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  • Is it inefficient to access a python class member container in a loop statement?

    - by Dave
    Hi there. I'm trying to adopt some best practices to keep my python code efficient. I've heard that accessing a member variable inside of a loop can incur a dictionary lookup for every iteration of the loop, so I cache these in local variables to use inside the loop. My question is about the loop statement itself... if I have the following class: class A(object): def init(self) self.myList = [ 'a','b','c', 'd', 'e' ] Does the following code in a member function incur one, or one-per-loop-iteration (5) dictionary lookups? for letter in self.myList: print letter IE, should I adopt the following pattern, if I am concerned about efficiency... localList = self.myList for letter in localList: print letter or is that actually LESS efficient due to the local variable assign? Note, I am aware that early optimization is a dangerous pitfall if I'm concerned about the overall efficiency of code development. Here I am specifically asking about the efficiency of the code, not the coding. Thanks in advance! D

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  • C/C++ memory usage API in Linux/Windows

    - by minjang
    I'd like to obtain memory usage information for both per process and system wide. In Windows, it's pretty easy. GetProcessMemoryInfo and GlobalMemoryStatusEx do these jobs greatly and very easily. For example, GetProcessMemoryInfo gives "PeakWorkingSetSize" of the given process. GlobalMemoryStatusEx returns system wide available memory. However, I need to do it on Linux. I'm trying to find Linux system APIs that are equivalent GetProcessMemoryInfo and GlobalMemoryStatusEx. I found 'getrusage'. However, max 'ru_maxrss' (resident set size) in struct rusage is just zero, which is not implemented. Also, I have no idea to get system-wide free memory. Current workaround for it, I'm using "system("ps -p %my_pid -o vsz,rsz");". Manually logging to the file. But, it's dirty and not convenient to process the data. I'd like to know some fancy Linux APIs for this purpose.

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  • Which of FILE* or ifstream has better memory usage?

    - by Viet
    I need to read fixed number of bytes from files, whose sizes are around 50MB. To be more precise, read a frame from YUV 4:2:0 CIF/QCIF files (~25KB to ~100KB per frame). Not very huge number but I don't want whole file to be in the memory. I'm using C++, in such a case, which of FILE* or ifstream has better (less/minimal) memory usage? Please kindly advise. Thanks! EDIT: I read fixed number of bytes: 25KB or 100KB (depending on QCIF/CIF format). The reading is in binary mode and forward-only. No seeking needed. No writing needed, only reading. EDIT: If identifying better of them is hard, which one does not require loading the whole file into memory?

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  • Customized generation/filtering resources with maven

    - by zamza
    I wonder what is the Maven way in my situation. My application has a bunch of configuration files, let's call them profiles. Each profile configuration file is a *.properties file, that contains keys/values and some comments on these keys/values semantics. The idea is to generate these *.properties to have unified comments in all of them. My plan is to create a template.properties file that contains something like #Comments for key1/value1 key1=${key1.value} #Comments for key2/value2 key2=${key2.value} and a bunch of files like #profile_data_1.properties key1.value=profile_1_key_1_value key2.value=profile_1_key_2_value #profile_data_2.properties key1.value=profile_2_key_1_value key2.value=profile_2_key_2_value Then bind to generate-resources phase to create a copy of template.properties per profile_data_*, and filter that copy with profile_data_*.properties as a filter. The easiest way is probably to create an ant build file and use antrun plugin. But that is not a Maven way, is it? Other option is to create a Maven plugin for that tiny task. Somehow, I don't like that idea (plugin deployment is not what I want very much).

