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• Why is doing a top(1) on an indexed column in SQL Server slow?

  - by reinier

  I'm puzzled by the following. I have a DB with around 10 million rows, and (among other indices) on 1 column (campaignid_int) is an index. Now I have 700k rows where the campaignid is indeed 3835 For all these rows, the connectionid is the same. I just want to find out this connectionid. use messaging_db; SELECT TOP (1) connectionid FROM outgoing_messages WITH (NOLOCK) WHERE (campaignid_int = 3835) Now this query takes approx 30 seconds to perform! I (with my small db knowledge) would expect that it would take any of the rows, and return me that connectionid If I test this same query for a campaign which only has 1 entry, it goes really fast. So the index works. How would I tackle this and why does this not work? edit: estimated execution plan: select (0%) - top (0%) - clustered index scan (100%)

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• Nginx , Apache , Mysql , Memcache with server 4G ram. How optimize to enoigh of memory?

  - by TomSawyer

  i have 1 dedicated server with Nginx proxy for Apache. Memcache, mysql, 4G Ram. These day, my visitor on my site wasn't increased, but my server get overload always in some specified time. (9AM - 15PM) Ram in use is increased second by second to full. that's moment, my server will get overload. i have to kill all apache , mysql service and reboot it to get free memory. and it'll full again. that's the terrible circle. here is my ram in use at the moment 160(nginx) 220(apache) 512(memcache) 924(mysql) here's process number 4(nginx) 14(apache) 5(memcache) 20(mysql) and here's my my.cnf config. someone can help me to optimize it? [mysqld] datadir=/var/lib/mysql socket=/var/lib/mysql/mysql.sock user=mysql skip-locking skip-networking skip-name-resolve # enable log-slow-queries log-slow-queries = /var/log/mysql-slow-queries.log long_query_time=3 max_connections=200 wait_timeout=64 connect_timeout = 10 interactive_timeout = 25 thread_stack = 512K max_allowed_packet=16M table_cache=1500 read_buffer_size=4M join_buffer_size=4M sort_buffer_size=4M read_rnd_buffer_size = 4M max_heap_table_size=256M tmp_table_size=256M thread_cache=256 query_cache_type=1 query_cache_limit=4M query_cache_size=16M thread_concurrency=8 myisam_sort_buffer_size=128M # Disabling symbolic-links is recommended to prevent assorted security risks symbolic-links=0 [mysqldump] quick max_allowed_packet=16M [mysql] no-auto-rehash [isamchk] key_buffer=256M sort_buffer=256M read_buffer=64M write_buffer=64M [myisamchk] key_buffer=256M sort_buffer=256M read_buffer=64M write_buffer=64M [mysqlhotcopy] interactive-timeout [mysql.server] user=mysql basedir=/var/lib [mysqld_safe] log-error=/var/log/mysqld.log pid-file=/var/run/mysqld/mysqld.pid

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• Is there a faster TList implementation ?

  - by dmauric.mp

  My application makes heavy use of TList, so I was wondering if there are any alternative implementations that are faster or optimized for particular use case. I know of RtlVCLOptimize.pas 2.77, which has optimized implementations of several TList methods. But I'd like to know if there is anything else out there. I also don't require it to be a TList descendant, I just need the TList functionality regardless of how it's implemented. It's entirely possible, given the rather basic functionality TList provides, that there is not much room for improvement, but would still like to verify that, hence this question.

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• How to make Visual C++ 9 not emit code that is actually never called?

  - by sharptooth

  My native C++ COM component uses ATL. In DllRegisterServer() I call CComModule::RegisterServer(): STDAPI DllRegisterServer() { return _Module.RegisterServer(FALSE); // <<< notice FALSE here } FALSE is passed to indicate to not register the type library. ATL is available as sources, so I in fact compile the implementation of CComModule::RegisterServer(). Somewhere down the call stack there's an if statement: if( doRegisterTypeLibrary ) { //<< FALSE goes here // do some stuff, then call RegisterTypeLib() } The compiler sees all of the above code and so it can see that in fact the if condition is always false, yet when I inspect the linker progress messages I see that the reference to RegisterTypeLib() is still there, so the if statement is not eliminated. Can I make Visual C++ 9 perform better static analysis and actually see that some code is never called and not emit that code?

