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  • How do we greatly optimize our MySQL database (or replace it) when using joins?

    - by jkaz
    Hi there, This is the first time I'm approaching an extremely high-volume situation. This is an ad server based on MySQL. However, the query that is used incorporates a lot of JOINs and is generally just slow. (This is Rails ActiveRecord, btw) sel = Ads.find(:all, :select = '*', :joins = "JOIN campaigns ON ads.campaign_id = campaigns.id JOIN users ON campaigns.user_id = users.id LEFT JOIN countries ON countries.campaign_id = campaigns.id LEFT JOIN keywords ON keywords.campaign_id = campaigns.id", :conditions = [flashstr + "keywords.word = ? AND ads.format = ? AND campaigns.cenabled = 1 AND (countries.country IS NULL OR countries.country = ?) AND ads.enabled = 1 AND campaigns.dailyenabled = 1 AND users.uenabled = 1", kw, format, viewer['country'][0]], :order = order, :limit = limit) My questions: Is there an alternative database like MySQL that has JOIN support, but is much faster? (I know there's Postgre, still evaluating it.) Otherwise, would firing up a MySQL instance, loading a local database into memory and re-loading that every 5 minutes help? Otherwise, is there any way I could switch this entire operation to Redis or Cassandra, and somehow change the JOIN behavior to match the (non-JOIN-able) nature of NoSQL? Thank you!

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  • Why use bin2hex when inserting binary data from PHP into MySQL?

    - by Atli
    I heard a rumor that when inserting binary data (files and such) into MySQL, you should use the bin2hex() function and send it as a HEX-coded value, rather than just use mysql_real_escape_string on the binary string and use that. // That you should do $hex = bin2hex($raw_bin); $sql = "INSERT INTO `table`(`file`) VALUES (X'{$hex}')"; // Rather than $bin = mysql_real_escape_string($raw_bin); $sql = "INSERT INTO `table`(`file`) VALUES ('{$bin}')"; It is supposedly for performance reasons. Something to do with how MySQL handles large strings vs. how it handles HEX-coded values However, I am having a hard time confirming this. All my tests indicate the exact oposite; that the bin2hex method is ~85% slower and uses ~24% more memory. (I am testing this on PHP 5.3, MySQL 5.1, Win7 x64 - Using a farily simple insert loop.) For instance, this graph shows the private memory usage of the mysqld process while the test code was running: Does anybody have any explainations or reasources that would clarify this? Thanks.

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  • IE7 is making my life miserable! Getting gaps between html table columns (w/ colspan) with css togg

    - by Art Peterson
    Copy/paste this html code snippet and try it out in IE7. When you toggle the hidden columns it leaves a gap between the columns. In Firefox it works fine, the columns touch when minimized. Haven't tried IE8 yet, would be curious to hear how it works there. Any ideas? I've tried a bunch of things in the CSS like table-layout:fixed but no luck. Note: Not looking for a different toggling method because the table I'm really dealing with is 50+ columns wide and 4000+ rows so looping/jquery techniques are too slow. Here's the code - if someone can re-post a working version of it I'll instantly give them the check and be forever in your debt! <DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <script> function toggle() { var tableobj = document.getElementById("mytable"); if (tableobj.className == "") { tableobj.className = "hide1 hide2"; } else { tableobj.className = ""; } } </script> <style> table { border-collapse: collapse; } td, th { border: 1px solid silver; } .hide1 .col1 { display: none; } .hide2 .col2 { display: none; } </style> </head> <body> <input type="button" value="toggle" onclick="toggle();" /> <table id="mytable"> <tr> <th>A</th> <th colspan="2">B</th> <th colspan="2" class="col1">B1</th> <th colspan="2">C</th> <th colspan="2" class="col2">C1</th> </tr> <tr> <td>123</td> <td>456</td> <td>789</td> <td class="col1">123</td> <td class="col1">456</td> <td>789</td> <td>123</td> <td class="col2">456</td> <td class="col2">789</td> </tr> </table> </body> </html>

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  • How to display out the contents from mysql and path it to an image properly?

    - by Panda
    I was trying very hard to think of a solution for my problem but have drain all my brain cells into this...What happen is: I have a CK editor where it allows user to input both text and images. A good example would be http://ckeditor.com/demo. Something like the red riding good example in the demo. I would like to have text surrounding the image like the example. With CK editor, user can now do that. However, now they will submit the changes and i was wondering how should I save the data? What i have found: After reading my articles and solutions on the web, all the experts would advise not to put image into the mysql database together with the text. I would like to ask if this is the case what should I do to extract the text from the ck editor and store it into mysql database and separately store the images into my web server? I know how to retrieve text from mysql database. But how do you put the retrieved text abd images together such as it appears to be how the user have input in CK editor?? Guys I am sorry if my question is confusing you or is making you angry because i admit I am really a newbie in this and I will learn all that I can...Thanks for all your advice and teachings.

