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  • Sequential (comb) GUIDs for Oracle

    - by Eyvind
    We are in the process of switching from the C# Guid.NewGuid() random-ish guid generator to the sequential guid algorithm suggested in this post. While this seems to work well for MS SQL Server, I am unsure about the implications for Oracle databases, in which we store guids in a raw(16) field. Does anyone have any insight as to whether this algorithm would be good for creating sequential guids for Oracle as well as for MS SQL Server, or if a different variant should be used. Thanks!

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  • multi-shop orders table and sequential order numbers based on shop

    - by imanc
    Hey, I am looking at building a shop solution that needs to be scalable. Currently it retrieves 1-2000 orders on average per day across multiple country based shops (e.g. uk, us, de, dk, es etc.) but this order could be 10x this amount in two years. I am looking at either using separate country-shop databases to store the orders tables, or looking to combine all into one order table. If all orders exist in one table with a global ID (auto num) and country ID (e.g uk,de,dk etc.), each countries orders would also need to have sequential ordering. So in essence, we'd have to have a global ID and a country order ID, with the country order ID being sequential for countries only, e.g. global ID = 1000, country = UK, country order ID = 1000 global ID = 1001, country = DE, country order ID = 1000 global ID = 1002, country = DE, country order ID = 1001 global ID = 1003, country = DE, country order ID = 1002 global ID = 1004, country = UK, country order ID = 1001 THe global ID would be DB generated and not something I would need to worry about. But I am thinking that I'd have to do a query to get the current country order based ID+1 to find the next sequential number. Two things concern me about this: 1) query times when the table has potentially millions of rows of data and I'm doing a read before a write, 2) the potential for ID number clashes due to simultaneous writes/reads. With a MyISAM table the entire table could be locked whilst the last country order + 1 is retrieved, to prevent ID number clashes. I am wondering if anyone knows of a more elegant solution? Cheers, imanc

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  • How to sequential filter/Select multiple combobox w/ just one DataSet

    - by pee2002
    Hi! I´m communicating via webservices with the Server (where's installed the database) and the c# application. So, i dont have direct access with the database Somehow, i receive a DataSet with 3 tables inside: And would like to populate 3 combobox like this: Which (as you already see) has a sequential logic. If i perhaps select "Gabicontas1" instead "Gabicontas" from the first combobox, the next ones has to change.. Can anyone help? Regards

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  • sequential search homework question

    - by Phenom
    Consider a disk file containing 100 records a. How many comparisons would be required on the average to find a record using sequential search, if the record is known to be in the file? I figured out that this is 100/2 = 50. b. If the record has a 68% probability of being in the file, how many comparisons are required on average? This is the part I'm having trouble with. At first I thought it was 68% * 50, but then realized that was wrong after thinking about it. Then I thought it was (100% - 68%) * 50, but I still feel that that is wrong. Any hints?

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  • Concurrent Generation of Sequential Keys

