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• Working with the Objective-C/Cocoa flat namespace

  - by Stephen Blinkhorn

  I've not found anything that addresses my specific name space question as yet. I am working on some AudioUnit plug-ins featuring Cocoa based GUIs. The plug-ins use a common library of user interface classes (sliders, buttons etc) which are simply added to each Xcode project. When I recompile and distribute updates it is pretty much guaranteed that at least one user interface class will have been updated since the last release. If the user launches an older plug-in before an updated plug-in then the old Cocoa classes are already loaded into the run time and the plug-in attempts to use the older implementations - often resulting in a failure one way or another. I know frameworks are the intended solution but the overhead and backwards compatibility issues are not ideal. I prefix all class names where possible but what options do I have to ensure that each plug-in contains unique class names for the shared user interface classes?

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• How to check for an active Internet Connection on iPhone SDK?

  - by Brock Woolf

  I would like to check to see if I have an Internet connection on the iPhone using the Cocoa Touch libraries. I came up with a way to do this using an NSUrl. The way I did it seems a bit unreliable (because even Google could one day be down and relying on a 3rd party seems bad) and while I could check to see for a response from some other websites if Google didn't respond, it does seem wasteful and an unnecessary overhead on my application. - (BOOL) connectedToInternet { NSString *URLString = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://www.google.com"]]; return ( URLString != NULL ) ? YES : NO; } Is what I have done bad? (Not to mention 'stringWithContentsOfURL' is deprecated in 3.0) And if so what is a better way to accomplish this?

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• Is there performance to be gained by moving storage allocation local to a member function to its cla

  - by neuviemeporte

  Suppose I have the following C++ class: class Foo { double bar(double sth); }; double Foo::bar(double sth) { double a,b,c,d,e,f a = b = c = d = e = f = 0; /* do stuff with a..f and sth */ } The function bar() will be called millions of times in a loop. Obviously, each time it's called, the variables a..f have to be allocated. Will I gain any performance by making the variables a..f members of the Foo class and just initializing them at the function's point of entry? On the other hand, the values of a..f will be dereferenced through this-, so I'm wondering if it isn't actually a possible performance degradation. Is there any overhead to accessing a value through a pointer? Thanks!

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• C sharp: read last "n" lines of log file

  - by frictionlesspulley

  need a snippet of code which would read out last "n lines" of a log file. I came up with the following code from the net.I am kinda new to C sharp. Since the log file might be quite large, I want to avoid overhead of reading the entire file.Can someone suggest any performance enhancement. I do not really want to read each character and change position. var reader = new StreamReader(filePath, Encoding.ASCII); reader.BaseStream.Seek(0, SeekOrigin.End); var count = 0; while (count <= tailCount) { if (reader.BaseStream.Position <= 0) break; reader.BaseStream.Position--; int c = reader.Read(); if (reader.BaseStream.Position <= 0) break; reader.BaseStream.Position--; if (c == '\n') { ++count; } } var str = reader.ReadToEnd();

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• How to change enum definition without impacting clients using it in C#

  - by Rohit

  I have the following enum defined. I have used underscores as this enum is used in logging and i don't want to incur the overhead of reflection by using custom attribute.We use very heavy logging. Now requirement is to change "LoginFailed_InvalidAttempt1" to "LoginFailed Attempt1". If i change this enum, i will have to change its value across application. I can replace underscore by a space inside logging SP. Is there any way by which i can change this without affecting whole application.Please suggest. public enum ActionType { None, Created, Modified, Activated, Inactivated, Deleted, Login, Logout, ChangePassword, ResetPassword, InvalidPassword, LoginFailed_LockedAccount, LoginFailed_InActiveAccount, LoginFailed_ExpiredAccount, ForgotPassword, LoginFailed_LockedAccount_InvalidAttempts, LoginFailed_InvalidAttempt1, LoginFailed_InvalidAttempt2, LoginFailed_InvalidAttempt3, ForgotPassword_InvalidAttempt1, ForgotPassword_InvalidAttempt2, ForgotPassword_InvalidAttempt3, SessionTimeOut, ForgotPassword_LockedAccount, LockedAccount, ReLogin, ChangePassword_Due_To_Expiration, ChangePassword_AutoExpired }

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• Reason for monolithic data files

  - by Ali Lown

  Primarily this seems to be a technique used by games, where they have all the sounds in one file, textures in another etc. With these files commonly reaching the GB size. What is the reason behind doing this over maintaining it all in subdirectories as small files - one per texture which many small games use this, with the monolithic system being favoured by larger companies? Is there some file system overhead with lots of small files? Are they trying to protect their property - although most just seem to be a compressed file with a new extension?

