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• Item in multiple lists

  - by Evan Teran

  So I have some legacy code which I would love to use more modern techniques. But I fear that given the way that things are designed, it is a non-option. The core issue is that often a node is in more than one list at a time. Something like this: struct T { T *next_1; T *prev_1; T *next_2; T *prev_2; int value; }; this allows the core have a single object of type T be allocated and inserted into 2 doubly linked lists, nice and efficient. Obviously I could just have 2 std::list<T*>'s and just insert the object into both...but there is one thing which would be way less efficient...removal. Often the code needs to "destroy" an object of type T and this includes removing the element from all lists. This is nice because given a T* the code can remove that object from all lists it exists in. With something like a std::list I would need to search for the object to get an iterator, then remove that (I can't just pass around an iterator because it is in several lists). Is there a nice c++-ish solution to this, or is the manually rolled way the best way? I have a feeling the manually rolled way is the answer, but I figured I'd ask.

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• Efficiently select top row for each category in the set

  - by VladV

  I need to select a top row for each category from a known set (somewhat similar to this question). The problem is, how to make this query efficient on the large number of rows. For example, let's create a table that stores temperature recording in several places. CREATE TABLE #t ( placeId int, ts datetime, temp int, PRIMARY KEY (ts, placeId) ) -- insert some sample data SET NOCOUNT ON DECLARE @n int, @ts datetime SELECT @n = 1000, @ts = '2000-01-01' WHILE (@n>0) BEGIN INSERT INTO #t VALUES (@n % 10, @ts, @n % 37) IF (@n % 10 = 0) SET @ts = DATEADD(hour, 1, @ts) SET @n = @n - 1 END Now I need to get the latest recording for each of the places 1, 2, 3. This way is efficient, but doesn't scale well (and looks dirty). SELECT * FROM ( SELECT TOP 1 placeId, temp FROM #t WHERE placeId = 1 ORDER BY ts DESC ) t1 UNION ALL SELECT * FROM ( SELECT TOP 1 placeId, temp FROM #t WHERE placeId = 2 ORDER BY ts DESC ) t2 UNION ALL SELECT * FROM ( SELECT TOP 1 placeId, temp FROM #t WHERE placeId = 3 ORDER BY ts DESC ) t3 The following looks better but works much less efficiently (30% vs 70% according to the optimizer). SELECT placeId, ts, temp FROM ( SELECT placeId, ts, temp, ROW_NUMBER() OVER (PARTITION BY placeId ORDER BY ts DESC) rownum FROM #t WHERE placeId IN (1, 2, 3) ) t WHERE rownum = 1 The problem is, during the latter query execution plan a clustered index scan is performed on #t and 300 rows are retrieved, sorted, numbered, and then filtered, leaving only 3 rows. For the former query three times one row is fetched. Is there a way to perform the query efficiently without lots of unions?

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• JQuery: using .LIVE problems

  - by TeddTedd

  I have the following JQuery code: $("#myDIV li:eq(0)").live('click',function(){ funcA(); }); $("#myDIV li:eq(1)").live('click',function(){ funcB(); }); $("#myDIV li:eq(2)").live('click',function(){ funcC(); }); $("#myDIV li:eq(3)").live('click',function(){ funcD(); }); And realized it's really inefficient. So I tried the following, which I believe is much more effect; however, the code does not work: var tab_node = $("#myDIV li"); tab_node.eq(0).live('click',function(){ funcA(); }); tab_node.eq(1).live('click',function(){ funcB(); }); tab_node.eq(2).live('click',function(){ funcC(); }); tab_node.eq(3).live('click',function(){ funcD(); }); Any idea how I can make my code more efficient while also work? UPDATE: From the answers below, it sounds like these two statements are not equalavent. New Question: Is there any way to run my original code more efficient?

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• Best (Java) book for understanding 'under the bonnet' for programming?

  - by Ben

  What would you say is the best book to buy to understand exactly how programming works under the hood in order to increase performance? I've coded in assembly at university, I studied computer architecture and I obviously did high level programming, but what I really dont understand is things like: -what is happening when I perform a cast -whats the difference in performance if I declare something global as opposed to local? -How does the memory layout for an ArrayList compare with a Vector or LinkedList? -Whats the overhead with pointers? -Are locks more efficient than using synchronized? -Would creating my own array using int[] be faster than using ArrayList -Advantages/disadvantages of declaring a variable volatile I have got a copy of Java Performance Tuning but it doesnt go down very low and it contains rather obvious things like suggesting a hashmap instead of using an ArrayList as you can map the keys to memory addresses etc. I want something a bit more Computer Sciencey, linking the programming language to what happens with the assembler/hardware. The reason im asking is that I have an interview coming up for a job in High Frequency Trading and everything has to be as efficient as possible, yet I cant remember every single possible efficiency saving so i'd just like to learn the fundamentals. Thanks in advance

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• How do I efficiently parse a CSV file in Perl?

  - by Mike

  I'm working on a project that involves parsing a large csv formatted file in Perl and am looking to make things more efficient. My approach has been to split() the file by lines first, and then split() each line again by commas to get the fields. But this suboptimal since at least two passes on the data are required. (once to split by lines, then once again for each line). This is a very large file, so cutting processing in half would be a significant improvement to the entire application. My question is, what is the most time efficient means of parsing a large CSV file using only built in tools? note: Each line has a varying number of tokens, so we can't just ignore lines and split by commas only. Also we can assume fields will contain only alphanumeric ascii data (no special characters or other tricks). Also, i don't want to get into parallel processing, although it might work effectively. edit It can only involve built-in tools that ship with Perl 5.8. For bureaucratic reasons, I cannot use any third party modules (even if hosted on cpan) another edit Let's assume that our solution is only allowed to deal with the file data once it is entirely loaded into memory. yet another edit I just grasped how stupid this question is. Sorry for wasting your time. Voting to close.

