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  • Read variable-length records from a buffer - weird memory issues

    - by bsg
    Hi, I'm trying to implement an i/o intensive quicksort (C++ qsort) on a very large dataset. In the interests of speed, I'd like to read in a chunk of data at a time into a buffer and then use qsort to sort it inside the buffer. (I am currently working with text files but would like to move to binary soon.) However, my data is composed of variable-length records, and qsort needs to be told the length of the record in order to sort. Is there any way to standardize this? The only thing I could think of was rather convoluted: my program currently reads from the buffer until it hits a linefeed character ('10' in ascii), transferring each character over to another array. When it finds a linefeed (the delimiter in the input file), it fills the number of spaces remaining in the buffer for that record (record size is set to 30) with null characters. This way, I should end up with a buffer full of fixed-size records to give qsort. I know there are several problems with my approach, one being that it's just clumsy, another that the record size might conceivably be larger than 30, but is generally much less. Is there a better way of doing this? As well, my current code doesn't even work. When I debug it, it seems to be transferring characters from one buffer to the other, but when I try to print out the buffer, it contains only the first record. Here is my code: FILE *fp; unsigned char *buff; unsigned char *realbuff; FILE *inputFiles[NUM_INPUT_FILES]; buff = (unsigned char *) malloc(2048); realbuff = (unsigned char *) malloc(NUM_RECORDS * RECORD_SIZE); fp = fopen("postings0.txt", "r"); if(fp) { fread(buff, 1, 2048, fp); /*for(int i=0; i <30; i++) cout << buff[i] <<endl;*/ int y=0; int recordcounter = 0; //cout << buff; for(int i=0;i <100; i++) { if(buff[i] != char(10)) { realbuff[y] = buff[i]; y++; recordcounter++; } else { if(recordcounter < RECORD_SIZE) for(int j=recordcounter; j < RECORD_SIZE;j++) { realbuff[y] = char(0); y++; } recordcounter = 0; } } cout << realbuff <<endl; cout << buff; } else cout << "sorry"; Thank you very much, bsg

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  • Create Duplicate Records on SELECT for Calendar Date Range

    - by peterallcdn
    Hey all, I've built a pretty shnazzy calendar system but there is one tweak that I need to make so that I'm completely happy with it. My calendar has three tables: calevents - The calendared event. caldates - The occurrences and date-range of each occurrence for each event. calcats - The categories that can be applied to an event. The short: For each calevent, there can be many caldates, one for each occurrence of calevent. So a calevent that repeats weekly and spans 3 days might have caldates like this: date_id date_eid date_start date_end 2 37 2010-06-21 2010-06-23 3 37 2010-06-28 2010-06-30 7 37 2010-07-05 2010-07-07 9 37 2010-07-12 2010-07-14 What I want to do, is when selecting all the caldates for a specified month such as 2010-06, to return not just the two records above, but instead a record for each date in the range of date_start and date_end for each caldate. So if I searched for 2010-06, I would get: date_id date_eid date_start date_end date_day 2 37 2010-06-21 2010-06-23 2010-06-21 2 37 2010-06-21 2010-06-23 2010-06-22 2 37 2010-06-21 2010-06-23 2010-06-23 3 37 2010-06-28 2010-06-30 2010-06-28 3 37 2010-06-28 2010-06-30 2010-06-29 3 37 2010-06-28 2010-06-30 2010-06-30 The Long: The reason I want to do this, is so when displaying a list of events(calevents) for a specified month, an occurrence(caldates) of that event will be displayed for EACH of the days it spans. I could do this with php by looping through each day of the current month and displaying a copy of each caldate if the month day falls between date_start and date_end. But doing it this way will prevent me from using record pagination if needed. For example, if for a specified month the following caldates were returned: date_id date_eid date_start date_end 2 37 2010-06-21 2010-06-27 94 53 2010-06-09 2010-07-08 Doing record pagination would see this as only 2 records("rows"). But looping through them with PHP would generate 29 "rows". So, I figure if I use mysql to create each row instead of PHP, I can achieve the same thing AND still be able to use pagination if a month has a lot of events/dates. As far as performance goes, I'm not sure which option is more efficient. Both would send the same amount of info to the browser, so it's really only the work required to generate the info that matters. My current query which fetches all the occurrences for a specified month, and to make things just a little more complicated... joins them with their event and category, looks like this: $sql_to_execute = " SELECT date_id, date_eid, date_start, date_end, event_id, event_title, event_category, event_private, event_location, SUBSTRING_INDEX(event_detailsstripped, ' ', 40) AS event_detailsstripped, event_time, event_starttime, event_endtime, event_active, cat_colour FROM ( caldates LEFT JOIN calevents ON caldates.date_eid = calevents.event_id ) LEFT JOIN calcats ON calevents.event_category = calcats.cat_id WHERE date_start <= '".mysql_real_escape_string($dbi_list_end_date)."' AND date_end >= '".mysql_real_escape_string($dbi_list_start_date)."' ".$dbi_category." ORDER BY date_start ASC "; Any help or advice would be greatly appreciated! Thanks, Peter

