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  • Hashtable is that fast

    - by Costa
    Hi s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]. Is the hash function of the java string, I assume the rest of languages is similar or close to this implementation. If we have hash-Table and a list of 50 elements. each element is 7 chars ABCDEF1, ABCDEF2, ABCDEF3..... ABCDEFn If each bucket of hashtable contains 5 strings (I think this function will make it one string per bucket, but let us assume it is 5). If we call col.Contains("ABCDEFn"); // will do 6 comparisons and discover the difference on the 7th. The hash-table will take around 70 operations (multiplication and additions) to get the hashcode and to compare with 5 strings in bucket. and BANG it found. For list it will take around 300 comparisons to find it. for the case that there is only 10 elements, the list will take around 70 operations but the Hashtable will take around 50 operations. and note that hashtable operations are more time consuming (it is multiplications). I conclude that HybirdDictionary in .Net probably is the best choice for that most cases that require Hashtable with unknown size, because it will let me use a list till the list becomes more than 10 elements. still need something like HashSet rather than a Dictionary of keys and values, I wonder why there is no HybirdSet!! So what do u think? Thanks

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  • How to do some preformance testing in asp.net mvc?

    - by chobo2
    Hi I am using asp.net mvc 2.0 and I want to test how long it takes to do some of my code. In one senario I do this load xml file up. validate xml file and deserailze. validate all rows in the xml file with more advanced validation that cannot be done in the schema validation. then I do a bulk insert. I want to know how long steps 1 to 3 take and how long step 4 takes. I tried to do like DateTime.UtcNow in areas and subtract them but it told me it took like 3 seconds but I know that is not right as steps 1 to 4 take 2mins to do.

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  • Queue-like data structure with fast search and insertion

    - by Max
    I need a datastructure with the following properties: It contains integer numbers, no duplicates. After it reaches the maximal size the first element is removed. So if the capacity is 3, then this is how it would look when putting in it sequential numbers: {}, {1}, {1, 2}, {1, 2, 3}, {2, 3, 4}, {3, 4, 5} etc. Only two operations are needed: inserting a number into this container (INSERT) and checking if the number is already in the container (EXISTS). The number of EXISTS operations is expected to be approximately 2 * number of INSERT operations. I need these operations to be as fast as possible. What would be the fastest data structure or combination of data structures for this scenario?

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  • Using VirtualMode on a DataGridView when the number of rows/columns isn't known

    - by Nathan Baulch
    I need to display an unknown length sequence of dictionaries with unknown keys efficiently in a data grid. This sequence is the result of a potentially slow LINQ query that could contain any number of results. At first I thought that VirtualMode on DataGridView was what I was looking for but it appears that the number of rows and columns must be known upfront. I tried adding a single row and column then adding more as needed from the CellValueNeeded event but this doesn't work. Is this even possible with VirtualMode? Or do I need to estimate how many rows are visible on the screen and manually build up the rows/columns? And if so, how do I ensure that a vertical scrollbar is present and react appropriately when a user uses it?

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  • How to populate a listview in ASP.NET 3.5 through a dataset?

