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  • Mysql concurrency: what happens if a locked table is accessed?

    - by PixelSapiens
    the question is rather simple but I couldn't find a precise answer: in a myisam db, what happens if a php file locks a table (with an atomic operation, say an INSERT) and another php file tries to access the same table (reading or writing)? Now, while it is obvious that the second session will not be able to access the table, what exactly happens? Does it return some kind of error? Does is wait in queue until it is able to access it? Thanks in advance!

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  • B-trees, databases, sequential inputs, and speed.

    - by IanC
    I know from experience that b-trees have awful performance when data is added to them sequentially (regardless of the direction). However, when data is added randomly, best performance is obtained. This is easy to demonstrate with the likes of an RB-Tree. Sequential writes cause a maximum number of tree balances to be performed. I know very few databases use binary trees, but rather used n-order balanced trees. I logically assume they suffer a similar fate to binary trees when it comes to sequential inputs. This sparked my curiosity. If this is so, then one could deduce that writing sequential IDs (such as in IDENTITY(1,1)) would cause multiple re-balances of the tree to occur. I have seen many posts argue against GUIDs as "these will cause random writes". I never use GUIDs, but it struck me that this "bad" point was in fact a good point. So I decided to test it. Here is my code: SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[T1]( [ID] [int] NOT NULL CONSTRAINT [T1_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO CREATE TABLE [dbo].[T2]( [ID] [uniqueidentifier] NOT NULL CONSTRAINT [T2_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO declare @i int, @t1 datetime, @t2 datetime, @t3 datetime, @c char(300) set @t1 = GETDATE() set @i = 1 while @i < 2000 begin insert into T2 values (NEWID(), @c) set @i = @i + 1 end set @t2 = GETDATE() WAITFOR delay '0:0:10' set @t3 = GETDATE() set @i = 1 while @i < 2000 begin insert into T1 values (@i, @c) set @i = @i + 1 end select DATEDIFF(ms, @t1, @t2) AS [Int], DATEDIFF(ms, @t3, getdate()) AS [GUID] drop table T1 drop table T2 Note that I am not subtracting any time for the creation of the GUID nor for the considerably extra size of the row. The results on my machine were as follows: Int: 17,340 ms GUID: 6,746 ms This means that in this test, random inserts of 16 bytes was almost 3 times faster than sequential inserts of 4 bytes. Would anyone like to comment on this? Ps. I get that this isn't a question. It's an invite to discussion, and that is relevant to learning optimum programming.

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  • How can i solve "An explicit value for the identity column in table"?

    - by Phsika
    if i try to add some data into my table error occurs: Error:Msg 8101, Level 16, State 1, Line 1 An explicit value for the identity column in table 'ENG_PREP' can only be specified when a column list is used and IDENTITY_INSERT is ON. insert into ENG_PREP VALUES('572012-01-1,572012-01-2,572012-01-3,572013-01-1,572013-01-2', '', '500', '', 'A320 P.001-A', 'Removal of the LH Wing Safety Rope', '', '', '', '0', '', 'AF', '12-00-00-081-001', '', '', '', '', '', '', '' )

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  • jQuery ajax post dynamic url insertion

    - by Kirill
    $.ajax({ type: "POST", url: "OMFG.php", data: info, success: function(){ }}); is what I'm using atm as a test and it works fine. I need to get the url from the link I'm clicking, so I do: var url = $(this).attr("href"); which works fine if I alert it out(the link includes http://samedomain.com/etc.php), but the ajax function doesn't post if I insert it into the ajax code: $.ajax({ type: "POST", url: url, data: info, success: function(){ }}); Please help, as I'm screwed without this working.

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  • SQL GUI Programs

    - by jake
    Are there any programs with a gui which let you create a SQL database, create tables, define the primary and foreign keys and insert data? I am tired of having to use the mysql command line client, very tedious.