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  • UTF-8 MySQL and Charset, pls help me understand this once and for all!

    - by FFish
    Can someone explain me when I set everything to UTF-8 I keep getting those damn ??? MySQL Server version: 5.1.44 MySQL charset: UTF-8 Unicode (utf8) I create a new database name: utf8test collation: utf8_general_ci MySQL connection collation: utf8_general_ci My SQL looks like this: SET SQL_MODE="NO_AUTO_VALUE_ON_ZERO"; CREATE TABLE IF NOT EXISTS `test_table` ( `test_id` int(11) NOT NULL, `test_text` text NOT NULL, PRIMARY KEY (`test_id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; INSERT INTO `test_table` (`test_id`, `test_text`) VALUES (1, 'hééélo'), (2, 'wööörld'); My PHP / HTML: <?php $db_conn = mysql_connect("localhost", "root", "") or die("Can't connect to db"); mysql_select_db("utf8test", $db_conn) or die("Can't select db"); // $result = mysql_query("set names 'utf8'"); // this works... why?? $query = "SELECT * FROM test_table"; $result = mysql_query($query); $output = ""; while($row = mysql_fetch_assoc($result)) { $output .= "id: " . $row['test_id'] . " - text: " . $row['test_text'] . "<br />"; } ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html lang="it" xmlns="http://www.w3.org/1999/xhtml" xml:lang="it"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>UTF-8 test</title> </head> <body> <?php echo $output; ?> </body> </html>

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  • Entity Framework + MySQL - Why is the performance so terrible?

    - by Cyril Gupta
    When I decided to use an OR/M (Entity Framework for MySQL this time) for my new project I was hoping it would save me time, but I seem to have failed it (for the second time now). Take this simple SQL Query SELECT * FROM POST ORDER BY addedOn DESC LIMIT 0, 50 It executes and gives me results in less than a second as it should (the table has about 60,000 rows). Here's the equivalent LINQ To Entities query that I wrote for this var q = (from p in db.post orderby p.addedOn descending select p).Take(50); var q1 = q.ToList(); //This is where the query is fetched and timed out But this query never even executes it times out ALWAYS (without orderby it takes 5 seconds to run)! My timeout is set to 12 seconds so you can imagine it is taking much more than that. Why is this happening? Is there a way I can see what is the actual SQL Query that Entity Framework is sending to the db? Should I give up on EF+MySQL and move to standard SQL before I lose all eternity trying to make it work? I've recalibrated my indexes, tried eager loading (which actually makes it fail even without the orderby clause) Please help, I am about to give up OR/M for MySQL as a lost cause.

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  • does entity framework or mysql provider swallows timeout exceptions on enumeration of result?!

    - by Freddy Rios
    I'm trying to make sense of a situation I have using entity framework on .net 3.5 sp1 + MySQL 6.1.2.0 as the provider. It involves the following code: Response.Write("Products: " + plist.Count() + "<br />"); var total = 0; foreach (var p in plist) { //... some actions total++; //... other actions } Response.Write("Total Products Checked: " + total + "<br />"); Basically the total products is varying on each run, and it isn't matching the full total in plist. Its varies widely, from ~ 1/5th to half. There isn't any control flow code inside the foreach i.e. no break, continue, try/catch, conditions around total++, anything that could affect the count. As confirmation, there are other totals captured inside the loop related to the actions, and those match the lower and higher total runs. I don't find any reason to the above, other than something in entity framework or the mysql provider that causes it to end the foreach when retrieving an item. The body of the foreach can have some good variation in time, as the actions involve file & network access, my best shot at the time is that when it takes beyond certain threshold there is some type of timeout in the underlying framework/provider and instead of causing an exception it is silently reporting no more items for enumeration. Can anyone give some light in the above scenario and/or confirm if the entity framework/mysql provider has the above behavior?

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  • Minimizing MySQL output with Compress() and by concatening results?

    - by johnrl
    Hi all. It is crucial that I transfer the least amount of data possible between server and client. Therefore I thought of using the mysql Compress() function. To get the max compression I also want to concatenate all my results in one large string (or several of max length allowed by MySql), to allow for similar results to be compressed, and then compress these/that string. 1st problem (concatenating mysql results): SELECT name,age FROM users returns 10 results. I want to concatenate all these results in one strign on the form: name,age,name,age,name,age... and so on. Is this possible? 2nd problem (compressing the results from above) When I have comstructed the concatenated string as above I want to compress it. If I do: SELECT COMPRESS('myname'); then it just gives me as output the character '-' - sometimes it even returns unprintable characters. How do I get COMPRESS() to return a compressed printable string that I can trasnfer in ex ASCII encoding?

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  • Is there a way to sync (two way) tables betwen a mysql server and a local MS Access?

