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  • How to guard against memory leaks?

    - by just_wes
    I was recently interviewing for a C++ position, and I was asked how I guard against creating memory leaks. I know I didn't give a satisfactory answer to that question, so I'm throwing it to you guys. What are the best ways to guard against memory leaks? Thanks!

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  • How many SQL queries per HTTP request is optimal?

    - by Chris Kooken
    I know the answer to this question for the most part is "It Depends", however I wanted to see if anyone had some pointers. We execute queries each request in ASP.NET MVC. Each request we need to get user rights information, and Various data for the Views that we are displaying. How many is too much, I know I should be conscious to the number of queries i am executing. I would assume if they are small queries and optimized out, half-a-dozen should be okay? Am I right? What do you think?

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  • SQL grouping query question; evaluating a group of rows based on the value of one field.

    - by user324575
    I've got table vendorparts that lists all my parts and their vendor(s). Parts with multiple vendors have multiple records in this table. I'm trying to write a query that only returns the partid, and vendor of parts that do not have a default vendor assigned. Partid Vendor Defaultflag 1 A 1 2 B 0 2 C 0 3 D 0 3 E 0 3 F 1 4 G 0 I would like to return the following: Partid Vendor 2 A 2 B 4 G I'm obviously having issues with partid 3 and getting the query to see it as having a default vendor assigned.

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  • I need help with a SQL query. Fetching an entry, it's most recent revision and it's fields.

    - by Tigger ate my dad
    Hi there, I'm building a CMS for my own needs, and finished planning my database layout. Basically I am abstracting all possible data-models into "sections" and all entries into one table. The final layout is as follows: Database diagram: I have yet to be allowed to post images, so here is a link to a diagram of my database. Entries (section_entries) are children of their section (sections). I save all edits to the entries in a new revision (section_entries_revisions), and also track revisions on the sections (section_revisions), in order to match the values of a revision, to the fields of the section that existed when the entry-revision was made. The section-revisions can have a number of fields (section_revision_fields) that define the attributes of entries in the section. There is a many-to-many relationship between the fields (section_revision_fields) and the entry-revisions (section_entry_revisions), that stores the values of the attributes defined by the section revision. Feel free to ask questions if the diagram is confusing. Now, this is the most complex SQL I've ever worked with, and the task of fetching my data is a little daunting. Basically what i want help with, is fetching an entry, when the only known variables are; section_id, section_entry_id. The query should fetch the most recent revision of that entry, and the section_revision model corresponding to section_revision_id in the section_entry_revisions table. It should also fetch the values of the fields in the section-revision. I was hoping for a query result, where there would be as many rows as fields in the section. Each row would contain the information of the entry and the section, and then information for one of the fields (e.g. each row corresponding to a field and it's value). I tried to explain the best I could. Again, feel free to ask questions if my description somehow lacking. I hope someone is up for the challenge. Best regards. :-)

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  • Why would SQL be very slow when doing updates?

    - by ooo
    Suddenly doing updates into a few tables have gotten 10 times slower than they used to be. What are some good recommendations to determine root cause and optimization? Could it be that indexing certain columns are causing updates to be slow? Any other recommendations? I guess more important than guesses would be help on the process of identifying the root cause or metrics around performance. Is there anything in Fluent NHibernate that you can use to help identify the root cause of performance issues?

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  • which sql query is more efficient: select count(*) or select ... where key>value?

    - by davka
    I need to periodically update a local cache with new additions to some DB table. The table rows contain an auto-increment sequential number (SN) field. The cache keeps this number too, so basically I just need to fetch all rows with SN larger than the highest I already have. SELECT * FROM table where SN > <max_cached_SN> However, the majority of the attempts will bring no data (I just need to make sure that I have an absolutely up-to-date local copy). So I wander if this will be more efficient: count = SELECT count(*) from table; if (count > <cache_size>) // fetch new rows as above I suppose that selecting by an indexed numeric field is quite efficient, so I wander whether using count has benefit. On the other hand, this test/update will be done quite frequently and by many clients, so there is a motivation to optimize it.

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  • What's up with this reversing bit order function?

    - by MattyW
    I'm rather ashamed to admit that I don't know as much about bits and bit manipulation as I probably should. I tried to fix that this weekend by writing some 'reverse the order of bits' and 'count the ON bits' functions. I took an example from here but when I implemented it as below, I found I had to be looping while < 29. If I loop while < 32 (as in the example) Then when I try to print the integer (using a printBits function i've written) I seem to be missing the first 3 bits. This makes no sense to me, can someone help me out? int reverse(int n) { int r = 0; int i = 0; for(i = 0; i < 29; i++) { r = (r << 1) + (n & 1); n >>=1; } return r; }

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  • Need help with this question: Write Java code which reads numbers from the keyboard.....

