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  • What are the benefits of left outer join vs nested aggregate selects to find the newest rows in a table?

    - by RenderIn
    I'm doing: select * from mytable y where y.year = (select max(yi.year) from mytable yi where yi.person = y.person) Is that better or worse from a performance aspect than: select y.* from mytable y left outer join mytable y2 on y.year < y2.year and y.person = y2.person where y2.year is null The explain plan/anecdotal evidence is inconclusive so I am wondering if in general one is better than the other.

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  • Scalability comparison between different DBMSs

    - by Björn Lindfors
    By what factor does the performance (read queries/sec) increase when a machine is added to a cluster of machines running either: a Bigtable-like database MySQL? Google's research paper on Bigtable suggests that "near-linear" scaling is achieved can be achieved with Bigtable. This page here featuring MySQL's marketing jargon suggests that MySQL is capable of scaling linearly. Where is the truth?

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  • Basic principles of computer encryption?

    - by Andrew
    I can see how a cipher can be developed using substitutions and keys, and how those two things can become more and more complex, thus offering some protection from decryption through brute-force approaches. But specifically I'm wondering: what other major concepts beyond substitution and key are involved? is the protection/secrecy of the key a greater vulnerability than the strength of the encryption? why does encryption still hold up when the key is 'public' ? are performance considerations a major obstacle to the development of more secure encryption?

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  • What should be the ideal number of parallel java threads for copying a large set of files from a qua

    - by ukgenie
    What should be the ideal number of parallel java threads for copying a large set of files from a quad core linux box to an external shared folder? I can see that with a single thread it is taking a hell lot of time to move the files one by one. Multiple threads is improving the copy performance, but I don't know what should be the exact number of threads. I am using Java executor service to create the thread pool.

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  • How to enable attachment using Apache File upload

    - by Stardust
    I am using Apache commons File upload API to Store the file from JSP to servlets in temp directory, but I don't know what should I do next to send the email as an attachment using javamail API. How can I retrieve those files which is written in temp directory using Apache Fileupload API to send them as attachment to mail Server. How will writing those files either to memory or disk will help me?

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  • Use Of Android NDK

    - by Shalini Singh
    Hi!!!! i am new for NDK. i want to know what is the benefit of native code in android . By this can we improve our application performance. and main thing exactly when we will use this native code. please clear it. and from where i can get more information............

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  • Books or resources for high-loaded sites.

    - by Alex
    Currently I'm developing high-loaded financial portal(we use LAMP to run our project). There are great number of incoming data to be processed and stored. So optimization tasks become very important for us. Could you suggest books, articles or resources, that discover optimization questions (especially bboks). NOTE: At the moment I'm reading great book High Performance MySQL, but besides I want to know other facilities of optimization.

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  • Components for creating Archives

    - by John
    Hello, I'm searching for a simple,free component for creating archives with the capability of adding files to an already existing archive.Compressions is not a matter as much as performance so even "store" will be useful. Please help me find one.

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  • External hard drive no detected in a vista ultimate

    - by raghavendra
    Hi, I have created a partition in my external HD and later i am trying to install XP over Vista . So i have entered into my DOS prompt and i choose the DISK TYPE and i choose external DD and i tried to CLEAN it , Immediately my external HD is asked for FORMAT and i rejected it . After that i restarted my system , therefore i cannot able to see my external HD on my sysmen External HD: Seagate Free agent(500GB)

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  • simpledb, sql azure, mysql + memcached

    - by sirmak
    For a new scalable high traffic global ecommerce website (asp.net) project which technology fits best (max. scalability & performance, min. price & maintenance)? amazon simpledb, microsoft sql azure, mysql + memcached combo, or your solution...

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  • Best practice for viewflipper containing 10 linearlayouts?

    - by Brad Hein
    I'm embarking on a GUI Activity composed of a viewflipper, which I would like to contain 10 linearlayout layouts. Is it advisable to put all of my layouts into the same XML resource/layout file? If not, is there a more organized approach to coding a viewflipper with many layouts? Will having everything in the same file come at a significant performance cost?

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  • Can you find a pattern to sync files knowing only dates and filenames?