    - by Kailen
    Help me figure out a solution to a (not so unique) problem. My research group has gps devices attached to migratory animals. Every once in a while, a research tech will be within range of an animal and will get the chance to download all the logged points. Each individual spits out a single dbf and new locations are just appended to the end (so the file is just cumulative). These data need to be shared among a research group. Everyone else (besides me) wants to use access, so they can make small edits and prefer that interface. They do not like using MySQL. The solution I came up with is: a) The person who downloads the file goes to a web page, enters animal ID into a form, chooses .dbf file and uploads to a mysql database on the server (I still have to write php code to read the dbf and write sql insert statements from it). b) Everyone syncs from their local access database to the server. (This is natively possible from access but very clunky). Is there a tool (preferably open source), that can compare a access table to mysql table and sync the two (both ways)? Alternatively, does anyone have a more elegant solution? The ultimate goal is to allow everyone to have access to the most current data on their computers using their preferred database app.

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  • Difference between SET autocommit=1 and START TRANSACTION in mysql (Have I missed something?)

    - by tkolar
    Hey there, I am reading up on transactions in mysql and am not sure whether I have grasped something specific correctly, and I want to be sure I understood that correctly, so here goes. I know what a transaction is supposed to do, I'm just not sure whether I understood the statement semantics or not. So, my question is, is anything wrong, (and, if that is the case, what is wrong) with the following: By default, autocommit mode is enabled in mysql. Now, SET autocommit=0; will begin a transaction, SET autocommit=1; will implicitly commit. It is possible to COMMIT; as well as ROLLBACK;, in both of which cases autocommit is still set to 0 afterwards (and a new transaction is implicitly started). START TRANSACTION; will basically SET autocommit=0; until a COMMIT; or ROLLBACK; takes place. In other words, START TRANSACTION; and SET autocommit=0; are equivalent, except for the fact that START TRANSACTION; does the equivalent of implicitly adding a SET autocommit=0; after COMMIT; or ROLLBACK; If that is the case, I don't understand http://dev.mysql.com/doc/refman/5.5/en/set-transaction.html#isolevel_serializable - seeing as having an isolation level implies that there is a transaction, meaning that autocommit should be off anyway? And if there is another difference (other than the one described above) between beginning a transaction and setting autocommit, what is it? Thanks a lot in advance for your help!

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  • Sorting the columns of an HTML table using JQuery

    - by nikolaosk
    In this post I will show you how easy is to sort the columns of an HTML table. I will use an external library,called Tablesorter which makes life so much easier for developers. ?here are other posts in my blog regarding JQuery.You can find them all here. You can find another post regarding HTML tables and JQuery here. We will demonstrate this with a step by step example. I will use Visual Studio 2012 Ultimate. You can also use Visual Studio 2012 Express Edition. You can also use VS 2010 editions.   1) Launch Visual Studio. Create an ASP.Net Empty Web application. Choose an appropriate name for your application. 2) Add a web form, default.aspx page to the application. 3) Add a table from the HTML controls tab control (from the Toolbox) on the default.aspx page 4) Now we need to download the JQuery library. Please visit the http://jquery.com/ and download the minified version.Then we need to download the Tablesorter JQuery plugin. Please donwload it, here. 5) We need to reference the JQuery library and the external JQuery Plugin. In the head section ? add the following lines.   <script src="jquery-1_8_2_min.js" type="text/javascript"></script>  <script src="jquery.tablesorter.js" type="text/javascript"></script>6) We need to type the HTML markup, the HTML table and its columns <body>    <form id="form1" runat="server">    <div>        <h1>Liverpool Legends</h1>        <table style="width: 50%;" border="1" cellpadding="10" cellspacing ="10" class="liverpool">            <thead>                <tr><th>Defenders</th><th>MidFielders</th><th>Strikers</th></tr>            </thead>            <tbody>            <tr>                <td>Alan Hansen</td>                <td>Graeme Souness</td>                <td>Ian Rush</td>            </tr>            <tr>                <td>Alan Kennedy</td>                <td>Steven Gerrard</td>                <td>Michael Owen</td>            </tr>            <tr>                <td>Jamie Garragher</td>                <td>Kenny Dalglish</td>                <td>Robbie Fowler</td>            </tr>            <tr>                <td>Rob Jones</td>                <td>Xabi Alonso</td>                <td>Dirk Kuyt</td>            </tr>                </tbody>        </table>            </div>    </form></body> 7) Inside the head section we also write the simple JQuery code.   <script type="text/javascript"> $(document).ready(function() { $('.liverpool').tablesorter(); }); </script> 8) Run your application.This is how the HTML table looks before the table is sorted on the basis of the selected column.   9) Now I will click on the Midfielders header.Have a look at the picture below  Tablesorter is an excellent JQuery plugin that makes sorting HTML tables a piece of cake. Hope it helps!!!

