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• fastest method for minimum of two numbers

  - by user85030

  I was going through mit's opencourseware related to performance engineering. The quickest method (requiring least number of clock cycles) for finding the minimum of two numbers(say x and y) is stated as: min= y^((x^y) & -(x<y)) The output of the expression x < y can be 0 or 1 (assuming C is being used) which then changes to -0 or -1. I understand that xor can be used to swap two numbers. Questions: 1. How is -0 different from 0 and -1 in terms of binary? 2. How is that result used with the and operator to get the minimum? Thanks in advance.

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• Understanding memory leak in Android app.

  - by sat

  After going through few articles about performance, Not able to get this statement exactly. "When a Drawable is attached to a view, the view is set as a callback on the drawable" Soln: "Setting the stored drawables’ callbacks to null when the activity is destroyed." What does that mean, e.g. In my app , I initialize an imageButton in onCreate() like this, imgButton= (ImageButton) findViewById(R.id.imagebtn); At later stage, I get an image from an url, get the stream and convert that to drawable, and set image btn like this, imgButton.setImageDrawable(drawable); According to the above statement, when I am exiting my app, say in onDestroy() I have to set stored drawables’ callbacks to null, not able to understand this part ! In this simple case what I have to set as null ? I am using Android 2.2 Froyo, whether this technique is required, or not necessary.

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• One database or many?

  - by dsims

  I am developing a website that will manage data for multiple entities. No data is shared between entities, but they may be owned by the same customer. A customer may want to manage all their entities from a single "dashboard". So should I have one database for everything, or keep the data seperated into individual databases? Is there a best-practice? What are the positives/negatives for having a: database for the entire site (entity has a "customerID", data has "entityID") database for each customer (data has "entityID") database for each entity (relation of database to customer is outside of database) Multiple databases seems like it would have better performance (fewer rows and joins) but may eventually become a maintenance nightmare.

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• What can we do to make XML processing faster?

  - by adpd

  We work on an internal corporate system that has a web front-end as one of its interfaces. The front-end (Java + Tomcat + Apache) communicates to the back-end (proprietary system written in a COBOL-like language) through SOAP web services. As a result, we pass large XML files back and forth. We believe that this architecture has a significant impact on performance due to the large overhead of XML transportation and parsing. Unfortunately, we are stuck with this architecture. How can we make this XML set-up more efficient? Any tips or techniques are greatly appreciated.

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• Which of these Array Initializations is better in Ruby?

  - by Bragaadeesh

  Hi, Which of these two forms of Array Initialization is better in Ruby? Method 1: DAYS_IN_A_WEEK = (0..6).to_a HOURS_IN_A_DAY = (0..23).to_a @data = Array.new(DAYS_IN_A_WEEK.size).map!{ Array.new(HOURS_IN_A_DAY.size) } DAYS_IN_A_WEEK.each do |day| HOURS_IN_A_DAY.each do |hour| @data[day][hour] = 'something' end end Method 2: DAYS_IN_A_WEEK = (0..6).to_a HOURS_IN_A_DAY = (0..23).to_a @data = {} DAYS_IN_A_WEEK.each do |day| HOURS_IN_A_DAY.each do |hour| @data[day] ||= {} @data[day][hour] = 'something' end end The difference between the first method and the second method is that the second one does not allocate memory initially. I feel the second one is a bit inferior when it comes to performance due to the numerous amount of Array copies that has to happen. However, it is not straight forward in Ruby to find what is happening. So, if someone can explain me which is better, it would be really great! Thanks

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• Using temporary arrays to cut down on code - inefficient?

  - by tommaisey

  I'm new to c++ (and SO) so sorry if this is obvious. I've started using temporary arrays in my code to cut down on repetition and to make it easier to do the same thing to multiple objects. So instead of: MyObject obj1, obj2, obj3, obj4; obj1.doSomming(arg); obj2.doSomming(arg); obj3.doSomming(arg); obj4.doSomming(arg); I'm doing: MyObject obj1, obj2, obj3, obj4; MyObject* objs[] = {&obj1, &obj2, &obj3, &obj4}; for (int i = 0; i !=4; ++i) objs[i]->doSomming(arg); Is this detrimental to performance? Like, does it cause unnecessary memory allocation? Is it good practice? Thanks.