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• Script Speed vs Memory Usage

  - by Doug Neiner

  I am working on an image generation script in PHP and have gotten it working two ways. One way is slow but uses a limited amount of memory, the second is much faster, but uses 6x the memory . There is no leakage in either script (as far as I can tell). In a limited benchmark, here is how they performed: -------------------------------------------- METHOD | TOTAL TIME | PEAK MEMORY | IMAGES -------------------------------------------- One | 65.626 | 540,036 | 200 Two | 20.207 | 3,269,600 | 200 -------------------------------------------- And here is the average of the previous numbers (if you don't want to do your own math): -------------------------------------------- METHOD | TOTAL TIME | PEAK MEMORY | IMAGES -------------------------------------------- One | 0.328 | 540,036 | 1 Two | 0.101 | 3,269,600 | 1 -------------------------------------------- Which method should I use and why? I anticipate this being used by a high volume of users, with each user making 10-20 requests to this script during a normal visit. I am leaning toward the faster method because though it uses more memory, it is for a 1/3 of the time and would reduce the number of concurrent requests.

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• In PHP is faster to get a value from an if statement or from an array?

  - by Vittorio Vittori

  Maybe this is a stupid question but what is faster? <?php function getCss1 ($id = 0) { if ($id == 1) { return 'red'; } else if ($id == 2) { return 'yellow'; } else if ($id == 3) { return 'green'; } else if ($id == 4) { return 'blue'; } else if ($id == 5) { return 'orange'; } else { return 'grey'; } } function getCss2 ($id = 0) { $css[] = 'grey'; $css[] = 'red'; $css[] = 'yellow'; $css[] = 'green'; $css[] = 'blue'; $css[] = 'orange'; return $css[$id]; } echo getCss1(3); echo getCss2(3); ?> I suspect is faster the if statement but I prefere to ask!

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• Alternate User select interface in django admin to reduce page size on large site?

  - by David Eyk

  I have a Django-based site with roughly 300,000 User objects. Admin pages for objects with a ForeignKey field to User take a very long time to load as the resulting form is about 6MB in size. Of course, the resulting dropdown isn't particularly useful, either. Are there any off-the-shelf replacements for handling this case? I've been googling for a snippet or a blog entry, but haven't found anything yet. I'd like to have a smaller download size and a more usable interface.

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• Why is Javascript's Math.floor the slowest way to calculate floor in Javascript?

  - by z5h

  I'm generally not a fan of microbenchmarks. But this one has a very interesting result. http://ernestdelgado.com/archive/benchmark-on-the-floor/ It suggests that Math.floor is the SLOWEST way to calculate floor in Javascript. ~~n, n|n, n&n all being faster. This seems pretty shocking as I would expect that people implementing Javascript in today's modern browsers would be some pretty smart people. Does floor do something important that the other methods fail to do? Is there any reason to use it?

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• How can I Query only __key__ on a Google Appengine PolyModel child?

  - by Gabriel

  So the situation is: I want to optimize my code some for doing counting of records. So I have a parent Model class Base, a PolyModel class Entry, and a child class of Entry Article: How would I query Article.key so I can reduce the query load but only get the Article count. My first thought was to use: q = db.GqlQuery("SELECT __key__ from Article where base = :1", i_base) but it turns out GqlQuery doesn't like that because articles are actually stored in a table called Entry. Would it be possible to Query the class attribute? something like: q = db.GqlQuery("select __key__ from Entry where base = :1 and :2 in class", i_base, 'Article') neither of which work. Turns out the answer is even easier. But I am going to finish this question because I looked everywhere for this. q = db.GqlQuery("select __key__ from Entry where base = :1 and class = :2", i_base, 'Article')

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• SEO Google - Navigation Title vs. Page Heading

  - by louism

  Hi, i was wondering if anyone knows if theres a connection between what a navigation item is named and the page heading it goes to - does this have an impact on SEO? so for example, if i had in my navigation menu an item called About Us, but when you click it you come to a page with the heading Learn Who We Are (i.e. wrapped in [h1] heading tags) because there isnt an exact one-to-one match, is that a bad thing in terms of SEO? thanks

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• Splitting tables by field to optimize MySQL?

