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• T-SQL Re-Assigning Order Numbering

  - by Meltdown

  Say I have a table with a field called "ordernum" that denotes the order of a given set of rows. Now imagine that I delete one of these rows. What type of query would work best for re-assigning the order numbers so that they remain sequential? Here's an example: id group_id name ordernum active --------------------------------------------------- 0_____0______'Name1'___5__true 1_____0______'Name2'___4__true 2_____0______'Name3'___3__true 3_____1______'Name4'___2__true 4_____1______'Name5'__1__true 5_____1______'Name6'__NULL___false Now if I deleted the column with id='4' how would I reset the values in the 'ordernum' field for that specific group? Is this even possible? Or if I added a new row. (The first time the rows are created they are sorted by date, but then the user has the option to set the order himself.) In my table design I have a column 'active' boolean. If 'active' is set to false, then 'ordernum' is set to NULL. Otherwise it should be given an order number.

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• Grouping Months of a particular Time span together using DateTime.

  - by Calibre2010

  public static string TimeLine2(this HtmlHelper helper, string myString2) { StringBuilder myString3 = new StringBuilder(); DateTime start = new DateTime(2010, 1, 1); DateTime end = new DateTime(2011, 12, 12); myString3.Append("<table>"); myString3.Append("<tr>"); for (DateTime date = start; date <= end; date = date.AddDays(1)) { DayOfWeek dw = date.DayOfWeek; var g = date.Month; var sun = " "; switch (dw) { case DayOfWeek.Sunday: sun = "S"; break; case DayOfWeek.Monday: sun = "M"; break; case DayOfWeek.Tuesday: sun = "T"; break; case DayOfWeek.Wednesday: sun = "W"; break; case DayOfWeek.Thursday: sun = "T"; break; case DayOfWeek.Friday: sun = "F"; break; case DayOfWeek.Saturday: sun = "S"; break; } myString3.Append("<td>" + sun + " " + g + "</td>"); } myString3.Append("</tr>"); myString3.Append("<tr>"); for (DateTime date = start; date <= end; date = date.AddDays(1)) { var f = date.Day; myString3.Append("<td>" + f + "</td>"); } myString3.Append("</tr>"); myString3.Append("</table>"); return myString3.ToString(); } Basically, what I have here is a few loops showing all the days of the week and also all the days in a month. This is all placed inside of a table, so you get MTWTFSSMT W T F S S M M TWTFSSM 12345678910 11 12 13 14 + + to 31 1234567 I'm trying to code a way in which I can split all of these days of the week and days in months so that my code returns each month with all its days in the month and all its days of the week, not just all my months between my timeSpan but splits them so MAY MTWTFSSMTWTFSSMTWTFSSMTWTFSSMTWTF 12345678 JUNE MTWTFSSMTWTFSSMTWTFSSMTWTFSSMTWTF 123456789

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• Multiple Tables or Multiple Schema

  - by Yan Cheng CHEOK

  http://stackoverflow.com/questions/1152405/postgresql-is-better-using-multiple-databases-with-1-schema-each-or-1-database I am new in schema concept for PostgreSQL. For the above mentioned scenario, I was wondering Why don't we use a single database (with default schema named public) Why don't we have a single table, to store multiple users row? Other tables which hold users related information, with foreign key point to the user table. Can anyone provide me a real case scenario, which single database, multiple schema will be extremely useful, and can't solve by conventional single database, single schema.

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• How to implement multi relationship in MS SQL?

  - by Ethan

  I’m trying to design a database to use with ASP.net MVC application. Here is the scenario: There are three entities and users can post their comments for each of these different entities. I just wonder how just put one table for Comments and link all other entities to it. Obviously, Comments table needs 3 references (foreign key) to those tables but as you know these foreign keys can’t be null and just one of them can be filled for each row. Is there any better way than implementing three different tables for each entity’s comments? Cheers Ethan

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• TinyMCE: Double forecolor and backcolor buttons?