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• Why do these seemingly similar queries have such drastically different run times?

  - by Jherico

  I'm working with an oracle DB trying to tune some queries and I'm having trouble understanding why working a particular clause in a particular way has such a drastic impact on the query performance. Here is a performant version of the query I'm doing select * from ( select a.*, rownum rn from ( select * from table_foo ) a where rownum < 3 ) where rn >= 2 The same query by replacing the last two lines with this ) a where rownum >=2 rownum < 3 ) performs horribly. Several orders of magnitude worse ) a where rownum between 2 and 3 ) also performs horribly. I don't understand the magic from the first query and how to apply it to further similar queries.

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• How does Array.ForEach() compare to standard for loop in C#?

  - by DaveN59

  I pine for the days when, as a C programmer, I could type: memset( byte_array, '0xFF' ); and get a byte array filled with 'FF' characters. So, I have been looking for a replacement for this: for (int i=0; i < byteArray.Length; i++) { byteArray[i] = 0xFF; } Lately, I have been using some of the new C# features and have been using this approach instead: Array.ForEach<byte>(byteArray, b => b = 0xFF); Granted, the second approach seems cleaner and is easier on the eye, but how does the performance compare to using the first approach? Am I introducing needless overhead by using Linq and generics? Thanks, Dave

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• Faster way of initializing arrays in Delphi

  - by Max

  I'm trying to squeeze every bit of performance in my Delphi application and now I came to a procedure which works with dynamic arrays. The slowest line in it is SetLength(Result, Len); which is used to initialize the dynamic array. When I look at the code for the SetLength procedure I see that it is far from optimal. The call sequence is as follows: _DynArraySetLength - DynArraySetLength DynArraySetLength gets the array length (which is zero for initialization) and then uses ReallocMem which is also unnecessary for initilization. I was doing SetLength to initialize dynamic array all the time. Maybe I'm missing something? Is there a faster way to do this?

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• PHP Try and Catch for SQL Insert

  - by meme

  I have a page on my website (high traffic) that does an insert on every page load. I am curious of the fastest and safest way to (catch an error) and continue if the system is not able to do the insert into MySQL. Should I use try/catch or die or something else. I want to make sure the insert happens but if for some reason it can't I want the page to continue to load anyway. ... $db = mysql_select_db('mobile', $conn); mysql_query("INSERT INTO redirects SET ua_string = '$ua_string'") or die('Error #10'); mysql_close($conn); ...

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• Small and fast .NET programs? - 65% runtime in ResolvePolicy

  - by forki23

  Hi, I tried to build a very very small .NET app in F#. It just has to convert a small string into another string and print the result to the console like: convert.exe myString == prints something like "myConvertedString" I used dottrace to analyze the performance: 26% (168ms) in my actual string conversion (I thinks this is ok.) 65,80% (425ms) in ResolvePolicy in System.Security.SecurityManager A runtime 500ms on every execution is way too slow. Can I do something to improve this? It would be Ok if only the first call needs this time. Regards, forki

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• Quantifying the Performance of Garbage Collection vs. Explicit Memory Management

  - by EmbeddedProg

  I found this article here: Quantifying the Performance of Garbage Collection vs. Explicit Memory Management http://www.cs.umass.edu/~emery/pubs/gcvsmalloc.pdf In the conclusion section, it reads: Comparing runtime, space consumption, and virtual memory footprints over a range of benchmarks, we show that the runtime performance of the best-performing garbage collector is competitive with explicit memory management when given enough memory. In particular, when garbage collection has five times as much memory as required, its runtime performance matches or slightly exceeds that of explicit memory management. However, garbage collection’s performance degrades substantially when it must use smaller heaps. With three times as much memory, it runs 17% slower on average, and with twice as much memory, it runs 70% slower. Garbage collection also is more susceptible to paging when physical memory is scarce. In such conditions, all of the garbage collectors we examine here suffer order-of-magnitude performance penalties relative to explicit memory management. So, if my understanding is correct: if I have an app written in native C++ requiring 100 MB of memory, to achieve the same performance with a "managed" (i.e. garbage collector based) language (e.g. Java, C#), the app should require 5*100 MB = 500 MB? (And with 2*100 MB = 200 MB, the managed app would run 70% slower than the native app?) Do you know if current (i.e. latest Java VM's and .NET 4.0's) garbage collectors suffer the same problems described in the aforementioned article? Has the performance of modern garbage collectors improved? Thanks.