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• What's the best way to get a bunch of rows from MySQL if you have an array of integer primary keys?

  - by Evan P.

  I have a MySQL table with an auto-incremented integer primary key. I want to get a bunch of rows from the table based on an array of integers I have in memory in my program. The array ranges from a handful to about 1000 items. What's the most efficient query syntax to get the rows? I can think of a few: "SELECT * FROM thetable WHERE id IN (1, 2, 3, 4, 5)" (this is what I do now) "SELECT * FROM thetable where id = 1 OR id = 2 OR id = 3" Multiple queries of the form "SELECT * FROM thetable WHERE id = 1". Probably the most friendly to the query cache, but expensive due to having lots of query parsing. A union, like "SELECT * FROM thetable WHERE id = 1 UNION SELECT * FROM thetable WHERE id = 2 ..." I'm not sure if MySQL caches the results of each query; it's also the most verbose format. I think using the NoSQL interface in MySQL 5.6+ would be the most efficient way to do this, but I'm not yet up to MySQL 5.6.

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• How string accepting interface should look like?

  - by ybungalobill

  Hello, This is a follow up of this question. Suppose I write a C++ interface that accepts or returns a const string. I can use a const char* zero-terminated string: void f(const char* str); // (1) The other way would be to use an std::string: void f(const string& str); // (2) It's also possible to write an overload and accept both: void f(const char* str); // (3) void f(const string& str); Or even a template in conjunction with boost string algorithms: template<class Range> void f(const Range& str); // (4) My thoughts are: (1) is not C++ish and may be less efficient when subsequent operations may need to know the string length. (2) is bad because now f("long very long C string"); invokes a construction of std::string which involves a heap allocation. If f uses that string just to pass it to some low-level interface that expects a C-string (like fopen) then it is just a waste of resources. (3) causes code duplication. Although one f can call the other depending on what is the most efficient implementation. However we can't overload based on return type, like in case of std::exception::what() that returns a const char*. (4) doesn't work with separate compilation and may cause even larger code bloat. Choosing between (1) and (2) based on what's needed by the implementation is, well, leaking an implementation detail to the interface. The question is: what is the preffered way? Is there any single guideline I can follow? What's your experience?

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• Reading HTML header info of files via JS

  - by Morten Repsdorph Husfeldt

  I have a product list that is generated in ASP. I have product descriptions for each product in an HTML file. Each HTML file is named: <product.id>.html. Each HTML file size is only 1-3 kb. Within the HTML file is <title> and <meta name="description" content="..." />. I want to access these in an efficient way so that I can output this as e.g.: document.write(<product.id>.html.title);<br/> document.write(<product.id>.html.description); I have a working solution for the individual products, where I use the description file - but I hope to find a more efficient / simple approach. Preferably, I want to avoid having 30+ hidden iframes - Google might think that I am trying to tamper with search result and blacklist my page. Current code: <script type="text/javascript"> document.getElementById('produkt').onload = function(){ var d = window.frames[frame].document; document.getElementById('pfoto').title = d.title : ' '; document.getElementById('pfoto').alt = d.getElementsByName('description')[0].getAttribute('content', 0) : ' '; var keywords = d.getElementsByName('keywords')[0].getAttribute('content', 0) : ' '; }; </script>

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• Selenium : Handling Loading screens obscuring the web elements. (Java)

  - by Sheldon Cooper

  I'm writing an automated test case for a web page. Here's my scenario. I have to click and type on various web elements in an html form. But, sometimes while typing on a text field, an ajax loading image appears , fogging all elements i want to interact with. So, I'm using web-driver wait before clicking on the actual elements like below, WebdriverWait innerwait=new WebDriverWait(driver,30); innerwait.until(ExpectedConditions.elementToBeClickable(By.xpath(fieldID))); driver.findelement(By.xpath(fieldID)).click(); But the wait function returns the element even if it is fogged by another image and is not clickable. But the click() throws an exception as Element is not clickable at point (586.5, 278). Other element would receive the click: <div>Loading image</div> Do I have to check every time if the loading image appeared before interacting with any elements?.(I can't predict when the loading image will appear and fog all elements.) Is there any efficient way to handle this? Currently I'm using the following function to wait till the loading image disappears, public void wait_for_ajax_loading() throws Exception { try{ Thread.sleep(2000); if(selenium.isElementPresent("id=loadingPanel")) while(selenium.isElementPresent("id=loadingPanel")&&selenium.isVisible("id=loadingPanel"))//wait till the loading screen disappears { Thread.sleep(2000); System.out.println("Loading...."); }} catch(Exception e){ Logger.logPrint("Exception in wait_for_ajax_loading() "+e); Logger.failedReport(report, e); driver.quit(); System.exit(0); } } But I don't know exactly when to call the above function, calling it at a wrong time will fail. Is there any efficient way to check if an element is actually clickable? or the loading image is present? Thanks..