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  • Optimum php.ini and my.cnf settings for a small Drupal 7 site on a virtual server

    - by the other dude
    I looking for advice on how to set up the default configuration of php.ini and my.cnf for a small site (100 pages) with very little traffic (300 visitors per day). All pages have a bit of text, some images, no video, no audio, no flash/silverlight, very little javascript and jquery. For tracking I'm using GA and Piwik. The main site database is around 50MB. The site is hosted on a virtual server with 20GB RAM and 6 vCPUs so there's hopefully a lot of muscle to make it run very fast. I don't know much about tweaking php and mysql settings and would appreciate it if your answers can be as detailed as possible. Thanks

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  • Caching stored procedure results in Linq'u

    - by itdebeloper
    In our web application we have a lots of stored procedures look like this one: getSomeData(/* 7 diffrent params */) This stored procedure don't make any updates. We are using Linq'u. I know that the date are changing no often than once per day so the results for the same sets of parameters values will be the same. Does Linqu have cache simple solution? I know how to 'manually' write cache mechanism in .net, but I supposed that in Linqu this problem was solved. I'm a lazy guy :) so I'm looking for something realy simple like: Linqu_global_store_procedure_configuration.CacheDuration="600" Linqu_global_store_procedure_configuration.CacheVaryByParam="*" I'm using .net 3.5 but its not any problem to move for 4.0.

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  • Using locks inside a loop

    - by Xaqron
    // Member Variable private readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile shared int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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  • Generate MySQL data dump in SQL from PHP

    - by Álvaro G. Vicario
    I'm writing a PHP script to generate SQL dumps from my database for version control purposes. It already dumps the data structure by means of running the appropriate SHOW CREATE .... query. Now I want to dump data itself but I'm unsure about the best method. My requirements are: I need a record per row Rows must be sorted by primary key SQL must be valid and exact no matter the data type (integers, strings, binary data...) Dumps should be identical when data has not changed I can detect and run mysqldump as external command but that adds an extra system requirement and I need to parse the output in order to remove headers and footers with dump information I don't need (such as server version or dump date). I'd love to keep my script as simple as I can so it can be hold in an standalone file. What are my alternatives?

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  • message queue : selection and sizing

    - by user238591
    Hi, I have 20 messages/s, each 1 - 1.5 Mbytes. I need High Availability (2 to 4 servers min). I need low latencey (high daily volume - full RAM prefered). I need persistent poisoned messages queue. Only few clients (about 16), locally. I can have 12-16G bytes RAM per server (brooker). Which JMS message queue / messaging would you recommend ? On what configuration (CPU/RAM) ? Can I propose optionnal NAS persistence (in case of final delivery failure) ? Thanks

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  • MVC framework for huge JEE application

    - by chaKa
    Which MVC-framework is the best option (performance/ease of development) for a web application, that will have + 2 million visits per week. Basically the site is a search engine,but also there will be large amounts of xml parsing, and high db traffic. We are using Java, over Jboss 4.2.3x, with PG as DB, and Solr for the searches. We were thinking on code JSPs with taglibs, and Servlets, but we were feeling like there would be a better alternative, which don't know yet, as we are starting on the Java Web applications world. Any opinions, and shares of your experience will be appreciated! Thanks in advance!

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  • iphone memory management: alloc and retain properties.

    - by Jonathan
    According to the docs, you do one release per alloc or retain (etc) However what about when using retain propertys? eg: HEADER @property(retain)UIView *someView; IMPLEMENTATION /*in some method*/ UIView *tempView = [[UIView alloc] init]; //<<<<<ALLOC - retain count = +1 [tempView setBackgroundColor:[UIColor redColor]]; self.someView = tempView; ///<<<<<RETAIN - retain count = +2 [tempView release]; ///should I do this? or a different version of the IMPLEMENTATION self.someView = [[UIView alloc] init]; //<<<<<ALLOC & RETAIN - retain count = +2 //now what??? [self.someView release]; ???? EDIT: I didn't make it clear, but I meant what to do in both circumstances, not just the first.

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  • SQL Server - Select one random record not showing duplicates

    - by Lukes123
    I have two tables, events and photos, which relate together via the 'Event_ID' column. I wish to select ONE random photo from each event and display them. How can I do this? I have the following which displays all the photos which are associated. How can I limit it to one per event? SELECT Photos.Photo_Id, Photos.Photo_Path, Photos.Event_Id, Events.Event_Title, Events.Event_StartDate, Events.Event_EndDate FROM Photos, Events WHERE Photos.Event_Id = Events.Event_Id AND Events.Event_EndDate < GETDATE() AND Events.Event_EndDate IS NOT NULL AND Events.Event_StartDate IS NOT NULL ORDER BY NEWID() Thanks Luke Stratton

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  • Push a variable into global scope?