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  • Issue in Adding data into database using hibernate

    - by sarah
    Hi , I am getting the following exception "org.hibernate.HibernateException: The database returned no natively generated identity value "while adding data into database i am using the following code.Please let me know what is wrong Sesion session=HibernateUtil.getSession(); Transaction tx = session.beginTransaction(); session.save(user); logger.info("Successfully data insert in database"); tx.commit(); isSaved=true; Thankx

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  • how to implement a counter in label which decrements every time page is loaded in asp.net(vb)?

    - by Parth
    how to implement a counter in label which decrements every time page is loaded in asp.net(vb)? It would be better if that counter value is accessed from and updated into database.. I've tried this on buttonclick but the value is reset automatically to intial value everytime as the button is insert and page is reloaded Protected Sub InsertButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Dim entries As Label = FindControl("label1") entries.Text = entries.Text - 1 End Sub

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  • NHibernate: inserting additional calculated column

    - by Andrey Shchekin
    What would be your approach with NHibernate to do the following: When Comment is inserted into DB, and its property Text is inserted into column Text (due to a mapping), insert into column TextHash a hash of this property value. It seems trivial if I map TextHash, but how should I do this without mapping it? I do not need it in the domain model, its a DB-level optimization (I would use computed HashBytes if not for the length limit).

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  • How to parse a midlet JAD file in C#?

    - by codemonkie
    Besides doing it manually using regular expression search, is there other better ways to parse a JAD file? I need to be able to search for and replace/insert a new MIdlet-Install-Notify property to a JAD file given, also updating the value of the MIDlet-Jar-URL property. Using ANTLR or TinyPG is a bit overkill for my case. TIA

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  • Fastest way to check array items existence in mySQL table

    - by Enrique
    User writes a series of tags (, separated) and posts the form. I build an array containing the tags and delete dupes with array_unique() php function. I'm thinking of doing: go through the array with foreach($newarray as $item) { ... } check each $item for existence in the tags mySQL table if item does not exists, insert into tags table Is there a FASTER or MORE OPTIMUM way for doing this?

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  • How do I get fine-grained undo in Vim

    - by MDCore
    I find Vim's undo to be a bit too coarse. E.g. if I type something like this: a // to go into edit mode to be or not to ve <esc> // to exit insert mode Oops! I made a typo. I want to start undoing so I press u, but then it clears the whole line. Is there a way to undo word-by-word or character-by-character?

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  • Pound symbol not displaying on web page

    - by Gublooo
    Hello I have a mysql database table to store country name and currency symbol - the CHARSET has correctly set to UTF8. This is example data inserted into the table insert into country ( country_name, currency_name, currency_code, currency_symbol) values ('UK','Pounds','GBP','£'); When I look in the database - the pound symbol appears fine - but when I retrieve it from the database and display it on the website - a weird square symbol shows up with a question mark inside instead of the pound symbol. You can look at it here - http://www.didyouswipe.com/profile/view-profile/user_id/181 Please advice Thanks

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  • convert date string to mysql datetime field

    - by mjr
    I have a bunch of records with dates formatted as a string such as '04/17/2009' I want to convert them to a mysql datetime field I plan to use a foreach loop to read the old date value and insert the newly formatted value into a new field in each record what would be the best way to convert that string...I thought php might have a way to do it automatically? thanks

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  • Multiline code in Word 2007

    - by WaelJ
    I am using word 2007 and am inserting code into the document. I have a style with a fixed-width font and light grey background and all, and I use Notepad++ for syntax highlighting. My problem is with a "line" of code that is too long to display, so is there a way to auto-insert an arrow symbol at the beginning of a such lines to indicate that it is the same line (kind of like hyphenating, except on long lines instead of long words) So for e.g. something like this: public static void foo(String abcdefg, Boolean 123, ?String xyz)

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  • main.out.xml error

    - by husainsn
    Hello I installed Eclipse and Android ADT. When I create android project and try to run, I get following on main.out.xml file: This document is empty. Right click here to insert content However, main.xml file has xml data for layout. Please help what I need to do after right clicking. Thanks

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