    - by EasyDot
    Is it possible to populate a listview with a dataset? I have a function that returns a dataset. Why im asking this is because my SQL is quite complicated and i can't convert it to a SQLDataSource... Public Function getMessages() As DataSet Dim dSet As DataSet = New DataSet Dim da As SqlDataAdapter Dim cmd As SqlCommand Dim SQL As StringBuilder Dim connStr As StringBuilder = New StringBuilder("") connStr.AppendFormat("server={0};", ConfigurationSettings.AppSettings("USERserver").ToString()) connStr.AppendFormat("database={0};", ConfigurationSettings.AppSettings("USERdb").ToString()) connStr.AppendFormat("uid={0};", ConfigurationSettings.AppSettings("USERuid").ToString()) connStr.AppendFormat("pwd={0};", ConfigurationSettings.AppSettings("USERpwd").ToString()) Dim conn As SqlConnection = New SqlConnection(connStr.ToString()) Try SQL = New StringBuilder cmd = New SqlCommand SQL.Append("SELECT m.MESSAGE_ID, m.SYSTEM_ID, m.DATE_CREATED, m.EXPIRE_DATE, ISNULL(s.SYSTEM_DESC,'ALL SYSTEMS') AS SYSTEM_DESC, m.MESSAGE ") SQL.Append("FROM MESSAGE m ") SQL.Append("LEFT OUTER JOIN [SYSTEM] s ") SQL.Append("ON m.SYSTEM_ID = s.SYSTEM_ID ") SQL.AppendFormat("WHERE m.SYSTEM_ID IN ({0}) ", sSystems) SQL.Append("OR m.SYSTEM_ID is NULL ") SQL.Append("ORDER BY m.DATE_CREATED DESC; ") SQL.Append("SELECT mm.MESSAGE_ID, mm.MODEL_ID, m.MODEL_DESC ") SQL.Append("FROM MESSAGE_MODEL mm ") SQL.Append("JOIN MODEL m ") SQL.Append(" ON m.MODEL_ID = mm.MODEL_ID ") cmd.CommandText = SQL.ToString cmd.Connection = conn da = New SqlDataAdapter(cmd) da.Fill(dSet) dSet.Tables(0).TableName = "BASE" dSet.Tables(1).TableName = "MODEL" Return dSet Catch ev As Exception cLog.EventLog.logError(ev, cmd) Finally 'conn.Close() End Try End Function

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  • Partitioning requests in code among several servers

    - by Jacques René Mesrine
    I have several forum servers (what they are is irrelevant) which stores posts from users and I want to be able to partition requests among these servers. I'm currently leaning towards partitioning them by geographic location. To improve the locality of data, users will be separated into regions e.g. North America, South America and so on. Is there any design pattern on how to implement the function that maps the partioning property to the server, so that this piece of code has high availability and would not become a single point of failure ? f( Region ) -> Server IP

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  • C++ & proper TDD

    - by Kotti
    Hi! I recently tried developing a small-sized project in C# and during the whole project our team used the Test-Driven-Development (TDD) technique (xunit, moq). I really think this was awesome, because (when paired with C#) this approach allowed to relax when coding, relax when projecting and relax when refactoring. I suspect that all this TDD-stuff actually simplifies the coding process and, well, it allowed (eventually, for me) to get the same result with fewer brain cells working. Right after that I tried using TDD paired with C++ (I used Google Test and Google Mock libraries), and, I don't know why but I actually think that TDD here was a step back in terms of rapid application development. I had some moments when I had to spend huge amounts of time thinking of my tests, building proper mocks, rebuilding them and swearing at my monitor. And, well, I obviously can't ask something like "what I did wrong?" or "what was wrong in my approach?", because I don't know what to describe. But if there are any people who are used to TDD in C++ (and, probably C#) too, could you please advise me how to do this properly. Framework recommendations, architecture approaches, plain coding advices - if you are experienced in TDD & C++, please respond.

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  • Which memory related Tomcat JVM startup parameters are worth tuning?

    - by knorv
    I'm trying to understand the fine art of tuning Tomcat memory settings. In this quest I have the following three questions: Which memory related JVM startup parameters are worth setting when running Tomcat? Why? What are useful rule-of-thumbs when fine-tuning the memory settings for a Tomcat installation? How do you monitor the memory consumption of your live Tomcat installation?

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  • How can I monitor the rendering time in a browser?

    - by adpd
    I work on an internal corporate system that has a web front-end as one of its interfaces. The web front-end is served up using Tomcat. How can I monitor the rendering time of specific pages in a browser (IE6)? I would like to be able to record the results in a log file (separate log file or the Tomcat access log).