    - by Spot
    We use instantiate and put system critical objects in $GLOBALS for easy access from anywhere (e.g. DB, Cache, User, etc.). We use $GLOBALS so much that it would (yes, really) drop the amount of code quite a bit if I could reference it like $G = &$GLOBALS for a shorthand call. The problem is that, per my experience and several hours of Googling, I have not found any construct in PHP which allows you to 'flag' a var as global, making $GLOBALS first class, and everything else second class. Am I missing something? Is this possible?

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  • Percentage difference between different values in the same keys of two different arrays.

    - by Paul
    Hey. I'm looking for a solution to this problem. I got 2 arrays, like this: array(2) { [20100526]=> array(1) { ["ga:pageviews"]=> string(5) "19088" } [20100527]=> array(1) { ["ga:pageviews"]=> string(5) "15566" } } array(2) { [20100526]=> array(1) { ["ga:pageviews"]=> string(5) "12043" } [20100527]=> array(1) { ["ga:pageviews"]=> string(5) "11953" } } Now I'd like to create a new array, with the % difference between the values per key. Would be something like this: array(2) { [20100526]=> array(1) { ["ga:pageviews"]=> string(5) "88,23" } [20100527]=> array(1) { ["ga:pageviews"]=> string(5) "74,54" } } Can anyone help me how to create that array?

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  • Can the Sequence of RecordSets in a Multiple RecordSet ADO.Net resultset be determined, controlled?

    - by Shiva
    I am using code similar to this Support / KB article to return multiple recordsets to my C# program. But I don't want C# code to be dependant on the physical sequence of the recordsets returned, in order to do it's job. So my question is, "Is there a way to determine which set of records from a multiplerecordset resultset am I currently processing?" I know I could probably decipher this indirectly by looking for a unique column name or something per resultset, but I think/hope there is a better way. P.S. I am using Visual Studio 2008 Pro & SQL Server 2008 Express Edition.

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  • group by, order by, with join

    - by Scarface
    Hey guys, quick question, I have this query, and I am trying to get the latest comment for each topic and then sort those results in descending order (therefore one comment per topic). I have what I think should work, but my join always messes my results up. Somehow, it seems to have sorted the end results properly, but has not taken the latest comment from each topic instead it seems to have just taken a random comment. If anyone has any ideas, would really appreciate any advice SELECT * FROM comments JOIN topic ON topic.topic_id=comments.topic_id WHERE topic.creator='admin' GROUP BY comments.topic_id ORDER BY comments.time DESC table comments is structured like id time user message topic_id table topic is structured like topic_id subject_id topic_title creator timestamp description

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  • Sql Server as logging, best connection practise

    - by ozz
    I'm using SqlServer as logging. Yes this is wrong decision, there are better dbs for this requirement. But I have no other option for now. Logging interval is 3 logs per second. So I've static Logger class and it has static Log method. Using "Open Connection" as static member is better for performance. But what is the best implemantation of it? This is not that I know. public static class OzzLogger { static SqlConnection Con; static OzzLogger() { Con=ne SqlConnection(....); Con.Open(); } public static void Log(....) { Con.ExecuteSql(......); } } UPDATE I asked because of my old information. People say "connection pooling performance is enough". If there is no objection I'm closing the issue :)

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  • Execute a method less times possible - PHP

    - by serhio
    I have a site in multiple languages. I have a method that returns me the today currencies in a array. I display that currencies in a table then. // --- en/index.php <?php include_once "../exchangeRates.php"; $currencies = ReadExchangeRates(); // --- fr/index.php <?php include_once "../exchangeRates.php"; $currencies = ReadExchangeRates(); ... // somewhere in the page <td><?php echo $currencies["eur"]["today"]; ?></td> So, every time I load, en/ or fr/ or other language, I request the exchange rates from a external site. Can I optimize this behavior (reading once per day or session)? maybe to store a global variable and check the update date?

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  • Can the dirtiness of pages of a mmap be found from userspace?