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  • Updating several records at once using Django

    - by 47
    I want to create a list of records with checkboxes on the left side....kinda like the inbox in Gmail. Then if a user selects some or all of these checkboxes, then the selected record(s) can be updated (only one field will be updated BTW), possibly by clicking a button. I'm stuck on how to do this though....ideas?

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  • Rtti for Variant Records

    - by Coco
    I try to write a kind of object/record serializer with Delphi 2010 and wonder if there is a way to detect, if a record is a variant record. E.g. the TRect record as defined in Types.pas: TRect = record case Integer of 0: (Left, Top, Right, Bottom: Longint); 1: (TopLeft, BottomRight: TPoint); end; As my serializer should work recursively on my data structures, it will descent on the TPoint records and generate redundant information in my serialized file. Is there a way to avoid this, by getting detailed information on the record?

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  • saving a records containing a member of type string to a file (Delphi, Windows)

    - by wonderer
    I have a record that looks similar to: type TNote = record Title : string; Note : string; Index : integer; end; Simple. The reason I chose to set the variables as string (as opposed to an array of chars) is that I have no idea how long those strings are going to be. They can be 1 char long, 200 or 2000. Of course when I try to save the record to a type file (file of...) the compiler complains that I have to give a size to string. Is there a way to overcome this? or a way to save those records to an untyped file and still maintain a sort of searchable way? Please do not point me to possible solutions, if you know the solution please post code. Thank you

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  • delphi Ado (mdb) update records

    - by ml
    I´m trying to copy data from one master table and 2 more child tables when i select one record in the master table i copy all the fields from that table for the other (table1 copy from ADOQuery the selected record) procedure TForm1.copyButton7Click(Sender: TObject); SQL.Clear; SQL.Add('SELECT * from ADOQuery'); SQL.Add('Where numeracao LIKE ''%'+NInterv.text);// locate record selected in Table1 NInterv.text) Open; // initiate copy of records begin while not tableADoquery.Eof do begin Table1.Last; Table1.Append;// how to append if necessary! Table1.Edit; Table1.FieldByName('C').Value := ADoquery.FieldByName('C').Value; Table1.FieldByName('client').Value := ADoquery.FieldByName('client').Value; Table1.FieldByName('Cnpj_cpf').Value := ADoquery.FieldByName('Cnpj_cpf').Value; table1.Post; table2.next;/// end; end; //How can i update the TableChield, TableChield1 field´s at the same time? do the same for the child tables TableChield <= TableChield_1 TableChield1 <= TableChield_2 thanks

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  • Advice on "Invalid Pointer Operation" when using complex records

    - by Xaz
    Env: Delphi 2007 <JustificationI tend to use complex records quite frequently as they offer almost all of the advantages of classes but with much simpler handling.</Justification Anyhoo, one particularly complex record I have just implemented is trashing memory (later leading to an "Invalid Pointer Operation" error). This is an example of the memory trashing code: sSignature := gProfiles.Profile[_stPrimary].Signature.Formatted(True); On the second time i call it i get "Invalid Pointer Operation" It works OK if i call it like this: AProfile := gProfiles.Profile[_stPrimary]; ASignature := AProfile.Signature; sSignature := ASignature.Formatted(True); Background Code: gProfiles: TProfiles; TProfiles = Record private FPrimaryProfileID: Integer; FCachedProfile: TProfile; ... public < much code removed > property Profile[ProfileType: TProfileType]: TProfile Read GetProfile; end; function TProfiles.GetProfile(ProfileType: TProfileType): TProfile; begin case ProfileType of _stPrimary : Result := ProfileByID(FPrimaryProfileID); ... end; end; function TProfiles.ProfileByID(iID: Integer): TProfile; begin <snip> if LoadProfileOfID(iID, FCachedProfile) then begin Result := FCachedProfile; end else ... end; TProfile = Record private ... public ... Signature: TSignature; ... end; TSignature = Record private public PlainTextFormat : string; HTMLFormat : string; // The text to insert into a message when using this profile function Formatted(bHTML: boolean): string; end; function TSignature.Formatted(bHTML: boolean): string; begin if bHTML then result := HTMLFormat else result := PlainTextFormat; < SNIP MUCH CODE > end; OK, so I have a record within a record within a record, which is approaching Inception level confusion and I'm the first to admit is not really a good model. Clearly i am going to have to restructure it. What I would like from you gurus is a better understanding of why it is trashing the memory (something to do with the string object that is created then freed...) so that i can avoid making these kinds of errors in future. Thanks