    - by GenTiradentes
    I'm working on a project which generates a very large number of sequential text strings, in a very tight loop. My application makes heavy use of SIMD instruction set extensions like SSE and MMX, in other parts of the program, but the key generator is plain C++. The way my key generator works is I have a keyGenerator class, which holds a single char array that stores the current key. To get the next key, there is a function called "incrementKey," which treats the string as a number, adding one to the string, carrying where necessary. Now, the problem is, the keygen is somewhat of a bottleneck. It's fast, but it would be nice if it were faster. One of the biggest problems is that when I'm generating a set of sequential keys to be processed using my SSE2 code, I have to have the entire set stored in an array, which means I have to sequentially generate and copy 12 strings into an array, one by one, like so: char* keys[12]; for(int i = 0; i < 12; i++) { keys[i] = new char[16]; strcmp(keys[i], keygen++); } So how would you efficiently generate these plaintext strings in order? I need some ideas to help move this along. Concurrency would be nice; as my code is right now, each successive key depends on the previous one, which means that the processor can't start work on the next key until the current one has been completely generated. Here is the code relevant to the key generator: KeyGenerator.h class keyGenerator { public: keyGenerator(unsigned long long location, characterSet* charset) : location(location), charset(charset) { for(int i = 0; i < 16; i++) key[i] = 0; charsetStr = charset->getCharsetStr(); integerToKey(); } ~keyGenerator() { } inline void incrementKey() { register size_t keyLength = strlen(key); for(register char* place = key; place; place++) { if(*place == charset->maxChar) { // Overflow, reset char at place *place = charset->minChar; if(!*(place+1)) { // Carry, no space, insert char *(place+1) = charset->minChar; ++keyLength; break; } else { continue; } } else { // Space available, increment char at place if(*place == charset->charSecEnd[0]) *place = charset->charSecBegin[0]; else if(*place == charset->charSecEnd[1]) *place = charset->charSecBegin[1]; (*place)++; break; } } } inline char* operator++() // Pre-increment { incrementKey(); return key; } inline char* operator++(int) // Post-increment { memcpy(postIncrementRetval, key, 16); incrementKey(); return postIncrementRetval; } void integerToKey() { register unsigned long long num = location; if(!num) { key[0] = charsetStr[0]; } else { num++; while(num) { num--; unsigned int remainder = num % charset->length; num /= charset->length; key[strlen(key)] = charsetStr[remainder]; } } } inline unsigned long long keyToInteger() { // TODO return 0; } inline char* getKey() { return key; } private: unsigned long long location; characterSet* charset; std::string charsetStr; char key[16]; // We need a place to store the key for the post increment operation. char postIncrementRetval[16]; }; CharacterSet.h struct characterSet { characterSet() { } characterSet(unsigned int len, int min, int max, int charsec0, int charsec1, int charsec2, int charsec3) { init(length, min, max, charsec0, charsec1, charsec2, charsec3); } void init(unsigned int len, int min, int max, int charsec0, int charsec1, int charsec2, int charsec3) { length = len; minChar = min; maxChar = max; charSecEnd[0] = charsec0; charSecBegin[0] = charsec1; charSecEnd[1] = charsec2; charSecBegin[1] = charsec3; } std::string getCharsetStr() { std::string retval; for(int chr = minChar; chr != maxChar; chr++) { for(int i = 0; i < 2; i++) if(chr == charSecEnd[i]) chr = charSecBegin[i]; retval += chr; } return retval; } int minChar, maxChar; // charSec = character set section int charSecEnd[2], charSecBegin[2]; unsigned int length; };

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  • Trouble with a sequential search algorithm

    - by shinjuo
    I need to use this sequential search algorithm, but I am not really sure how. I need to use it with an array. Can someone point me in the correct direction or something on how to use this. bool seqSearch (int list[], int last, int target, int* locn){ int looker; looker = 0; while(looker < last && target != list[looker]){ looker++; } *locn = looker; return(target == list[looker]); }

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  • Bonnie does not provide speed for Sequential Input / Block

    - by Lqp1
    I'm using ProxmoxVE and I would like to run some benchmarks regarding performances of this product. One of these benchmarks is bonnie++ ; it runs very well in a VM (qemu-kvm) but when I run it in a conainer (openVZ), it does not provide me reading speed (only writing). I don't understand why... Does anyone know what's happenning ? VMs ans Containers are Debian 7.4. Here's the output of bonnie in the container: root@ct2:/# bonnie++ -u root Using uid:0, gid:0. Writing a byte at a time...done Writing intelligently...done Rewriting...done Reading a byte at a time...done Reading intelligently...done start 'em...done...done...done...done...done... Create files in sequential order...done. Stat files in sequential order...done. Delete files in sequential order...done. Create files in random order...done. Stat files in random order...done. Delete files in random order...done. Version 1.96 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP ct2 1G 843 99 59116 8 60351 4 4966 99 +++++ +++ 2745 8 Latency 9558us 3582ms 527ms 1672us 936us 5248us Version 1.96 ------Sequential Create------ --------Random Create-------- ct2 -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ Latency 19567us 358us 368us 107us 59us 25us 1.96,1.96,ct2,1,1401810323,1G,,843,99,59116,8,60351,4,4966,99,+++++,+++,2745,8,16,,,,,+++++,+++,+++++,+++,+++++,+++,+++++,+++,+++++,+++,+++++,+++,9558us,3582ms,527ms,1672us,936us,5248us,19567us,358us,368us,107us,59us,25us The filesystem for / is of type "simfs", which is a pseudo filesystem for openVZ. Maybe it's related to this issue but I can't find anyone with the same issue with bonnie and openVZ... Thanks for your help. Regards, Thomas.