  - by petsson

  I'm having a problem using TinyMCE. In IE8, the forecolor and backcolor, for some random reason, is displayed twice. See picture below. Source code (I add the forecolor and backcolor in theme_advanced_buttons2): tinyMCE.init({ mode : "exact", elements : "<%= editArea.ClientID %>", custom_shortcuts : false, language : "en", relative_urls : false, convert_urls : false, forced_root_block : false, force_p_newlines : true, force_br_newlines : false, fix_nesting : true, plugins : "pagebreak,table", pagebreak_separator : '<div style="page-break-after:always;"></div>', theme : "advanced", skin : "o2k7", skin_variant : "blue", width : "540", height : "470", theme_advanced_toolbar_location : "top", theme_advanced_statusbar_location : "none", theme_advanced_font_sizes : "1,2,3,4,5,6,7", font_size_style_values : "0.6em,0.8em,1em,1.2em,1.5em,2em,3em", theme_advanced_buttons1 : "newdocument,|,copy,cut,paste,|,hr,pagebreak,|,undo,redo,|,code|,image,code", theme_advanced_buttons2 : "fontselect,fontsizeselect,|,bold,italic,underline,strikethrough,|,justifyleft,justifycenter,justifyright,justifyfull,|,forecolor,backcolor", // <-- This gives me double forecolor and backcolor theme_advanced_buttons3 : "table,|,row_props,cell_props,|,col_before,col_after,row_before,row_after,|,split_cells,merge_cells,|,delete_col,delete_row," });

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• SQLite and PostgreSql longtext

  - by Nik

  Hello all, Does anyone know how to change a column in SQLite and PostgreSQL to LONGTEXT? I have done so in MySQL successfully with: "ALTER TABLE projects MODIFY description LONGTEXT;" But this clause doesn't seem to work on SQLite. I tried hard to find documentation on PostgreSQL, but that site's format really makes people puke. SQLite's website is better but the only command I find relevant, alter table, doesn't seem to support changing column data type at all. ( infact, it doesn't even allow changing column name!!!) Thanks all!

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• checkUnique function?

  - by Chris Leah

  Hey, so I have created a function to check the DB for unique entries, but when I call the function it doesn't seem to work and gives me a fatal error any ideas from the function or do you wish to see the sign up page calling it. Thanks :) //Check for unique entries function checkUnique($table, $field, $compared) { $query = $mysqli->query('SELECT '.$mysqli->real_escape_string($field).' FROM '.$mysqli->real_escape_string($table).' WHERE "'.$mysqli->real_escape_string($field).'" = "'.$mysqli->real_escape_string($compared).'"'); if(!$query){ return TRUE; } else { return FALSE; } } The page calling it..... if (!empty($_POST['username']) && !empty($_POST['password']) && $_POST['password']==$_POST['password_confirm'] && !empty($_POST['email']) && validateEmail($_POST['email']) == TRUE && checkUnqiue('users', 'email', $_POST['email']) == TRUE && checkUnique('users', 'username', $_POST['username']) == TRUE)

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• SQL Server - Query Short-Circuiting?

  - by Sam Schutte

  Do T-SQL queries in SQL Server support short-circuiting? For instance, I have a situation where I have two database and I'm comparing data between the two tables to match and copy some info across. In one table, the "ID" field will always have leading zeros (such as "000000001234"), and in the other table, the ID field may or may not have leading zeros (might be "000000001234" or "1234"). So my query to match the two is something like: select * from table1 where table1.ID LIKE '%1234' To speed things up, I'm thinking of adding an OR before the like that just says: table1.ID = table2.ID to handle the case where both ID's have the padded zeros and are equal. Will doing so speed up the query by matching items on the "=" and not evaluating the LIKE for every single row (will it short circuit and skip the LIKE)?

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• Microsoft Business Intelligence. Is what I am trying to do possible?

  - by Nai

  Hi guys, I have been charged with the task of analysing the log table of my company's website. This table contains a user's click path throughout the website for a given session. My company is looking to understand/spot trends based on the 'click paths' of our users. In doing so, identify groups of users that take on a certain 'click path' based on age/geography and so on. As you can tell from the title, I am completely new to BI and its capabilities so I was wondering: Are our objectives attainable? How should I go about doing this? I am currently reading books online as well as other e-books I have found. All signs seem to suggest this is possible via sequence clustering. Although the exact implementation and tweaks involved are currently lost on me. Therefore, if anyone has first hand experience in such an undertaking, I would be awesome if you could share it here. Cheers!