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  • How to Plug a Small Hole in NetBeans JSF (Join Table) Code Generation

    - by MarkH
    I was asked recently to provide an assist with designing and building a small-but-vital application that had at its heart some basic CRUD (Create, Read, Update, & Delete) functionality, built upon an Oracle database, to be accessible from various locations. Working from the stated requirements, I fleshed out the basic application and database designs and, once validated, set out to complete the first iteration for review. Using SQL Developer, I created the requisite tables, indices, and sequences for our first run. One of the tables was a many-to-many join table with three fields: one a primary key for that table, the other two being primary keys for the other tables, represented as foreign keys in the join table. Here is a simplified example of the trio of tables: Once the database was in decent shape, I fired up NetBeans to let it have first shot at the code. NetBeans does a great job of generating a mountain of essential code, saving developers what must be millions of hours of effort each year by building a basic foundation with a few clicks and keystrokes. Lest you think it (or any tool) can do everything for you, however, occasionally something tosses a paper clip into the delicate machinery and makes you open things up to fix them. Join tables apparently qualify.  :-) In the case above, the entity class generated for the join table (New Entity Classes from Database) included an embedded object consisting solely of the two foreign key fields as attributes, in addition to an object referencing each one of the "component" tables. The Create page generated (New JSF Pages from Entity Classes) worked well to a point, but when trying to save, we were greeted with an error: Transaction aborted. Hmm. A quick debugger session later and I'd identified the issue: when trying to persist the new join-table object, the embedded "foreign-keys-only" object still had null values for its two (required value) attributes...even though the embedded table objects had populated key attributes. Here's the simple fix: In the join-table controller class, find the public String create() method. It will look something like this:     public String create() {        try {            getFacade().create(current);            JsfUtil.addSuccessMessage(ResourceBundle.getBundle("/Bundle").getString("JoinEntityCreated"));            return prepareCreate();        } catch (Exception e) {            JsfUtil.addErrorMessage(e, ResourceBundle.getBundle("/Bundle").getString("PersistenceErrorOccured"));            return null;        }    } To restore balance to the force, modify the create() method as follows (changes in red):     public String create() {         try {            // Add the next two lines to resolve:            current.getJoinEntityPK().setTbl1id(current.getTbl1().getId().toBigInteger());            current.getJoinEntityPK().setTbl2id(current.getTbl2().getId().toBigInteger());            getFacade().create(current);            JsfUtil.addSuccessMessage(ResourceBundle.getBundle("/Bundle").getString("JoinEntityCreated"));            return prepareCreate();        } catch (Exception e) {            JsfUtil.addErrorMessage(e, ResourceBundle.getBundle("/Bundle").getString("PersistenceErrorOccured"));            return null;        }    } I'll be refactoring this code shortly, but for now, it works. Iteration one is complete and being reviewed, and we've met the milestone. Here's to happy endings (and customers)! All the best,Mark

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  • CakePHP 'Cake is NOT able to connect to the database'

    - by kand
    I've looked at this post about a similar issue: CakePHP: Can't access MySQL database and I've tried everything they mentioned in there including: Changing my database.php so that the 'port' attribute for both $default and $test are the location of my mysqld.sock file Changing the 'port' attribute to the actual integer that represents the port in my my.cnf mysql config Changing the mysql socket locations in php.ini to the location of my mysqld.sock file I'm using ubuntu 11.04, apache 2.2.17, mysql 5.1.54, and CakePHP 1.3.10. My install of mysql and apache don't seem to match any conventions, as in, all the config files are there, they are all just in really weird places--I'm not sure why that is, but I've tried reinstalling both programs multiple times with the same results... At any rate, I can log into mysql from the terminal and use it normally, and apache is working because I can see the CakePHP default homepage. I just can't get it to change the message 'Cake is NOT able to connect to the database'. SOLVED: Figured it out, had to change php.ini so that extension_dir pointed to the correct directory and had to add a line extension=mysql.so.

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  • tcpdf table header in each page

