micro optimization - Page 73

Efficiently draw a grid in Windows Forms

- by Joel

I'm writing an implementation of Conway's Game of Life in C#. This is the code I'm using to draw the grid, it's in my panel_Paint event. g is the graphics context. for (int y = 0; y < numOfCells * cellSize; y += cellSize) { for (int x = 0; x < numOfCells * cellSize; x += cellSize) { g.DrawLine(p, x, 0, x, y + numOfCells * cellSize); g.DrawLine(p, 0, x, y + size * drawnGrid, x); } } When I run my program, it is unresponsive until it finishes drawing the grid, which takes a few seconds at numOfCells = 100 & cellSize = 10. Removing all the multiplication makes it faster, but not by very much. Is there a better/more efficient way to draw my grid? Thanks

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Optimize SELECT DISTINCT CONCAT query in MySQL

- by L. Cosio

Hello! I'm running this query: SELECT DISTINCT CONCAT(ALFA_CLAVE, FECHA_NACI) FROM listado GROUP BY ALFA_CLAVE HAVING count(CONCAT(ALFA_CLAVE, FECHA_NACI)) > 1 Is there any way to optimize it? Queries are taking 2-3 hours on a table with 850,000 rows. Adding an index to ALFA_CLAVE and FECHA_NACI would work? Thanks in advanced

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Does the compiler optimize the function parameters passed by value?

- by Naveen

Lets say I have a function where the parameter is passed by value instead of const-reference. Further, lets assume that only the value is used inside the function i.e. the function doesn't try to modify it. In that case will the compiler will be able to figure out that it can pass the value by const-reference (for performance reasons) and generate the code accordingly? Is there any compiler which does that?

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Get count matches in query on large table very slow

- by Roy Roes

I have a mysql table "items" with 2 integer fields: seid and tiid The table has about 35000000 records, so it's very large. seid tiid ----------- 1 1 2 2 2 3 2 4 3 4 4 1 4 2 The table has a primary key on both fields, an index on seid and an index on tiid. Someone types in 1 or more tiid values and now I would like to get the seid with most results. For example when someone types 1,2,3, I would like to get seid 2 and 4 as result. They both have 2 matches on the tiid values. My query so far: SELECT COUNT(*) as c, seid FROM items WHERE tiid IN (1,2,3) GROUP BY seid HAVING c = (SELECT COUNT(*) as c, seid FROM items WHERE tiid IN (1,2,3) GROUP BY seid ORDER BY c DESC LIMIT 1) But this query is extremly slow, because of the large table. Does anyone know how to construct a better query for this purpose?

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Java - Optimize finding a string in a list

- by Mark

I have an ArrayList of objects where each object contains a string 'word' and a date. I need to check to see if the date has passed for a list of 500 words. The ArrayList could contain up to a million words and dates. The dates I store as integers, so the problem I have is attempting to find the word I am looking for in the ArrayList. Is there a way to make this faster? In python I have a dict and mWords['foo'] is a simple lookup without looping through the whole 1 million items in the mWords array. Is there something like this in java? for (int i = 0; i < mWords.size(); i++) { if ( word == mWords.get(i).word ) { mLastFindIndex = i; return mWords.get(i); } }

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Read large amount of data from file in Java

- by Crozin

Hello I've got text file that contains 1 000 002 numbers in following formation: 123 456 1 2 3 4 5 6 .... 999999 100000 Now I need to read that data and allocate it to int variables (the very first two numbers) and all the rest (1 000 000 numbers) to an array int[]. It's not a hard task, but - it's horrible slow. My first attempt was java.util.Scanner: Scanner stdin = new Scanner(new File("./path")); int n = stdin.nextInt(); int t = stdin.nextInt(); int array[] = new array[n]; for (int i = 0; i < n; i++) { array[i] = stdin.nextInt(); } It works as excepted but it takes about 7500 ms to execute. I need to fetch that data in up to several hundred of milliseconds. Then I tried java.io.BufferedReader: Using BufferedReader.readLine() and String.split() I got the same results in about 1700 ms, but it's still too many. How can I read that amount of data in less that 1 second? The final result should be equal to: int n = 123; int t = 456; int array[] = { 1, 2, 3, 4, ..., 999999, 100000 };