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• How to get bearable 2D and 3D performance on AMD Radeon HD 6950?

  - by l0b0

  I have had an AMD Radeon HD 6950 (i.e., Cayman series) for a couple years now, and I have tried a lot of combinations of drivers and settings with terrible results. I'm completely at a loss as to how to proceed. The open source driver has much better 2D performance, but it offloads all OpenGL rendering to the CPU. What I've tried so far: All the latest stable Ubuntu releases in the period, plus one Linux Mint release. All the latest stable AMD Catalyst Proprietary Display Drivers, and currently 13.1. The unofficial wiki installation instructions for every Ubuntu version and the semi-official Ubuntu instructions. All the tips and tweaks I could find for Minecraft (Optifine, reducing settings to minimum), VLC (postprocessing at minimum, rendering at native video size), Catalyst Control Center (flipped every lever in there) and X11 (some binary toggles I can no longer remember). Results: Typically 13-15 FPS in Minecraft, 30 max (100+ in Windows with the same driver version). Around 10 FPS in Team Fortress 2 using the official Steam client. Choppy video playback, in Flash and with VLC. CPU use goes through the roof when rendering video (150% for 1080p on YouTube in Chromium, 100% for 1080p H264 in VLC). glxgears shows 12.5 FPS when maximized. fgl_glxgears shows 10 FPS when maximized. Hardware details from lshw: Motherboard ASUS P6X58D-E CPU Intel Core i7 CPU 950 @ 3.07GHz (never overclocked; 64 bit) 6 GB RAM Video card product "Cayman PRO [Radeon HD 6950]", vendor "Hynix Semiconductor (Hyundai Electronics)" 2 x 1920x1200 monitors, both connected with HDMI. I feel I must be missing something absolutely fundamental here. Is there no accelerated support for anything on 64-bit architectures? Does a dual monitor completely mess up the driver? $ fglrxinfo display: :0 screen: 0 OpenGL vendor string: Advanced Micro Devices, Inc. OpenGL renderer string: AMD Radeon HD 6900 Series OpenGL version string: 4.2.11995 Compatibility Profile Context $ glxinfo | grep 'direct rendering' direct rendering: Yes I am currently using the open source driver, with the following results: Full frame rate and low CPU load when playing 1080p video. Black screen (but music in the background) in Team Fortress 2. Similar performance in Minecraft as the Catalyst driver. In hindsight obvious, since both end up offloading the rendering to the CPU. My /var/log/Xorg.0.log after upgrading to AMD Catalyst 13.1. Some possibly important lines: (WW) Falling back to old probe method for fglrx (WW) fglrx: No matching Device section for instance (BusID PCI:0@3:0:1) found The generated xorg.conf. The disabled "monitor" 0-DFP9 is actually an A/V receiver, which sometimes confuses the monitor drivers when turned on/off (but not in Windows). All three "monitor" devices are connected with HDMI. Edit: Chris Carter's suggestion to use the xorg-edgers PPA (Catalyst 13.1) resulted in some improvement, but still pretty bad performance overall: Minecraft stabilizes at 13-17 FPS, but at least the CPU load is "only" at 45-60%. Still 150% CPU use for 1080p video rendering on YouTube in Chromium. Massive improvement for 1080p H264 in VLC: 40-50% CPU use and no visible jitter glxgears performance about doubled to 25-30 FPS when maximized. fgl_glxgears still at ~10 FPS when maximized.

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• Administer, manage, monitor, and fine tune the performance of your Oracle SOA Suite 11g Service Infrastructure and SOA composite applications.