    - by DragoN
    i am using tcpdf to create pdf files with rows of table in the first page of pdf i display some info like : List of table .... and header of table after that i display the rows in table if there much rows it contiunes in the next page without the info [List of table... and header of table] i want to display the header of table only in the next pages here is my code $pdf->SetFont('aefurat', '', 15); $pdf->AddPage('P', 'A4'); $pdf->SetFontSize(17); $pdf->Cell(0, 13, 'List of the Byan Table,'C'); $pdf->SetFont('dejavusans', '', 14); $htmlpersian = 'In / Out List'; $pdf->WriteHTML($htmlpersian, true, 0, true, 0); $pdf->setRTL(false); $pdf->SetFontSize(11); $pdf->setRTL(true); Connect(); $resultsc = mysql_query("SELECT * FROM byan Order By Date "); while($r = mysql_fetch_array($resultsc)) { $printresult .= ' <tr> <td ><center>'.$r['Date'].'</center></td> <td ><center>'.$r['In'].'</center></td> <td ><center>'.$r['Out'].'</center></td> <td ><center>'.$r['Balance'].'</center></td> <td ><center>'.$r['Info'].'</center></td> <td ><center>'.$r['Number'].'</center></td> </tr>'; } $tbl = ' <table cellspacing="0" cellpadding="1" border="1" align="center"> <tr> <td style="width: 13%; background-color:black; color:white;"><center>Date</center></td> <td style="width: 11%; background-color:black; color:white;"><center>In</center></td> <td style="width: 11%; background-color:black; color:white;"><center>Out</center></td> <td style="width: 12%; background-color:black; color:white;"><center>Balance</center></td> <td style="width: 45%; background-color:black; color:white;"><center>Info</center></td> <td style="width: 11%; background-color:black; color:white;"><center>Number</center></td> </tr> '.$printresult.' </table> '; $pdf->writeHTML($tbl, true, false, true, false, ''); the output is First Page: List of the Byan Table In / Out List Table Header rows Second Page: Rows Third Page: Rows i want the output to be like that First Page: List of the Byan Table In / Out List Table Header Rows Second Page: Table Header Rows Third Page: Table Header Rows

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  • Dynamically change MYSQL query within a PHP file using jQuery .post?

    - by John
    Hi, Been trying this for quite a while now and I need help. Basically I have a PHP file that queries database and I want to change the query based on a logged in users name. What happens on my site is that a user logs on with Twitter Oauth and I can display their details (twitter username etc.). I have a database which the user has added information to and I what I would like to happen is when the user logs in with Twitter Oauth, I could use jQuery to take the users username and update the mysql query to show only the results where the user_name = that particular users name. At the moment the mysql query is: "SELECT * FROM markers WHERE user_name = 'dave'" I've tried something like: "SELECT * FROM markers WHERE user_name = '$user_name'" And elsewhere in the PHP file I have $user_name = $_POST['user_name'];. In a separate file (the one in which the user is redirected to after they log in through Twitter) I have some jQuery like this: $(document).ready(function(){ $.post('phpsqlinfo_resultb.php',{user_name:"<?PHP echo $profile_name?>"})}); $profile_name has been defined earlier on that page. I know i'm clearly doing something wrong, i'm still learning. Is there a way to achieve what I want using jQuery to post the users username to the PHP file to change the mysql query to display only the results related to the user that is logged in. I've included the PHP file with the query below: <?php // create a new XML document //$doc = domxml_new_doc('1.0'); $doc = new DomDocument('1.0'); //$root = $doc->create_element('markers'); //$root = $doc->append_child($root); $root = $doc->createElement('markers'); $root = $doc->appendChild($root); $table_id = 'marker'; $user_name = $_POST['user_name']; // Make a MySQL Connection include("phpsqlinfo_addrow.php"); $result = mysql_query("SELECT * FROM markers WHERE user_name = '$user_name'") or die(mysql_error()); // process one row at a time //header("Content-type: text/xml"); header('Content-type: text/xml; charset=utf-8'); while($row = mysql_fetch_assoc($result)) { // add node for each row $occ = $doc->createElement($table_id); $occ = $root->appendChild($occ); $occ->setAttribute('lat', $row['lat']); $occ->setAttribute('lng', $row['lng']); $occ->setAttribute('type', $row['type']); $occ->setAttribute('user_name', utf8_encode($row['user_name'])); $occ->setAttribute('name', utf8_encode($row['name'])); $occ->setAttribute('tweet', utf8_encode($row['tweet'])); $occ->setAttribute('image', utf8_encode($row['image'])); } // while $xml_string = $doc->saveXML(); $user_name2->response; echo $xml_string; ?> This is for use with a google map mashup im trying to do. Many thanks if you can help me. If my question isn't clear enough, please say and i'll try to clarify for you. I'm sure this is a simple fix, i'm just relatively inexperienced to do it. Been at this for two days and i'm running out of time unfortunately.

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  • nginx+mysql5 loadtesting configuration strangeness

    - by genseric
    i am trying to setup a new server running on debian6 and trying to make it work smooth under load. i ve used a wordpress site as a test object, and tried the configurations on http://blitz.io. when i increase the mysql max_connections from 50 to 200 lots of timeouts start to occur. but on 50 , no timeouts and pretty well response times. nginx configuration is fine , i tuned the config so i dont see errors. so i presume it's related to the other configuration options of my.cnf . i read some about options but still cant find what max_connections problem is all about. btw, the server has 16gb of ram and a fine i7 cpu. here is the current my.cnf [client] port = 3306 socket = /var/run/mysqld/mysqld.sock [mysqld_safe] socket = /var/run/mysqld/mysqld.sock nice = 0 [mysqld] wait_timeout=60 connect_timeout=10 interactive_timeout=120 user = mysql pid-file = /var/run/mysqld/mysqld.pid socket = /var/run/mysqld/mysqld.sock port = 3306 basedir = /usr datadir = /var/lib/mysql tmpdir = /tmp language = /usr/share/mysql/english skip-external-locking bind-address = 127.0.0.1 key_buffer = 384M max_allowed_packet = 16M thread_stack = 192K thread_cache_size = 20 myisam-recover = BACKUP max_connections = 50 table_cache = 1024 thread_concurrency = 8 query_cache_limit = 2M query_cache_size = 128M expire_logs_days = 10 max_binlog_size = 100M [mysqldump] quick quote-names max_allowed_packet = 16M [mysql] #no-auto-rehash # faster start of mysql but no tab completition [isamchk] key_buffer = 16M thanks in advance. i asked this question on SO but it's closed as off topic so i believe this is a SF question.