    - by Robert MacLean
    Imagine if you will a operating system that had the following methods for files Create File: Creates (writes) a new file to disk. Calling this if a file exists causes a fault. Update File: Updates an existing file. Call this if a file doesn't exist causes a fault. Read File: Reads data from a file. Enumerate files: Gets all files in a folder. Files themselves in this operating system only have the following meta data: Created Time: The original date and time the file was created, by the Create File method. Modified Time: The date and time the file was last modified by the Update File method. If the file has never been modified, this will equal the Create Time. You have been given the task of writing an application which will sync the files between two directories (lets call them bill and ted) on a machine. However it is not that simple, the client has required that The application never faults (see methods above). That while the application is running the users can add and update files and those will be sync'd next time the application runs. Files can be added to either the ted or bill directories. File names cannot be altered. The application will perform one sync per time it is run. The application must be almost entirely in memory, in other words you cannot create a log of filenames and write that to disk and then check that the next time. The exception to point 6 is that you can store date and times between runs. Each date/time is associated with a key labeled A through J (so you have 10 to use) so you can compare keys between runs. There is no way to catch exceptions in the application. Answer will be accepted based on the following conditions: First answer to meet all requirements will be accepted. If there is no way to meet all requirements, the answer which ensures the smallest amount of missed changes per sync will be accepted. A bounty will be created (100 points) as soon as possible for the prize. The winner will be selected one day before the bounty ends. Please ask questions in the comments and I will gladly update and refine the question on those.

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  • Is there any reason to prefer UTF-16 over UTF-8?

    - by Oak
    Examining the attributes of UTF-16 and UTF-8, I can't find any reason to prefer UTF-16. However, checking out Java and C#, it looks like strings and chars there default to UTF-16. I was thinking that it might be for historic reasons, or perhaps for performance reasons, but couldn't find any information. Anyone knows why these languages chose UTF-16? And is there any valid reason for me to do that as well?

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  • Zend_Paginator - Increase querys

    - by poru
    Hello, I started using Zend_Paginator, it works everything fine but I noticed that there is one more query which slows the load time down. The additional query: SELECT COUNT(1) AS `zend_paginator_row_count` FROM `content` The normal query: SELECT `content`.`id`, `content`.`name` FROM `content` LIMIT 2 PHP: $adapter = new Zend_Paginator_Adapter_DbSelect($table->select()->from($table, array('id', 'name'))); $paginator = new Zend_Paginator($adapter); Could I merge the two querys into one (for better performance)?

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  • Multithreaded Haskell

    - by Ingdas
    Hi I'm learning Haskell and I'd like to write some multithreaded programs now to see the performance gains from that in a functional language. I can find some references to it on the internet but never a proper introduction to it. Can anyone point me to a guide which is understandable for someone who knows the syntax fairly well, but is not a wizard in Haskell?

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  • Experience of moving to 64 bit JVM

    - by Fazal
    Our company is planning to move to 64 bit JVM in order to get away from 2 GB maximum heap size limit. Google gave me very mixed results about 64 bit JVM performance. Has anyone tried moving to 64 bit java and share your experience

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  • Titanium vs The Native Tools

    - by Elfira
    Hi, I'm still checking everything out. I'm wondering what the limitations are if we develop the app using Titanium. What cannot be done using Titanium, for iPhone and for Android? What things can only be done using only the the native tools? I heard that performance could be an issue. How bad is this going to be? Thank you in advance. :)

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  • Basic concepts in file system implementation

    - by darkie15
    I am a unclear about file system implementation. Specifically (Operating Systems - Tannenbaum (Edition 3), Page 275) states "The first word of each block is used as a pointer to the next one. The rest of block is data". Can anyone please explain to me the hierarchy of the division here? Like, each disk partition contains blocks, blocks contain words, and so on...

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  • What's the different between these 2 mysql queries? one using left join

    - by Lyon
    Hi, I see people using LEFT JOIN in their mysql queries to fetch data from two tables. But I normally do it without left join. Is there any differences besides the syntax, e.g. performance? Here's my normal query style: SELECT * FROM table1 as tbl1, table2 as tbl2 WHERE tbl1.id=tbl2.table_id as compared to SELECT * FROM table1 as tbl1 LEFT JOIN table2 as tbl2 on tbl1.id=tbl2.id Personally I prefer the first style...hmm..

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  • Types of PNG image in iPhone app

    - by user297491
    I have an iPhone app that picks images from my internet server. It picks images with png extension but only PNG-24 is workings. The problem is that PNG-24 need some disk space and internet bandwith in iphone. I tried using PNG-8 but the iphone does not recognize it. Someone knows if I have a way to use PNG-8 into my app? Thanks!