  - by JuergenKress

  Key Features of the book If you are an Oracle SOA suite administrator, then this book is your bible. It gives you everything you need to know about all your tasks and help you to apply what you learn in your everyday life right from the first chapter. The book walks through promoting code across environments, performance tuning the service infrastructure, monitoring the environment, configuring security policies, managing the dehydration store, backing and restoring environments and so on. Packed with real-world examples from authors' own experiences, this books offers a unique insight into Oracle SOA Suite Administration. Detailed description The book begins with an introduction of SOA and quickly moves on to management of SOA composite applications. Readers will learn how to manage composite applications, their deployments and lifecycles. Equipped with this knowledge, readers will be introduced to monitoring and performance tuning SOA Suite, monitoring instances, messages, and composite applications, managing faults and exceptions, configuring audit levels of composite applications to include end-to-end monitoring through the use of extended logging as well as administering and configuring all SOA Suite components. A very important aspect of administration is tuning and optimizing the infrastructure for performance and book offers real work recommendations to monitor and performance tune service engines, the underlying WebLogic server, threads and timeouts, files systems, and composite applications. It also covers detailed administration of individual service components, configuring the infrastructure MBeans using both Oracle Enterprise Manager Fusion Middleware Control and WLST based scripts, migrating worklist preferences and BAM data across environments, setting up Email, LDAP and custom XPath. An administrator is always trusted with troubleshooting and root causing problems in the infrastructure and this book will help you through the troubleshooting approaches as how to identify faults and exception through extended logging and thread dumps and find solutions to common startup problems and deployment issues. The advanced contents of this book explains OWSM security framework and how to secure components deployed to the infrastructure along with the details of all groundwork needed to ready the environment. Last few chapters help you to understand and deal with managing the metadata services repository and dehydration store, backup and recovery and concluding with advanced topics such as silent/scripted installations, cloning, upgrading, patching and high availability installations. Packed with real-world examples, and tips straight from the trench; this book offers insights into SOA Suite administration that you will not find elsewhere. Part of our writing style in this book draws heavily on the philosophy of reuse and as such the book provide an ample of executable SQL queries and WLST scripts that administrators can reuse and extend to perform most of the administration tasks such as monitoring instances, processing times, instance states and perform automatic deployments, tuning, migration, and installation. These scripts are spread over each of the chapters in the book and can also be downloaded from here. The book is available in different formats at the following websites: Paperback and eBook versions & Kindle version. It is available for order and signed copies are available through our web site. SOA & BPM Partner Community For regular information on Oracle SOA Suite become a member in the SOA & BPM Partner Community for registration please visit  www.oracle.com/goto/emea/soa (OPN account required) If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Mix Forum Technorati Tags: SOA book,SOA Suite Adminsitration,SOA Community,Oracle SOA,Oracle BPM,Community,OPN,Jürgen Kress

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• Persisting high score table in flash game without a network. (Featuring: HttpListenerException)

  - by bearcdp

  Hi everyone, this question is very programming-centric, but it's for a game so I figured I might as well post it here. I'm doing polishing work on a GGJ '11 game because it will be shown at an indie arcade tomorrow afternoon, and they're expecting our final build in the morning. We'd like to have a high score table that displays during attract mode, but since it's Flash (Flixel) it would require some networking, Mochi, or something to keep a record of these scores. Only problem is the machine we'd be running on probably won't have network access. As a quick solution, I thought I'd just write up a dinky little high score server in C#/.NET that could take basic GET requests for submitting scores and getting the score list. We're talking REAL basic, like blocking while waiting for an incoming request, run & forget console app, etc. There's no guarantee that our .swf won't get reloaded, and we'd like the scores to persist, so this server would pretty much exists to keep a safe copy of the scores that the game can add to and request, and occasionally the server will write the scores to a flat text file. But, HttpListener is giving me Error Code 87 'The parameter is incorrect.' Have any idea what I'm doing wrong? Or better yet, am I barking up the wrong tree and missing an obviously simpler solution? This is all I've got so far in my Main(): HttpListener listener = new HttpListener(); listener.Prefixes.Add("http://localhost:66666/"); listener.Start(); The exception happens at listener.Start(); and the stack trace is: at System.Net.HttpListener.AddAllPrefixes() at System.Net.HttpListener.Start() at WOSEBCE_ScoreServer.Program.Main(String[] args) in C:\Users\Michael\Documents\Visual Studio 2010\VS2010 Projects\WOSEBCE_ScoreServer\WOSEBCE_ScoreServer\Program.cs:line 24 at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args) at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart()

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• How much multiple style sheets slow down to website?

