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• Best way to daemonize Java application on Linux

  - by SyBer

  Hi. While I found this question being answered here on SW several times, I didn't find a concluding answer what is the best approach. I'm not looking to use any external wrapper, as I found them launching the java process under a nice level lower then themselves which potentially lowers the performance, so it seems only the shell methods are left. I so far found 3 different shell methods: start-stop-daemon RedHat daemon init.d function nohup on start / disown after start What you people are using, and can recommend as the most reliable method? Thanks.

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• Validating Column Data Stored as CSV Against Another Table

  - by Jakkwylde

  I wanted to see what some suggested approaches would be to validate a field that is stored as a CSV against a table containing appropriate values. Althought it would be desired, it is NOT an option to split the CSV list into another related table. In the example data below I would be trying to capture the code 99 for widget A. Below is an example data representation. Table: Widgets WidgetName WidgetCodeList A 1, 2, 3 B 1 C 2, 3 D 99 Table: WidgetCodes WidgetCode 1 2 3 An earlier approach was to query the CSV column as rows using various string manipulations and CONNECT_BY_LEVEL however the performance was not acceptible.

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• NSMutableSet addObject question

  - by Jacob Relkin

  I've got a class that wraps around an NSMutableSet object, and I have an instance method that adds objects (using the addObject: method) to the NSMutableSet. This works well, but I'm smelling a performance hitch because inside the method i'm explicitly calling containsObject: before adding the object to the set. Three part question: Do I need to be calling containsObject: before I add an object to the set? If so, then what actual method should I be using, containsObject or containsObjectIdenticalTo:? If that is not so, what contains method gets invoked under the hood of addObject:? This is important to me because if I pass an object to containsObject: it would return true, but if I pass it to containsObjectIdenticalTo: it would return false.

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• Why are gettimeofday() intervals occasionally negative?

  - by Andres Jaan Tack

  I have an experimental library whose performance I'm trying to measure. To do this, I've written the following: struct timeval begin; gettimeofday(&begin, NULL); { // Experiment! } struct timeval end; gettimeofday(&end, NULL); // Print the time it took! std::cout << "Time: " << 100000 * (end.tv_sec - begin.tv_sec) + (end.tv_usec - begin.tv_usec) << std::endl; Occasionally, my results include negative timings, some of which are nonsensical. For instance: Time: 226762 Time: 220222 Time: 210883 Time: -688976 What's going on?

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• How to implement a mailing system with Rails that sends emails in the background

  - by Tam

  I want to implement a reliable mailing system with Ruby on Rails that sends emails in the background as sending email sometimes takes like 10 seconds or more so I don't want the user to wait. Some ideas I thought of: 1- Write to a table in DB a have a background process that go over and send email (concern: potential many reads/writes to DB slows down my application) 2- Messaging Queue background process / Rake task (concern: if server crashes queued mails will be lost also might eat up a lot of memory if many emails) I was wondering if you a know of a good solution that provides a balance between reliability and performance.

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• Is there such a thing as too many tables?

  - by Stacey

  I've been searching stackoverflow for about an hour now and couldn't find any topics related, so I apologize if this is a duplicate question. My inquery is this. Is there a point at which there are too many tables in a database? Even if the structure is well organized, thought out, and perfectly facilitates the design intent? I have a database that is quickly approaching 40 tables - about 10 main ones, and over 30 ancillary tables (junction tables, 'enumeration' tables, etc). Am I just a bad developer - or should I be trying something different? It seems like so many to me, I'm really afraid at how it will impact the performance of the project. I have done a lot of condensing where possible, grouped similar things where possible, etc. The database is built in MS-SQL 2008.

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• Why don't scripting languages output Unicode to the Windows console?

  - by hippietrail

  The Windows console has been Unicode aware for at least a decade and perhaps as far back as Windows NT. However for some reason the major cross-platform scripting languages including Perl and Python only ever output various 8-bit encodings, requiring much trouble to work around. Perl gives a "wide character in print" warning, Pythong gives a charmap error and quits. Why on earth after all these years do they not just simply call the Win32 -W APIs that output UTF-16 Unicode instead of forcing everything through the ANSI/codepage bottleneck? Is it just that cross-platform performance is low priority? Is it that the languages use UTF-8 internally and find it too much bother to output UTF-16? Or are the -W APIs inherently broken to such a degree that they can't be used as-is?

