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  • How to change size of STL container in C++

    - by Jaime Pardos
    I have a piece of performance critical code written with pointers and dynamic memory. I would like to rewrite it with STL containers, but I'm a bit concerned with performance. Is there a way to increase the size of a container without initializing the data? For example, instead of doing ptr = new BYTE[x]; I want to do something like vec.insert(vec.begin(), x, 0); However this initializes every byte to 0. Isn't there a way to just make the vector grow? I know about reserve() but it just allocates memory, it doesn't change the size of the vector, and doesn't allows me to access it until I have inserted valid data. Thank you everyone.

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  • Javascript large number array compression

    - by gatapia
    Hi All, I've got a javascript application that sends a large amount of numerical data down the wire. This data is then stored in a database. I am having size issues (too much bandwidth, database getting too big). I am now ready to sacrifice some performance for compression. I was thinking of implementing a base 62 number.toString(62) and parseInt(compressed, 62). This would certainly reduce the size of the data but before I go ahead and do this I thought I would put it to the folks here as I know there must be some outside the box solution I have not considered. The basic specs are: - Compress large number arrays into strings for JSONP transfer (So I think UTF is out) - Be relatively fast, look I'm not expecting same performance as I have now but I also don't want gzip compression either. Any ideas would be greatly appreciated. Thanks Guido Tapia

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  • Clustered index on frequently changing reference table of one or more foreign keys

    - by Ian
    My specific concern is related to the performance of a clustered index on a reference table that has many rapid inserts and deletes. Table 1 "Collection" collection_pk int (among other fields) Table 2 "Item" item_pk int (among other fields) Reference Table "Collection_Items" collection_pk int, item_pk int (combined primary key) Because the primary key is composed of both pks, a clustered index is created and the data physically ordered in the table according to the combined keys. I have many users creating and deleting collections and adding and removing items to those collections very frequently affecting the "Collection_Items" table, and its clustered index. QUESTION PART: Since the "Collection_Items" table is so dynamic, wouldn't there be a big performance hit on constantly resorting the table rows because of the clustered index ? If yes, what should I do to minimize this ?

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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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  • c++ programming for clusters and HPC

    - by Abruzzo Forte e Gentile
    HI All I need to write a scientific application in C++ doing a lot of computations and using a lot of memory. I have part of the job but due to high requirements in terms of resources I was thinking to start moving to OpenMPI. Before doing that I have a simple curiosity: If I understood the principle of OpenMPI is the developer that has the task of splitting the jobs over different nodes calling SEND and RECEIVE based on node available at that time. Do you know if it does exist some library or OS or whatever that has this capability letting my code reamain as it is now? Basically something that connects all computers and let share as one their memory and CPU? I am a bit confused because of the high material available on the topic. Should I look at cloud computing? or Distributed Shared Memory? Can you help me or address me a bit? Thanks

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  • Adding more OR searches with CONTAINS Brings Query to Crawl

    - by scolja
    I have a simple query that relies on two full-text indexed tables, but it runs extremely slow when I have the CONTAINS combined with any additional OR search. As seen in the execution plan, the two full text searches crush the performance. If I query with just 1 of the CONTAINS, or neither, the query is sub-second, but the moment you add OR into the mix the query becomes ill-fated. The two tables are nothing special, they're not overly wide (42 cols in one, 21 in the other; maybe 10 cols are FT indexed in each) or even contain very many records (36k recs in the biggest of the two). I was able to solve the performance by splitting the two CONTAINS searches into their own SELECT queries and then UNION the three together. Is this UNION workaround my only hope? Thanks. SELECT a.CollectionID FROM collections a INNER JOIN determinations b ON a.CollectionID = b.CollectionID WHERE a.CollrTeam_Text LIKE '%fa%' OR CONTAINS(a.*, '"*fa*"') OR CONTAINS(b.*, '"*fa*"') Execution Plan (guess I need more reputation before I can post the image):

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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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  • Video chat application : Which technology to choose ?

    - by WarDoGG
    I have to undertake a project which is to make a video chat application. The video has to be streamed from one location and can be viewed by multiple people spread out over the globe. Performance is really an issue and a delay of more than 2-3 seconds is unacceptable. From what i gather, this can be done in Flex and also in JAVA. Any performance issues and caveats with a particular approach ? I would really like the pros to comment on this and guide me through. Will be very very helpful. Are there any open source libraries available for video recording in flash / JAVA which i can integrate into my app and customize according to my needs ?

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  • What is the best solution to replace a new memory allocator in an existing code?

    - by O. Askari
    During the last few days I've gained some information about memory allocators other than the standard malloc(). There are some implementations that seem to be much better than malloc() for applications with many threads. For example it seems that tcmalloc and ptmalloc have better performance. I have a C++ application that uses both malloc and new operators in many places. I thought replacing them with something like ptmalloc may improve its performance. But I wonder how does the new operator act when used in C++ application that runs on Linux? Does it use the standard behavior of malloc or something else? What is the best way to replace the new memory allocator with the old one in the code? Is there any way to override the behavior or new and malloc or do I need to replace all the calls to them one by one?

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  • List filtering: list comprehension vs. lambda + filter

    - by Agos
    I happened to find myself having a basic filtering need: I have a list and I have to filter it by an attribute of the items. My code looked like this: list = [i for i in list if i.attribute == value] But then i thought, wouldn't it be better to write it like this? filter(lambda x: x.attribute == value, list) It's more readable, and if needed for performance the lambda could be taken out to gain something. Question is: are there any caveats in using the second way? Any performance difference? Am I missing the Pythonic Way™ entirely and should do it in yet another way (such as using itemgetter instead of the lambda)? Thanks in advance

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  • How to set a custom font for a spinner?