  - by metal-gear-solid

  Here is 3 css file (one is only for IE) <link rel="stylesheet" href="css/blueprint/screen.css" type="text/css" media="screen, projection"> <link rel="stylesheet" href="css/blueprint/print.css" type="text/css" media="print"> <!--[if lt IE 8]><link rel="stylesheet" href="css/blueprint/ie.css" type="text/css" media="screen, projection"><![endif]--> If i keep divide scree.css into these css in my website Now it will be 6 css ( one is only for IE) <link rel="stylesheet" href="css/blueprint/reset.css" type="text/css" media="screen, projection"> <link rel="stylesheet" href="css/blueprint/grid.css" type="text/css" media="screen, projection"> <link rel="stylesheet" href="css/blueprint/typography.css" type="text/css" media="screen, projection"> <link rel="stylesheet" href="css/blueprint/forms.css" type="text/css" media="screen, projection"> <link rel="stylesheet" href="css/blueprint/print.css" type="text/css" media="print"> <!--[if lt IE 8]><link rel="stylesheet" href="css/blueprint/ie.css" type="text/css" media="screen, projection"><![endif]--> If i go for method two for a website even after production . Does it really slowdown the website page loading speed? if yes then how much? How much these 3 extra style sheet will affect site performance?

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• Fastest way to remove non-numeric characters from a VARCHAR in SQL Server

  - by Dan Herbert

  I'm writing an import utility that is using phone numbers as a unique key within the import. I need to check that the phone number does not already exist in my DB. The problem is that phone numbers in the DB could have things like dashes and parenthesis and possibly other things. I wrote a function to remove these things, the problem is that it is slow and with thousands of records in my DB and thousands of records to import at once, this process can be unacceptably slow. I've already made the phone number column an index. I tried using the script from this post: http://stackoverflow.com/questions/52315/t-sql-trim-nbsp-and-other-non-alphanumeric-characters But that didn't speed it up any. Is there a faster way to remove non-numeric characters? Something that can perform well when 10,000 to 100,000 records have to be compared. Whatever is done needs to perform fast. Update Given what people responded with, I think I'm going to have to clean the fields before I run the import utility. To answer the question of what I'm writing the import utility in, it is a C# app. I'm comparing BIGINT to BIGINT now, with no need to alter DB data and I'm still taking a performance hit with a very small set of data (about 2000 records). Could comparing BIGINT to BIGINT be slowing things down? I've optimized the code side of my app as much as I can (removed regexes, removed unneccessary DB calls). Although I can't isolate SQL as the source of the problem anymore, I still feel like it is.

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• SQL Server slow in production environment

  - by Lieven Cardoen

  I have a weird problem in a customer's production environment. I can't give any details on the infrastructure, except that SQL server runs on a virtual server. The data, log and filestream file are on another storage server (data and filestream together and log on a separate server). In our local Test environment, there's one particular query that executes with these durations: first we clear the cache 300ms (First time it takes longer, but from then on it's cached.) 20ms 15ms 17ms In the customer's production environment, the SQL Server is more powerful, these are the durations (I didn't have the rights to clear the cache. Will try this tomorrow). 2500ms 2600ms 2400ms The servers in the customer's production environment are more powerful but they do have virtual servers (we don't). What could be the cause... Not enough memory? Fragmentation? Physical storage? How would you tackle this performance problem? EDIT: Some people have asked me if the data set is equal and it is. I restored their database on our environment. It's true that this was the first thing I looked at. (@Everyone: I added the edit because it will be the first thing that many will think off).