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Optimizing JS Array Search

- by The.Anti.9

I am working on a Browser-based media player which is written almost entirely in HTML 5 and JavaScript. The backend is written in PHP but it has one function which is to fill the playlist on the initial load. And the rest is all JS. There is a search bar that refines the playlist. I want it to refine as the person is typing, like most media players do. The only problem with this is that it is very slow and laggy as there are about 1000 songs in the whole program and there is likely to be more as time goes on. The original playlist load is an ajax call to a PHP page that returns the results as JSON. Each item has 4 attirbutes: artist album file url I then loop through each object and add it to an array called playlist. At the end of the looping a copy of playlist is created, backup. This is so that I can refine the playlist variable when people refine their search, but still repopulated it from backup without making another server request. The method refine() is called when the user types a key into the searchbox. It flushes playlist and searches through each property (not including url) of each object in the backup array for a match in the string. If there is a match in any of the properties, it appends the information to a table that displays the playlist, and adds it to the object to playlist for access by the actual player. Code for the refine() method: function refine() { $('#loadinggif').show(); $('#library').html("<table id='libtable'><tr><th>Artist</th><th>Album</th><th>File</th><th> </th></tr></table>"); playlist = []; for (var j = 0; j < backup.length; j++) { var sfile = new String(backup[j].file); var salbum = new String(backup[j].album); var sartist = new String(backup[j].artist); if (sfile.toLowerCase().search($('#search').val().toLowerCase()) !== -1 || salbum.toLowerCase().search($('#search').val().toLowerCase()) !== -1 || sartist.toLowerCase().search($('#search').val().toLowerCase()) !== -1) { playlist.push(backup[j]); num = playlist.length-1; $("<tr></tr>").html("<td>" + num + "</td><td>" + sartist + "</td><td>" + salbum + "</td><td>" + sfile + "</td><td><a href='#' onclick='setplay(" + num +");'>Play</a></td>").appendTo('#libtable'); } } $('#loadinggif').hide(); } As I said before, for the first couple of letters typed, this is very slow and laggy. I am looking for ways to refine this to make it much faster and more smooth.

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Need help optimizing this Django aggregate query

- by Chris Lawlor

I have the following model class Plugin(models.Model): name = models.CharField(max_length=50) # more fields which represents a plugin that can be downloaded from my site. To track downloads, I have class Download(models.Model): plugin = models.ForiegnKey(Plugin) timestamp = models.DateTimeField(auto_now=True) So to build a view showing plugins sorted by downloads, I have the following query: # pbd is plugins by download - commented here to prevent scrolling pbd = Plugin.objects.annotate(dl_total=Count('download')).order_by('-dl_total') Which works, but is very slow. With only 1,000 plugins, the avg. response is 3.6 - 3.9 seconds (devserver with local PostgreSQL db), where a similar view with a much simpler query (sorting by plugin release date) takes 160 ms or so. I'm looking for suggestions on how to optimize this query. I'd really prefer that the query return Plugin objects (as opposed to using values) since I'm sharing the same template for the other views (Plugins by rating, Plugins by release date, etc.), so the template is expecting Plugin objects - plus I'm not sure how I would get things like the absolute_url without a reference to the plugin object. Or, is my whole approach doomed to failure? Is there a better way to track downloads? I ultimately want to provide users some nice download statistics for the plugins they've uploaded - like downloads per day/week/month. Will I have to calculate and cache Downloads at some point? EDIT: In my test dataset, there are somewhere between 10-20 Download instances per Plugin - in production I expect this number would be much higher for many of the plugins.

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What is the absolute fastest way to implement a concurrent queue with ONLY one consumer and one producer?

