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  • List of divisors of an integer n (Haskell)

    - by Code-Guru
    I currently have the following function to get the divisors of an integer: -- All divisors of a number divisors :: Integer -> [Integer] divisors 1 = [1] divisors n = firstHalf ++ secondHalf where firstHalf = filter (divides n) (candidates n) secondHalf = filter (\d -> n `div` d /= d) (map (n `div`) (reverse firstHalf)) candidates n = takeWhile (\d -> d * d <= n) [1..n] I ended up adding the filter to secondHalf because a divisor was repeating when n is a square of a prime number. This seems like a very inefficient way to solve this problem. So I have two questions: How do I measure if this really is a bottle neck in my algorithm? And if it is, how do I go about finding a better way to avoid repetitions when n is a square of a prime?

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  • Slow query with unexpected scan

    - by zerkms
    Hello I have this query: SELECT * FROM SAMPLE SAMPLE INNER JOIN TEST TEST ON SAMPLE.SAMPLE_NUMBER = TEST.SAMPLE_NUMBER INNER JOIN RESULT RESULT ON TEST.TEST_NUMBER = RESULT . TEST_NUMBER WHERE SAMPLED_DATE BETWEEN '2010-03-17 09:00' AND '2010-03-17 12:00' the biggest table here is RESULT, contains 11.1M records. The left 2 tables about 1M. this query works slowly (more than 10 minutes) and returns about 800 records. executing plan shows clustered index scan over all 11M records. RESULT.TEST_NUMBER is a clustered primary key. if I change 2010-03-17 09:00 to 2010-03-17 10:00 - i get about 40 records. it executes for 300ms. and plan shows clustered index seek if i replace * in SELECT clause to RESULT.TEST_NUMBER (covered with index) - then all become fast in first case too. this points to hdd io issues, but doesn't clarifies changing plan. so, any ideas?

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  • Quickest way to compare a bunch of array or list of values.

    - by zapping
    Can you please let me know on the quickest and efficient way to compare a large set of values. Its like there are a list of parent codes(string) and each code has a series of child values(string). The child lists have to be compared with each other and find out duplicates and count how many times they repeat. code1(code1_value1, code1_value2, code3_value3, ..., code1_valueN); code2(code2_value1, code1_value2, code2_value3, ..., code2_valueN); code3(code2_value1, code3_value2, code3_value3, ..., code3_valueN); . . . codeN(codeN_value1, codeN_value2, codeN_value3, ..., codeN_valueN); The lists are huge say like there are 100 parent codes and each has about 250 values in them. There will not be duplicates within a code list. Doing it in java and the solution i could figure out is. Store the values of first set of code in as codeMap.put(codeValue, duplicateCount). The count initialized to 0. Then compare the rest of the values with this. If its in the map then increment the count otherwise append it to the map. The downfall of this is to get the duplicates. Another iteration needs to be performed on a very large list. An alternative is to maintain another hashmap for duplicates like duplicateCodeMap.put(codeValue, duplicateCount) and change the initial hashmap to codeMap.put(codeValue, codeValue). Speed is what is requirement. Hope one of you can help me with it.

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  • Time to start a counter on client-side.

    - by Felipe
    Hi everybody, I'm developing an web application using asp.net mvc, and i need to do a stopwatch (chronometer) (with 30 seconds preprogrammed to start in a certain moment) on client-side using the time of the server, by the way, the client's clock can't be as the server's clock. So, i'm using Jquery to call the server by JSon and get the time, but it's very stress because each one second I call the server to get time, something like this: $(function() { GetTimeByServer(); }); function GetTimeByServer() { $.getJSon('/Home/Time', null, function(result) { if (result.SecondsPending < 30) { // call another function to start an chronometer } else { window.SetTimeout(GetTimeByServer, 1000); //call again each 1 second! } }); } It works fine, but when I have more than 3 or 4 call like this, the browser slowly but works! I'd like to know, how improve more performace in client side, or if is there any way to do this... is there any way to client listen the server like a "socket" to know if the chronometer should start... PS: Sorry for my english! thanks Cheers

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  • Windows Workflow runs very slowlyh on my DEV machine

    - by Joon
    I am developing an app using WF hosted in IIS as WCF services as a business layer. This runs quickly on any machine running Windows Server 2008 R2, but very slowly on our dev machines, running Windows XP SP3. Yesterday, the workflows were as fast on my dev machine as they are on the server for the whole day. Today, they are back to running slowly again (I rebooted overnight) Has anyone else experienced this problem with workflows running slowly on IIS in XP? What did you do to fix it?