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  • Refactor: Sequential Coupling => Template Method

    Another colleague brought me present today - the blog post. Thank you. You were right!We will do some refactoring which will lead us from Anti-Pattern to Pattern. From Sequential Coupling to Template Method. And as I see it could be very common way to refactor bad code that represents mentioned anti

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  • Mocking successive calls of similar type via sequential mocking

    In this post , i show how you can benefit from  sequential mocking feature[In JustMock] for setting up expectations with successive calls of same type.  To start lets first consider the following dummy database and entity class. public class Person { public virtual string Name { get; set; } public virtual int Age { get; set; } }   public interface IDataBase { T Get<T>(); } Now, our test goal is to return different entity for successive calls on IDataBase.Get<T>()....Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Mocking successive calls of similar type via sequential mocking

    - by mehfuzh
    In this post , i show how you can benefit from  sequential mocking feature[In JustMock] for setting up expectations with successive calls of same type.  To start let’s first consider the following dummy database and entity class. public class Person {     public virtual string Name { get; set; }     public virtual int Age { get; set; } }   public interface IDataBase {     T Get<T>(); } Now, our test goal is to return different entity for successive calls on IDataBase.Get<T>(). By default, the behavior in JustMock is override , which is similar to other popular mocking tools. By override it means that the tool will consider always the latest user setup. Therefore, the first example will return the latest entity every-time and will fail in line #12: Person person1 = new Person { Age = 30, Name = "Kosev" }; Person person2 = new Person { Age = 80, Name = "Mihail" };   var database = Mock.Create<IDataBase>();   Queue<Person> queue = new Queue<Person>();   Mock.Arrange(() => database.Get<Person>()).Returns(() => queue.Dequeue()); Mock.Arrange(() => database.Get<Person>()).Returns(person2);   // this will fail Assert.Equal(person1.GetHashCode(), database.Get<Person>().GetHashCode());   Assert.Equal(person2.GetHashCode(), database.Get<Person>().GetHashCode()); We can solve it the following way using a Queue and that removes the item from bottom on each call: Person person1 = new Person { Age = 30, Name = "Kosev" }; Person person2 = new Person { Age = 80, Name = "Mihail" };   var database = Mock.Create<IDataBase>();   Queue<Person> queue = new Queue<Person>();   queue.Enqueue(person1); queue.Enqueue(person2);   Mock.Arrange(() => database.Get<Person>()).Returns(queue.Dequeue());   Assert.Equal(person1.GetHashCode(), database.Get<Person>().GetHashCode()); Assert.Equal(person2.GetHashCode(), database.Get<Person>().GetHashCode()); This will ensure that right entity is returned but this is not an elegant solution. So, in JustMock we introduced a  new option that lets you set up your expectations sequentially. Like: Person person1 = new Person { Age = 30, Name = "Kosev" }; Person person2 = new Person { Age = 80, Name = "Mihail" };   var database = Mock.Create<IDataBase>();   Mock.Arrange(() => database.Get<Person>()).Returns(person1).InSequence(); Mock.Arrange(() => database.Get<Person>()).Returns(person2).InSequence();   Assert.Equal(person1.GetHashCode(), database.Get<Person>().GetHashCode()); Assert.Equal(person2.GetHashCode(), database.Get<Person>().GetHashCode()); The  “InSequence” modifier will tell the mocking tool to return the expected result as in the order it is specified by user. The solution though pretty simple and but neat(to me) and way too simpler than using a collection to solve this type of cases. Hope that helps P.S. The example shown in my blog is using interface don’t require a profiler  and you can even use a notepad and build it referencing Telerik.JustMock.dll, run it with GUI tools and it will work. But this feature also applies to concrete methods that includes JM profiler and can be implemented for more complex scenarios.