    - by chrisdew
    Can dirtiness of pages of a (non-shared) mmap be accessed from userspace under linux 2.6.30+? Platform-specific hacks and kludges welcome. Ideally, I'm looking for an array of bits, one per page (4kB?) of the mmap'ed region, which are set if that page has been written to since the region was mmap'ed. (I am aware, that the process doing the writing could keep track of this information - but it seems silly to do so if the kernel is doing it anyway.) Thanks, Chris.

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  • Looking for suggestions about an architecture of a MultiThreaded app.

    - by Dimitri
    Hello everyone. I am looking to develop a multithreaded application that will be running in unconditional loop and processing high volume of data. High volume is 2000+ records per minute. Processing will involve data retrieval, calculations and data updates. I need the application to perform so that there is virtually no back log, meaning i need to be able to finish up all of the 2000 points in one minute or even faster. Our current implementation features a multithreaded application that is spawn multiple times (from 10 to 20) and we are noticing that it's not handling data as expected and i even feel that instances of the application compete with each other for processor time and eventually if not slowing, not benefiting each other for sure. I would like to know what would be the best approach: have a single instance running but maximize threads that can run simultaneously? or is there other ways i don't know? I'm open to suggestions. Thank you in advance

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  • CodeIgnitor is generating multiple sessions in the database, why?

    - by Derrick
    Ive got a site that does a few ajax calls on page load, now for some reason, codeIgnitor is inserting 4 sessions (I'm assuming for each ajax call) as you load the page. I'm storing the sessions in the database. I'm pretty sure there should only be one session per browser? FF seems to only generate one, other browsers seem to create a whole bunch of sessions. Multiple sessions for the same user are giving me some serious authentication problems. any ideas?

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  • Getting Top (starting no , Ending no) rows from sqlserver

    - by Krishna Thota
    I'm using Grid view in my asp.net page and I'm fetching data from SQL Server and placing in my grid view. Now my problem is, I'm using paging and placing 50 rows per page in Grid view. I would like to fetch top 50 rows from database in the start up and bind to the Grid View and when i click on next page, then again go to the database and fetch Second Top 50 rows and bind to GV. and this process hasto continue until last row is fetched from Database. Can you tell me How to write Query in achieving this??

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  • Export a MYSQL column to a plain txt file with no headings

    - by Kohl Sharples
    So what I'm trying to do is write a script or CRON job (Linux- CentOS) to export the usernames listed in my wordpress database to a simple .txt file with just on username per line. So with the picture, I would like the .txt file to read like this: Sir_Fluffulus NunjaX007 (Except with all the username in the user_login column.) See screenshot at: http://i.stack.imgur.com/lZQai.png I have found how to export the entire table to a CVS file, but that contains about 10+ fields (Columns) that I DO NOT what to show up in this text file. Can anyone point me in the right direction on how to do this? If it helps, this is going to be for exporting users that have signed up on our website (Wordpress) to a whitelist.txt file for Minecraft. Thanks!

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  • C++ DWORD* to BYTE*

    - by NomeSkavinski
    My issue, i am trying to convert and array of dynamic memory of type DWORD to a BYTE. Fair enough i can for loop through this and convert the DWORD into a BYTE per entry. But is their a faster way to do this? to take a pointer to DWORD data and convert the whole piece of data into a pointer to BYTE data? such as using a memcpy operation? I feel this is not possible, im not requesting an answer just an experienced opinion on my approach, as i have tried testing both approaches but seem to fail getting to a solution on my second solution. Thanks for any input, again no answers just a point in the right direction. Nor is this a homework question, i felt that had to be mentioned.

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  • Why does ElapsedTicks X 10 000 not equal ElapsedMilliseconds for .Net's Stopwatch?

    - by uriDium
    I am trying to performance test some code. I am using a stopwatch. When I output the number of milliseconds it always tells me 0 so I thought that I would try the number of ticks. I am seeing that the number of ticks is about 20 000 to 30 000. Looking at the MSDN at TimeSpan.TicksPerMillisecond it says that is 10 000 ticks per millisecond. In that case why are the elapsed milliseconds on my stopwatch not appearing as 2 or 3? What am I missing? I have even outputed the result on the same line. This is what I get. Time taken: 26856 ticks, 0 ms And it is constant.

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