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• Php efficiency question --> Database call vs. File Write vs. Calling C++ executable

  - by JP19

  Hi, What I wish to achieve is - log all information about each and every visit to every page ofmy website (like ip address, browser, referring page, etc). Now this is easy to do. What I am interested is doing this in a way so as to cause minimum overhead (runtime) in the php scripts. What is the best approach for this efficiency-wise: 1) Log all information to a database table 2) Write to a file (from php directly) 3) Call a C++ executable, that will write this info to a file in parallel [so the script can continue execution without waiting for the file write to occur ...... is this even possible] I may be trying to optimize unnecessarily/prematurely, but still - any thoughts / ideas on this would be appreciated. (I think efficiency of file write/logging can really be a concern if I have say 100 visits per minute...) Thanks & Regards, JP

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• Google App Engine - About how much quota does a single datastore put use?

  - by Spines

  The latency for a datastore put is about 150ms (http://code.google.com/status/appengine/detail/datastore/2010/03/11#ae-trust-detail-datastore-put-latency). About how much CPUTime is used by a single datastore put with data size of 100 bytes, into an entity that has only 2 columns, and no indexes? I plan to do some testing with this later today to figure it out, but if anyone already knows that would help me out :). Also, does anyone know about how much extra overhead in CPUTime doing this datastore put through the task queue would be? Note: This is kind of a follow up to this question: http://stackoverflow.com/questions/2421075/google-app-engine-how-reliable-are-the-logs.

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• Correct model for a database with a table for each user.

  - by BAH

  Kinda stuck here... I have an application with lets say 5000 rows of data per user and was wondering if it was right or wrong to do it this way: On user account creation a new table is created (UserData_[UserID]) or should I just have 1 table for userdata and have everything in there with a column for userid? The reason I am stuck at the moment is that it seems NHibernate isn't able to be mapped to dynamic table names without creating another ISessionFactory which has alot of overhead AFAIK. Any help would be greatly appreciated. Thanks.

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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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• Eval IronPython Scripts during ASP.NET Web Request; Static Engine or Not

  - by Josh Pearce

  I would like to create an ASP.NET MVC web application which has extensible logic that does not require a re-build. I was thinking of creating a filter which had an instance of the IronPython engine. What I would like to know is: how much overhead is there in creating a new engine during each web request, and would it be a better idea to keep a static engine around? However, if I were to keep a single static engine around, what are the issues I might run into as far as locking and script scope? Is it possible to have multiple scopes in the same IropPython engine so I don't get variable collision and security issues between web requests?

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• Build Pipelining and Continuous Integration with Maven and Hudson

  - by Brandon

  Currently the my team is considering splitting our single CI build process into a more streamlined multi-stage process to speed up basic build feedback and isolate different ci concerns. The idea we had was to have each stage exist in Hudson as a different build with the correct maven goal or maven plugin execution, then chain them together using the post-build hooks of Hudson. However to my knowledge, Maven as a build tool mandates that any lifecycle phase which is performed automatically builds every preceding lifecycle phase. This presents a number of problems the most significant of which is that maven is recreating the build resources with each distinct call and not using those of the previous stage. This not only breaks the consistency of the build lifecycle but has much more unnecessary processing overhead. Is there a way to accomplish pipelining with CI using Maven? Assuming there is, is there a way to let Hudson know to use those resources built from the previous stage in the next one?