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• Generate regular expression to match strings from the list A, but not from list B

  - by Vlad

  I have two lists of strings ListA and ListB. I need to generate a regular expression that will match all strings in ListA and will not match any string in ListB. The strings could contain any combination of characters, numbers and punctuation. If a string appears on ListA it is guaranteed that it will not be in the ListB. If a string is not in either of these two lists I don't care what the result of the matching should be. The lists typically contain thousands of strings, and strings are fairly similar to each other. I know the trivial answer to this question, which is just generate a regular expression of the form (Str1)|(Str2)|(Str3) where StrN is the string from ListA. But I am looking for a more efficient way to do this. Ideal solution would be some sort of tool that will take two lists and generate a Java regular expression for this. Update 1: By "efficient", I mean to generate expression that is shorter than trivial solution. The ideal algorithm would generate the shorted possible expression. Here are some examples. ListA = { C10 , C15, C195 } ListB = { Bob, Billy } The ideal expression would be /^C1.+$/ Another example, note the third element of ListB ListA = { C10 , C15, C195 } ListB = { Bob, Billy, C25 } The ideal expression is /^C[^2]{1}.+$/ The last example ListA = { A , D ,E , F , H } ListB = { B , C , G , I } The ideal expression is the same as trivial solution which is /^(A|D|E|F|H)$/ Also, I am not looking for the ideal solution, anything better than trivial would help. I was thinking along the lines of generating the list of trivial solutions, and then try to merge the common substrings while watching that we don't wander into ListB territory. *Update 2: I am not particularly worried about the time it takes to generate the RegEx, anything under 10 minutes on the modern machine is acceptable

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• What is the optimal way to animate a drawable within a view using the animator classes?

  - by littleFluffyKitty

  I have read about Property Animation and Hardware Acceleration but I am still uncertain what is the most efficient way to use the animator classes. (For the sake of this question I don't need to support devices before Honeycomb. So I want to use the animator classes.) For example, say I have a View. In this view I have a BitmapDrawable that I want to fade in. There are also many other elements within the view that won't change. What property or object would be best to use with the animator? The drawable? A paint that I am drawing the bitmap with in onDraw? Something else? How can this be done to be most efficient with hardware acceleration? Will this require calling invalidate for each step of the animation or is there a way to animate just the drawable and not cause the rest of the view to be redrawn completely for each step of the animation? I guess I imagine an optimal case would be the rest of the view not having to be completely redrawn in software, but rather hardware acceleration efficiently fading the drawable. Any suggestions or pointers to recommended approaches? Thanks!

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• Socket Performance C++ Or C#

  - by modernzombie

  I have to write an application that is essentially a proxy server to handle all HTTP and HTTPS requests from our server (web browsing, etc). I know very little C++ and am very comfortable writing the application features in C#. I have experimented with the proxy from Mentalis (socket proxy) which seems to work fine for small webpages but if I go to large sites like tigerdirect.ca and browse through a couple of layers it is very slow and sometimes requests don't complete and I see broken images and javascript errors. This happens with all of our vendor sites and other content heavy sites. Mentalis uses HTTP 1.0 which I know is not as efficient but should a proxy be that slow? What is an acceptable amount of performance loss from using a proxy? Would HTTP 1.1 make a noticeable difference? Would a C++ proxy be much faster than one in C#? Is the Mentalis code just not efficient? Would I be able to use a premade C++ proxy and import the DLL to C# and still get good performance or would this project call for all C++? Sorry if these are obvious questions but I have not done network programming before.

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• Processing a resultset to look up foriegn keys (and poulate a new table!)

  - by Gilly

  Hi, I've been handed a dataset that has some fairly basic table structures with no keys at all. eg {myRubishTable} - Area(varchar),AuthorityName(varchar),StartYear(varchar),StartMonth(varcha),EndYear(varchar),EndMonth(varchar),Amount(Money) there are other tables that use the Area and AuthorityName columns as well as a general use of Month and Years so I I figured a good first step was to pull Area and Authority into their own tables. I now want to process the data in the original table and lookup the key value to put into my new table with foreign keys which looks like this. (lookup Tables) {Area} - id (int, PK), name (varchar(50)) {AuthorityName} - id(int, PK), name(varchar(50) (TargetTable) {myBetterTable} - id (int,PK), area_id(int FK-Area),authority_name_id(int FK-AuthorityName),StartYear (varchar),StartMonth(varchar),EndYear(varchar),EndMonth(varchar),Amount(money) so row one in the old table read MYAREA, MYAUTHORITY,2009,Jan,2010,Feb,10000 and I want to populate the new table with 1,1,1,2009,Jan,2010,Feb,10000 where the first '1' is the primary key and the second two '1's are the ids in the lookup tables. Can anyone point me to the most efficient way of achieving this using just SQL? Thanks in advance Footnote:- I've achieved what I needed with some pretty simple WHERE clauses (I had left a rogue tablename in the FROM which was throwing me :o( ) but would be interested to know if this is the most efficient. ie SELECT [area].[area_id], [authority].[authority_name_id], [myRubishTable].[StartYear], [myRubishTable].[StartMonth], [myRubishTable].[EndYear], [myRubishTable].[EndMonth], [myRubishTable].[Amount] FROM [myRubishTable],[Area],[AuthorityName] WHERE [myRubishTable].[Area]=[Area].[name] AND [myRubishTable].[Authority Name]=[dim_AuthorityName].[name] TIA

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• MySQL/PHP Search Efficiency

  - by iMaster

  Hi! I'm trying to create a small search for my site. I've tried using full-text index search, but I could never get it to work. Here is what I've come up with: if(isset($_GET['search'])) { $search = str_replace('-', ' ', $_GET['search']); $result = array(); $titles = mysql_query("SELECT title FROM Entries WHERE title LIKE '%$search%'"); while($row = mysql_fetch_assoc($titles)) { $result[] = $row['title']; } $tags = mysql_query("SELECT title FROM Entries WHERE tags LIKE '%$search%'"); while($row = mysql_fetch_assoc($tags)) { $result[] = $row['title']; } $text = mysql_query("SELECT title FROM Entries WHERE entry LIKE '%$search%'"); while($row = mysql_fetch_assoc($text)) { $result[] = $row['title']; } $result = array_unique($result); } So basically, it searches through all the titles, body-text, and tags of all the entries in the DB. This works decently well, but I'm just wondering how efficient would it be? This would only be for a small blog, too. Either way I'm just wondering if this could be made any more efficient.

