; set; } } How would I replicate such a query in LINQ? I've tried several variations, but I seem unable to get the correct join syntax. Is this simply a case of a query that is too complicated for LINQ? Can it be done using nested queries some how? The purpose of the query is to find the most recently updated posts i.e. replying to a post would bump it to the top of the list. Replies are defined by the ParentID column, which is self-referencing.

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• Whats wrong with this HQL query?

  - by ManBugra

  did i encounter a hibernate bug or do i have an error i dont see: select enty.number from EntityAliasName enty where enty.myId in ( select cons.myId from Consens cons where cons.number in ( select ord.number from Orders ord where ord.customer = :customer and ord.creationDate < ( select max(ord.creationDate) from Orders ord where ord.customer = :customer ) ) ) what i do get is the following: org.hibernate.util.StringHelper.root(StringHelper.java:257) Caused by: java.lang.NullPointerException at org.hibernate.util.StringHelper.root(StringHelper.java:257) at org.hibernate.persister.entity.AbstractEntityPersister.getSubclassPropertyTableNumber(AbstractEntityPersister.java:1391) at org.hibernate.persister.entity.BasicEntityPropertyMapping.toColumns(BasicEntityPropertyMapping.java:54) at org.hibernate.persister.entity.AbstractEntityPersister.toColumns(AbstractEntityPersister.java:1367) at org.hibernate.hql.ast.tree.FromElement.getIdentityColumn(FromElement.java:320) at org.hibernate.hql.ast.tree.IdentNode.resolveAsAlias(IdentNode.java:154) at org.hibernate.hql.ast.tree.IdentNode.resolve(IdentNode.java:100) at org.hibernate.hql.ast.tree.FromReferenceNode.resolve(FromReferenceNode.java:117) at org.hibernate.hql.ast.tree.FromReferenceNode.resolve(FromReferenceNode.java:113) at org.hibernate.hql.ast.HqlSqlWalker.resolve(HqlSqlWalker.java:854) at org.hibernate.hql.antlr.HqlSqlBaseWalker.propertyRef(HqlSqlBaseWalker.java:1172) at org.hibernate.hql.antlr.HqlSqlBaseWalker.propertyRefLhs(HqlSqlBaseWalker.java:5167) at org.hibernate.hql.antlr.HqlSqlBaseWalker.propertyRef(HqlSqlBaseWalker.java:1133) at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectExpr(HqlSqlBaseWalker.java:1993) at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectExprList(HqlSqlBaseWalker.java:1932) at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectClause(HqlSqlBaseWalker.java:1476) at org.hibernate.hql.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:580) at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:288) at org.hibernate.hql.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:231) at org.hibernate.hql.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:254) at org.hibernate.hql.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:185) at org.hibernate.hql.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:136) at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:101) at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:80) at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:94) at org.hibernate.impl.SessionFactoryImpl.checkNamedQueries(SessionFactoryImpl.java:484) at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:394) at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1341) using: Hibernate 3.3.2.GA / postgresql

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• Is this possible to join tables in doctrine ORM without using relations?

  - by piemesons

  Suppose there are two tables. Table X-- Columns: id x_value Table Y-- Columns: id x_id y_value Now I dont want to define relationship in doctrine classes and i want to retrieve some records using these two tables using a query like this: Select x_value from x, y where y.id="variable_z" and x.id=y.x_id; I m not able to figure out how to write query like this in doctrine orm EDIT: Table structures: Table 1: CREATE TABLE IF NOT EXISTS `image` ( `id` int(11) NOT NULL AUTO_INCREMENT, `random_name` varchar(255) NOT NULL, `user_id` int(11) NOT NULL, `community_id` int(11) NOT NULL, `published` varchar(1) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=259 ; Table 2: CREATE TABLE IF NOT EXISTS `users` ( `id` int(11) NOT NULL AUTO_INCREMENT, `city` varchar(20) DEFAULT NULL, `state` varchar(20) DEFAULT NULL, `school` varchar(50) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=20 ; Query I am using: $q = new Doctrine_RawSql(); $q ->select('{u.*}, {img.*}') ->from('users u LEFT JOIN image img ON u.id = img.user_id') ->addComponent('u', 'Users u') ->addComponent('img', 'u.Image img') ->where("img.community_id='$community_id' AND img.published='y' AND u.state='$state' AND u.city='$city ->orderBy('img.id DESC') ->limit($count+12) ->execute(); Error I am getting: Fatal error: Uncaught exception 'Doctrine_Exception' with message 'Couldn't find class u' in C:\xampp\htdocs\fanyer\doctrine\lib\Doctrine\Table.php:290 Stack trace: #0 C:\xampp\htdocs\fanyer\doctrine\lib\Doctrine\Table.php(240): Doctrine_Table- >initDefinition() #1 C:\xampp\htdocs\fanyer\doctrine\lib\Doctrine\Connection.php(1127): Doctrine_Table->__construct('u', Object(Doctrine_Connection_Mysql), true) #2 C:\xampp\htdocs\fanyer\doctrine\lib\Doctrine\RawSql.php(425): Doctrine_Connection- >getTable('u') #3 C:\xampp\htdocs\fanyer\doctrine\models\Image.php(33): Doctrine_RawSql- >addComponent('img', 'u.Image imga') #4 C:\xampp\htdocs\fanyer\community_images.php(31): Image->get_community_images_gallery_filter(4, 0, 'AL', 'ALBERTVILLE') #5 {main} thrown in C:\xampp\htdocs\fanyer\doctrine\lib\Doctrine\Table.php on line 290