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  • C#:checking existing record in database Mysql

    - by Meko
    HI.I searched this question inform and I found solution to change column property Unique Index.Now If I try to insert same record cmd.ExecuteNonQuery() gives error that record exist ,but how can use this exception to give user a message that record exist and must enter new one ? I am trying to make some thing like if(cmd.ExecuteNonQuery() !=true ) { MessageBox.Show("User Exists"); } But I dont know what returns cmd.ExecuteNonQuery() ? Or I must get records using reader in table and compare them with text in Textfiel?

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  • iphone coredata removing records between two entities connected by relation ship

    - by satyam
    I'm implementing core data in my iphone app. It has two entities. Entity1: LatestData Entity2: LatestDetailedData LatestData has URL, publishedDate, heading LatestDetailedData has URL, NewsDescription, PublishedDate, Author Both entities have same URL for a record. Both the entities are connected with inverse relation ship. And the relation ship is "delete-Cascaded" What I want: If I remove a record in LatestData, I want the record with same URL in LatestDetailedData must also be deleted. How?

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  • How to quickly search through a very large list of strings / records on a database

    - by Giorgio
    I have the following problem: I have a database containing more than 2 million records. Each record has a string field X and I want to display a list of records for which field X contains a certain string. Each record is about 500 bytes in size. To make it more concrete: in the GUI of my application I have a text field where I can enter a string. Above the text field I have a table displaying the (first N, e.g. 100) records that match the string in the text field. When I type or delete one character in the text field, the table content must be updated on the fly. I wonder if there is an efficient way of doing this using appropriate index structures and / or caching. As explained above, I only want to display the first N items that match the query. Therefore, for N small enough, it should not be a big issue loading the matching items from the database. Besides, caching items in main memory can make retrieval faster. I think the main problem is how to find the matching items quickly, given the pattern string. Can I rely on some DBMS facilities, or do I have to build some in-memory index myself? Any ideas? EDIT I have run a first experiment. I have split the records into different text files (at most 200 records per file) and put the files in different directories (I used the content of one data field to determine the directory tree). I end up with about 50000 files in about 40000 directories. I have then run Lucene to index the files. Searching for a string with the Lucene demo program is pretty fast. Splitting and indexing took a few minutes: this is totally acceptable for me because it is a static data set that I want to query. The next step is to integrate Lucene in the main program and use the hits returned by Lucene to load the relevant records into main memory.

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  • Mysql: Working With 192 Trillion Records... (Yes, 192 Trillion)

    - by Sarah
    Here's the question... Considering 192 trillion records, what should my considerations be? My main concern is speed. Here's the table... CREATE TABLE `ref` ( `id` INTEGER(13) AUTO_INCREMENT DEFAULT NOT NULL, `rel_id` INTEGER(13) NOT NULL, `p1` INTEGER(13) NOT NULL, `p2` INTEGER(13) DEFAULT NULL, `p3` INTEGER(13) DEFAULT NULL, `s` INTEGER(13) NOT NULL, `p4` INTEGER(13) DEFAULT NULL, `p5` INTEGER(13) DEFAULT NULL, `p6` INTEGER(13) DEFAULT NULL, PRIMARY KEY (`id`), KEY (`s`), KEY (`rel_id`), KEY (`p3`), KEY (`p4`) ); Here's the queries... SELECT id, s FROM ref WHERE red_id="$rel_id" AND p3="$p3" AND p4="$p4" SELECT rel_id, p1, p2, p3, p4, p5, p6 FROM ref WHERE id="$id" INSERT INTO rel (rel_id, p1, p2, p3, s, p4, p5, p6) VALUES ("$rel_id", "$p1", "$p2", "$p3", "$s", "$p4", "$p5", "$p6") Here's some notes... The SELECT's will be done much more frequently than the INSERT. However, occasionally I want to add a few hundred records at a time. Load-wise, there will be nothing for hours then maybe a few thousand queries all at once. Don't think I can normalize any more (need the p values in a combination) The database as a whole is very relational. This will be the largest table by far (next largest is about 900k) UPDATE (08/11/2010) Interestingly, I've been given a second option... Instead of 192 trillion I could store 2.6*10^16 (15 zeros, meaning 26 Quadrillion)... But in this second option I would only need to store one bigint(18) as the index in a table. That's it - just the one column. So I would just be checking for the existence of a value. Occasionally adding records, never deleting them. So that makes me think there must be a better solution then mysql for simply storing numbers... Given this second option, should I take it or stick with the first... [edit] Just got news of some testing that's been done - 100 million rows with this setup returns the query in 0.0004 seconds [/edit]