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• How to get results efficiently out of an Octree/Quadtree?

  - by Reveazure

  I am working on a piece of 3D software that has sometimes has to perform intersections between massive numbers of curves (sometimes ~100,000). The most natural way to do this is to do an N^2 bounding box check, and then those curves whose bounding boxes overlap get intersected. I heard good things about octrees, so I decided to try implementing one to see if I would get improved performance. Here's my design: Each octree node is implemented as a class with a list of subnodes and an ordered list of object indices. When an object is being added, it's added to the lowest node that entirely contains the object, or some of that node's children if the object doesn't fill all of the children. Now, what I want to do is retrieve all objects that share a tree node with a given object. To do this, I traverse all tree nodes, and if they contain the given index, I add all of their other indices to an ordered list. This is efficient because the indices within each node are already ordered, so finding out if each index is already in the list is fast. However, the list ends up having to be resized, and this takes up most of the time in the algorithm. So what I need is some kind of tree-like data structure that will allow me to efficiently add ordered data, and also be efficient in memory. Any suggestions?

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• How can I use SQL Server's full text search across multiple rows at once?

  - by Morbo

  I'm trying to improve the search functionality on my web forums. I've got a table of posts, and each post has (among other less interesting things): PostID, a unique ID for the individual post. ThreadID, an ID of the thread the post belongs to. There can be any number of posts per thread. Text, because a forum would be really boring without it. I want to write an efficient query that will search the threads in the forum for a series of words, and it should return a hit for any ThreadID for which there are posts that include all of the search words. For example, let's say that thread 9 has post 1001 with the word "cat" in it, and also post 1027 with the word "hat" in it. I want a search for cat hat to return a hit for thread 9. This seems like a straightforward requirement, but I don't know of an efficient way to do it. Using the regular FREETEXT and CONTAINS capabilities for N'cat AND hat' won't return any hits in the above example because the words exist in different posts, even though those posts are in the same thread. (As far as I can tell, when using CREATE FULLTEXT INDEX I have to give it my index on the primary key PostID, and can't tell it to index all posts with the same ThreadID together.) The solution that I currently have in place works, but sucks: maintain a separate table that contains the entire concatenated post text of every thread, and make a full text index on THAT. I'm looking for a solution that doesn't require me to keep a duplicate copy of the entire text of every thread in my forums. Any ideas? Am I missing something obvious?

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• Java ORM related question - SQL Vs Google DB (Big Table?) GAE

  - by StackerFlow

  I was wondering about the following two options when one is not using SQL tables but ORM based DBs (Example - when you are using GAE) Would the second option be less efficient? Requirement: There is an object. The object has a collection of similar items. I need to store this object. Example, say the object is a tree and it has a collection of leaves. Option 1: Traditional SQL type structure: Table for the Tree (with TreeId as the identifier for a row in the Table.) Table for the Leaves (where each leaf has a TreeId and to show the leaves of a tree, I query all leaves where the TreeId is the Id of the tree.) Here, the Tree structure DOES NOT have a field with leaves. Option 2: ORM / GAE Tables: Using the same example above, I have an object for Tree where the object has a collection (Set/List in Java/C++) of leaves. I store and retrieve the Tree together with the leaves (as the leaves are implemented as a Set in the Tree object) My question is, will the second one be less efficient that the first option? If so, why? Are there other alternatives? Thank you!

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• How to current snapshot of MySQL Table and store it into CSV file(after creating it) ?

  - by Rachel

  I have large database table, approximately 5GB, now I wan to getCurrentSnapshot of Database using "Select * from MyTableName", am using PDO in PHP to interact with Database. So preparing a query and then executing it // Execute the prepared query $result->execute(); $resultCollection = $result->fetchAll(PDO::FETCH_ASSOC); is not an efficient way as lots of memory is being user for storing into the associative array data which is approximately, 5GB. My final goal is to collect data returned by Select query into an CSV file and put CSV file at an FTP Location from where Client can get it. Other Option I thought was to do: SELECT * INTO OUTFILE "c:/mydata.csv" FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY "\n" FROM my_table; But I am not sure if this would work as I have cron that initiates the complete process and we do not have an csv file, so basically for this approach, PHP Scripts will have to create an CSV file. Do a Select query on the database. Store the select query result into the CSV file. What would be the best or efficient way to do this kind of task ? Any Suggestions !!!

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• SQL Table design question

  - by Projapati

  Please ignore this question if it sounds stupid to you. I have SQL table (SQL Server) for photo albums and it has 20+ columns & it will hold millions of albums. I need to designate some albums as Promoted and some as Featured every week. I also need a very efficient way to get these albums (page by page) when I show it to users. How should I design this? option 1: I can create another table just to store the ids of the promoted and featured albums like this and then join the main albums table to get the set of columns I need. table designated_albums: album_id promoted_featured 1 1 5 0 7 1 15 0 The query for promoted will return 1, 7 The query for featured will return 5, 15 Option 2: I can add 1 column store 1 if promoted and 0 if featured. Otherwise it is null I can then query to check for 1 in that column for promoted albums & 0 for featured. Option 3: I can add 2 bit columns: one for promoted (0/1) and one for featured(0/1) Which way would perform better? EDIT: The design should be efficient in SQL 2008 as well. Right now I have SQL 2005.