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• Converting delimited string to multiple values in mysql

  - by epo

  I have a mysql legacy table which contains an client identifier and a list of items, the latter as a comma-delimited string. E.g. "xyz001", "foo,bar,baz". This is legacy stuff and the user insists on being able to edit a comma delimited string. They now have a requirement for a report table with the above broken into separate rows, e.g. "xyz001", "foo" "xyz001", "bar" "xyz001", "baz" Breaking the string into substrings is easily doable and I have written a procedure to do this by creating a separate table, but that requires triggers to deal with deletes, updates and inserts. This query is required rarely (say once a month) but has to be absolutely up to date when it is run, so e.g. the overhead of triggers is not warranted and scheduled tasks to create the table might not be timely enough. Is there any way to write a function to return a table or a set so that I can join the identifier with the individual items on demand?

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• In a process using lots of memory, how can I spawn a shell without a memory-hungry fork()?

  - by kdt

  On an embedded platform (with no swap partition), I have an application whose main process occupies most of the available physical memory. The problem is that I want to launch an external shell script from my application, but using fork() requires that there be enough memory for 2x my original process before the child process (which will ultimately execl itself to something much smaller) can be created. So is there any way to invoke a shell script from a C program without incurring the memory overhead of a fork()? I've considered workarounds such as having a secondary smaller process which is responsible for creating shells, or having a "watcher" script which I signal by touching a file or somesuch, but I'd much rather have something simpler.

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• Caveats to be aware of when using threading in Python?

  - by knorv

  I'm quite new to threading in Python and have a couple of beginner questions. When starting more than say fifty threads using the Python threading module I start getting MemoryError. The threads themselves are very slim and not very memory hungry, so it seems like it is the overhead of the threading that causes the memory issues. Is there something I can do to increase the memory capacity or otherwise make Python allow for a larger number of threads? What is the maximum number of threads you've been able to run in your Python code using the threading module? Did you do any tricks to achieve that number? Are there any other caveats to be aware of when using the threading module?

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• In a virtual machine monitor such as VMware's ESXi Server, how are shadow page tables implemented?

  - by ali01

  My understanding is that VMMs such as VMware's ESXi Server maintain shadow page tables to map virtual page addresses of guest operating systems directly to machine (hardware) addresses. I've been told that shadow page tables are then used directly by the processor's paging hardware to allow memory access in the VM to execute without translation overhead. I would like to understand a bit more about how the shadow page table mechanism works in a VMM. Is my high level understanding above correct? What kind of data structures are used in the implementation of shadow page tables? What is the flow of control from the guest operating system all the way to the hardware? How are memory access translations made for a guest operating system before its shadow page table is populated? How is page sharing supported? Short of straight up reading the source code of an open source VMM, what resources can I look into to learn more about hardware virtualization?

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• Is this a valid benefit of using embedded SQL over stored procedures?

  - by George

  Here's an argument for SPs that I haven't heard. Flamers, be gentle with the down tick, Since there is overhead associated with each trip to the database server, I would suggest that a POSSIBLE reason for placing your SQL in SPs over embedded code is that you are more insulated to change without taking a performance hit. For example. Let's say you need to perform Query A that returns a scalar integer. Then, later, the requirements change and you decide that it the results of the scalar is x that then, and only then, you need to perform another query. If you performed the first query in a SP, you could easily check the result of the first query and conditionally execute the 2nd SQL in the same SP. How would you do this efficiently in embedded SQL w/o perform a separate query or an unnecessary query? Here's an example: --This SP may return 1 or two queries. SELECT @CustCount = COUNT(*) FROM CUSTOMER IF @CustCount 10 SELECT * FROM PRODUCT Can this/what is the best way to do this in embedded SQL?

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• Java data structure to use with Hibernate to store unknown number of parameters?

  - by Lunikon

  Following problem: I want to render a news stream of short messages based on localized texts. In various places of these messages I have to insert parameters to "customize" them. I guess you know what I mean ;) My question probably falls into the "Which is the best style to do it?" category: How would you store these parameters (they may be Strings and Numbers that need to be formatted according to Locale) in the database? I'm using Hibernate to do the ORM and I can think of the following solutions: build a combined String and save it as such (ugly and hard to maintain I think) do some kind of fancy normalization and and make every parameter a single row on the database (clean I guess, but a performance nightmare) Put the params into an Array, Map or other Java data structure and save it in binary format (probably causes a lot of overhead size-wise) I tend towards option #3 but I'm afraid that it might be to costly in terms of size in the database. What do you think?