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  • Joins in single-table queries

    - by Rob Farley
    Tables are only metadata. They don’t store data. I’ve written something about this before, but I want to take a viewpoint of this idea around the topic of joins, especially since it’s the topic for T-SQL Tuesday this month. Hosted this time by Sebastian Meine (@sqlity), who has a whole series on joins this month. Good for him – it’s a great topic. In that last post I discussed the fact that we write queries against tables, but that the engine turns it into a plan against indexes. My point wasn’t simply that a table is actually just a Clustered Index (or heap, which I consider just a special type of index), but that data access always happens against indexes – never tables – and we should be thinking about the indexes (specifically the non-clustered ones) when we write our queries. I described the scenario of looking up phone numbers, and how it never really occurs to us that there is a master list of phone numbers, because we think in terms of the useful non-clustered indexes that the phone companies provide us, but anyway – that’s not the point of this post. So a table is metadata. It stores information about the names of columns and their data types. Nullability, default values, constraints, triggers – these are all things that define the table, but the data isn’t stored in the table. The data that a table describes is stored in a heap or clustered index, but it goes further than this. All the useful data is going to live in non-clustered indexes. Remember this. It’s important. Stop thinking about tables, and start thinking about indexes. So let’s think about tables as indexes. This applies even in a world created by someone else, who doesn’t have the best indexes in mind for you. I’m sure you don’t need me to explain Covering Index bit – the fact that if you don’t have sufficient columns “included” in your index, your query plan will either have to do a Lookup, or else it’ll give up using your index and use one that does have everything it needs (even if that means scanning it). If you haven’t seen that before, drop me a line and I’ll run through it with you. Or go and read a post I did a long while ago about the maths involved in that decision. So – what I’m going to tell you is that a Lookup is a join. When I run SELECT CustomerID FROM Sales.SalesOrderHeader WHERE SalesPersonID = 285; against the AdventureWorks2012 get the following plan: I’m sure you can see the join. Don’t look in the query, it’s not there. But you should be able to see the join in the plan. It’s an Inner Join, implemented by a Nested Loop. It’s pulling data in from the Index Seek, and joining that to the results of a Key Lookup. It clearly is – the QO wouldn’t call it that if it wasn’t really one. It behaves exactly like any other Nested Loop (Inner Join) operator, pulling rows from one side and putting a request in from the other. You wouldn’t have a problem accepting it as a join if the query were slightly different, such as SELECT sod.OrderQty FROM Sales.SalesOrderHeader AS soh JOIN Sales.SalesOrderDetail as sod on sod.SalesOrderID = soh.SalesOrderID WHERE soh.SalesPersonID = 285; Amazingly similar, of course. This one is an explicit join, the first example was just as much a join, even thought you didn’t actually ask for one. You need to consider this when you’re thinking about your queries. But it gets more interesting. Consider this query: SELECT SalesOrderID FROM Sales.SalesOrderHeader WHERE SalesPersonID = 276 AND CustomerID = 29522; It doesn’t look like there’s a join here either, but look at the plan. That’s not some Lookup in action – that’s a proper Merge Join. The Query Optimizer has worked out that it can get the data it needs by looking in two separate indexes and then doing a Merge Join on the data that it gets. Both indexes used are ordered by the column that’s indexed (one on SalesPersonID, one on CustomerID), and then by the CIX key SalesOrderID. Just like when you seek in the phone book to Farley, the Farleys you have are ordered by FirstName, these seek operations return the data ordered by the next field. This order is SalesOrderID, even though you didn’t explicitly put that column in the index definition. The result is two datasets that are ordered by SalesOrderID, making them very mergeable. Another example is the simple query SELECT CustomerID FROM Sales.SalesOrderHeader WHERE SalesPersonID = 276; This one prefers a Hash Match to a standard lookup even! This isn’t just ordinary index intersection, this is something else again! Just like before, we could imagine it better with two whole tables, but we shouldn’t try to distinguish between joining two tables and joining two indexes. The Query Optimizer can see (using basic maths) that it’s worth doing these particular operations using these two less-than-ideal indexes (because of course, the best indexese would be on both columns – a composite such as (SalesPersonID, CustomerID – and it would have the SalesOrderID column as part of it as the CIX key still). You need to think like this too. Not in terms of excusing single-column indexes like the ones in AdventureWorks2012, but in terms of having a picture about how you’d like your queries to run. If you start to think about what data you need, where it’s coming from, and how it’s going to be used, then you will almost certainly write better queries. …and yes, this would include when you’re dealing with regular joins across multiples, not just against joins within single table queries.

