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  • How many layers are between my program and the hardware?

    - by sub
    I somehow have the feeling that modern systems, including runtime libraries, this exception handler and that built-in debugger build up more and more layers between my (C++) programs and the CPU/rest of the hardware. I'm thinking of something like this: 1 + 2 OS top layer Runtime library/helper/error handler a hell lot of DLL modules OS kernel layer Do you really want to run 1 + 2?-Windows popup (don't take this serious) OS kernel layer Hardware abstraction Hardware Go through at least 100 miles of circuits Eventually arrive at the CPU ADD 1, 2 Go all the way back to my program Nearly all technical things are simply wrong and in some random order, but you get my point right? How much longer/shorter is this chain when I run a C++ program that calculates 1 + 2 at runtime on Windows? How about when I do this in an interpreter? (Python|Ruby|PHP) Is this chain really as dramatic in reality? Does Windows really try "not to stand in the way"? e.g.: Direct connection my binary < hardware?

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  • MySQL query cache vs caching result-sets in the application layer

    - by GetFree
    I'm running a php/mysql-driven website with a lot of visits and I'm considering the possibility of caching result-sets in shared memory in order to reduce database load. However, right now MySQL's query cache is enabled and it seems to be doing a pretty good job since if I disable query caching, the use of CPU jumps to 100% immediately. Given that situation, I dont know if caching result-sets (or even the generated HTML code) locally in shared memory with PHP will result in any noticeable performace improvement. Does anyone out there have any experience on this matter? PS: Please avoid suggesting heavy-artillery solutions like memcached. Right now I'm looking for simple solutions that dont require too much time to implement, deploy and maintain.

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  • Efficient data structure design

    - by Sway
    Hi there, I need to match a series of user inputed words against a large dictionary of words (to ensure the entered value exists). So if the user entered: "orange" it should match an entry "orange' in the dictionary. Now the catch is that the user can also enter a wildcard or series of wildcard characters like say "or__ge" which would also match "orange" The key requirements are: * this should be as fast as possible. * use the smallest amount of memory to achieve it. If the size of the word list was small I could use a string containing all the words and use regular expressions. however given that the word list could contain potentially hundreds of thousands of enteries I'm assuming this wouldn't work. So is some sort of 'tree' be the way to go for this...? Any thoughts or suggestions on this would be totally appreciated! Thanks in advance, Matt

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  • Question about Cost in Oracle Explain Plan

    - by Will
    When Oracle is estimating the 'Cost' for certain queries, does it actually look at the amount of data (rows) in a table? For example: If I'm doing a full table scan of employees for name='Bob', does it estimate the cost by counting the amount of existing rows, or is it always a set cost?

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  • JVM tuning on Amazon EC2

    - by Shadowman
    We will be deploying a production application to Amazon EC2 very shortly. Initially, we'll just be using a "small" instance, but have plans to scale up not long afterwards. My question is, has any investigation been done on JVM tuning for the EC2 environment? Are there any specific changes that we should make to our JVM parameters to compensate for quirks/characteristics of Amazon EC2? Or, do the normal tuning methodologies apply here as they would in a physical environment? Our application will be deployed on Tomcat 6.x. It is built using JBoss Seam 2.2.x, and uses PostgreSQL 8.x as the backend database. Any advice you can give is greatly appreciated!

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  • SQL indexing on varchar

    - by alex
    I have a table whose columns are varchar(50) and a float - I need to (very quickly) look get the float associated with a given string. Even with indexing, this is rather slow. I know, however, that each string is associated with an integer, which I know at the time of lookup, so that each string maps to a unique integer, but each integer does not map to a unique string. One might think of it as a tree structure. Is there anything to be gained by adding this integer to the table, indexing on it, and using a query like SELECT floatval FROM mytable WHERE phrase=givenstring AND assoc=givenint? This is Postgres, and if you couldn't tell, I have very little experience with databases.

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  • Increasing speed of webservice - howto

    - by Koran
    Hi, Our client-server product has the protocol between them as XML over HTTP. Here, the client asks a GET/POST query to the web server and the server responds with XML. The server is written using django. The server has to be on the web because there are many clients across the world using this. The server code uses extensive memoization and also there is very less db queries - most queries dont have any db queries, some of them has max 1. The biggest problem is the speed. Every query takes close to 5 seconds for the reply. The data replied is also very less - in the range of 4-6 Kb. What are the mechanisms to improve speed of the web service? Is this the usual way of writing a client-server? Are there other technologies and are we missing out on it? Thank you K

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  • Suggested (simple) approach for drawing large numbers of visual elements in WPF?