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  • Testing a codebase with sequential cohesion

    - by iveqy
    I've this really simple program written in C with ncurses that's basically a front-end to sqlite3. I would like to implement TDD to continue the development and have found a nice C unit framework for this. However I'm totally stuck on how to implement it. Take this case for example: A user types a letter 'l' that is captured by ncurses getch(), and then an sqlite3 query is run that for every row calls a callback function. This callback function prints stuff to the screen via ncurses. So the obvious way to fully test this is to simulate a keyboard and a terminal and make sure that the output is the expected. However this sounds too complicated. I was thinking about adding an abstraction layer between the database and the UI so that the callback function will populate a list of entries and that list will later be printed. In that case I would be able to check if that list contains the expected values. However, why would I struggle with a data structure and lists in my program when sqlite3 already does this? For example, if the user wants to see the list sorted in some other way, it would be expensive to throw away the list and repopulate it. I would need to sort the list, but why should I implement sorting when sqlite3 already has that? Using my orginal design I could just do an other query sorted differently. Previously I've only done TDD with command line applications, and there it's really easy to just compare the output with what I'm expected. An other way would be to add CLI interface to the program and wrap a test program around the CLI to test everything. (The way git.git does with it's test-framework). So the question is, how to add testing to a tightly integrated database/UI.

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  • Utility to record IO statistics (random/sequential, block sizes, read/write ratio) in Unix

    - by Michael Pearson
    As part of provisioning our new server (see other SF) I'd like to find out the following: ratio of random to sequential reads & writes amount of data read & written at a time (pref in histogram form) I can already figure out our reads/writes on a per-operation and overall data level using iostat & dstat, but I'd like to know more. For example, I'd like to know that we're mostly random 16kb reads, or a lot of sequential 64kb reads with random writes. We're (currently) on an Ubuntu 10.04 VM. Is there a utility that I can run that will record and present this information for me?

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  • How to test a project with multiple python versions in a sequential way?

    - by ecolell
    I am developing a python adapter to interact with a 3rd party website, without any json or xml api (http://www.class.noaa.gov/). I have a problem when Travis CI run multiple python tests (of the The Travis CI Build Matrix) concurrently. The project is on GitHub at ecolell/noaaclass and the .travis.yml file is: language: python python: - "2.6" - "2.7" - "3.2" - "3.3" install: - "make deploy" script: "make test-coverage-travis-ci" #nosetests after_success: - "make test-coveralls" Specifically, I have a problem when at least 2 python versions were running their unit tests at the same time, because they use the same account of a website. Is there any option to specify to The Build Matrix the execution of each python version in a secuential way? Or maybe, Is there a better way to do this?

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  • B-trees, databases, sequential inputs, and speed.

    - by IanC
    I know from experience that b-trees have awful performance when data is added to them sequentially (regardless of the direction). However, when data is added randomly, best performance is obtained. This is easy to demonstrate with the likes of an RB-Tree. Sequential writes cause a maximum number of tree balances to be performed. I know very few databases use binary trees, but rather used n-order balanced trees. I logically assume they suffer a similar fate to binary trees when it comes to sequential inputs. This sparked my curiosity. If this is so, then one could deduce that writing sequential IDs (such as in IDENTITY(1,1)) would cause multiple re-balances of the tree to occur. I have seen many posts argue against GUIDs as "these will cause random writes". I never use GUIDs, but it struck me that this "bad" point was in fact a good point. So I decided to test it. Here is my code: SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[T1]( [ID] [int] NOT NULL CONSTRAINT [T1_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO CREATE TABLE [dbo].[T2]( [ID] [uniqueidentifier] NOT NULL CONSTRAINT [T2_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO declare @i int, @t1 datetime, @t2 datetime, @t3 datetime, @c char(300) set @t1 = GETDATE() set @i = 1 while @i < 2000 begin insert into T2 values (NEWID(), @c) set @i = @i + 1 end set @t2 = GETDATE() WAITFOR delay '0:0:10' set @t3 = GETDATE() set @i = 1 while @i < 2000 begin insert into T1 values (@i, @c) set @i = @i + 1 end select DATEDIFF(ms, @t1, @t2) AS [Int], DATEDIFF(ms, @t3, getdate()) AS [GUID] drop table T1 drop table T2 Note that I am not subtracting any time for the creation of the GUID nor for the considerably extra size of the row. The results on my machine were as follows: Int: 17,340 ms GUID: 6,746 ms This means that in this test, random inserts of 16 bytes was almost 3 times faster than sequential inserts of 4 bytes. Would anyone like to comment on this? Ps. I get that this isn't a question. It's an invite to discussion, and that is relevant to learning optimum programming.