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• Query data using LINQ to SQL and Entity Framework with foreign key? (Help me please)

  - by The Wind

  Hello! There is a problem I need help with your query on the data using LINQ to SQL and Entity Framework (I'm using Visual Studio 2010). My picure here: http://img.tamtay.vn/files/photo2/2010/5/28/10/962/4bff3a3b_1093f58f_untitled-1.gif I have three tables: tbl NewsDetails tblNewsCategories tblNewsInCategories (See screen 1 in my picture) Now, I want to retrieve records in the tblNewsDetails table, with condition: CategoryId=1, as the following results: (See screen 2 in my picture) But NewsID and CategoryId in tblNewsInCategories table is two foreign key, I do not see them and I do not know how to use them in your code. My code has errors: (See screen 3 in my picture) Please help me. Thanks! (I am a new member, should not have the right to insert images)

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• privmsg system db schema

  - by Bartek

  I'm making a PM-system on my site. And I want to know ultimate db schema. I have always just used only 1 table. But my users have started complained that the messages in their outbox suddently dissapers =D Thats because if the other users deletes it, the one who sent it wont see it to. So im thinking of making another table with the same fields So im thinking something like this: privmsgs id | to | from | subject | message | date -- -- ---- ------- ------- ---- 1 76 893 blabla. blabla. 20100404 sent_msgs id | to | from | subject | message | date -- -- ---- ------- ------- ---- 1 76 893 blabla. blabla. 20100404 Whatya think? Sorry for my bad english

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• datatables-multi-filter-select

  - by user1871603

  I am using the jquery plug-in datatables. I am using the feature, datatables-multi-filter-select on my website with php code. I want to move the drop down filter from the footer to the header like in the following example: http://www.datatables.net/extras/thirdparty/ColumnFilterWidgets/DataTables/extras/ColumnFilterWidgets/ Can anyone please update the following PHP code sample to accomplish this? Code: /** * Register necessary Plugin Filters */add_filter( 'tablepress_shortcode_table_default_shortcode_atts', 'tablepress_add_shortcode_parameters_multi_filter_select' );add_filter( 'tablepress_table_render_options', 'tablepress_set_table_foot_option', 10, 2 );add_filter( 'tablepress_table_js_options', 'tablepress_add_multi_filter_select_js_options', 10, 3 );add_filter( 'tablepress_datatables_command', 'tablepress_add_multi_filter_select_js_command', 10, 5 ); /** * Add "datatables_multi_filter_select" as a valid parameter to the [table /] Shortcode */function tablepress_add_shortcode_parameters_multi_filter_select( $default_atts ) { $default_atts['datatables_multi_filter_select'] = false; return $default_atts;} /** * Make sure that "table_foot" and "datatables_scrollX" are false, if "datatables_multi_filter_select" is true, * as the footer will be appended by the JS. Scrolling will not work with automatically added content */function tablepress_set_table_foot_option( $render_options, $table ) { if ( $render_options['datatables_multi_filter_select'] ) { $render_options['table_foot'] = false; $render_options['datatables_scrollX'] = false; } return $render_options;} /** * Pass "datatables_multi_filter_select" from Shortcode parameters to JavaScript arguments */function tablepress_add_multi_filter_select_js_options( $js_options, $table_id, $render_options ) { $js_options['datatables_multi_filter_select'] = $render_options['datatables_multi_filter_select']; // register the JS if ( $js_options['datatables_multi_filter_select'] ) { $suffix = ( defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ) ? '' : '.min'; $js_multi_filter_select_url = plugins_url( "multi-filter-select{$suffix}.js", __FILE__ ); wp_enqueue_script( 'tablepress-multi_filter_select', $js_multi_filter_select_url, array( 'tablepress-datatables' ), '1.0', true ); } return $js_options;} /** * Evaluate "datatables_multi_filter_select" parameter and add corresponding JavaScript code, if needed */function tablepress_add_multi_filter_select_js_command( $command, $html_id, $parameters, $table_id, $js_options ) { if ( ! $js_options['datatables_multi_filter_select'] ) return $command; $name = str_replace( '-', '_', $html_id ); $datatables_name = "DT_{$name}"; $command = <<<JSvar {$name} = $('#{$html_id}'), {$datatables_name} = {$name}.dataTable({$parameters}), {$name}_tfoot, {$name}_selects, ths = '<tfoot>';{$name}.find('thead th').each( function( i ) { ths += '<th>' + datatables_fnCreateSelect( {$datatables_name}.fnGetColumnData(i) ) + '</th>';} );ths += '</tfoot>';{$name}_tfoot = {$name}.append(ths).find('tfoot');{$name}_selects = {$name}_tfoot.find('select');{$name}_tfoot.on( 'change', 'select', function() { {$datatables_name}.fnFilter( $(this).val(), {$name}_selects.index(this) );} );JS; return $command;} (function($) {/* * Function: fnGetColumnData * Purpose: Return an array of table values from a particular column. * Returns: array string: 1d data array * Inputs: object:oSettings - dataTable settings object. This is always the last argument past to the function * int:iColumn - the id of the column to extract the data from * bool:bUnique - optional - if set to false duplicated values are not filtered out * bool:bFiltered - optional - if set to false all the table data is used (not only the filtered) * bool:bIgnoreEmpty - optional - if set to false empty values are not filtered from the result array * Author: Benedikt Forchhammer <b.forchhammer /AT\ mind2.de> */$.fn.dataTableExt.oApi.fnGetColumnData = function ( oSettings, iColumn, bUnique, bFiltered, bIgnoreEmpty ) { // check that we have a column id if ( typeof iColumn == "undefined" ) return new Array(); // by default we only wany unique data if ( typeof bUnique == "undefined" ) bUnique = true; // by default we do want to only look at filtered data if ( typeof bFiltered == "undefined" ) bFiltered = true; // by default we do not wany to include empty values if ( typeof bIgnoreEmpty == "undefined" ) bIgnoreEmpty = true; // list of rows which we're going to loop through var aiRows; // use only filtered rows if (bFiltered == true) aiRows = oSettings.aiDisplay; // use all rows else aiRows = oSettings.aiDisplayMaster; // all row numbers // set up data array var asResultData = new Array(); for (var i=0,c=aiRows.length; i<c; i++) { iRow = aiRows[i]; var aData = this.fnGetData(iRow); var sValue = aData[iColumn]; // ignore empty values? if (bIgnoreEmpty == true && sValue.length == 0) continue; // ignore unique values? else if (bUnique == true && jQuery.inArray(sValue, asResultData) > -1) continue; // else push the value onto the result data array else asResultData.push(sValue); } return asResultData;}}(jQuery)); function datatables_fnCreateSelect( aData ) { var r = '<select><option value=""></option>', i, iLen = aData.length; for ( i=0 ; i<iLen ; i++ ) { r += '<option value="'+aData[i]+'">'+aData[i]+'</option>'; } return r + '</select>';}