  - by AK

  Do splitting fields into multiple tables ever yield faster queries? Consider the following two scenarios: Table1 ----------- int PersonID text Value1 float Value2 or Table1 ----------- int PersonID text Value1 Table2 ----------- int PersonID float Value2 If Value1 and Value2 are always being displayed together, I imagine Table1 is always faster because the second schema would require two SELECT statements. But are there any situations where you would choose the second? If the number of records were expected to be really large?

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• Avoid the use of loops (for) with R

  - by albergali

  Hi, I'm working with R and I have a code like this: i<-1 j<-1 for (i in 1:10) for (j in 1:100) if (data[i] == paths[j,1]) cluster[i,4] <- paths[j,2] where : data is a vector with 100 rows and 1 column paths is a matrix with 100 rows and 5 columns cluster is a matrix with 100 rows and 5 columns My question is: how could I avoid the use of "for" loops to iterate through the matrix? I don't know whether apply functions (lapply, tapply...) are useful in this case. This is a problem when j=10000 for example, because execution time is very long. Thank you

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• MySQL Paritioning performance

  - by Imran Pathan

  Measured performance on key partitioned tables and normal tables separately. But we couldn't find any performance improvement with partitioning. Queries are pruned. Using MySQL 5.1.47 on RHEL 4. Table details: UserUsage - Will have entries for user mobile number and data usage for each date. Mobile number and Date as PRI KEY. UserProfile - Queries prev table and stores summary for each mobile number. Mobile number PRI KEY. CREATE TABLE `UserUsage` ( `Msisdn` decimal(20,0) NOT NULL, `Date` date NOT NULL, . . PRIMARY KEY USING BTREE (`Msisdn`,`Date`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 PARTITION BY KEY(Msisdn) PARTITIONS 50; CREATE TABLE `UserProfile` ( `Msisdn` decimal(20,0) NOT NULL, . . PRIMARY KEY (`Msisdn`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 PARTITION BY KEY(Msisdn) PARTITIONS 50; Second table is updated by query select and order by date in first table in a perl program, query is select * from UserUsage where Msisdn=number order by Date desc limit 7 [Process data in perl] update UserProfile values(....) where Msisdn=number explain partition for select, shows row being scanned in a particular partition only. Is something wrong with partition design or queries as partitioning is taking almost same or more time compared to normal tables?

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• Drawbacks of Dynamic Query in Sqlserver 2005 ?

  - by KuldipMCA

  I have using the many dynamic Query in my database for the procedures because my filter is not fix so i have taken @filter as parameter and pass in the procedure. Declare @query as varchar(8000) Declare @Filter as varchar(1000) set @query = 'Select * from Person.Address where 1=1 and ' + @Filter exec(@query) Like that my filter contain any Field from the table for comparison. It will affect my performance or not ? is there any alternate way to achieve this type of things

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• Optimize slow ranking query