    - by AndrewC
    Is there anyway to set a custom font or color for the selected item in a Spinner? For example, I open the spinner and click a priority of "High". I'm my layout containing the spinner, I would like to see the word "High" in red or a custom font. I can't seem to obtain the textview to make the necessary change. I always obtain a NullPointerException if I typecast the spinner.getSelectedView() to textview and attempt to set the color. any ideas? thanks in advance!

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  • which is better, creating a view or a new table?

    - by Carson
    I have some demanding mysql queries that are needed to grap same datasets from several mysql tables. I am thinking of creating a table or view to gather all demanding columns from other tables, so as to increase performance. If I create that table, I may need to do extra insert / update / delete operation each time other tables updated. if I create view, I am worrying if the performance can be greatly improved. Because data from other tables are changing very frequently. Most likely, the view may need to be created first everytime before selecting it. Any ideas? e.g. how to cache? other extra measures I can do?

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  • Marvell C++ compiler (for Windows CE) for building Qt

    - by vnm
    Hello, I was able to build Qt 4.5 for Windows CE (ARM4VI) using MS VisualC++ compiler. Now, I am trying to compile Qt 4.5 for Windows CE 5.0 using Marvel C++ compiler v 2.2 (former Intel C++ compiler for XScale architecture) for achieving some performance benefit. It seems, that this compiler not officially supported for building Qt by trolltech (no appropriate mkspec in mkspec's folder of Qt folder). So, my questions: Is it worth to trying build Qt by this compiler for achieving performance enhancement ? Is there any way for building Qt using Marvell C++ compiler (by creating my own mkspec or something like that)?

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  • mysql twitter/facebook like status feed

    - by barjonah
    Hi, I have two tables. One named status like this... user_id | status --------+----------- 1 | random status from user 1 2 | random status from user 2 3 | random message from user 3 4 | staus from user 4 1 | second status for user1 etc... and another named users_following like this... user_id | is_following --------+----------- 1 | 2 1 | 3 2 | 1 3 | 2 meaning that user 1 is following both users 2 and 3 etc... So, let's say I chose user 1. What is the best query (performance wise) to show the status updates of users that user 1 is following, in this case users 2 and 3 currently I have something like SELECT * from status WHERE user_id IN(SELECT is_following FROM users_following WHERE user_id='1') LIMIT 0,5 but I don't think this is good for performance if a user was following thousands+ of users

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  • Checking exception before using GETITEMBYID()

    - by ps123
    Hello, I am getting item by getiembyid...but I want to check before using it that whether item exist or not...I don't want to use query as main purpose of using Getitembyid is performance.....any idea how to achieve this... itemid = Response.QueryString["loc"]; SPList mylist = myweb.GetList(SPUrlUtility.CombineUrl(myweb.ServerRelativeUrl, "/Lists/Location")); //now id itemid does not exist it throws exception...so i want to check before using following statement that itemid exist...I know i can check throw SPQuery but as i said above because of performance issue only i m using itemid.... SPListItem myitem = mylist.GetItemById(Convert.ToInt32(itemid)); Any idea how to achieve this?

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  • Why is numpy c extension slow?

    - by Bitwise
    I am working on large numpy arrays, and some native numpy operations are too slow for my needs (for example simple operations such as "bitwise" A&B). I started looking into writing C extensions to try and improve performance. As a test case, I tried the example given here, implementing a simple trace calculation. I was able to get it to work, but was surprised by the performance: for a (1000,1000) numpy array, numpy.trace() was about 1000 times faster than the C extension! This happens whether I run it once or many times. Is this expected? Is the C extension overhead that bad? Any ideas how to speed things up?

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  • Web GUI frameworks for Phone development

    - by Runner
    I looked already and could't find anyting good. So a question is, are there any good web frameworks that would allow to easily develop GUI for the majority of high end phones? By this I mean It would have to work the same on majority of high end phones (forget the low cost ones) It would have to simplify the development and hide the ugly details from developer Clear design and good documentation. Also some stability on the market. The focus in on good looking and easy to make GUI. Javascript is only a plus. So basically I am looking for something like jQuery or maybe ExtJS for phone development. EDIT: It would be a big plus if it could be consumed in Delphi EDIT 2: If it was not clear, I am looking for a web base solution. So the target is HTML output and not native code.

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  • Javascript === vs == : Does it matter which "equal" operator I use?

    - by bcasp
    I'm using JSLint to go through some horrific JavaScript at work and it's returning a huge number of suggestions to replace == with === when doing things like comparing 'idSele_UNVEHtype.value.length == 0' inside of an if statement. I'm basically wondering if there is a performance benefit to replacing == with ===. Any performance improvement would probably be welcomed as there are hundreds (if not thousands) of these comparison operators being used throughout the file. I tried searching for relevant information to this question, but trying to search for something like '=== vs ==' doesn't seem to work so well with search engines...

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  • Does the order of the columns in a SELECT statement make a difference?

    - by Frank Computer
    This question was inspired by a previous question posted on SO, "Does the order of the WHERE clause make a differnece?". Would it improve a SELECT statement's performance if the the columns used in the WHERE section are placed at the begining of the SELECT statement? example: SELECT customer.id, transaction.id, transaction.efective_date, transaction.a, [...] FROM customer, transaction WHERE customer.id = transaction.id; I do know that limiting the list of columns to only the needed ones in a SELECT statement improves performance as opposed to using SELECT * because the current list is smaller.

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