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  • Migrate Data and Schema from MySQL to MSSQL

    - by colithium
    Are there any free solutions for automatically migrating a database from MySQL to MSSQL Server that "just works"? I've been attempting this simple (at least I thought so) task all day now. I've tried: MSSQL Server Management Studio's Import Data feature Create an empty database Tasks - Import Data... .NET Framework Data Provider for Odbc Valid DSN (verified it connects) Copy data from one or more tables or views Check 1 VERY simple table Click Preview Get Error: The preview data could not be retrieved. ADDITIONAL INFORMATION: ERROR [42000] [MySQL][ODBC 5.1 Driver][mysqld-5.1.45-community]You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '"table_name"' at line 1 (myodbc5.dll) A similar error occurs if I go through the rest of the wizard and perform the operation. The failed step is "Setting Source Connection" the error refers to retrieving column information and then lists the above error. It can retrieve column information just fine when I modify column mappings so I really don't know what the issue is. I've also tried getting various MySql tools to output ddl statements that MSSQL understand but haven't succeeded. I've tried with MySQL v5.1.11 to SQL Server 2005 and with MySQL v5.1.45 to SQL Server 2008 (with ODBC drivers 3.51.27.00 and 5.01.06.00 respectively)

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  • Tuning JVM (GC) for high responsive server application

    - by elgcom
    I am running an application server on Linux 64bit with 8 core CPUs and 6 GB memory. The server must be highly responsive. After some inspection I found that the application running on the server creates rather a huge amount of short-lived objects, and has only about 200~400 MB long-lived objects(as long as there is no memory leak) After reading http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html I use these JVM options -Xms2g -Xmx2g -XX:MaxPermSize=256m -XX:NewRatio=1 -XX:+UseConcMarkSweepGC Result: the minor GC takes 0.01 ~ 0.02 sec, the major GC takes 1 ~ 3 sec the minor GC happens constantly. How can I further improve or tune the JVM? larger heap size? but will it take more time for GC? larger NewSize and MaxNewSize (for young generation)? other collector? parallel GC? is it a good idea to let major GC take place more often? and how?

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  • Fastest XML parser for small, simple documents in Java

    - by Varkhan
    I have to objectify very simple and small XML documents (less than 1k, and it's almost SGML: no namespaces, plain UTF-8, you name it...), read from a stream, in Java. I am using JAXP to process the data from my stream into a Document object. I have tried Xerces, it's way too big and slow... I am using Dom4j, but I am still spending way too much time in org.dom4j.io.SAXReader. Does anybody out there have any suggestion on a faster, more efficient implementation, keeping in mind I have very tough CPU and memory constraints? [Edit 1] Keep in mind that my documents are very small, so the overhead of staring the parser can be important. For instance I am spending as much time in org.xml.sax.helpers.XMLReaderFactory.createXMLReader as in org.dom4j.io.SAXReader.read [Edit 2] The result has to be in Dom format, as I pass the document to decision tools that do arbitrary processing on it, like switching code based on the value of arbitrary XPaths, but also extracting lists of values packed as children of a predefined node. [Edit 3] In any case I eventually need to load/parse the complete document, since all the information it contains is going to be used at some point. (This question is related to, but different from, http://stackoverflow.com/questions/373833/best-xml-parser-for-java )

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  • Django: Update order attribute for objects in a queryset

    - by lazerscience
    I'm having a attribute on my model to allow the user to order the objects. I have to update the element's order depending on a list, that contains the object's ids in the new order; right now I'm iterating over the whole queryset and set one objects after the other. What would be the easiest/fastest way to do the same with the whole queryset? def update_ordering(model, order): """ order is in the form [id,id,id,id] for example: [8,4,5,1,3] """ id_to_order = dict((order[i], i) for i in range(len(order))) for x in model.objects.all(): x.order = id_to_order[x.id] x.save()

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  • Database structure for ecommerce site

    - by imanc
    Hey Guys, I have been tasked with designing an ecommerce solution. The aspect that is causing me the most problems is the database. Currently the site consists of 10+ country based shops each with their own database (all residing on the same mysql instance). For the new site I'd rather all these shop databases be merged into one database so that all tables (products, orders, customers etc.) have a shop_id field. From a programming perspective this seems to make the most sense as we won't have to manage data across multiple databases. Currently the entire site generates about 120k orders a year, but is experiencing fairly heavy growth and we need to design a solution that will scale. In 5 years there may be more than a million orders per year and a database that contains 5 years order history (archiving maybe a solution here). The question is - do we use a single database, or do we keep the database-per-shop structure? I am currently trying to find supporting evidence for either avenue. The company I am designing the solution for prefer the per-shop database structure because they believe it will allow the sites to scale. But my argument is that the shop's database probably won't get that busy over the next few years that they exceed the capacity of a mysql database and a "no expenses spared" hardware set-up. I am wondering if anyone has any advice either way? Does anyone have experience with websites / ecommerce sites that have tables containing millions of records? I know there is probably not a clear answer here, but at what stage do we have too many records or too large table files to have a fast loading site? Also, if anyone has any advice on sources of information - books, websites, etc. where I can do further research, it would be highly appreciated! Cheers, imanc