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• I'm trying to populate a MySQL table with some data, but, mysqli won't let me insert every 10th stat

  - by Tunji Gbadamosi

  I want to initialise a 'ticket' table with some ticket IDs. To do this, I want to insert 120 ticket IDs into the table. However, at every 10th statement, MySQL tells me that the ID already exists and thus won't let me insert it. Here's my code: //make a query $insert_ticket_query = "INSERT INTO ticket (id) VALUES (?)"; $insert_ticket_stmt = $mysqli->stmt_init(); $insert_ticket_stmt->prepare($insert_ticket_query); $insert_ticket_stmt->bind_param('s', $ticket_id); $mysqli->autocommit(FALSE); //start transaction for($i=0;$i<NO_GUESTS;$i++){ $id = generate_id($i); $ticket_id = format_id($id, $prefix['ticket'], $suffix['ticket']); $t_id = $ticket_id; //echo '<p>'.$ticket_id.'</p>'; //$result = $mysqli->query("SELECT * FROM ticket WHERE id='".$ticket_id."'"); //$row_count = $result->num_rows; if(($result = $mysqli->query("SELECT * FROM ticket WHERE id='".$t_id."'")) == FALSE){ $result->close(); if($insert_ticket_stmt->execute()){ $mysqli->commit(); echo "<p>".$t_id."added to the ticket table!</p>"; } else{ $mysqli->rollback(); echo "problem inserting'".$t_id."' to the ticket table"; } } else{ echo "<p>".$t_id."already exists, so not adding it!</p>"; $result->close(); } } $mysqli->autocommit(TRUE); $insert_ticket_stmt->close(); ?>

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• Does replace into have a where clause?

  - by Lajos Arpad

  I'm writing an application and I'm using MySQL as DBMS, we are downloading property offers and there were some performance issues. The old architecture looked like this: A property is updated. If the number of affected rows is not 1, then the update is not considered successful, elseway the update query solves our problem. If the update was not successful, and the number of affected rows is more than 1, we have duplicates and we delete all of them. After we deleted duplicates if needed if the update was not successful, an insert happens. This architecture was working well, but there were some speed issues, because properties are deleted if they were not updated for 15 days. Theoretically the main problem is deleting properties, because some properties are alive for months and the indexes are very far from each other (we are talking about 500, 000+ properties). Our host told me to use replace into instead of deleting properties and all deprecated properties should be considered as DEAD. I've done this, but problems started to occur because of syntax error and I couldn't find anywhere an example of replace into with a where clause (I'd like to replace a DEAD property with the new property instead of deleting the old property and insert a new to assure optimization). My query looked like this: replace into table_name(column1, ..., columnn) values(value1, ..., valuen) where ID = idValue Of course, I've calculated idValue and handled everything but I had a syntax error. I would like to know if I'm wrong and there is a where clause for replace into. I've found an alternative solution, which is even better than replace into (using simply an update query) because deletes are happening behind the curtains if I use replace into, but I would like to know if I'm wrong when I say that replace into doesn't have a where clause. For more reference, see this link: http://dev.mysql.com/doc/refman/5.0/en/replace.html Thank you for your answers in advance, Lajos Árpád

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• Compiler optimization of reference variables

  - by Phineas

  I often use references to simplify the appearance of code: vec3f& vertex = _vertices[index]; // Calculate the vertex position vertex[0] = startx + col * colWidth; vertex[1] = starty + row * rowWidth; vertex[2] = 0.0f; Will compilers recognize and optimize this so it is essentially the following? _vertices[index][0] = startx + col * colWidth; _vertices[index][1] = starty + row * rowWidth; _vertices[index][2] = 0.0f;

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