    - by Chris
    Write Java code which reads numbers from the keyboard until zero is entered. Only the positive numbers entered are to be added to a variable-sized collection. This is what I have so far: import java.lang.*; import java.util.*; import java.io.*; import java.net.*; public class Demo1App extends Object { public static void main(String[] argStrings) throws Exception { ArrayList myArrayList = new ArrayList(); Scanner input = new Scanner(System.in); System.out.println ("NUMBERS:"); while (int input > 0) { myArrayList.add(input); } while (int input < 0) { System.out.println ("ENTER NUMBERS GREATER THAN 0!"); } } } This code doesn't work, I'm not sure why but any help with it would be appreciated.

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  • How do I remove database name from SQL Server generated script?

    - by bucha
    Anytime I use 'script table as' - 'Insert To' (or other command), the script generated automatically places the database name in the script. Such as: INSERT INTO [DatabaseName].[dbo].[tblToBeInserted] ... While not a huge problem to just delete it, it has slipped by a few times and the script breaks if run on a different server with a different database name but has the same schema. (Such as running on [DatabaseName.Test]) Is there an option I can change, or can I modify the output in any way to remove this?

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  • Compare two integer arrays with same length

    - by meta
    [Description] Given two integer arrays with the same length. Design an algorithm which can judge whether they're the same, the definition of "same" is that, if these two arrays are in sorted order, the elements in corresponding position should be the same. [Example] <1 2 3 4> = <3 1 2 4> <1 2 3 4> != <3 4 1 1> [Limitation] The algorithm should require constant extra space, and O(n) running time.

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  • Optimal strategy to make a C++ hash table, thread safe

    - by Ajeet
    (I am interested in design of implementation NOT a readymade construct that will do it all.) Suppose we have a class HashTable (not hash-map implemented as a tree but hash-table) and say there are eight threads. Suppose read to write ratio is about 100:1 or even better 1000:1. Case A) Only one thread is a writer and others including writer can read from HashTable(they may simply iterate over entire hash table) Case B) All threads are identical and all could read/write. Can someone suggest best strategy to make the class thread safe with following consideration 1. Top priority to least lock contention 2. Second priority to least number of locks My understanding so far is thus : One BIG reader-writer lock(semaphore). Specialize the semaphore so that there could be eight instances writer-resource for case B, where each each writer resource locks one row(or range for that matter). (so i guess 1+8 mutexes) Please let me know if I am thinking on the correct line, and how could we improve on this solution.

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  • SQL Reporting Services 2005 - Date field based on a user entered date?

    - by Pierce
    Hi, I have a report in report services 2005 that has two date fields. The problem is that if users run this for a large section of time it uses too much resources on our server. It is possible to only allow the end user to enter the start date and then the end date be auto populated/derived from this field (for example they enter the 1st of a month and this automatically change the end date to the last of a month.)

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  • Can you define values in a SQL statement that you can join/union, but are not stored in a table outs

    - by Mervyn
    I'm trying to create a query and need to join against something that I can define values in without creating a table. I'll attempt to describe what I'm trying to do: table1 is joined on field a with table2 (titles for FK in table 1) - Table1 has values outside of what exists in table2 - I want to add an additional 'table' to be unioned with table2 and then joined with table 1 Thanks

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  • SQL query to get lowest 2 values of a counted query selection (using db2)?

    - by jNoob
    Hi, Imagine I already have a query that returns the following: Col1 | Col2 ------------ A | 2 B | 3 C | 3 D | 4 E | 8 ... Say I used something like this: select Col1, count ( * ) as Col2 \ from ... where ... order by Col2 \ group by Col1 \ So now, all I want to select are (Col1, Col2) such that it returns the selections (a, b) and (c, d) where (b >= all (Col2)) and (d >= ((all (Col2)) - a)). So for the above example, it would return {(A, 2), (B, 3), (C, 3)}. How do I go about doing this? Any help would be highly appreciated. Thanks.

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  • Number of the different elements in an array.

    - by AB
    Is it possible to compute the number of the different elements in an array in linear time and constant space? Let us say it's an array of long integers, and you can not allocate an array of length sizeof(long). P.S. Not homework, just curious. I've got a book that sort of implies that it is possible.

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  • PHP SQL, SELECT corresponding data from 3 tables at once?

    - by user346325
    I have 3 tables, 'u' 'd' 's' 'u' has userid divid 'd' has divid divname 's' has sname primaryuserid secondaryuserid Now what I'd like to do is display a table with rows of the following format userid, divname, sname Plus figure out a way to decipher whether userid is a primary or secondary for this sname table. I'm able to show userid and divname using a left join, but I don't know how I would add a third table? To make it trickier, there can be more than 1 snames for each userid, up to ~20. Is there a way to display 0-20 snames depending on the userid, seperated with commas?

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