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• jQuery fn.extend ({bla: function(){}} vs. jQuery.fn.bla

  - by tixrus

  OK I think I get http://stackoverflow.com/questions/1991126/difference-jquery-extend-and-jquery-fn-extend in that the general extend can extend any object, and that fn.extend is for plugin functions that can be invoked straight off the jquery object with some internal jquery voodoo. So it appears one would invoke them differently. If you use general extend to extend object obj by adding function y, then the method would attach to that object, obj.y() but if you use fn.extend then they are attach straight to the jquery object $.y().... Have I got that correct yes or no and if no what do I have wrong in my understanding? Now MY question: The book I am reading advocates using jQuery.fn.extend ({a: function(){}, b: function(){}}); syntax but in the docs it says jQuery.fn.a (function(){}); and I guess if you wanted b as well it would be jQuery.fn.b (function(){}); Are these functionally and performance-wise equivalent and if not what is the difference? Thank you very much. I am digging jQuery!

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• Debugging SQL Server Slowness: Same Database, Different Servers

  - by Craig Walker

  For a while now we've been having anecdotal slowness on our newly-minted (VMWare-based) SQL Server 2005 database servers. Recently the problem has come to a head and I've started looking for the root cause of the issue. Here's the weird part: on the stored procedure that I'm using as a performance test case, I get a 30x difference in the execution speed depending on which DB server I run it on. This is using the same database (mdf) and log (ldf) files, detached, copied, and reattached from the slow server to the fast one. This doesn't appear to be a (virtualized) hardware issue: he slow server has 4x the CPU capacity and 2x the memory as the fast one. As best as I can tell, the problem lies in the environment/configuration of the servers (either operating system or SQL Server installation). However, I've checked a bunch of variables (SQL Server config options, running services, disk fragmentation) and found nothing that has made a difference in testing. What things should I be looking at? What tools can I use to investigate why this is happening?

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• SQL Server 2008 Running trigger after Insert, Update locks original table

  - by Polity

  Hi Folks, I have a serious performance problem. I have a database with (related to this problem), 2 tables. 1 Table contains strings with some global information. The second table contains the string stripped down to each individual word. So the string is like indexed in the second table, word by word. The validity of the data in the second table is of less important then the validity of the data in the first table. Since the first table can grow like towards 1*10^6 records and the second table having an average of like 10 words for 1 string can grow like 1*10^7 records, i use a nolock in order to read the second this leaves me free for inserting new records without locking it (Expect many reads on both tables). I have a script which keeps on adding and updating rows to the first table in a MERGE statement. On average, the data beeing merged are like 20 strings a time and the scripts runs like ones every 5 seconds. On the first table, i have a trigger which is beeing invoked on a Insert or Update, which takes the newly inserted or updated data and calls a stored procedure on it which makes sure the data is indexed in the second table. (This takes some significant time). The problem is that when having the trigger disbaled, Reading the first table happens in a few ms. However, when enabling the trigger and your in bad luck of trying to read the first table while this is beeing updated, Our webserver gives you a timeout after 10 seconds (which is way to long anyways). I can quess from this part that when running the trigger, the first table is kept (partially) in a lock untill the trigger is completed. What do you think, if i'm right, is there a easy way around this? Thanks in advance! Cheers, Koen

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• The cost of passing by shared_ptr

  - by Artem

  I use std::tr1::shared_ptr extensively throughout my application. This includes passing objects in as function arguments. Consider the following: class Dataset {...} void f( shared_ptr< Dataset const > pds ) {...} void g( shared_ptr< Dataset const > pds ) {...} ... While passing a dataset object around via shared_ptr guarantees its existence inside f and g, the functions may be called millions of times, which causes a lot of shared_ptr objects being created and destroyed. Here's a snippet of the flat gprof profile from a recent run: Each sample counts as 0.01 seconds. % cumulative self self total time seconds seconds calls s/call s/call name 9.74 295.39 35.12 2451177304 0.00 0.00 std::tr1::__shared_count::__shared_count(std::tr1::__shared_count const&) 8.03 324.34 28.95 2451252116 0.00 0.00 std::tr1::__shared_count::~__shared_count() So, ~17% of the runtime was spent on reference counting with shared_ptr objects. Is this normal? A large portion of my application is single-threaded and I was thinking about re-writing some of the functions as void f( const Dataset& ds ) {...} and replacing the calls shared_ptr< Dataset > pds( new Dataset(...) ); f( pds ); with f( *pds ); in places where I know for sure the object will not get destroyed while the flow of the program is inside f(). But before I run off to change a bunch of function signatures / calls, I wanted to know what the typical performance hit of passing by shared_ptr was. Seems like shared_ptr should not be used for functions that get called very often. Any input would be appreciated. Thanks for reading. -Artem