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• IE8 alignment in div issue

  - by xrx215

  How to align the the button in center of div in IE8. Works fine in IE7 but not in IE8 <div id="dPopupFooter" style="background-color: #d9d9d9; position: absolute; z-index: 5; bottom: 0px; width: 100%; height: 30px; border-top: solid 1px #acacac; text-align: center; padding-top: 3px;"> <table><tr><td><xrx:CustomButton id="btnClose" runat="server" OnClientClick="ClosePopup();" /></td></tr></table> </div>

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• How do you make a Custom Data Generator for SQL XML DataType.

  - by Keith Sirmons

  Howdy, I am using Visual Studio 2010 and am playing around with the Database Projects. I am creating a DataGenerationPlan to insert data into a simple table, in which one of the column datatypes is XML. Out of the box, the generation plan uses the Regular Expression generator and generates something like this : HGcSv9wa7yM44T9x5oFT4pmBkEmv62lJ7OyAmCnL6yqXC2X.......... I am looking at creating a custom data Generator for this data type and have followed this site for the basics: http://msdn.microsoft.com/en-us/library/aa833244.aspx This example works if I am creating a string datatype and using it for a nvarchar datatype. What do I need to change to hook this Generator to the XML Datatype? Below are my code files. The string property works for nvarchar. The XElement property does not work for the xml datatype, and the RecordXMLDataGenerator is not listed as an option in the Generator column for the generation plan. CustomDataGenerators: using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Data.Schema.Tools.DataGenerator; using Microsoft.Data.Schema.Extensibility; using Microsoft.Data.Schema; using Microsoft.Data.Schema.Sql; using System.Xml.Linq; namespace CustomDataGenerators { [DatabaseSchemaProviderCompatibility(typeof(SqlDatabaseSchemaProvider))] public class RecordXMLDataGenerator : Generator { private XElement _RecordData; [Output(Description = "Generates string of XML Data for the Record.", Name = "RecordDataString")] public string RecordDataString { get { return _RecordData.ToString(SaveOptions.None); } } [Output(Description = "Generates XML Data for the Record.", Name = "RecordData")] public XElement RecordData { get { return _RecordData; } } protected override void OnGenerateNextValues() { base.OnGenerateNextValues(); XElement element = new XElement("Root", new XElement("Children1", 1), new XElement("Children6", 6) ); _RecordData = element; } } } XML Extensions File: <?xml version="1.0" encoding="utf-8" ?> <extensions assembly="" version="1" xmlns="urn:Microsoft.Data.Schema.Extensions" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:Microsoft.Data.Schema.Extensions Microsoft.Data.Schema.Extensions.xsd"> <extension type="CustomDataGenerators.RecordXMLDataGenerator" assembly="CustomDataGenerators, Version=1.0.0.0, Culture=neutral, PublicKeyToken=xxxxxxxxxxxx" enabled="true"/> </extensions> Table.sql: CREATE TABLE [dbo].[Record] ( id int IDENTITY (1,1) NOT NULL, recordData xml NULL, userId int NULL, test nvarchar(max) NULL, rowver rowversion NULL, CONSTRAINT pk_RecordID PRIMARY KEY (id) )