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  • Best practice for handling memory leaks in large Java projects?

    - by knorv
    In almost all larger Java projects I've been involved with I've noticed that the quality of service of the application degrades with the uptime of the container. This is most probably due to memory leaks in the code. The correct way to solve this problem is obviously to trace back to the root cause of the problem and fix the leaks in the code. The quick and dirty way of solving the problem is simply restarting Tomcat (or whichever servlet container you're using). These are my three questions: Assume that you choose to solve the problem by tracing the root cause of the problem (the memory leaks), how would you collect data to zoom in on the problem? Assume that you choose the quick and dirty way of speeding things up by simply restarting the container, how would you collect data to choose the optimal restart cycle? Have you been able to deploy and run projects over an extended period of time without ever restarting the servlet container to regain snappiness? Or is an occasional servlet restart something that one has to simply accept?

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  • How to clear APC cache entries?

    - by lo_fye
    I need to clear all APC cache entries when I deploy a new version of the site. APC.php has a button for clearing all opcode caches, but I don't see buttons for clearing all User Entries, or all System Entries, or all Per-Directory Entries. Is it possible to clear all cache entries via the command-line, or some other way?

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  • Spring Web application internal visual monitoring heap space and permgen.

    - by Veniamin
    If I have created web application used Spring framework(based on maven), can I include some module/dependency/plugin into my app to monitor Heap space, Permgen, etc. It whould be greate to get some charts output likes as in VisuaVM. For example: http://localhost:8080/monitoring = Including something likes VisualVM I have found next dependency without link to repo: <dependency> <groupId>com.sun.tools.visualvm</groupId> <artifactId>core</artifactId> <version>1.3.3</version> </dependency> How to use it?

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  • How to increase query speed without using full-text search?

    - by andre matos
    This is my simple query; By searching selectnothing I'm sure I'll have no hits. SELECT nome_t FROM myTable WHERE nome_t ILIKE '%selectnothing%'; This is the EXPLAIN ANALYZE VERBOSE Seq Scan on myTable (cost=0.00..15259.04 rows=37 width=29) (actual time=2153.061..2153.061 rows=0 loops=1) Output: nome_t Filter: (nome_t ~~* '%selectnothing%'::text) Total runtime: 2153.116 ms myTable has around 350k rows and the table definition is something like: CREATE TABLE myTable ( nome_t text NOT NULL, ) I have an index on nome_t as stated below: CREATE INDEX idx_m_nome_t ON myTable USING btree (nome_t); Although this is clearly a good candidate for Fulltext search I would like to rule that option out for now. This query is meant to be run from a web application and currently it's taking around 2 seconds which is obviously too much; Is there anything I can do, like using other index methods, to improve the speed of this query?

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  • Time complexity O() of isPalindrome()

    - by Aran
    I have this method, isPalindrome(), and I am trying to find the time complexity of it, and also rewrite the code more efficiently. boolean isPalindrome(String s) { boolean bP = true; for(int i=0; i<s.length(); i++) { if(s.charAt(i) != s.charAt(s.length()-i-1)) { bP = false; } } return bP; } Now I know this code checks the string's characters to see whether it is the same as the one before it and if it is then it doesn't change bP. And I think I know that the operations are s.length(), s.charAt(i) and s.charAt(s.length()-i-!)). Making the time-complexity O(N + 3), I think? This correct, if not what is it and how is that figured out. Also to make this more efficient, would it be good to store the character in temporary strings?

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  • Why does Go compile quickly?