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• Perf4j Not Logging to Separate File

  - by Jehud

  I setup some stop watch calls in my code to measure some code blocks and all the messages are going into my primary log and not into the timing log. The perfStats.log file gets created just fine but all the messages go to the root log which I didn't think was supposed to happen according to the docs I've read. Is there something obvious I'm missing here? Example log4j.xml <!-- This file appender is used to output aggregated performance statistics --> <appender name="fileAppender" class="org.apache.log4j.FileAppender"> <param name="File" value="perfStats.log"/> <layout class="org.apache.log4j.PatternLayout"> <param name="ConversionPattern" value="%m%n"/> </layout> </appender> <!-- Loggers --> <!-- The Perf4J logger. Note that org.perf4j.TimingLogger is the value of the org.perf4j.StopWatch.DEFAULT_LOGGER_NAME constant. Also, note that additivity is set to false, which is usually what is desired - this means that timing statements will only be sent to this logger and NOT to upstream loggers. --> <logger name="org.perf4j.TimingLogger" additivity="false"> <level value="INFO"/> <appender-ref ref="CoalescingStatistics"/> </logger> <root> <priority value="info"/> <appender-ref ref="STDOUT-DEBUG"/> </root>

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• Linux 2.6.31 Scheduler and Multithreaded Jobs

  - by dsimcha

  I run massively parallel scientific computing jobs on a shared Linux computer with 24 cores. Most of the time my jobs are capable of scaling to 24 cores when nothing else is running on this computer. However, it seems like when even one single-threaded job that isn't mine is running, my 24-thread jobs (which I set for high nice values) only manage to get ~1800% CPU (using Linux notation). Meanwhile, about 500% of the CPU cycles (again, using Linux notation) are idle. Can anyone explain this behavior and what I can do about it to get all of the 23 cores that aren't being used by someone else? Notes: In case it's relevant, I have observed this on slightly different kernel versions, though I can't remember which off the top of my head. The CPU architecture is x64. Is it at all possible that the fact that my 24-core jobs are 32-bit and the other jobs I'm competing w/ are 64-bit is relevant? Edit: One thing I just noticed is that going up to 30 threads seems to alleviate the problem to some degree. It gets me up to ~2100% CPU.

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• Big-O of PHP functions?

  - by Kendall Hopkins

  After using PHP for a while now, I've noticed that not all PHP built in functions as fast as expected. Consider the below two possible implementations of a function that finds if a number is prime using a cached array of primes. //very slow for large $prime_array $prime_array = array( 2, 3, 5, 7, 11, 13, .... 104729, ... ); $result_array = array(); foreach( $array_of_number => $number ) { $result_array[$number] = in_array( $number, $large_prime_array ); } //still decent performance for large $prime_array $prime_array => array( 2 => NULL, 3 => NULL, 5 => NULL, 7 => NULL, 11 => NULL, 13 => NULL, .... 104729 => NULL, ... ); foreach( $array_of_number => $number ) { $result_array[$number] = array_key_exists( $number, $large_prime_array ); } This is because in_array is implemented with a linear search O(n) which will linearly slow down as $prime_array grows. Where the array_key_exists function is implemented with a hash lookup O(1) which will not slow down unless the hash table gets extremely populated (in which case it's only O(logn)). So far I've had to discover the big-O's via trial and error, and occasionally looking at the source code. Now for the question... I was wondering if there was a list of the theoretical (or practical) big O times for all* the PHP built in functions. *or at least the interesting ones For example find it very hard to predict what the big O of functions listed because the possible implementation depends on unknown core data structures of PHP: array_merge, array_merge_recursive, array_reverse, array_intersect, array_combine, str_replace (with array inputs), etc.

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