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• SD Card reader not working on Sony Vaio

  - by TessellatingHeckler

  This laptop (Sony Vaio VGN-Z31MN/B PCG-6z2m) has been installed with Windows 7 64 bit, all the drivers from Sony's VAIO site are installed, and everything in Device Manager both (a) has a driver and (b) shows as working, no exclamation marks or warnings. "Hide empty drives" in Folder options is disabled so the card reader appears, but will not read the card ("please insert a disk in drive O:"). Previously, when the laptop had Windows XP on it, it could read the same card. Also, Windows update suggested driver ("SD Card Reader") doesn't work, Ricoh own drivers install properly but do the same behaviour. Other 3rd party driver suggestions from forums (Acer and Texas-Instruments FlashMedia) do not seem to install properly. I would post the PCI id if I had it, but it was just showing up as rimsptsk\diskricohmemorystickstorage (while it had the Ricoh Driver installed). Edit: If there are any lower level diagnostic utlities which might shed more light on it I'd welcome hearing of them. Anything which might show get it to put troubleshooting logs in the event log or identify chipsets or whatever... Update: Device details are: SD\VID_03&OID_5344&PID_SD04G&REV_8.0\5&4617BC3&0&0 : SD Memory Card PCI\VEN_8086&DEV_2934&SUBSYS_9025104D&REV_03\3&21436425&0&E8: Intel(R) ICH9 Family USB Universal Host Controller - 2934 PCI\VEN_1180&DEV_0476&SUBSYS_9025104D&REV_BA\4&1BD7BFCD&0&20F0: Ricoh R/RL/5C476(II) or Compatible CardBus Controller RIMSPTSK\DISK&VEN_RICOH&PROD_MEMORYSTICKSTORAGE&REV_1.00\MS0001: SD Storage Card PCI\VEN_1180&DEV_0592&SUBSYS_9025104D&REV_11\4&1BD7BFCD&0&24F0: Ricoh Memory Stick Host Controller WPDBUSENUMROOT\UMB\2&37C186B&1&STORAGE#VOLUME#_??_RIMSPTSK#DISK&VEN_RICOH&PROD_MEMORYSTICKSTORAGE&REV_1.00#MS0001#: O:\ STORAGE\VOLUME\{C82A81B8-5A4F-11E0-AACC-806E6F6E6963}#0000000000100000: Generic volume PCI\VEN_1180&DEV_0822&SUBSYS_9025104D&REV_21\4&1BD7BFCD&0&22F0: SDA Standard Compliant SD Host Controller ROOT\LEGACY_FVEVOL\0000 : Bitlocker Drive Encryption Filter Driver PCI\VEN_1180&DEV_0832&SUBSYS_9025104D&REV_04\4&1BD7BFCD&0&21F0: Ricoh 1394 OHCI Compliant Host Controller Now going to search for drivers for that.

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• Intermittent Windows Server 2008 BSOD and restart

  - by Timka

  Our EC2 Instance (Windows Server 2008) crashed multiple times for the past 3 months (last time was today at 1:05 EST). Upon reviewing MEMORY.DMP file we noticed that possible cause of the crashes is rhelnet.sys (RedHat PV NIC Driver). Server's Event Viewer has the following records right after the crash: Critical - Kernel Power: The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly. BugCheck: The computer has rebooted from a bugcheck. The bugcheck was: 0x000000d1 (0x000000000000002d, 0x0000000000000002, 0x0000000000000000, 0xfffff88001402d14). A dump was saved in: C:\Windows\MEMORY.DMP. Report Id: 100113-35849-01. Could this be a hardware issue? Would it help if we stop and start the instance? Or is this more likely that this is caused by the software running on the system? [Update 10.01.2013] Amazon Rep suggested to update RH drivers to Citrix PV drivers on our instance: Upgrading PV Drivers [Update 10.08.2013] We performed a drivers upgrade on the cloned instance. Right after the upgrade we noticed the following errors in our Event viewer: Xennet6 errors in Event Viewer (Event ID# 5001) After digging a bit more I found this article suggesting to install the latest Citrix drivers. Unfortunately, this didn't help us at all and our cloned instance became unresponsive. [Update 10.08.2013 2] I recreated an instance and updated PV drivers again. After searching on Internet I found this article where Amazon Rep explains that: "Event ID 5001 from source Xennet6 cannot be found" message does not indicate anything wrong, just that the PV driver is looking for a feature that we have not implemented in our version of Xen. I will keep my test system running for a while to see if there any issues with it.

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• How to stop DW20.exe running on Win 2003 Server (usual solutions already tried)

  - by Laurence

  Periodically my ASP.NET application crashes (usually because memory consumption exceeds maximum allowed by application pool) and DW20.exe starts up. This is a big problem because it uses huge amounts of memory and CPU for minutes at a time. I want to know how to stop DW20.exe from running. Please note, I have already tried these often mentioned solutions: Disabling error reporting in Control Panel System Advanced Error Reporting Disabling the Error Reporting Service Modifying the registry as in http://support.microsoft.com/kb/841477 (however I might have done this wrong - this doc says "add a DWReportee value of 1" - what I did was add a DWORD entry with hexadecimal value of 1 - is this right? Also only 2 of the 4 keys were present, so I only modified these, e.g. there was no HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\PCHealth key at all) So, zero points for suggesting any of the above (unless you can see I have modified the registry incorrectly) ! Also zero points for suggesting I resolve whatever is causing the application crashes :) - I am figuring this out, I just want something in the mean time to stop DW20.exe eating up all the server resources. By the way, this is a Windows 2003 SP1 server, with IIS 6 and SQL 2005 installed. There is no MS Office. Thx

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• FreeBSD performance tuning. Sysctls, loader.conf, kernel.