  - by Juan Pablo Califano

  I need to optimize a query for a ranking that is taking forever (the query itself works, but I know it's awful and I've just tried it with a good number of records and it gives a timeout). I'll briefly explain the model. I have 3 tables: player, team and player_team. I have players, that can belong to a team. Obvious as it sounds, players are stored in the player table and teams in team. In my app, each player can switch teams at any time, and a log has to be mantained. However, a player is considered to belong to only one team at a given time. The current team of a player is the last one he's joined. The structure of player and team is not relevant, I think. I have an id column PK in each. In player_team I have: id (PK) player_id (FK -> player.id) team_id (FK -> team.id) Now, each team is assigned a point for each player that has joined. So, now, I want to get a ranking of the first N teams with the biggest number of players. My first idea was to get first the current players from player_team (that is one record top for each player; this record must be the player's current team). I failed to find a simple way to do it (tried GROUP BY player_team.player_id HAVING player_team.id = MAX(player_team.id), but that didn't cut it. I tried a number of querys that didn't work, but managed to get this working. SELECT COUNT(*) AS total, pt.team_id, p.facebook_uid AS owner_uid, t.color FROM player_team pt JOIN player p ON (p.id = pt.player_id) JOIN team t ON (t.id = pt.team_id) WHERE pt.id IN ( SELECT max(J.id) FROM player_team J GROUP BY J.player_id ) GROUP BY pt.team_id ORDER BY total DESC LIMIT 50 As I said, it works but looks very bad and performs worse, so I'm sure there must be a better way to go. Anyone has any ideas for optimizing this? I'm using mysql, by the way. Thanks in advance Adding the explain. (Sorry, not sure how to format it properly) id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY t ALL PRIMARY NULL NULL NULL 5000 Using temporary; Using filesort 1 PRIMARY pt ref FKplayer_pt77082,FKplayer_pt265938,new_index FKplayer_pt77082 4 t.id 30 Using where 1 PRIMARY p eq_ref PRIMARY PRIMARY 4 pt.player_id 1 2 DEPENDENT SUBQUERY J index NULL new_index 8 NULL 150000 Using index

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• Optimizing BeautifulSoup (Python) code

  - by user283405

  I have code that uses the BeautifulSoup library for parsing, but it is very slow. The code is written in such a way that threads cannot be used. Can anyone help me with this? I am using BeautifulSoup for parsing and than save into a DB. If I comment out the save statement, it still takes a long time, so there is no problem with the database. def parse(self,text): soup = BeautifulSoup(text) arr = soup.findAll('tbody') for i in range(0,len(arr)-1): data=Data() soup2 = BeautifulSoup(str(arr[i])) arr2 = soup2.findAll('td') c=0 for j in arr2: if str(j).find("<a href=") > 0: data.sourceURL = self.getAttributeValue(str(j),'<a href="') else: if c == 2: data.Hits=j.renderContents() #and few others... c = c+1 data.save() Any suggestions? Note: I already ask this question here but that was closed due to incomplete information.

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• Feedback on Optimizing C# NET Code Block

  - by Brett Powell

  I just spent quite a few hours reading up on TCP servers and my desired protocol I was trying to implement, and finally got everything working great. I noticed the code looks like absolute bollocks (is the the correct usage? Im not a brit) and would like some feedback on optimizing it, mostly for reuse and readability. The packet formats are always int, int, int, string, string. try { BinaryReader reader = new BinaryReader(clientStream); int packetsize = reader.ReadInt32(); int requestid = reader.ReadInt32(); int serverdata = reader.ReadInt32(); Console.WriteLine("Packet Size: {0} RequestID: {1} ServerData: {2}", packetsize, requestid, serverdata); List<byte> str = new List<byte>(); byte nextByte = reader.ReadByte(); while (nextByte != 0) { str.Add(nextByte); nextByte = reader.ReadByte(); } // Password Sent to be Authenticated string string1 = Encoding.UTF8.GetString(str.ToArray()); str.Clear(); nextByte = reader.ReadByte(); while (nextByte != 0) { str.Add(nextByte); nextByte = reader.ReadByte(); } // NULL string string string2 = Encoding.UTF8.GetString(str.ToArray()); Console.WriteLine("String1: {0} String2: {1}", string1, string2); // Reply to Authentication Request MemoryStream stream = new MemoryStream(); BinaryWriter writer = new BinaryWriter(stream); writer.Write((int)(1)); // Packet Size writer.Write((int)(requestid)); // Mirror RequestID if Authenticated, -1 if Failed byte[] buffer = stream.ToArray(); clientStream.Write(buffer, 0, buffer.Length); clientStream.Flush(); } I am going to be dealing with other packet types as well that are formatted the same (int/int/int/str/str), but different values. I could probably create a packet class, but this is a bit outside my scope of knowledge for how to apply it to this scenario. If it makes any difference, this is the Protocol I am implementing. http://developer.valvesoftware.com/wiki/Source_RCON_Protocol

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• Which fieldtype is best for storing PRICE values?