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• sql server 2005 indexes and low cardinality

  - by Peanut

  How does SQL Server determine whether a table column has low cardinality? The reason I ask is because query optimizer would most probably not use an index on a gender column (values 'm' and 'f'). However how would it determine the cardinality of the gender column to come to that decision? On top of this, if in the unlikely event that I had a million entries in my table and only one entry in the gender column was 'm', would SQL server be able to determine this and use the index to retrieve that single row? Or would it just know there are only 2 distinct values in the column and not use the index? I appreciate the above discusses some poor db design, but I'm just trying to understand how query optimizer comes to its decisions. Many thanks.

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• MySQL - how long to create an index?

  - by user293594

  Can anyone tell me how adding a key scales in MySQL? I have 500,000,000 rows in a database, trans, with columns i (INT UNSIGNED), j (INT UNSIGNED), nu (DOUBLE), A (DOUBLE). I try to index a column, e.g. ALTER TABLE trans ADD KEY idx_A (A); and I wait. For a table of 14,000,000 rows it took about 2 minutes to execute on my MacBook Pro, but for the whole half a billion, it's taking 15hrs and counting. Am I doing something wrong, or am I just being naive about how indexing a database scales with the number of rows?

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• Help Reading Binary Image Data from SQL Server into PHP

  - by Joe Majewski

  I cannot seem to figure out a way to read binary data from SQL server into PHP. I am working on a project where I need to be able to store the image directly in the SQL table, not on the file system. Currently, I have been using a query like this one: INSERT INTO myTable(Document) SELECT * FROM OPENROWSET(BULK N'C:\image.jpg', SINGLE_BLOB) as BLAH This works fine to actually insert the image into the table, but I haven't yet figured a way to retrieve it and get my image back. I am doing this with PHP, and ultimately will have to make a stored procedure out of it, but can anyone enlighten me on a way to get that binary data (varbinary(MAX)) and generate an image on the fly. I expected it to be simple to use a SELECT statement and add a content-type to the headers that indicated it was an image, but it's simply not working. Instead, the page will just display the name of the file, which I have encountered in the past and understand it to be an error with the image data.

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• Why might SQL execute more quickly on SQL Server 2000 when NOT using a stored procedure?

  - by Kofi Sarfo

  I could see nothing wrong with the execution plan. Besides, as I understand it, SQL Server 2000 extended many of the performance benefits of stored procedures to all SQL statements by recognising new T-SQL statements against T-SQL statements of existing execution plans (by retaining execution plans for all SQL statements in the procedure cache, not just stored procedure execution plans) It's a fairly straight forward SELECT statement with sensible table joins, no transactions included or linked servers being referenced within the query and WITH (NOLOCK) table hints applied. The stored procedure was created by dbo and the user has all the necessary permissions. So my question is this: What are the likely reasons for a query to take only a few seconds to run but then take several minutes when identical T-SQL is run via a stored procedure?

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• How to drop columns using Rails migration

  - by Ethan

  What's the syntax for dropping a database table column through a Rails migration?