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  • fatal error 'stdio.h' Python 2.7 on Mc OS X 10.7.5 [closed]

    - by DjangoRocks
    I have this weird issue on my Mac OS X 10.7.5 /Library/Frameworks/Python.framework/Versions/2.7/include/python2.7/Python.h:33:10: fatal error: 'stdio.h' file not found What caused the above error? This error has been bugging me and i can't install mysql-python as i'm stuck with this step. I'm using Python 2.7.3. Things like Google App Engine ( python ), python script, tornado generally works on my mac. But not mysql-python. I've install MySQL using the dmg image and have copied the mysql folder to /usr/local/ How do i fix this? ======UPDATE====== I've ran the command, and tried to install mysql-python by running sudo python setup.py install. But received the following: running install running bdist_egg running egg_info writing MySQL_python.egg-info/PKG-INFO writing top-level names to MySQL_python.egg-info/top_level.txt writing dependency_links to MySQL_python.egg-info/dependency_links.txt writing MySQL_python.egg-info/PKG-INFO writing top-level names to MySQL_python.egg-info/top_level.txt writing dependency_links to MySQL_python.egg-info/dependency_links.txt reading manifest file 'MySQL_python.egg-info/SOURCES.txt' reading manifest template 'MANIFEST.in' writing manifest file 'MySQL_python.egg-info/SOURCES.txt' installing library code to build/bdist.macosx-10.6-intel/egg running install_lib running build_py copying MySQLdb/release.py -> build/lib.macosx-10.6-intel-2.7/MySQLdb running build_ext gcc-4.2 not found, using clang instead building '_mysql' extension clang -fno-strict-aliasing -fno-common -dynamic -g -O2 -DNDEBUG -g -O3 -Dversion_info=(1,2,4,'rc',5) -D__version__=1.2.4c1 -I/usr/local/mysql/include -I/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c _mysql.c -o build/temp.macosx-10.6-intel-2.7/_mysql.o -Os -g -fno-common -fno-strict-aliasing -arch x86_64 In file included from _mysql.c:29: /Library/Frameworks/Python.framework/Versions/2.7/include/python2.7/Python.h:33:10: fatal error: 'stdio.h' file not found #include <stdio.h> ^ 1 error generated. error: command 'clang' failed with exit status 1 What other possible ways can i fix it? thanks! Best Regards.

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  • Learning PostgreSql: old versions of rows are stored right in the table

    - by Alexander Kuznetsov
    PostgreSql features multi-version concurrency control aka MVCC. To implement MVCC, old versions of rows are stored right in the same table, and this is very different from what SQL Server does, and it leads to some very interesting consequences. Let us play with this thing a little bit, but first we need to set up some test data. Setting up. First of all, let us create a numbers table. Any production database must have it anyway: CREATE TABLE Numbers ( i INTEGER ); INSERT INTO Numbers ( i ) VALUES...(read more)

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  • Configuration data: single-row table vs. name-value-pair table

    - by Heinzi
    Let's say you write an application that can be configured by the user. For storing this "configuration data" into a database, two patterns are commonly used. The single-row table CompanyName | StartFullScreen | RefreshSeconds | ... ---------------+-------------------+------------------+-------- ACME Inc. | true | 20 | ... The name-value-pair table ConfigOption | Value -----------------+------------- CompanyName | ACME Inc. StartFullScreen | true (or 1, or Y, ...) RefreshSeconds | 20 ... | ... I've seen both options in the wild, and both have obvious advantages and disadvantages, for example: The single-row tables limits the number of configuration options you can have (since the number of columns in a row is usually limited). Every additional configuration option requires a DB schema change. In a name-value-pair table everything is "stringly typed" (you have to encode/decode your Boolean/Date/etc. parameters). (many more) Is there some consensus within the development community about which option is preferable?

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  • Use alpha or opacity on a table row using CSS [migrated]

    - by mserin
    I have a CSS stylesheet for a webpage. The webpage has a table with a background color of white (set in the rows, not the table). I would like to set the opacity or alpha to 50%. I have tried so many variations, but come up with no luck. A typical row in the HTML file is: <tr> <td>&nbsp;</td> <td>Twitter</td> </tr> The CSS settings for table rows (which works perfectly) is: tr { font-family: Arial, Helvetica, sans-serif; background:rgb(255,255,255); } To get the alpha, I tried tr { font-family: Arial, Helvetica, sans-serif; background-color:rgba(255,255,255,0.5); } I have also tried background-color-opacity: 0.5; Any other suggestions?