  - by BerggreenDK

  Hi there I am wondering whats the best "price field" in MSSQL for a shoplike structure? Looking at this overview: http://www.teratrax.com/sql_guide/data_types/sql_server_data_types.html We have datatypes called money, smallmoney, then we have decimal/numeric and lastly float and real Name, memory/disk-usage and value ranges: Money: 8 bytes (values: -922,337,203,685,477.5808 to +922,337,203,685,477.5807) Smallmoney: 4 bytes (values: -214,748.3648 to +214,748.3647) Decimal: 9 [default, min. 5] bytes (values: -10^38 +1 to 10^38 -1 ) Float: 8 bytes (values: -1.79E+308 to 1.79E+308 ) Real: 4 bytes (values: -3.40E+38 to 3.40E+38 ) My question is: is it really wise to store pricevalues in those types? what about eg. INT? Int: 4 bytes (values: -2,147,483,648 to 2,147,483,647) Lets say a shop uses dollars, they have cents, but I dont see prices being $49.2142342 so the use of a lot of decimals showing cents seems waste of SQL bandwidth. Secondly, most shops wouldn't show any prices near 200.000.000 (not in normal webshops at least... unless someone is trying to sell me a famous tower in Paris) So why not go for an int? An int is fast, its only 4 bytes and you can easily make decimals, by saving values in cents instead of dollars and then divide when you present the values. The other approach would be to use smallmoney which is 4 bytes too, but this will require the math part of the CPU to do the calc, where as Int is integer power... on the downside you will need to divide every single outcome. Are there any "currency" related problems with regionalsettings when using smallmoney/money fields? what will these transfer too in C#/.NET ? Any pros/cons? Go for integer prices or smallmoney or some other? Whats does your experience tell?

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• Should Python import statements always be at the top of a module?

  - by Adam J. Forster

  PEP 08 states: Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants. However if the class/method/function that I am importing is only used in rare cases, surely it is more efficient to do the import when it is needed? Isn't this: class SomeClass(object): def not_often_called(self) from datetime import datetime self.datetime = datetime.now() more efficient than this? from datetime import datetime class SomeClass(object): def not_often_called(self) self.datetime = datetime.now()

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• Python Profiling In Windows, How do you ignore Builtin Functions

  - by Tim McJilton

  I have not been capable of finding this anywhere online. I was looking to find out using a profiler how to better optimize my code, and when sorting by which functions use up the most time cumulatively, things like str(), print, and other similar widely used functions eat up much of the profile. What is the best way to profile a python program to get the user-defined functions only to see what areas of their code they can optimize? I hope that makes sense, any light you can shed on this subject would be very appreciated.

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• Queries within queries: Is there a better way?

  - by mririgo

  As I build bigger, more advanced web applications, I'm finding myself writing extremely long and complex queries. I tend to write queries within queries a lot because I feel making one call to the database from PHP is better than making several and correlating the data. However, anyone who knows anything about SQL knows about JOINs. Personally, I've used a JOIN or two before, but quickly stopped when I discovered using subqueries because it felt easier and quicker for me to write and maintain. Commonly, I'll do subqueries that may contain one or more subqueries from relative tables. Consider this example: SELECT (SELECT username FROM users WHERE records.user_id = user_id) AS username, (SELECT last_name||', '||first_name FROM users WHERE records.user_id = user_id) AS name, in_timestamp, out_timestamp FROM records ORDER BY in_timestamp Rarely, I'll do subqueries after the WHERE clause. Consider this example: SELECT user_id, (SELECT name FROM organizations WHERE (SELECT organization FROM locations WHERE records.location = location_id) = organization_id) AS organization_name FROM records ORDER BY in_timestamp In these two cases, would I see any sort of improvement if I decided to rewrite the queries using a JOIN? As more of a blanket question, what are the advantages/disadvantages of using subqueries or a JOIN? Is one way more correct or accepted than the other?