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• sql query to get the sql server 2005

  - by subash

  i have table with filmname and actors column in sql server 2005 i want the sql query to get all the actors of the film starred by both "bradpitt" and "rusellcrowe"

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• SQLServer 2008 Pivot

  - by Mitch

  I need to show some information in a graph, the data is held in a SQL Server 2008 table. The graph is expecting 2 columns, one for QuestionNumber and the other for Score. The table containing the data has column names that correspond to the question numbers ie A1, A2, A3, A4, B1, B2, B3, B4, C1, C2. Each question is given a score of 1 to 5. I need to show a graph where the X axis shows A1, A2, A3 etc and the Y axis shows the score. I'm thinking I somehow need to rotate the data to achive this, but I'm not sure how. Maybe a different technique can acheive this rather that a Rotate, so I'm open to any ideas.

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• JPA entitymanager remove operation is not performant

  - by Samuel

  When I try to do an entityManager.remove(instance) the underlying JPA provider issues a separate delete operation on each of the GroupUser entity. I feel this is not right from a performance perspective, since if a Group has 1000 users there will be 1001 calls issued to delete the entire group and itr groupuser entity. Would it make more sense to write a named query to remove all entries in groupuser table (e.g. delete from group_user where group_id=?), so I would have to make just 2 calls to delete the group. @Entity @Table(name = "tbl_group") public class Group { @OneToMany(mappedBy = "group", cascade = CascadeType.ALL, fetch = FetchType.LAZY) @Cascade(value = DELETE_ORPHAN) private Set<GroupUser> groupUsers = new HashSet<GroupUser>(0);

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• Why doesn't this (translated) VB.NET code work?

  - by ropstah

  I had a piece of C# code converted, but the translated code isn't valid... Can somebody help out? C# <table> <% Html.Repeater<Hobby>("Hobbies", "row", "row-alt", (hobby, css) => { %> <tr class="<%= css %>"> <td><%= hobby.Title%></td> </tr> <% }); %> </table> VB <% Html.Repeater(of Jrc3.BLL.Product)(Model.ProductCollectionByPrcAutoKey, "row", "row-alt", Function(product, css) Do %> <tr class="<%= css %>"> <td><%= hobby.Title%></td> </tr> <% End Function)%>

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• Stop duplicate icmp echo replies when bridging to a dummy interface?