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• Self-Configuring Classes W/ Command Line Args: Pattern or Anti-Pattern?

  - by dsimcha

  I've got a program where a lot of classes have really complicated configuration requirements. I've adopted the pattern of decentralizing the configuration and allowing each class to take and parse the command line/configuration file arguments in its c'tor and do whatever it needs with them. (These are very coarse-grained classes that are only instantiated a few times, so there is absolutely no performance issue here.) This avoids having to do shotgun surgery to plumb new options I add through all the levels they need to be passed through. It also avoids having to specify each configuration option in multiple places (where it's parsed and where it's used). What are some advantages/disadvantages of this style of programming? It seems to reduce separation of concerns in that every class is now doing configuration stuff, and to make programs less self-documenting because what parameters a class takes becomes less explicit. OTOH, it seems to increase encapsulation in that it makes each class more self-contained because no other part of the program needs to know exactly what configuration parameters a class might need.

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• How to implement square root and exponentiation on arbitrary length numbers?

  - by tomp

  I'm working on new data type for arbitrary length numbers (only non-negative integers) and I got stuck at implementing square root and exponentiation functions (only for natural exponents). Please help. I store the arbitrary length number as a string, so all operations are made char by char. Please don't include advices to use different (existing) library or other way to store the number than string. It's meant to be a programming exercise, not a real-world application, so optimization and performance are not so necessary. If you include code in your answer, I would prefer it to be in either pseudo-code or in C++. The important thing is the algorithm, not the implementation itself. Thanks for the help.

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• Google App Engine - Dealing with concurrency issues of storing an object

  - by Spines

  My User object that I want to create and store in the datastore has an email, and a username. How do I make sure when creating my User object that another User object doesn't also have either the same email or the same username? If I just do a query to see if any other users have already used the username or the email, then there could be a race condition. UPDATE: The solution I'm currently considering is to use the MemCache to implement a locking mechanism. I would acquire 2 locks before trying to store the User object in the datastore. First a lock that locks based on email, then another that locks based on username. Since creating new User objects only happens at user registration time, and it's even rarer that two people try to use either the same username or the same email, I think it's okay to take the performance hit of locking. I'm thinking of using the MemCache locking code that is here: http://appengine-cookbook.appspot.com/recipe/mutex-using-memcache-api/ What do you guys think?

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• Which is the best API/Library to use when accessing a WebCam in .Net?

  - by Doctor Jones

  Which is the best API to use when accessing a WebCam in .Net? (I know they can be webcam specific, I am willing to buy a new webcam if it means better results). I want to write a desktop application that will take video from a webcam and store it in MPEG4 formats (DivX, Xvid, etc...). I would also like to access bitmap stills from the device so I can do image comparison between frames. I have tried various libraries, and none have really been a great fit (some have performance issues (very inconsistent framerates), some have image quality limitations, some just crash out for seemingly no reason. I want to get high quality video (as high as I can get) and a decent framerate. My webcam is more than up to the job and I was hoping that there would be a nice Managed .Net library around that would help my cause. Are webcam APIs all just incredibly bad?

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• Tips for a successful AppStore submission?

  - by Andrew Grant

  In a day or two I'll be ready to submit my iPhone app to the AppStore and I'm curious whether people who have gone through this process have any tips / suggestions for a smooth submission process. Here's things I've covered; No memory leaks Tested performance on an actual device Doesn't crash :) Using correct certificates / profile What I'm a little unsure about are how to configure the "Bundle Display Name" /"Bundle Identifier" and "Bundle Name" in info.plist. I understand the first is the text that's shown on the iPhone itself, but what about the last? Does this have to match Bundle Identifier? Are there any other things I should add to the info.plist? I've noticed that when built for Adhoc distribution my app does not have any author/title information in iTunes.