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  • Sequential coupling in code

    - by dotnetdev
    Hi, Is sequential coupling (http://en.wikipedia.org/wiki/Sequential_coupling) really a bad thing in code? Although it's an anti-pattern, the only risk I see is calling methods in the wrong order but documentation of an API/class library with this anti-pattern should take care of that. What other problems are there from code which is sequential? Also, this pattern could easily be fixed by using a facade it seems. Thanks

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  • Changing an MSSQL clustered index field from containing "random" GUIDs to sequential GUIDs - how wil

    - by Eyvind
    We have an MSSQL database in which all the primary keys are GUIDs (uniqueidentifiers). The GUIDs are produced on the client (in C#), and we are considering changing the client to generate sequential (comb) GUIDs instead of just using Guid.NewGuid(), to improve db performance. If we do this, how will this affect installations that already have data with "random" GUIDs as clustered PKs? Can anything be done (short of changing all the PK values) to rebuild the indexes to avoid further fragmentation and bad insert performance? Please give explicit and detailed answers if you can; I am a C# developer at heart and not all too familiar with all the intricacies of SQL Server. Thanks!

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  • Filling cells with sequential numbers in an Excel (2003) macro

    - by Fred Hamilton
    I need to fill an excel column with a sequential series, in this case from -500 to 1000. I've got a macro to do it, but it takes a lot of lines for something that seems like it should be a single function [something like FillRange(A2:A1502, -500, 1000, 1)]. But if that function exists, I can't find it. Is the following as simple and elegant as it gets? 'Draw X axis scale Cells(1, 1).Value = "mV" Cells(2, 1).Value = -500 Cells(3, 1).Value = -499 Cells(4, 1).Value = -498 Dim selection1 As Range, selection2 As Range Set selection1 = Sheet1.Range("A2:A4") Set selection2 = Sheet1.Range("A2:A1502") selection1.AutoFill Destination:=selection2

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  • Maven antrun with sequential ant-contrib fails to run

    - by codevour
    We have a special routine to explode files in a subfolder into extensions, which will be copied and jared into single extension files. For this special approach I wanted to use the maven-antrun-plugin, for the sequential iteration and jar packaging through the dirset, we need the library ant-contrib. The upcoming plugin configuration fails with an error. What did I misconfigured? Thank you. Plugin configuration <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-antrun-plugin</artifactId> <version>1.6</version> <executions> <execution> <phase>validate</phase> <goals> <goal>run</goal> </goals> <configuration> <target> <for param="extension"> <path> <dirset dir="${basedir}/src/main/webapp/WEB-INF/resources/extensions/"> <include name="*" /> </dirset> </path> <sequential> <basename property="extension.name" file="${extension}" /> <echo message="Creating JAR for extension '${extension.name}'." /> <jar destfile="${basedir}/target/extension-${extension.name}-1.0.0.jar"> <zipfileset dir="${extension}" prefix="WEB-INF/resources/extensions/${extension.name}/"> <include name="**/*" /> </zipfileset> </jar> </sequential> </for> </target> </configuration> </execution> </executions> <dependencies> <dependency> <groupId>ant-contrib</groupId> <artifactId>ant-contrib</artifactId> <version>1.0b3</version> <exclusions> <exclusion> <groupId>ant</groupId> <artifactId>ant</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.apache.ant</groupId> <artifactId>ant-nodeps</artifactId> <version>1.8.1</version> </dependency> </dependencies> </plugin> Error [ERROR] Failed to execute goal org.apache.maven.plugins:maven-antrun-plugin:1.6:run (default) on project extension-platform: An Ant BuildException has occured: Problem: failed to create task or type for [ERROR] Cause: The name is undefined. [ERROR] Action: Check the spelling. [ERROR] Action: Check that any custom tasks/types have been declared. [ERROR] Action: Check that any <presetdef>/<macrodef> declarations have taken place. [ERROR] -> [Help 1] [ERROR] [ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch. [ERROR] Re-run Maven using the -X switch to enable full debug logging. [ERROR] [ERROR] For more information about the errors and possible solutions, please read the following articles: [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