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• What algorithm can I use to determine points within a semi-circle?

  - by khayman218

  I have a list of two-dimensional points and I want to obtain which of them fall within a semi-circle. Originally, the target shape was a rectangle aligned with the x and y axis. So the current algorithm sorts the pairs by their X coord and binary searches to the first one that could fall within the rectangle. Then it iterates over each point sequentially. It stops when it hits one that is beyond both the X and Y upper-bound of the target rectangle. This does not work for a semi-circle as you cannot determine an effective upper/lower x and y bounds for it. The semi-circle can have any orientation. Worst case, I will find the least value of a dimension (say x) in the semi-circle, binary search to the first point which is beyond it and then sequentially test the points until I get beyond the upper bound of that dimension. Basically testing an entire band's worth of points on the grid. The problem being this will end up checking many points which are not within the bounds.

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• Delphi fast large bitmap creation (without clearing)

  - by Ritsaert Hornstra

  When using the TBitmap wrapper for a GDI bitmap from the unit Graphics I noticed it will always clear out the bitmap (using a PatBlt call) when setting up a bitmap with SetSize( w, h ). When I copy in the bits later on (see routine below) it seems ScanLine is the fastest possibility and not SetDIBits. function ToBitmap: TBitmap; var i, N, x: Integer; S, D: PAnsiChar; begin Result := TBitmap.Create(); Result.PixelFormat := pf32bit; Result.SetSize( width, height ); S := Src; D := Result.ScanLine[ 0 ]; x := Integer( Result.ScanLine[ 1 ] ) - Integer( D ); N := width * sizeof( longword ); for i := 0 to height - 1 do begin Move( S^, D^, N ); Inc( S, N ); Inc( D, x ); end; end; The bitmaps I need to work with are quite large (150MB of RGB memory). With these iomages it takes 150ms to simply create an empty bitmap and a further 140ms to overwrite it's contents. Is there a way of initializing a TBitmap with the correct size WITHOUT initializing the pixels itself and leaving the memory of the pixels uninitialized (eg dirty)? Or is there another way to do such a thing. I know we could work on the pixels in place but this still leaves the 150ms of unnessesary initializtion of the pixels.

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• C# question to ex-C++/ASM guys. Speed optimisation

  - by maxima120

  Which in C# compiled for x64 is faster? a. int * int; b. if(int < 0) int = -int; c. Math.Abs(int) I need pure theoretical answer. Please do not tell me to write loop and measure it with stopwatch. Thanks

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• Resize an image and maintain quality?

  - by JasonS

  Hi, I have a problem with resizing images. What happens is that if you upload a file larger than the stated parameters, the image is cropped, then saved at 100% quality. So if I upload a large jpeg which is 272Kb. The image is cropped by 100 odd pixels. The file size then goes up to 1.2Mb. We are saving images at a 100% quality. I assume that this is what is causing the problem. The image is exported from Photoshop at 30% quality which reduces the file size. Resaving the image at 100% quality creates the same image but I assume with a lot of redundant file data. Has anyone encountered this before? Does anyone have a solution? This is what we are using. $source_im = imagecreatefromjpeg ($file); $dest_im = imagecreatetruecolor ($newsize_x, $newsize_y); imagecopyresampled ( $dest_im, $source_im, 0, 0, $offset_x, $offset_y, $newsize_x, $newsize_y, $sourceWidth, $sourceHeight ); imagedestroy ($source_im); if ($greyscale) { $dest_im = $this->imageconvertgreyscale ($dest_im); } imagejpeg($dest_im, $save_to_file, $quality); break;

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