- by JohnPristine

java.util.concurrent.ConcurrentLinkedQueue comes to mind, but is it really optimum for this two-thread scenario? I am looking for the minimum latency possible on both sides (producer and consumer). If the queue is empty you can immediately return null AND if the queue is full you can immediately discard the entry you are offering. Does ConcurrentLinkedQueue use super fast and light locks (AtomicBoolean) ? Has anyone benchmarked ConcurrentLinkedQueue or knows about the ultimate fastest way of doing that? Additional Details: I imagine the queue should be a fair one, meaning the consumer should not make the consumer wait any longer than it needs (by front-running it) and vice-versa.

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Write file need to optimised for heavy traffic part 2

- by Clayton Leung

For anyone interest to see where I come from you can refer to part 1, but it is not necessary. write file need to optimised for heavy traffic Below is a snippet of code I have written to capture some financial tick data from the broker API. The code will run without error. I need to optimize the code, because in peak hours the zf_TickEvent method will be call more than 10000 times a second. I use a memorystream to hold the data until it reaches a certain size, then I output it into a text file. The broker API is only single threaded. void zf_TickEvent(object sender, ZenFire.TickEventArgs e) { outputString = string.Format("{0},{1},{2},{3},{4}\r\n", e.TimeStamp.ToString(timeFmt), e.Product.ToString(), Enum.GetName(typeof(ZenFire.TickType), e.Type), e.Price, e.Volume); fillBuffer(outputString); } public class memoryStreamClass { public static MemoryStream ms = new MemoryStream(); } void fillBuffer(string outputString) { byte[] outputByte = Encoding.ASCII.GetBytes(outputString); memoryStreamClass.ms.Write(outputByte, 0, outputByte.Length); if (memoryStreamClass.ms.Length > 8192) { emptyBuffer(memoryStreamClass.ms); memoryStreamClass.ms.SetLength(0); memoryStreamClass.ms.Position = 0; } } void emptyBuffer(MemoryStream ms) { FileStream outStream = new FileStream("c:\\test.txt", FileMode.Append); ms.WriteTo(outStream); outStream.Flush(); outStream.Close(); } Question: Any suggestion to make this even faster? I will try to vary the buffer length but in terms of code structure, is this (almost) the fastest? When memorystream is filled up and I am emptying it to the file, what would happen to the new data coming in? Do I need to implement a second buffer to hold that data while I am emptying my first buffer? Or is c# smart enough to figure it out? Thanks for any advice

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Performance considerations of a large hard-coded array in the .cs file

- by terence

I'm writing some code where performance is important. In one part of it, I have to compare a large set of pre-computed data against dynamic values. Currently, I'm storing that pre-computed data in a giant array in the .cs file: Data[] data = { /* my data set */ }; The data set is about 90kb, or roughly 13k elements. I was wondering if there's any downside to doing this, as opposed to loading it in from an external file? I'm not entirely sure how C# works internally, so I just wanted to be aware of any performance issues I might encounter with this method.

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Overhead of serving pages - JSPs vs. PHP vs. ASPXs vs. C

- by John Shedletsky

I am interested in writing my own internet ad server. I want to serve billions of impressions with as little hardware possible. Which server-side technologies are best suited for this task? I am asking about the relative overhead of serving my ad pages as either pages rendered by PHP, or Java, or .net, or coding Http responses directly in C and writing some multi-socket IO monster to serve requests (I assume this one wins, but if my assumption is wrong, that would actually be most interesting). Obviously all the most efficient optimizations are done at the algorithm level, but I figure there has got to be some speed differences at the end of the day that makes one method of serving ads better than another. How much overhead does something like apache or IIS introduce? There's got to be a ton of extra junk in there I don't need. At some point I guess this is more a question of which platform/language combo is best suited - please excuse the in-adroitly posed question, hopefully you understand what I am trying to get at.

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Optimizing GDI+ drawing?