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  • What happened to HTML table tags?

    - by John
    I started to code HTML in 1998, and in that time I was used to code a lot table tags, playing with tr and td, I learned many things analysing the source code of many portals on the internet with notepad and Microsoft FrontPage, the latter, aw, how many tables overlapping others, it was fun, I loved that time. However, I abandoned web programming for almost seven years and this year I decided to see what's the web programming today likes. Completely different, there are not table tags anymore, it's full of div and span tags. Why happened ? What are these new tags and why nobody codes in table tags anymore ?

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  • SQL SERVER – Check If Column Exists in SQL Server Table

    - by Pinal Dave
    A very frequent task among SQL developers is to check if any specific column exists in the database table or not. Based on the output developers perform various tasks. Here are couple of simple tricks which you can use to check if column exists in your database table or not. Method 1 IF EXISTS(SELECT * FROM sys.columns WHERE Name = N'columnName' AND OBJECT_ID = OBJECT_ID(N'tableName')) BEGIN PRINT 'Your Column Exists' END   For AdventureWorks sample database IF EXISTS(SELECT * FROM sys.columns WHERE Name = N'Name' AND OBJECT_ID = OBJECT_ID(N'[HumanResources].[Department]')) BEGIN PRINT 'Your Column Exists' END   Method 2 IF COL_LENGTH('table_name','column_name') IS NOT NULL BEGIN PRINT 'Your Column Exists' END For AdventureWorks sample database IF COL_LENGTH('[HumanResources].[Department]','Name') IS NOT NULL BEGIN PRINT 'Your Column Exists' END Method 3 IF EXISTS( SELECT TOP 1 * FROM INFORMATION_SCHEMA.COLUMNS WHERE [TABLE_NAME] = 'TableName' AND [COLUMN_NAME] = 'ColumnName' AND [TABLE_SCHEMA] = 'SchemaName') BEGIN PRINT 'Your Column Exists' END For AdventureWorks sample database IF EXISTS( SELECT TOP 1 * FROM INFORMATION_SCHEMA.COLUMNS WHERE [TABLE_NAME] = 'Department' AND [COLUMN_NAME] = 'Name' AND [TABLE_SCHEMA] = 'HumanResources') BEGIN PRINT 'Your Column Exists' END Let me know if you know any other method to find if Column Exists in SQL Server Table. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Can't login to phpMyAdmin on a WAMP server running Windows 2008

    - by Richard West
    I am setting up a new server. I have installed Apache 2.2.17, PHP 5.3.3, MySQL 5.1.53 and phpMyAdmin 3.3.8 running on a Windows 2008 (32 bit) OS. I have configured Apache and PHP so they appear to be working fine. I have created the standard test php page with the following code and everything appears to be working fine. <?php //index.php phpinfo(); ?> I also see the mySQL and mySQLi section in the above webpage, so it appears that that I have the proper extensions loaded for mySQL access. The problem that I am having centeres around myPHPAdmin. I have this installed and I can access to the login screen at http://localhost/pma I login using "root" and the password I have setup for root. After a delay of 30 seconds or so the web page goes to a blank screen, and the url is now http://localhost/pma/index.php?token= No error is ever displayed - however nothing usable is either. I have confirmed that mySQL is running by going to the command line and logging into mySQL from there. I have double checked my configuration but I am not having any luck getting this to work. I have also disabled the Windows firewall, but that did not change anything. I installed mySQL using the standard port 3306. Any advice would be greatly appreciated.

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  • PhpMyAdmin import/export - strange character encoding issues.

    - by John Hunt
    Hello, I'm migrating a site to a new host, and there are a couple of databases on there. There's no SSH access so I'm stuck with phpmyadmin. The issue is that certain characters (namely just whitespace) seems to being corrupt on the new site (same html, and apache doesn't seem to be messing with any encodings - you can see the strange characters have changed when I use less on my linux machine after downloading a table dump from both servers.) The issue isn't as bad if I import into the new database as utf-8 - whitespace characters only have one funny A type symbol instead of two. I've been trying various combinations of character encoding etc to no avail. Exporting from: phpMyAdmin 2.6.2 MySQL 4.1.20 MySQL connection collation: utf8_general_ci MySQL charset: UTF-8 Unicode (utf8) Collation on tables and their fields is: latin1_swedish_ci Importing to: phpMyAdmin - 2.11.9.2 MySQL client version: 5.0.45 MySQL charset: UTF-8 Unicode (utf8) MySQL connection collation: utf8_general_ci The import sql has this kind of thing in it: ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=192 ; I get the impression this is actually a bug or something with mysqldump as nothing seems to work.. does anyone have any insight into this? Cheers, John.

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