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• Count of memory copies in *nix systems between packet at NIC and user application?

  - by Michael_73

  Hi there, This is just a general question relating to some high-performance computing I've been wondering about. A certain low-latency messaging vendor speaks in its supporting documentation about using raw sockets to transfer the data directly from the network device to the user application and in so doing it speaks about reducing the messaging latency even further than it does anyway (in other admittedly carefully thought-out design decisions). My question is therefore to those that grok the networking stacks on Unix or Unix-like systems. How much difference are they likely to be able to realise using this method? Feel free to answer in terms of memory copies, numbers of whales rescued or areas the size of Wales ;) Their messaging is UDP-based, as I understand it, so there's no problem with establishing TCP connections etc. Any other points of interest on this topic would be gratefully thought about! Best wishes, Mike

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• postgres SQL - pg_class question

  - by Sachin Chourasiya

  PostgreSQL stores statistics about tables in the system table called pg_class. The query planner accesses this table for every query. These statistics may only be updated using the analyze command. If the analyze command is not run often, the statistics in this table may not be accurate and the query planner may make poor decisions which can degrade system performance. Another strategy is for the query planner to generate these statistics for each query (including selects, inserts, updates, and deletes). This approach would allow the query planner to have the most up-to-date statistics possible. Why postgres always rely on pg_class instead?

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• A linq join combined with a regex

  - by Geert Beckx

  Is it possible to combine these 2 queries or would this make my code too complex? Also I think there should be a performance gain by combining these queries since I think in the near future my source table could be over 11000 records. This is what i came up with so far : Dim lit As LiteralControl ' check characters not in alphabet Dim r As New Regex("^[^a-zA-Z]+") Dim query = From o In source.ToTable _ Where r.IsMatch(o.Field(Of String)("nam")) lit = New LiteralControl(String.Format("letter: {0}, count: {1}<br />", "0-9", query.Count)) plhAlpabetLinks.Controls.Add(lit) Dim q = From l In "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToLower.ToCharArray _ Group Join o In source.ToTable _ On l Equals o.Field(Of String)("nam").ToLowerInvariant(0) Into g = Group _ Select l, g.Count ' iterate the alphabet to generate all the links. For Each letter In q.AsEnumerable lit = New LiteralControl(String.Format("letter: {0}, count: {1}<br />", letter.l, letter.Count)) plhAlpabetLinks.Controls.Add(lit) Next Kind regards, G.

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• Element point map for html5 canvas element, need algorithm

  - by Artiom Chilaru

  I'm currently working on a pure html 5 canvas implementation of the "flying tag cloud sphere", which many of you have undoubtedly seen as a flash object in some pages. The tags are drawn fine, and the performance is satisfactory, but there's one thing in the canvas element that's kind of breaking this idea: you can't identify the objects that you've drawn on a canvas, as it's just a simple flat "image".. What I have to do in this case is catch the click event, and try to "guess" which element was clicked. So I have to have some kind of matrix, which stores a link to a tag object for each pixel on the canvas, AND I have to update this matrix on every redraw. Now this sounds incredibly inefficient, and before I even start trying to implement this, I want to ask the community - is there some "well known" algorithm that would help me in this case? Or maybe I'm just missing something, and the answer is right behind the corner? :)

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• BDD-testing using a UI driver (e.g. Selenium for a web-application)

  - by jonathanconway

  Can BDD (Behavior Driven Design) tests be implemented using a UI driver? For example, given a web application, instead of: Writing tests for the back-end, and then more tests in Javascript for the front-end Should I: Write the tests as Selenium macros, which simulate mouse-clicks, etc in the actual browser? The advantages I see in doing it this way are: The tests are written in one language, rather than several They're focussed on the UI, which gets developers thinking outside-in They run in the real execution environment (the browser), which allows us to Test different browsers Test different servers Get insight into real-world performance Thoughts?

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• How can I configure different worker pools using celery?