- by user146780

I'm using C++ and GDI+ I'm going to be making a vector drawing application and want to use GDI+ for the drawing. I'v created a simple test to get familiar with it: case WM_PAINT: GetCursorPos(&mouse); GetClientRect(hWnd,&rct); hdc = BeginPaint(hWnd, &ps); MemDC = CreateCompatibleDC(hdc); bmp = CreateCompatibleBitmap(hdc, 600, 600); SelectObject(MemDC,bmp); g = new Graphics(MemDC); for(int i = 0; i < 1; ++i) { SolidBrush sb(Color(255,255,255)); g->FillRectangle(&sb,rct.top,rct.left,rct.right,rct.bottom); } for(int i = 0; i < 250; ++i) { pts[0].X = 0; pts[0].Y = 0; pts[1].X = 10 + mouse.x * i; pts[1].Y = 0 + mouse.y * i; pts[2].X = 10 * i + mouse.x; pts[2].Y = 10 + mouse.y * i; pts[3].X = 0 + mouse.x; pts[3].Y = (rand() % 600) + mouse.y; Point p1, p2; p1.X = 0; p1.Y = 0; p2.X = 300; p2.Y = 300; g->FillPolygon(&b,pts,4); } BitBlt(hdc,0,0,900,900,MemDC,0,0,SRCCOPY); EndPaint(hWnd, &ps); DeleteObject(bmp); g->ReleaseHDC(MemDC); DeleteDC(MemDC); delete g; break; I'm wondering if I'm doing it right, or if I have areas killing the cpu. Because right now it takes ~ 1sec to render this and I want to be able to have it redraw itself very quickly. Thanks In a real situation would it be better just to figure out the portion of the screen to redraw and only redraw the elements withing bounds of this?

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Efficient SQL to count an occurrence in the latest X rows

- by pulegium

For example I have: create table a (i int); Assume there are 10k rows. I want to count 0's in the last 20 rows. Something like: select count(*) from (select i from a limit 20) where i = 0; Is that possible to make it more efficient? Like a single SQL statement or something? PS. DB is SQLite3 if that matters at all...

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Word frequency tally script is too slow

- by Dave Jarvis

Background Created a script to count the frequency of words in a plain text file. The script performs the following steps: Count the frequency of words from a corpus. Retain each word in the corpus found in a dictionary. Create a comma-separated file of the frequencies. The script is at: http://pastebin.com/VAZdeKXs Problem The following lines continually cycle through the dictionary to match words: for i in $(awk '{if( $2 ) print $2}' frequency.txt); do grep -m 1 ^$i\$ dictionary.txt >> corpus-lexicon.txt; done It works, but it is slow because it is scanning the words it found to remove any that are not in the dictionary. The code performs this task by scanning the dictionary for every single word. (The -m 1 parameter stops the scan when the match is found.) Question How would you optimize the script so that the dictionary is not scanned from start to finish for every single word? The majority of the words will not be in the dictionary. Thank you!

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C++ DWORD* to BYTE*

- by NomeSkavinski

My issue, i am trying to convert and array of dynamic memory of type DWORD to a BYTE. Fair enough i can for loop through this and convert the DWORD into a BYTE per entry. But is their a faster way to do this? to take a pointer to DWORD data and convert the whole piece of data into a pointer to BYTE data? such as using a memcpy operation? I feel this is not possible, im not requesting an answer just an experienced opinion on my approach, as i have tried testing both approaches but seem to fail getting to a solution on my second solution. Thanks for any input, again no answers just a point in the right direction. Nor is this a homework question, i felt that had to be mentioned.

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Help on MySQL table indexing when GROUP BY is used in a query

- by Silver Light

Thank you for your attention. There are two INNODB tables: Table authors id INT nickname VARCHAR(50) status ENUM('active', 'blocked') about TEXT Table books author_id INT title VARCHAR(150) I'm running a query against these tables, to get each author and a count of books he has: SELECT a. * , COUNT( b.id ) AS book_count FROM authors AS a, books AS b WHERE a.status != 'blocked' AND b.author_id = a.id GROUP BY a.id ORDER BY a.nickname This query is very slow (takes about 6 seconds to execute). I have an index on books.author_id and it works perfectly, but I do not know how to create an index on authors table, so that this query could use it. Here is how current EXPLAIN looks: id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE a ALL PRIMARY,id_status_nickname NULL NULL NULL 3305 Using where; Using temporary; Using filesort 1 SIMPLE b ref key_author_id key_author_id 5 a.id 2 Using where; Using index I've looked at MySQL manual on optimizing queries with group by, but could not figure out how I can apply it on my query. I'll appreciate any help and hints on this - what must be the index structure, so that MySQL could use it?