  - by mbrownnyc

  I recently configured a bridge br0 with members as eth0 (real if) and dummy0 (dummy.ko if). When I ping this machine, I receive duplicate replies as: # ping SERVERA PING SERVERA.domain.local (192.168.100.115) 56(84) bytes of data. 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=1 ttl=62 time=113 ms 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=1 ttl=62 time=114 ms (DUP!) 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=2 ttl=62 time=113 ms 64 bytes from SERVERA.domain.local (192.168.100.115): icmp_seq=2 ttl=62 time=113 ms (DUP!) Using tcpdump on SERVERA, I was able to see icmp echo replies being sent from eth0 and br0 itself as follows (oddly two echo request packets arrive "from" my Windows box myhost): 23:19:05.324192 IP myhost.domain.local > SERVERA.domain.local: ICMP echo request, id 512, seq 43781, length 40 23:19:05.324212 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324217 IP myhost.domain.local > SERVERA.domain.local: ICMP echo request, id 512, seq 43781, length 40 23:19:05.324221 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324264 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 23:19:05.324272 IP SERVERA.domain.local > myhost.domain.local: ICMP echo reply, id 512, seq 43781, length 40 It's worth noting, testing reveals that hosts on the same physical switch do not see DUP icmp echo responses (a host on the same VLAN on another switch does see a dup icmp echo response). I've read that this could be due to the ARP table of a switch, but I can't find any info directly related to bridges, just bonds. I have a feeling my problem lay in the stack on linux, not the switch, but am opened to any suggestions. The system is running centos6/el6 kernel 2.6.32-71.29.1.el6.i686. How do I stop ICMP echo replies from being sent in duplicate when dealing with a bridge interface/bridged interfaces? Thanks, Matt [edit] Quick note: It was recommended in #linux to: [08:53] == mbrownnyc [gateway/web/freenode/] has joined ##linux [08:57] <lkeijser> mbrownnyc: what happens if you set arp_ignore to 1 for the dummy interface? [08:59] <lkeijser> also set arp_announce to 2 for that interface [09:24] <mbrownnyc> lkeijser: I set arp_annouce to 2, arp_ignore to 2 in /etc/sysctl.conf and rebooted the machine... verifying that the bits are set after boot... the problem is still present I did this and came up empty. Same dup problem. I will be moving away from including the dummy interface in the bridge as: [09:31] == mbrownnyc [gateway/web/freenode/] has joined #Netfilter [09:31] <mbrownnyc> Hello all... I'm wondering, is it correct that even with an interface in PROMISC that the kernel will drop /some/ packets before they reach applications? [09:31] <whaffle> What would you make think so? [09:32] <mbrownnyc> I ask because I am receiving ICMP echo replies after configuring a bridge with a dummy interface in order for ipt_netflow to see all packets, only as reported in it's documentation: http://ipt-netflow.git.sourceforge.net/git/gitweb.cgi?p=ipt-netflow/ipt-netflow;a=blob;f=README.promisc [09:32] <mbrownnyc> but I do not know if PROMISC will do the same job [09:33] <mbrownnyc> I was referred here from #linux. any assistance is appreciated [09:33] <whaffle> The following conditions need to be met: PROMISC is enabled (bridges and applications like tcpdump will do this automatically, otherwise they won't function). [09:34] <whaffle> If an interface is part of a bridge, then all packets that enter the bridge should already be visible in the raw table. [09:35] <mbrownnyc> thanks whaffle PROMISC must be set manually for ipt_netflow to function, but [09:36] <whaffle> promisc does not need to be set manually, because the bridge will do it for you. [09:36] <whaffle> When you do not have a bridge, you can easily create one, thereby rendering any kernel patches moot. [09:36] <mbrownnyc> whaffle: I speak without the bridge [09:36] <whaffle> It is perfectly valid to have a "half-bridge" with only a single interface in it. [09:36] <mbrownnyc> whaffle: I am unfamiliar with the raw table, does this mean that PROMISC allows the raw table to be populated with packets the same as if the interface was part of a bridge? [09:37] <whaffle> Promisc mode will cause packets with {a dst MAC address that does not equal the interface's MAC address} to be delivered from the NIC into the kernel nevertheless. [09:37] <mbrownnyc> whaffle: I suppose I mean to clearly ask: what benefit would creating a bridge have over setting an interface PROMISC? [09:38] <mbrownnyc> whaffle: from your last answer I feel that the answer to my question is "none," is this correct? [09:39] <whaffle> Furthermore, the linux kernel itself has a check for {packets with a non-local MAC address}, so that packets that will not enter a bridge will be discarded as well, even in the face of PROMISC. [09:46] <mbrownnyc> whaffle: so, this last bit of information is quite clearly why I would need and want a bridge in my situation [09:46] <mbrownnyc> okay, the ICMP echo reply duplicate issue is likely out of the realm of this channel, but I sincerely appreciate the info on the kernels inner-workings [09:52] <whaffle> mbrownnyc: either the kernel patch, or a bridge with an interface. Since the latter is quicker, yes [09:54] <mbrownnyc> thanks whaffle [edit2] After removing the bridge, and removing the dummy kernel module, I only had a single interface chilling out, lonely. I still received duplicate icmp echo replies... in fact I received a random amount: http://pastebin.com/2LNs0GM8 The same thing doesn't happen on a few other hosts on the same switch, so it has to do with the linux box itself. I'll likely end up rebuilding it next week. Then... you know... this same thing will occur again. [edit3] Guess what? I rebuilt the box, and I'm still receiving duplicate ICMP echo replies. Must be the network infrastructure, although the ARP tables do not contain multiple entries. [edit4] How ridiculous. The machine was a network probe, so I was (ingress and egress) mirroring an uplink port to a node that was the NIC. So, the flow (must have) gone like this: ICMP echo request comes in through the mirrored uplink port. (the real) ICMP echo request is received by the NIC (the mirrored) ICMP echo request is received by the NIC ICMP echo reply is sent for both. I'm ashamed of myself, but now I know. It was suggested on #networking to either isolate the mirrored traffic to an interface that does not have IP enabled, or tag the mirrored packets with dot1q.

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• operating systems - TLBs

  - by stabGreeol

  I'm trying to get my head round this (okay, tbh cramming a night before the exams :) but i can't figure out (nor find a good high level overview on the net) of this: 'page table entries can be mapped to more than one TLB entry.. if for example every page table entry is mappped to two TLB entries, this is know as 2-way set associative TLB' My question is, why would we want to map this more than once? surely we want to have the maximum number of possible entries represented in the TLB, and duplication would waste space right ? What am i missing? Many thanks

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