    - by Evan Kroske
    I've Googled and poked around the Go website, but I can't seem to find an explanation for Go's extraordinary build times. Are they products of the language features (or lack thereof), a highly optimized compiler, or something else? I'm not trying to promote Go; I'm just curious.

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  • percentage of memory used used by a process

    - by benjamin button
    percentage of memory used used by a process. normally prstat -J will give the memory of process image and RSS(resident set size) etc. how do i knowlist of processes with percentage of memory is used by a each process. i am working on solaris unix. addintionally ,what are the regular commands that you use for monitoring processes,performences of processes that might be very useful to all!

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  • Scalable way of doing self join with many to many table

    - by johnathan
    I have a table structure like the following: user id name profile_stat id name profile_stat_value id name user_profile user_id profile_stat_id profile_stat_value_id My question is: How do I evaluate a query where I want to find all users with profile_stat_id and profile_stat_value_id for many stats? I've tried doing an inner self join, but that quickly gets crazy when searching for many stats. I've also tried doing a count on the actual user_profile table, and that's much better, but still slow. Is there some magic I'm missing? I have about 10 million rows in the user_profile table and want the query to take no longer than a few seconds. Is that possible?

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  • How can I most accurately calculate the execution time of an ASP.NET page while also displaying it o

    - by henningst
    I want to calculate the execution time of my ASP.NET pages and display it on the page. Currently I'm calculating the execution time using a System.Diagnostics.Stopwatch and then store the value in a log database. The stopwatch is started in OnInit and stopped in OnPreRenderComplete. This seems to be working quite fine, and it's giving a similar execution time as the one shown in the page trace. The problem now is that I'm not able to display the execution time on the page because the stopwatch is stopped too late in the life cycle. What is the best way to do this?

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  • Is Java serialization a tool to shrink the memory footprint?

    - by Pentius
    Hey folks, does serialization in Java always have to shrink the memory that is used to hold an object structure? Or is it likely that serialization will have higher costs? In other words: Is serialization a tool to shrink the memory footprint of object structures in Java? Edit I'm totally aware of what serialization was intended for, but thanks anyway :-) But you know, tools can be misused. My question is, whether it is a good tool to decrease the memory usage. So what reasons can you imagine, why memory usage should increase/decrease? What will happen in most cases?

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  • Cache layer for MVC - Model or controller?

    - by Industrial
    Hi everyone, I am having some second thoughts about where to implement the caching part. Where is the most appropriate place to implement it, you think? Inside every model, or in the controller? Approach 1 (psuedo-code): // mycontroller.php MyController extends Controller_class { function index () { $data = $this->model->getData(); echo $data; } } // myModel.php MyModel extends Model_Class{ function getData() { $data = memcached->get('data'); if (!$data) { $query->SQL_QUERY("Do query!"); } return $data; } } Approach 2: // mycontroller.php MyController extends Controller_class { function index () { $dataArray = $this->memcached->getMulti('data','data2'); foreach ($dataArray as $key) { if (!$key) { $data = $this->model->getData(); $this->memcached->set($key, $data); } } echo $data; } } // myModel.php MyModel extends Model_Class{ function getData() { $query->SQL_QUERY("Do query!"); return $data; } } Thoughts: Approach 1: No multiget/multi-set. If a high number of keys would be returned, overhead would be caused. Easier to maintain, all database/cache handling is in each model Approach 2: Better performancewise - multiset/multiget is used More code required Harder to maintain Tell me what you think!

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  • mySQL & Relational databases: How to handle sharding/splitting on application level?

    - by Industrial
    Hi everybody, I have thought a bit about sharding tables, since partitioning cannot be done with foreign keys in a mySQL table. Maybe there's an option to switch to a different relational database that features both, but I don't see that as an option right now. So, the sharding idea seems like a pretty decent thing. But, what's a good approach to do this on a application level? I am guessing that a take-off point would be to prefix tables with a max value for the primary key in each table. Something like products_4000000 , products_8000000 and products_12000000. Then the application would have to check with a simple if-statement the size of the id (PK) that will be requested is smaller then four, eight or twelve million before doing any actual database calls. So, is this a step in the right direction or are we doing something really stupid?