  - by Chris R

  I need to deploy a queued execution service with (generally) the following three classes of worker: A periodic, low-priority job class that takes a long time and can be processed serially; these jobs should only use 0..2 workers in the system at most. A periodic, deadline-sensitive job class that take a short to medium amount of time (say, topping out at 5 minutes) An ad-hoc job class, that is higher priority than #1, but can interleave with #2. Any workers from class #2 that are inactive when this type of job comes in should handle it, without ever starving the pool of workers for #2 All three job classes are the same task, the only difference between them is how they're requested; they'll take the same input and generate the same output, but each one has different performance guarantees. How can I implement this using celery?

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• Should I use a hosted version of JQuery? Which one?

  - by ataylor

  Should I use a local copy of jquery, or should I link to a copy provided by Google or Microsoft? I'm primarily concerned about speed. I've heard that just pulling content from other domains can have performance advantages related to how browsers limit connections. In particular, has anyone benchmarked the speed and latency of Google vs. Microsoft vs. local? Also, do I have to agree to any conditions or licenses to link from a third-party?

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• How can I measure TForm deserialization time in Delphi?

  - by mjustin

  For performance tests I need a way to measure the time needed for a form to load its definition from the DFM. All existing forms inherit a custom form class. To capture the current time, this base class needs overriden methods as "extension points": before the beginning of the deserialization process after the completion of deserialization (can be implemented by overriding the Loaded procedure) the moment just before the execution of the OnFormCreate event Which TObject (or TComponent) methods are best suited? Maybe there are other extension points in the form creation process, please feel free to make suggestions.

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• Should we use a CSS frame work ? Are they worth it ?

  - by Gaurav M

  CSS frameworks have nice styles inbuilt and ask you to focuses on the grids but still there is a bit of dependency and lack of freedom it provide.. If I need to generate a webpage by looking on a PSD based mockup screen ..either i will use the classes provided by the framework but if that actual measurements does not exist I need to again specify my own rules that will add upto my CSS filesize and if performance is a constraint as always it is...you need not a big size file..though its in kb but every drop counts. Any comments and suggestions to use the framework in a best possible way.

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• How do I calculate a good hash code for a list of strings?

  - by Ian Ringrose

  Background: I have a short list of strings. The number of strings is not always the same, but are nearly always of the order of a “handful” In our database will store these strings in a 2nd normalised table These strings are never changed once they are written to the database. We wish to be able to match on these strings quickly in a query without the performance hit of doing lots of joins. So I am thinking of storing a hash code of all these strings in the main table and including it in our index, so the joins are only processed by the database when the hash code matches. So how do I get a good hashcode? I could: Xor the hash codes of all the string together Xor with multiply the result after each string (say by 31) Cat all the string together then get the hashcode Some other way So what do people think? (If you care we are using .NET and SqlServer)

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• data between pages: $_SESSION vs. $_GET ?

  - by Haroldo

  Ok, firstly this is not about forms this is about consistent layout as a user explores a site. let me explain: If we imagine a (non-ajax) digital camera online store, say someone was on the DSLR section and specified to view the cameras in Gallery mode and order by price. They then click onto the Compact camera's page. It would be in the users interests if the 'views' they selected we're carried over to this new page. Now, i'd say use a session - am i wrong? are there performance issues i should be aware of for a few small session vars ( ie view=1 , orderby=price) ?

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• How do I view how many concurrent long polling requests there are on my server?

  - by Pascal

  My host is Joyent. My host says I have 15 process limit and prstat -J shows those processes but that doesn't tell me how many long polling requests are currently being served. I could record it myself but that would add alot of performance overhead. I need to know when the server is at its long polling limits. I know this limit occurs far before the memory or CPU is used up. From experimentation, I've already verified that the number of long polls open is NOT equivalant to the number of processes running, probably because each process has multiple threads, each serving a request. thanks.

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• Is the web hosting location important these days?

  - by kristof

  I was recently looking at some web hosting solutions and some of the providers offered various hosting locations e.g. US or UK based servers. My question is: does it really make a difference from the performance point of view? Lets say that I am expecting most of the traffic coming from continental Europe? Would the fact that the servers are based in UK make bigger difference if the traffic was coming from the UK. Any pros and cons of having a website hosted in the same county as the most of the expected traffic?

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