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• How do I find the previous/default value of a radio button in JS?

  - by royrules22

  I'm not sure if this is even possible, but I figured I'd ask before clubbing togehter an ugly solution. What I have is a group of radio buttons and I want to trigger a function if the radio button value is changed. For example say there are three buttons X Y and Z with Y default selected. If a user clicks on an unselected button (i.e. X or Z) then the function gets triggered but if he/she clicks on Y (which is already selected) nothing happens. Naturally the best solution would be to fire the function on an onchange event but IE6 doesn't fire onchange until the focus is no longer on the element which is not satisfactory. So is there a way to know what the previous value of the radio button was or at least what its default value is? I could easily create an array of default values and check against that but I'm trying to reduce the overhead. Please no jQuery suggestions ;)

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• Will .NET 4.0 apps work on Win 2008 R2 Server Core?

  - by markus

  When Windows Server 2008 R2 was launched, the "server core" edition started to become useful to me, because it lets me deploy .NET background applications isolated on their own virtual machine instance with only a small fraction of all the disk space overhead of a default Windows Server installation, and very few Windows Updates. It comes with a subset of .NET 3.5 SP1 integrated (as an optional feature). Now that .NET 4.0 is released, the redistributables explicitly state that it's not support on Server Core. Any chance that there will be a separate download available for Server Core (e. g. without WPF) any time soon, has anybody heard about it?

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• Secure password transmission over unencrypted tcp/ip

  - by academicRobot

  I'm in the designing stages of a custom tcp/ip protocol for mobile client-server communication. When not required (data is not sensitive), I'd like to avoid using SSL for overhead reasons (both in handshake latency and conserving cycles). My question is, what is the best practices way of transmitting authentication information over an unencrypted connection? Currently, I'm liking SRP or J-PAKE (they generate secure session tokens, are hash/salt friendly, and allow kicking into TLS when necessary), which I believe are both implemented in OpenSSL. However, I am a bit wary since I don't see many people using these algorithms for this purpose. Would also appreciate pointers to any materials discussing this topic in general, since I had trouble finding any.

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• How can I intercept a Tomcat request at socket level?

  - by Miguel Pardal

  Hi, I'm doing a performance study for a web application framework running on Apache Tomcat 6. I'm trying to measure the time overhead of handling HTTP requests. What I would like to do is: / // just before first request byte is read long t1 = System.nanoTime(); // request is processed... // just after final byte is written to response long t2 = System.nanoTime(); / Then I would compute the total time (t2 - t1). Is there a way to do this? Thanks for your help!

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• Is it a good idea to close and open hibernate sessions frequently?

  - by Gaurav

  Hi, I'm developing an application which requires that state of entities be read from a database at frequent intervals or triggers. However, once hibernate reads the state, it doesn't re-read it unless I explicitly close the session and read the entity in a new session. Is it a good idea to open a session everytime I want to read the entity and then close it afterwards? How much of an overhead does this put on the application and the database (we use a c3p0 connection pool also)? Will it be enough to simply evict the entity from the session before reading it again?

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• Use of private constructor to prevent instantiation of class?

  - by cringe

  Hi guys! Right now I'm thinking about adding a private constructor to a class that only holds some String constants. public class MyStrings { // I want to add this: private MyString() {} public static final String ONE = "something"; public static final String TWO = "another"; ... } Is there any performance or memory overhead if I add a private constructor to this class to prevent someone to instantiate it? Do you think it's necessary at all or that private constructors for this purpose are a waste of time and code clutter?

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• when to use StringBuilder in java

  - by kostja

  It is supposed to be generally preferable to use a StringBuilder for String concatenation in Java. Is it always the case? What i mean is : Is the overhead of creating a StringBuilder object, calling the append() method and finally toString() smaller then concatenating existing Strings with + for 2 Strings already or is it only advisable for more Strings? If there is such a threshold, what does it depend on (the String length i suppose, but in which way)? And finally - would you trade the readability and conciseness of the + concatenation for the performance of the StringBuilder in smaller cases like 2, 3, 4 Strings?

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