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  • Why are compilers so stupid?

    - by martinus
    I always wonder why compilers can't figure out simple things that are obvious to the human eye. They do lots of simple optimizations, but never something even a little bit complex. For example, this code takes about 6 seconds on my computer to print the value zero (using java 1.6): int x = 0; for (int i = 0; i < 100 * 1000 * 1000 * 1000; ++i) { x += x + x + x + x + x; } System.out.println(x); It is totally obvious that x is never changed so no matter how often you add 0 to itself it stays zero. So the compiler could in theory replace this with System.out.println(0). Or even better, this takes 23 seconds: public int slow() { String s = "x"; for (int i = 0; i < 100000; ++i) { s += "x"; } return 10; } First the compiler could notice that I am actually creating a string s of 100000 "x" so it could automatically use s StringBuilder instead, or even better directly replace it with the resulting string as it is always the same. Second, It does not recognize that I do not actually use the string at all, so the whole loop could be discarded! Why, after so much manpower is going into fast compilers, are they still so relatively dumb? EDIT: Of course these are stupid examples that should never be used anywhere. But whenever I have to rewrite a beautiful and very readable code into something unreadable so that the compiler is happy and produces fast code, I wonder why compilers or some other automated tool can't do this work for me.

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  • Prepending to a multi-gigabyte file.

    - by dafmetal
    What would be the most performant way to prepend a single character to a multi-gigabyte file (in my practical case, a 40GB file). There is no limitation on the implementation to do this. Meaning it can be through a tool, a shell script, a program in any programming language, ...

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  • Why does SQLite take such a long time to fetch the data?

    - by Derk
    I have two possible queries, both giving the result set I want. Query one takes about 30ms, but 150ms to fetch the data from the database. SELECT id FROM featurevalues as featval3 WHERE featval3.feature IN (?,?,?,?) AND EXISTS ( SELECT 1 FROM product_to_value, product_to_value as prod2, features, featurevalues WHERE product_to_value.feature = features.int AND product_to_value.value = featurevalues.id AND features.id = ? AND featurevalues.id IN (?,?) AND product_to_value.product = prod2.product AND prod2.value = featval3.id ) Query two takes about 3ms -this is the one I therefore prefer-, but also takes 170ms to fetch the data. SELECT ( SELECT prod2.value FROM product_to_value, product_to_value as prod2, features, featurevalues WHERE product_to_value.feature = features.int AND product_to_value.value = featurevalues.id AND features.id = ? AND featurevalues.id IN (?,?) AND product_to_value.product = prod2.product AND prod2.value = featval3.id ) as id FROM featurevalues as featval3 WHERE featval3.feature IN (?,?,?,?) The 170ms seems to be related to the number of rows from table featval3. After an index is used on featval3.feature IN (?,?,?,?), 151 items "remain" in featval3. Is there something obvious I am missing regarding the slow fetching? As far as I know everything is properly indexed.. I am confused because the second query only takes a blazing 3ms to run.

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  • Should I go with Varnish instead of nginx?

    - by gotts
    I really like nginx. But recently I've found that varnish gives you an opportunity to implement smart caching revers proxy layer(with URL purging). I have a cluster of mongrels which are pretty resource-intensive so if this caching layer can remove some load from mongrels this can be a great thing. I didn't find a way to implement the caching layer(with for application pages; static content is cacheable of course) same with nginx.. Should I use Varnish instead? What would you recommend?

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  • SSMS Tools Pack 1.9.4 is out! Now with SQL Server 2011 (Denali) CTP1 support.