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  • Restoring multiple database backups in a transaction

    - by Raghu Dodda
    I wrote a stored procedure that restores as set of the database backups. It takes two parameters - a source directory and a restore directory. The procedure looks for all .bak files in the source directory (recursively) and restores all the databases. The stored procedure works as expected, but it has one issue - if I uncomment the try-catch statements, the procedure terminates with the following error: error_number = 3013 error_severity = 16 error_state = 1 error_message = DATABASE is terminating abnormally. The weird part is sometimes (it is not consistent) the restore is done even if the error occurs. The procedure: create proc usp_restore_databases ( @source_directory varchar(1000), @restore_directory varchar(1000) ) as begin declare @number_of_backup_files int -- begin transaction -- begin try -- step 0: Initial validation if(right(@source_directory, 1) <> '\') set @source_directory = @source_directory + '\' if(right(@restore_directory, 1) <> '\') set @restore_directory = @restore_directory + '\' -- step 1: Put all the backup files in the specified directory in a table -- declare @backup_files table ( file_path varchar(1000)) declare @dos_command varchar(1000) set @dos_command = 'dir ' + '"' + @source_directory + '*.bak" /s/b' /* DEBUG */ print @dos_command insert into @backup_files(file_path) exec xp_cmdshell @dos_command delete from @backup_files where file_path IS NULL select @number_of_backup_files = count(1) from @backup_files /* DEBUG */ select * from @backup_files /* DEBUG */ print @number_of_backup_files -- step 2: restore each backup file -- declare backup_file_cursor cursor for select file_path from @backup_files open backup_file_cursor declare @index int; set @index = 0 while(@index < @number_of_backup_files) begin declare @backup_file_path varchar(1000) fetch next from backup_file_cursor into @backup_file_path /* DEBUG */ print @backup_file_path -- step 2a: parse the full backup file name to get the DB file name. declare @db_name varchar(100) set @db_name = right(@backup_file_path, charindex('\', reverse(@backup_file_path)) -1) -- still has the .bak extension /* DEBUG */ print @db_name set @db_name = left(@db_name, charindex('.', @db_name) -1) /* DEBUG */ print @db_name set @db_name = lower(@db_name) /* DEBUG */ print @db_name -- step 2b: find out the logical names of the mdf and ldf files declare @mdf_logical_name varchar(100), @ldf_logical_name varchar(100) declare @backup_file_contents table ( LogicalName nvarchar(128), PhysicalName nvarchar(260), [Type] char(1), FileGroupName nvarchar(128), [Size] numeric(20,0), [MaxSize] numeric(20,0), FileID bigint, CreateLSN numeric(25,0), DropLSN numeric(25,0) NULL, UniqueID uniqueidentifier, ReadOnlyLSN numeric(25,0) NULL, ReadWriteLSN numeric(25,0) NULL, BackupSizeInBytes bigint, SourceBlockSize int, FileGroupID int, LogGroupGUID uniqueidentifier NULL, DifferentialBaseLSN numeric(25,0) NULL, DifferentialBaseGUID uniqueidentifier, IsReadOnly bit, IsPresent bit ) insert into @backup_file_contents exec ('restore filelistonly from disk=' + '''' + @backup_file_path + '''') select @mdf_logical_name = LogicalName from @backup_file_contents where [Type] = 'D' select @ldf_logical_name = LogicalName from @backup_file_contents where [Type] = 'L' /* DEBUG */ print @mdf_logical_name + ', ' + @ldf_logical_name -- step 2c: restore declare @mdf_file_name varchar(1000), @ldf_file_name varchar(1000) set @mdf_file_name = @restore_directory + @db_name + '.mdf' set @ldf_file_name = @restore_directory + @db_name + '.ldf' /* DEBUG */ print 'mdf_logical_name = ' + @mdf_logical_name + '|' + 'ldf_logical_name = ' + @ldf_logical_name + '|' + 'db_name = ' + @db_name + '|' + 'backup_file_path = ' + @backup_file_path + '|' + 'restore_directory = ' + @restore_directory + '|' + 'mdf_file_name = ' + @mdf_file_name + '|' + 'ldf_file_name = ' + @ldf_file_name restore database @db_name from disk = @backup_file_path with move @mdf_logical_name to @mdf_file_name, move @ldf_logical_name to @ldf_file_name -- step 2d: iterate set @index = @index + 1 end close backup_file_cursor deallocate backup_file_cursor -- end try -- begin catch -- print error_message() -- rollback transaction -- return -- end catch -- -- commit transaction end Does anybody have any ideas why this might be happening? Another question: is the transaction code useful ? i.e., if there are 2 databases to be restored, will SQL Server undo the restore of one database if the second restore fails?

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