  - by SaveTheRbtz

  I wanted to share knowledge of tuning FreeBSD via sysctls, so i'm posting them with comments. Based on Igor Sysoev (author of nginx) presentation about FreeBSD tuning up to 100,000-200,000 active connections. Sysctls are for 7.x FreeBSD. Since 7.2 amd64 some of them are tuned well by default. Prior 7.0 some of them are boot only (set via /boot/loader.conf) or does not exist at all. Highload web server sysctls: # Max. backlog size kern.ipc.somaxconn=4096 # Shared memory // 7.2+ can use shared memory > 2Gb kern.ipc.shmmax=2147483648 # Sockets kern.ipc.maxsockets=204800 # Do not use lager sockbufs on 8.0 # ( http://old.nabble.com/Significant-performance-regression-for-increased-maxsockbuf-on-8.0-RELEASE-tt26745981.html#a26745981 ) kern.ipc.maxsockbuf=262144 # Recive clusters (on amd64 7.2+ 65k is default) # For such high value vm.kmem_size must be increased to 3G #kern.ipc.nmbclusters=229376 # Jumbo pagesize(4k/8k) clusters # Used as general packet storage for jumbo frames # can be monitored via `netstat -m` #kern.ipc.nmbjumbop=192000 # Jumbo 9k/16k clusters # If you are using them #kern.ipc.nmbjumbo9=24000 #kern.ipc.nmbjumbo16=10240 # Every socket is a file, so increase them kern.maxfiles=204800 kern.maxfilesperproc=200000 kern.maxvnodes=200000 # Turn off receive autotuning #net.inet.tcp.recvbuf_auto=0 # Small receive space, only usable on http-server, on file server this # should be increased to 65535 or even more #net.inet.tcp.recvspace=8192 # Small send space is useful for http servers that serve small files # Autotuned since 7.x net.inet.tcp.sendspace=16384 # This should be enabled if you going to use big spaces (>64k) #net.inet.tcp.rfc1323=1 # Turn this off on highspeed, lossless connections (LAN 1Gbit+) #net.inet.tcp.delayed_ack=0 # This feature is useful if you are serving data over modems, Gigabit Ethernet, # or even high speed WAN links (or any other link with a high bandwidth delay product), # especially if you are also using window scaling or have configured a large send window. # You can try setting it to 0 on fileserver with 1GBit+ interfaces # Automatically disables on small RTT ( http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netinet/tcp_subr.c?#rev1.237 ) #net.inet.tcp.inflight.enable=0 # Disable randomizing of ports to avoid false RST # Before usage check SA here www.bsdcan.org/2006/papers/ImprovingTCPIP.pdf # (it's also says that port randomization auto-disables at some conn.rates, but I didn't tested it thou) #net.inet.ip.portrange.randomized=0 # Increase portrange # For outgoing connections only. Good for seed-boxes and ftp servers. net.inet.ip.portrange.first=1024 net.inet.ip.portrange.last=65535 # Security net.inet.ip.redirect=0 net.inet.ip.sourceroute=0 net.inet.ip.accept_sourceroute=0 net.inet.icmp.maskrepl=0 net.inet.icmp.log_redirect=0 net.inet.icmp.drop_redirect=1 net.inet.tcp.drop_synfin=1 # Security net.inet.udp.blackhole=1 net.inet.tcp.blackhole=2 # Increases default TTL, sometimes useful # Default is 64 net.inet.ip.ttl=128 # Lessen max segment life to conserve resources # ACK waiting time in miliseconds (default: 30000 from RFC) net.inet.tcp.msl=5000 # Max bumber of timewait sockets net.inet.tcp.maxtcptw=40960 # Don't use tw on local connections # As of 15 Apr 2009. Igor Sysoev says that nolocaltimewait has some buggy realization. # So disable it or now till get fixed #net.inet.tcp.nolocaltimewait=1 # FIN_WAIT_2 state fast recycle net.inet.tcp.fast_finwait2_recycle=1 # Time before tcp keepalive probe is sent # default is 2 hours (7200000) #net.inet.tcp.keepidle=60000 # Should be increased until net.inet.ip.intr_queue_drops is zero net.inet.ip.intr_queue_maxlen=4096 # Interrupt handling via multiple CPU, but with context switch. # You can play with it. Default is 1; #net.isr.direct=0 # This is for routers only #net.inet.ip.forwarding=1 #net.inet.ip.fastforwarding=1 # This speed ups dummynet when channel isn't saturated net.inet.ip.dummynet.io_fast=1 # Increase dummynet(4) hash #net.inet.ip.dummynet.hash_size=2048 #net.inet.ip.dummynet.max_chain_len # Should be increased when you have A LOT of files on server # (Increase until vfs.ufs.dirhash_mem becames lower) vfs.ufs.dirhash_maxmem=67108864 # Explicit Congestion Notification (see http://en.wikipedia.org/wiki/Explicit_Congestion_Notification) net.inet.tcp.ecn.enable=1 # Flowtable - flow caching mechanism # Useful for routers #net.inet.flowtable.enable=1 #net.inet.flowtable.nmbflows=65535 # Extreme polling tuning #kern.polling.burst_max=1000 #kern.polling.each_burst=1000 #kern.polling.reg_frac=100 #kern.polling.user_frac=1 #kern.polling.idle_poll=0 # IPFW dynamic rules and timeouts tuning # Increase dyn_buckets till net.inet.ip.fw.curr_dyn_buckets is lower net.inet.ip.fw.dyn_buckets=65536 net.inet.ip.fw.dyn_max=65536 net.inet.ip.fw.dyn_ack_lifetime=120 net.inet.ip.fw.dyn_syn_lifetime=10 net.inet.ip.fw.dyn_fin_lifetime=2 net.inet.ip.fw.dyn_short_lifetime=10 # Make packets pass firewall only once when using dummynet # i.e. packets going thru pipe are passing out from firewall with accept #net.inet.ip.fw.one_pass=1 # shm_use_phys Wires all shared pages, making them unswappable # Use this to lessen Virtual Memory Manager's work when using Shared Mem. # Useful for databases #kern.ipc.shm_use_phys=1 /boot/loader.conf: # Accept filters for data, http and DNS requests # Usefull when your software uses select() instead of kevent/kqueue or when you under DDoS # DNS accf available on 8.0+ accf_data_load="YES" accf_http_load="YES" accf_dns_load="YES" # Async IO system calls aio_load="YES" # Adds NCQ support in FreeBSD # WARNING! all ad[0-9]+ devices will be renamed to ada[0-9]+ # 8.0+ only #ahci_load= #siis_load= # Increase kernel memory size to 3G. # # Use ONLY if you have KVA_PAGES in kernel configuration, and you have more than 3G RAM # Otherwise panic will happen on next reboot! # # It's required for high buffer sizes: kern.ipc.nmbjumbop, kern.ipc.nmbclusters, etc # Useful on highload stateful