    - by Mladen Prajdic
    To end the year on a good note this release adds support for SQL Server 2011 (Denali) CTP1 and fixes a few bugs. Because of the new SSMS shell in SQL 2011 CTP1 the SSMS Tools Pack 1.9.4 doesn't have regions and debug sections functionality for now. The fixed bugs are: A bug that prevented to create insert statements for a database A bug that didn't script commas as decimal points correctly for non US settings. A bug with searching through grid results. A threading bug that sometimes happened when saving Window Content History. A bug with Window Connection Coloring throwing an error on startup if a server colors was undefined. A bug with changing shortcuts in SSMS for various features. You can download the new version 1.9.4 here. Enjoy it!

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  • A GUID as the MySQL table's Primary Key or as a separate column

    - by Ben
    I have a multi-process program that performs, in a 2 hour period, 5-10 million inserts to a 34GB table within a single Master/Slave MySQL setup (plus an equal number of reads in that period). The table in question has only 5 fields and 3 (single field) indexes. The primary key is auto-incrementing. I am far from a DBA, but the database appears to be crippled during this two hour period. So, I have a couple of general questions. 1) How much bang will I get out of batching these writes into units of 10? Currently, I am writing each insert serially because, after writing, I immediately need to know, in my program, the resulting primary key of each insert. The PK is the only unique field presently and approximating the order of insertion with something like a Datetime field or a multi-column value is not acceptable. If I perform a bulk insert, I won't know these IDs, which is a problem. So, I've been thinking about turning the auto-increment primary key into a GUID and enforcing uniqueness. I've also been kicking around the idea of creating a new column just for the purposes of the GUID. I don't really see the what that achieves though, that the PK approach doesn't already offer. As far as I can tell, the big downside to making the PK a randomly generated number is that the index would take a long time to update on each insert (since insertion order would not be sequential). Is that an acceptable approach for a table that is taking this number of writes? Thanks, Ben

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  • How do I make this nested for loop, testing sums of cubes, more efficient?

    - by Brian J. Fink
    I'm trying to iterate through all the combinations of pairs of positive long integers in Java and testing the sum of their cubes to discover if it's a Fibonacci number. I'm currently doing this by using the value of the outer loop variable as the inner loop's upper limit, with the effect being that the outer loop runs a little slower each time. Initially it appeared to run very quickly--I was up to 10 digits within minutes. But now after 2 full days of continuous execution, I'm only somewhere in the middle range of 15 digits. At this rate it may end up taking a whole year just to finish running this program. The code for the program is below: import java.lang.*; import java.math.*; public class FindFib { public static void main(String args[]) { long uLimit=9223372036854775807L; //long maximum value BigDecimal PHI=new BigDecimal(1D+Math.sqrt(5D)/2D); //Golden Ratio for(long a=1;a<=uLimit;a++) //Outer Loop, 1 to maximum for(long b=1;b<=a;b++) //Inner Loop, 1 to current outer { //Cube the numbers and add BigDecimal c=BigDecimal.valueOf(a).pow(3).add(BigDecimal.valueOf(b).pow(3)); System.out.print(c+" "); //Output result //Upper and lower limits of interval for Mobius test: [c*PHI-1/c,c*PHI+1/c] BigDecimal d=c.multiply(PHI).subtract(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)), e=c.multiply(PHI).add(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)); //Mobius test: if integer in interval (floor values unequal) Fibonacci number! if (d.toBigInteger().compareTo(e.toBigInteger())!=0) System.out.println(); //Line feed else System.out.print("\r"); //Carriage return instead } //Display final message System.out.println("\rDone. "); } } Now the use of BigDecimal and BigInteger was delibrate; I need them to get the necessary precision. Is there anything other than my variable types that I could change to gain better efficiency?

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  • oprofile unable to produce call graph

    - by aaa
    hello I am trying to use oprofile to generate call graph. Compiler is g++, platform is linux x86-64, linker is gfortran C++ code is compiled with -fno- omit-frame-pointer. oprofile is started with --callgraph=25. report I run with --callgraph. the call graph is produced but it's only includes self time, which is not much use what am I missing?

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