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  • sequential SSH command execution not working in Ubuntu/Bash

    - by kumar
    My requirement is I will have a set of commands that needs to be executed in a text file. My Shell script has to read each command, execute and store the results in a separate file. Here is the snippet which does the above requirement. while read command do echo 'Command :' $command >> "$OUTPUT_FILE" redirect_pos=`expr index "$command" '>>'` if [ `expr index "$command" '>>'` != 0 ];then redirect_fn "$redirect_pos" "$command"; else $command state=$? if [ $state != 0 ];then echo "command failed." >> "$OUTPUT_FILE" else echo "executed successfully." >> "$OUTPUT_FILE" fi fi echo >> "$OUTPUT_FILE" done < "$INPUT_FILE" Sample Commands.txt will be like this ... tar -rvf /var/tmp/logs.tar -C /var/tmp/ Commands_log.txt gzip /var/tmp/logs.tar rm -f /var/tmp/list.txt This is working fine for commands which needs to be executed in local machine. But When I am trying to execute the following ssh commands only the 1st command getting executed. Here are the some of the ssh commands added in my text file. ssh uname@hostname1 tar -rvf /var/tmp/logs.tar -C /var/tmp/ Commands_log.txt ssh uname@hostname2 gzip /var/tmp/logs.tar ssh .. etc When I am executing this in cli it is working fine. Could anybody help me in this?

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  • Using wget to save sequential files as well as renaming the file extension

    - by Ian
    I run a cron job that requests a snapshot from a remote webcam at a local address: wget http://user:[email protected]/snapshot.cgi This creates the files snapshot.cgi, snapshot.cgi.1, snapshot.cgi.2, each time it's run. My desired result would be for the file to be named similar to file.1.jpg, file.2.jpg. Basically, sequentially or date/time named files with the correct file extension instead of .cgi. Any ideas?

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  • Parallel processing slower than sequential?

    - by zebediah49
    EDIT: For anyone who stumbles upon this in the future: Imagemagick uses a MP library. It's faster to use available cores if they're around, but if you have parallel jobs, it's unhelpful. Do one of the following: do your jobs serially (with Imagemagick in parallel mode) set MAGICK_THREAD_LIMIT=1 for your invocation of the imagemagick binary in question. By making Imagemagick use only one thread, it slows down by 20-30% in my test cases, but meant I could run one job per core without issues, for a significant net increase in performance. Original question: While converting some images using ImageMagick, I noticed a somewhat strange effect. Using xargs was significantly slower than a standard for loop. Since xargs limited to a single process should act like a for loop, I tested that, and found it to be about the same. Thus, we have this demonstration. Quad core (AMD Athalon X4, 2.6GHz) Working entirely on a tempfs (16g ram total; no swap) No other major loads Results: /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 1 convert -auto-level real 0m3.784s user 0m2.240s sys 0m0.230s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 2 convert -auto-level real 0m9.097s user 0m28.020s sys 0m0.910s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 10 convert -auto-level real 0m9.844s user 0m33.200s sys 0m1.270s Can anyone think of a reason why running two instances of this program takes more than twice as long in real time, and more than ten times as long in processor time to complete the same task? After that initial hit, more processes do not seem to have as significant of an effect. I thought it might have to do with disk seeking, so I did that test entirely in ram. Could it have something to do with how Convert works, and having more than one copy at once means it cannot use processor cache as efficiently or something? EDIT: When done with 1000x 769KB files, performance is as expected. Interesting. /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 1 convert -auto-level real 3m37.679s user 5m6.980s sys 0m6.340s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 1 convert -auto-level real 3m37.152s user 5m6.140s sys 0m6.530s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 2 convert -auto-level real 2m7.578s user 5m35.410s sys 0m6.050s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 4 convert -auto-level real 1m36.959s user 5m48.900s sys 0m6.350s /media/ramdisk/img$ time for f in *.bmp; do echo $f ${f%bmp}png; done | xargs -n 2 -P 10 convert -auto-level real 1m36.392s user 5m54.840s sys 0m5.650s

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