firewalls, proxies or ZFS fileservers # (FreeBSD 7.2+ amd64 users: Check that current value is lower!) #vm.kmem_size="3G" # Older versions of FreeBSD can't tune maxfiles on the fly #kern.maxfiles="200000" # Useful for databases # Sets maximum data size to 1G # (FreeBSD 7.2+ amd64 users: Check that current value is lower!) #kern.maxdsiz="1G" # Maximum buffer size(vfs.maxbufspace) # You can check current one via vfs.bufspace # Should be lowered/upped depending on server's load-type # Usually decreased to preserve kmem # (default is 200M) #kern.maxbcache="512M" # Sendfile buffers # For i386 only #kern.ipc.nsfbufs=10240 # syncache Hash table tuning net.inet.tcp.syncache.hashsize=1024 net.inet.tcp.syncache.bucketlimit=100 # Incresed hostcache net.inet.tcp.hostcache.hashsize="16384" net.inet.tcp.hostcache.bucketlimit="100" # TCP control-block Hash table tuning net.inet.tcp.tcbhashsize=4096 # Enable superpages, for 7.2+ only # Also read http://lists.freebsd.org/pipermail/freebsd-hackers/2009-November/030094.html vm.pmap.pg_ps_enabled=1 # Usefull if you are using Intel-Gigabit NIC #hw.em.rxd=4096 #hw.em.txd=4096 #hw.em.rx_process_limit="-1" # Also if you have ALOT interrupts on NIC - play with following parameters # NOTE: You should set them for every NIC #dev.em.0.rx_int_delay: 250 #dev.em.0.tx_int_delay: 250 #dev.em.0.rx_abs_int_delay: 250 #dev.em.0.tx_abs_int_delay: 250 # There is also multithreaded version of em drivers can be found here: # http://people.yandex-team.ru/~wawa/ # # for additional em monitoring and statistics use # `sysctl dev.em.0.stats=1 ; dmesg` # #Same tunings for igb #hw.igb.rxd=4096 #hw.igb.txd=4096 #hw.igb.rx_process_limit=100 # Some useful netisr tunables. See sysctl net.isr #net.isr.defaultqlimit=4096 #net.isr.maxqlimit: 10240 # Bind netisr threads to CPUs #net.isr.bindthreads=1 # Nicer boot logo =) loader_logo="beastie" And finally here is my additions to GENERIC kernel # Just some of them, see also # cat /sys/{i386,amd64,}/conf/NOTES # This one useful only on i386 #options KVA_PAGES=512 # You can play with HZ in environments with high interrupt rate (default is 1000) # 100 is for my notebook to prolong it's battery life #options HZ=100 # Polling is goot on network loads with high packet rates and low-end NICs # NB! Do not enable it if you want more than one netisr thread #options DEVICE_POLLING # Eliminate datacopy on socket read-write # To take advantage with zero copy sockets you should have an MTU of 8K(amd64) # (4k for i386). This req. is only for receiving data. # Read more in man zero_copy_sockets #options ZERO_COPY_SOCKETS # Support TCP sign. Used for IPSec options TCP_SIGNATURE options IPSEC # This ones can be loaded as modules. They described in loader.conf section #options ACCEPT_FILTER_DATA #options ACCEPT_FILTER_HTTP # Adding ipfw, also can be loaded as modules options IPFIREWALL options IPFIREWALL_VERBOSE options IPFIREWALL_VERBOSE_LIMIT=10 options IPFIREWALL_DEFAULT_TO_ACCEPT options IPFIREWALL_FORWARD # Adding kernel NAT options IPFIREWALL_NAT options LIBALIAS # Traffic shaping options DUMMYNET # Divert, i.e. for userspace NAT options IPDIVERT # This is for OpenBSD's pf firewall device pf device pflog # pf's QoS - ALTQ options ALTQ options ALTQ_CBQ # Class Bases Queuing (CBQ) options ALTQ_RED # Random Early Detection (RED) options ALTQ_RIO # RED In/Out options ALTQ_HFSC # Hierarchical Packet Scheduler (HFSC) options ALTQ_PRIQ # Priority Queuing (PRIQ) options ALTQ_NOPCC # Required for SMP build # Pretty console # Manual can be found here http://forums.freebsd.org/showthread.php?t=6134 #options VESA #options SC_PIXEL_MODE # Disable reboot on Ctrl Alt Del #options SC_DISABLE_REBOOT # Change normal|kernel messages color options SC_NORM_ATTR=(FG_GREEN|BG_BLACK) options SC_KERNEL_CONS_ATTR=(FG_YELLOW|BG_BLACK) # More scroll space options SC_HISTORY_SIZE=8192 # Adding hardware crypto device device crypto device cryptodev # Useful network interfaces device vlan device tap #Virtual Ethernet driver device gre #IP over IP tunneling device if_bridge #Bridge interface device pfsync #synchronization interface for PF device carp #Common Address Redundancy Protocol device enc #IPsec interface device lagg #Link aggregation interface device stf #IPv4-IPv6 port # Also for my notebook, but may be used with Opteron #device amdtemp # Support for ECMP. More than one route for destination # Works even with default route so one can use it as LB for two ISP # For now code is unstable and panics (panic: rtfree 2) on route deletions. #options RADIX_MPATH # Multicast routing #options MROUTING #options PIM # DTrace options KDTRACE_HOOKS # all architectures - enable general DTrace hooks options DDB_CTF # all architectures - kernel ELF linker loads CTF data #options KDTRACE_FRAME # amd64-only # Adaptive spining in lockmgr (8.x+) # See http://www.mail-archive.com/[email protected]/msg10782.html options ADAPTIVE_LOCKMGRS # UTF-8 in console (9.x+) #options TEKEN_UTF8 #options TEKEN_XTERM # NCQ support # WARNING! all ad[0-9]+ devices will be renamed to ada[0-9]+ #options ATA_CAM # FreeBSD 9+ # Deadlock resolver thread # For additional information see http://www.mail-archive.com/[email protected]/msg18124.html #options DEADLKRES PS. Also most of FreeBSD's limits can be monitored by # vmstat -z and # limits PPS. variety of network counters can be monitored via # netstat -s In FreeBSD-9 netstat's -Q option appeared, try following command to display netisr stats # netstat -Q PPPS. also see # man 7 tuning PPPPS. I wanted to thank FreeBSD community, especially author of nginx - Igor Sysoev, nginx-ru@ and FreeBSD-performance@ mailing lists for providing useful information about FreeBSD tuning. So here is the question: What tunings are you using on yours FreeBSD servers? You can also post your /etc/sysctl.conf, /boot/loader.conf, kernel options, etc with description of its' meaning (do not copy-paste from sysctl -d). Don't forget to specify server type (web, smb, gateway, etc) Let's share experience!