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If statements inside or outside loops?

- by Timmy

Is it better if I do this: foreach my $item ( @array ) { if ( $bool ) { .. code .. } else { .. code .. } } or if ( $bool ) { foreach my $item ( @array ) { } } else { foreach my $item ( @array ) { } }

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Fastest way to compare Objects of type DateTime

- by radbyx

I made this. Is this the fastest way to find lastest DateTime of my collection of DateTimes? I'm wondering if there is a method for what i'm doing inside the foreach, but even if there is, I can't see how it can be faster than what i all ready got. List<StateLog> stateLogs = db.StateLog.Where(p => p.ProductID == product.ProductID).ToList(); DateTime lastTimeStamp = DateTime.MinValue; foreach (var stateLog in stateLogs) { int result = DateTime.Compare(lastTimeStamp, stateLog.TimeStamp); if (result < 0) lastTimeStamp = stateLog.TimeStamp; // sæt fordi timestamp er senere }

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Results from two queries at once in sqlite?

- by SF.

I'm currently trying to optimize the sluggish process of retrieving a page of log entries from the SQLite database. I noticed I almost always retrieve next entries along with count of available entries: SELECT time, level, type, text FROM Logs WHERE level IN (%s) ORDER BY time DESC, id DESC LIMIT LOG_REQ_LINES OFFSET %d* LOG_REQ_LINES ; together with total count of records that can match current query: SELECT count(*) FROM Logs WHERE level IN (%s); (for a display "page n of m") I wonder, if I could concatenate the two queries, and ask them both in one sqlite3_exec() simply concatenating the query string. How should my callback function look then? Can I distinguish between the different types of data by argc? What other optimizations would you suggest?

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Does a c/c++ compiler optimize constant divisions by power-of-two value into shifts?

- by porgarmingduod

Question says it all. Does anyone know if the following... size_t div(size_t value) { const size_t x = 64; return value / x; } ...is optimized into? size_t div(size_t value) { return value >> 6; } Do compilers do this? (My interest lies in GCC). Are there situations where it does and others where it doesn't? I would really like to know, because every time I write a division that could be optimized like this I spend some mental energy wondering about whether precious nothings of a second is wasted doing a division where a shift would suffice.

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Preventing objects from being linked if they are not needed?

- by Massif

I have an ARM project that I'm building with make. I'm creating the list of object files to link based on the names of all of the .c and .cpp files in my source directory. However, I would like to exclude objects from being linked if they are never used. Will the linker exclude these objects from the .elf file automatically even if I include them in the list of objects to link? If not, is there a way to generate a list of only the objects that need to be linked?

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learning sample of likely() and unlikely() compiler hints

- by osgx

Hello How can I demonstrate for students the usability of likely and unlikely compiler hints (__builtin_expect)? Can you write an sample code, which will be several times faster with these hints comparing the code without hints.

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How does JIT replace optimized machine code during runtime?

- by stacker

I'm browsing through OpenJDK sources and cannot find the place where optimized code is replaced. I wonder how this can be done in protected mode, isn't it some kind of selfmodifing code which should be prevented by the OS?

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MySql product\tag query optimisation - please help!

- by Nige

Search Results

Search found 4136 results on 166 pages for 'micro optimization'.

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- by Joel

- by L. Cosio

- by Naveen

- by Roy Roes

- by Mark

- by Crozin

- by The.Anti.9

- by Chris Lawlor

- by JohnPristine

- by Clayton Leung

- by terence

- by John Shedletsky

- by user146780

- by pulegium

- by Dave Jarvis

- by NomeSkavinski

- by Silver Light

- by Timmy

- by radbyx

- by SF.

- by porgarmingduod

- by Massif

- by osgx

- by stacker

- by Nige

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