    - by Ender
    I'm writing an interface that features a large (~50000px width) "canvas"-type area that is used to display a lot of data in a fairly novel way. This involves lots of lines, rectangles, and text. The user can scroll around to explore the entire canvas. At the moment I'm just using a standard Canvas panel with various Shapes placed on it. This is nice and easy to do: construct a shape, assign some coordinates, and attach it to the Canvas. Unfortunately, it's pretty slow (to construct the children, not to do the actual rendering). I've looked into some alternatives, it's a bit intimidating. I don't need anything fancy - just the ability to efficiently construct and place objects in a coordinate plane. If all I get are lines, colored rectangles, and text, I'll be happy. Do I need Geometry instances inside of Geometry Groups inside of GeometryDrawings inside of some Panel container? Note: I'd like to include text and graphics (i.e. colored rectangles) in the same space, if possible.

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  • How to calculate real-time stats?

    - by Diego Jancic
    I have a site with millions of users (well, actually it doesn't have any yet, but let's imagine), and I want to calculate some stats like "log-ins in the past hour". The problem is similar to the one described here: http://highscalability.com/blog/2008/4/19/how-to-build-a-real-time-analytics-system.html The simplest approach would be to do a select like this: select count(distinct user_id) from logs where date>='20120601 1200' and date <='20120601 1300' (of course other conditions could apply for the stats, like log-ins per country) Of course this would be really slow, mainly if it has millions (or even thousands) of rows, and I want to query this every time a page is displayed. How would you summarize the data? What should go to the (mem)cache? EDIT: I'm looking for a way to de-normalize the data, or to keep the cache up-to-date. For example I could increment an in-memory variable every time someone logs in, but that would help to know the total amount of logins, not the "logins in the last hour". Hope it's more clear now.

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  • Where should the partitioning column go in the primary key on SQL Server?

    - by Bialecki
    Using SQL Server 2005 and 2008. I've got a potentially very large table (potentially hundreds of millions of rows) consisting of the following columns: CREATE TABLE ( date SMALLDATETIME, id BIGINT, value FLOAT ) which is being partitioned on column date in daily partitions. The question then is should the primary key be on date, id or value, id? I can imagine that SQL Server is smart enough to know that it's already partitioning on date and therefore, if I'm always querying for whole chunks of days, then I can have it second in the primary key. Or I can imagine that SQL Server will need that column to be first in the primary key to get the benefit of partitioning. Can anyone lend some insight into which way the table should be keyed?

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  • NHibernate slow mapping

    - by Rob A
    My question is what can I do to determine the cause of the slowness, or what can I do to speed it up without knowing the exact cause. I am running a simple query and it appears that the mapping back to the entities is taking taking forever. The result set is 350, which is not much data in my opinion. IRepository repo = ObjectFactory.GetInstance<IRepository>(); var q = repo.Query<Order>(item => item.Ordereddate > DateTime.Now.AddDays(-40)); foreach (var order in q) { Console.WriteLine(order.TransactionNumber); } The profiler is telling me it is executing the query 7ms / 35257ms, I am assuming that the former is the actual response from the db and the latter is the time it takes NH to do it's magic. 35 seconds is too long. This is a simple mapping, one table, nested components, using fluent interface to do mappings. I just start up a simple console app and run the one query, the slowness is measured after the SessionFactory is initialized, there should only be one session, and I am not using a transaction. Thanks

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  • Optimizing a shared buffer in a producer/consumer multithreaded environment

    - by Etan
    I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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  • [C++]Advantage of using a static member function instead of an equivalent non-static member function

    - by jonathanasdf
    I was wondering whether there's any advantages to using a static member function when there is a non-static equivalent. Will it result in faster execution (because of not having to care about all of the member variables), or maybe less use of memory (because of not being included in all instances)? Basically, the function I'm looking at is an utility function to rotate an integer array representing pixel colours an arbitrary number of degrees around an arbitrary centre point. It is placed in my abstract Bullet base class, since only the bullets will be using it and I didn't want the overhead of calling it in some utility class. It's a bit too long and used in every single derived bullet class, making it probably not a good idea to inline. How would you suggest I define this function? As a static member function of Bullet, of a non-static member function of Bullet, or maybe not as a member of Bullet but defined outside of the class in Bullet.h? What are the advantages and disadvantages of each?

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  • Is it wise to use temporary tables?