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• Apachebench on node.js server returning "apr_poll: The timeout specified has expired (70007)" after ~30 requests

  - by Scott

  I just started working with node.js and doing some experimental load testing with ab is returning an error at around 30 requests or so. I've found other pages showing a lot better concurrency numbers than I am such as: http://zgadzaj.com/benchmarking-nodejs-basic-performance-tests-against-apache-php Are there some critical server configuration settings that need done to achieve those numbers? I've watched memory on top and I still see a decent amount of free memory while running ab, watched mongostat as well and not seeing anything that looks suspicious. The command I'm running, and the error is: ab -k -n 100 -c 10 postrockandbeyond.com/ This is ApacheBench, Version 2.0.41-dev <$Revision: 1.121.2.12 $> apache-2.0 Copyright (c) 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/ Copyright (c) 2006 The Apache Software Foundation, http://www.apache.org/ Benchmarking postrockandbeyond.com (be patient)...apr_poll: The timeout specified has expired (70007) Total of 32 requests completed Does anyone have any suggestions on things I should look in to that may be causing this? I'm running it on osx lion, but have also run the same command on the server with the same results. EDIT: I eventually solved this issue. I was using a TTAPI, which was connecting to turntable.fm through websockets. On the homepage, I was connecting on every request. So what was happening was that after a certain number of connections, everything would fall apart. If you're running into the same issue, check out whether you are hitting external services each request.

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• Ubuntu12.04 crashed while trying to install Ubuntu14.04, no longer have access

  - by FACE

  Posting from my laptop, as my Compaq desktop crashed. Not very computer saavy, and not sure what info I should provide...but here's a start: 9 year old desktop Compaq SR 1650NX, AMD Athlon 3500+ probably 1 gB ram (duh....) Was running 12.04....was attempting to upgrade to 14.04, not sure if I interrupted it. Pretty much stuck on (constantly redirected to) a page which says "GNU Grub version 1.99-2"; it offers several choices (as written): Ubuntu, with Linux 3.2.0-67-generic Ubuntu, with Linux 3.2.0-67-generic (recovery mode) Previous Linux versions Memory Test (memtest86+) Memory Test (memtest86+, serial console 115200) But none of the selections seem to be able to get me anywhere (i.e., I click yes, but can't seem to run any commands - not that I know anything useful); I escape from those pages by repeatedly hitting CTRL-ALT-DEL Any help would be appreciated; will provide additional info when requested. Thanx (hopefully), in advance. (If I don't respond immediately, it just means I had to attend to other concerns...will leave page open and check back in as often as possible). FACE

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