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  • NetNamedPipe: varying response time when communication is idling

    - by Sven Künzler
    I have two WCF apps communicating one-way over named pipes. All is nice, except for one thing: Normally, the request/response cycle takes zero (marginal) time. However, if there was a time span of, say, half a minute without any communication, the request/response increases up to ~300-500ms. I looked around the net and I got the idea of using a heart beat/ping mechanism to keep the communication channel busy. Using trial and error I found that when doing a request each 10 seconds, the response times stay low. Starting at around 15s intervals, the "hiccup" response times begin to appear. Now I'm wondering where this phenomenon is originating from. I tried setting alle conceivable timeouts on both sides to 1 minute, but that did not help. Can anybody explain what's going on there?

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  • MySQL Single Query Benchmarking Strategies

    - by Pepper
    Hello, I have a slow mySQL query in my application that I need to re-write. The problem is, it's only slow on my production server and only when it's not cached. The first time I run it, it will take 12 seconds, then anytime after that it'll be 500 milliseconds. Is there an easy way to test this query without it hitting the query cache so I can see the results of my refactoring? Thanks!

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  • Python Speeding Up Retrieving data from extremely large string

    - by Burninghelix123
    I have a list I converted to a very very long string as I am trying to edit it, as you can gather it's called tempString. It works as of now it just takes way to long to operate, probably because it is several different regex subs. They are as follow: tempString = ','.join(str(n) for n in coords) tempString = re.sub(',{2,6}', '_', tempString) tempString = re.sub("[^0-9\-\.\_]", ",", tempString) tempString = re.sub(',+', ',', tempString) clean1 = re.findall(('[-+]?[0-9]*\.?[0-9]+,[-+]?[0-9]*\.?[0-9]+,' '[-+]?[0-9]*\.?[0-9]+'), tempString) tempString = '_'.join(str(n) for n in clean1) tempString = re.sub(',', ' ', tempString) Basically it's a long string containing commas and about 1-5 million sets of 4 floats/ints (mixture of both possible),: -5.65500020981,6.88999986649,-0.454999923706,1,,,-5.65500020981,6.95499992371,-0.454999923706,1,,, The 4th number in each set I don't need/want, i'm essentially just trying to split the string into a list with 3 floats in each separated by a space. The above code works flawlessly but as you can imagine is quite time consuming on large strings. I have done a lot of research on here for a solution but they all seem geared towards words, i.e. swapping out one word for another. EDIT: Ok so this is the solution i'm currently using: def getValues(s): output = [] while s: # get the three values you want, discard the 3 commas, and the # remainder of the string v1, v2, v3, _, _, _, s = s.split(',', 6) output.append("%s %s %s" % (v1.strip(), v2.strip(), v3.strip())) return output coords = getValues(tempString) Anyone have any advice to speed this up even farther? After running some tests It still takes much longer than i'm hoping for. I've been glancing at numPy, but I honestly have absolutely no idea how to the above with it, I understand that after the above has been done and the values are cleaned up i could use them more efficiently with numPy, but not sure how NumPy could apply to the above. The above to clean through 50k sets takes around 20 minutes, I cant imagine how long it would be on my full string of 1 million sets. I'ts just surprising that the program that originally exported the data took only around 30 secs for the 1 million sets

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  • Better to combine & minify javascript or use Google CDN?

    - by jessegavin
    I am building a site which currently uses javascript from several sources: Group 1: Google Maps API v3 (hosted by Google) Group 2: jQuery & swfobject (hosted on Google CDN) Group 3: Several jQuery plugins and non-jquery javascript files (hosted on my server) I am using Justin Etheredge's tool SquishIt to combine and minify all the javascript files that are hosted on my server (group 3). I am wondering if the site would 'feel' faster to users if I were to host the files in (group 2) locally so that they can be combined with all the other files in (group 3) and requiring only one HTTP request for groups 2 & 3. This would mean that I don't get the benefits of the Google CDN however. Does anyone have any advice on this matter?

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