    - by Industrial
    Hi guys, We have a mySQL database table for products. We are utilizing a cache layer to reduce database load, but we think that it's a good idea to minimize the actual data needed to be stored in the cache layer to speed up the application further. All the products in the database, that is visible to visitors have a price attached to them: The prices are stored in a different table, called prices . There are multiple price categories depending on which discount level each visitor (customer) applies to. From time to time, there are campaigns which means that a special price for each product is available. The special prices are stored in a table called specials. Is it a bad to make a temp table that binds the tables together? It would only have the neccessary information and would ofcourse be cached. -------------|-------------|------------ | productId | hasPrice | hasSpecial -------------|-------------|------------ 1 | 1 | 0 2 | 1 | 1 By doing such, it would be super easy to know if the specific product really has a price, without having to iterate through the complete prices or specials table each time a product should be listed or presented. Are temp tables a common thing for web applications or is it just bad design?

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  • How to recognize what indexes are not used?

    - by tomaszs
    I have a table in MySQL with 7 indexes, most of them are on more than one column. I think here is too much indexes. Is there any way to get statistics of what indexes are used more by all thousands of queries to this database and what are less worthy so I know what index to consider to remove in first place?

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  • mysql query building output taking a long time

    - by user121196
    I have a simple query that does select * from t limit 1; on a remote mysql server. I use squirrel(mysql client) to run it, it shows: Query 1 of 1 elapsed time (seconds) - Total: 22.047, SQL query: 1.047, Building output: 21 why does building output take such a long time? what does this process do? when running from mysql command line, the whole process takes 0.3 secs (also remotely)

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  • comparing two cursors in oracle instead of using MINUS

    - by Omnipresent
    The following query takes more than 3 minutes to run because tables contain massive amounts of data: SELECT RTRIM(LTRIM(A.HEAD)), A.EFFECTIVE_DATE, FROM TABLE_1 A WHERE A.TYPE_OF_ACTION='6' AND A.EFFECTIVE_DATE >= ADD_MONTHS(SYSDATE,-15) MINUS SELECT RTRIM(LTRIM(B.head)), B.EFFECTIVE_DATE, FROM TABLE_2 B In our system a query gets killed if it is running for more than 8 seconds. Is there a way to run the queries individually ..put them in cursors..compare and then get the results? that way each query will be ran individually rather than as one massive query which takes 3 minutes. How would two cursors be compared to mimic the MINUS?

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  • Hitting a memory limit slows down the .Net application

    - by derdo
    We have a 64bit C#/.Net3.0 application that runs on a 64bit Windows server. From time to time the app can use large amount of memory which is available. In some instances the application stops allocating additional memory and slows down significantly (500+ times slower).When I check the memory from the task manager the amount of the memory used barely changes. The application keeps on running very slowly and never gives an out of memory exception. Any ideas? Let me know if more data is needed.

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  • Flash causing jerky javascript animations

    - by Matt Brailsford
    Hi Guys, I'm developing a site which has a flash background playing a small video loop scaled to fill the whole background. Over the top I have a number of HTML elements which are animated using javascript. The problem I am having is that (predominantly in FF, but also in others to a lesser degree) the flash seems to be causing my javascript animations to run rather jerky, and in some cases missing the animation altogether and just jumping to the end state. Does anybody have any thoughts on how to make the 2 work together nicely? Many thanks Matt

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  • ASP.NET How expensive is it to call an Application Variable many times?

    - by Matias Nino
    The short of it is: Is it costly to check an Application Variable such as Application("WebAppName") more 10-20 times each time a page loads? Background: (feel free to critique) Some includes in my site contain many links and images which cannot use relative urls due to their inclusion in different paths. Hence these includes contain frequent instances of <img src="<%=Application("Webroot")%>images\image.gif"> Is it expensive to keep calling an Application variable like this? Should I just put the Application value in some local variable to use where needed? IMPORTANT NOTE: I need my webapp to run fine on a server whether it be in the root web ("/") or in a virtual subweb ("/app"). Thanks in advance for any wisdom shared.

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  • Why does dojo parsing time depend on css and images availability?

    - by Kniganapolke
    I have been profiling javascript on my page that uses dojo widgets. I don't use explicit parsing - the parser runs on page load. What I noticed is that if I clear browser cache before refreshing the page, dojo parsing takes much more time than if all the files are already cached. Note that we build all the required dojo modules into a layer (a single file), so we don't lazy-load any js files. I wonder if dojo parsing process depends on images and css resources, as far as I know it only instantiates widgets and injects dom nodes. Do you have any ideas why dojo parser runs longer (2-3 times longer in my case) when the cache is cleared?

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