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  • Merge Records in Session bean by using ADF Drag/Drop

    - by shantala.sankeshwar
    This article describes how to merge multiple selected records in Session Bean using ADF drag & drop feature. Below described is simple use case that shows how exactly this can be achieved. Here we will have table & user input field.Table shows  EMP records & user input field accepts Salary.When we drag & drop multiple records on user input field,the selected records get updated with the new Salary provided. Steps: Let us suppose that we have created Java EE Web Application with Entities from Emp table.Then create EJB Session Bean & generate Data control for the same. Write a simple code in sessionEJBBean & expose this method to local interface :  public void updateEmprecords(List empList, Object sal) {       Emp emp = null;       for (int i = 0; i < empList.size(); i++)       {        emp = em.find(Emp.class, empList.get(i));         emp.setSal((BigDecimal)sal);       }      em.merge(emp);   } Now let us create updateEmpRecords.jspx page in viewController project & Drop empFindAll object as ADF Table Define custom SelectionListener method for the table :   public void selectionListener(SelectionEvent selectionEvent)     {     // This method gets the Empno of the selected record & stores in the list object      UIXTable table = (UIXTable)selectionEvent.getComponent();      FacesCtrlHierNodeBinding fcr      =(FacesCtrlHierNodeBinding)table.getSelectedRowData();      Number empNo = (Number)fcr.getAttribute("empno") ;      this.getSelectedRowsList().add(empNo);     }Set table's selectedRowKeys to #{bindings.empFindAll.collectionModel.selectedRow}"Drop inputText on the same jspx page that accepts Salary .Now we would like to drag records from the above table & drop that on the inputtext field.This feature can be achieved by inserting dragSource operation inside the table & dropTraget operation inside the inputText:<af:dragSource discriminant="tab"/> //Insert this inside the table<af:inputText label="Enter Salary" id="it13" autoSubmit="true"       binding="# {test.deptValue}">       <af:dropTarget dropListener="#{test.handleTableDrop}">       <af:dataFlavor        flavorClass="org.apache.myfaces.trinidad.model.RowKeySet"    discriminant="tab"/>       </af:dropTarget>       <af:convertNumber/> </af:inputText> In the above code when the user drags & drops multiple records on inputText,the dropListener method gets called.Goto the respective page definition file & create updateEmprecords method action& execute action dropListener method code:        public DnDAction handleTableDrop(DropEvent dropEvent)        {          //Below code gets the updateEmprecords method,passes parameters & executes method            DataFlavor<RowKeySet> df = DataFlavor.getDataFlavor(RowKeySet.class);            RowKeySet droppedKeySet = dropEvent.getTransferable().getData(df);            if (droppedKeySet != null && droppedKeySet.size() > 0)           {                  DCBindingContainer bindings =                  (DCBindingContainer)BindingContext.getCurrent().getCurrentBindingsEntry();                  OperationBinding updateEmp;                  updateEmp= bindings.getOperationBinding("updateEmprecords");                  updateEmp.getParamsMap().put("sal",                  this.getDeptValue().getAttributes().get("value"));                            updateEmp.getParamsMap().put("empList", this.getSelectedRowsList());                  updateEmp.execute(); //Below code performs execute operation to refresh the updated records                 OperationBinding executeBinding;                 executeBinding= bindings.getOperationBinding("Execute");                 executeBinding.execute(); AdfFacesContext.getCurrentInstance().addPartialTarget(dropEvent.getDragComponent());                this.getSelectedRowsList().clear();          }                 return DnDAction.NONE;        }Run updateEmpRecords.jspx page & enter any Salary say '5000'.Select multiple records in table & drop these selected records on the inputText Salary. Note that all the selected records salary value gets updated to 5000.Technorati Tags: ADF Drag and drop,EJB Session bean,ADF table,inputText,DropEvent  

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  • adding an existing implementation file to an xcode project won't work

    - by karsten
    As I write most of my code using MacVIM, I need to add the new files to the XCode project in order to compile them into the executable. Today however I encoutered an implementation file (.m) wich XCode won't allow to be added. It appears light gray the appropriate finder window as if it were already included in the project, but when I try to build, I get a linker error, stating that the symbol defined this implementation file could not be found. The corresponding header file could be added without problems. Any idea what could have caused this problem? Btw. I deleted a former version of the same file from the "Classes" tree before, as well as many others wich were successfully re-added. Thanks in advance.

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  • Migrating an Existing ASP.NET App to run on Windows Azure

    - by kaleidoscope
    Converting Existing ASP.NET application in to Windows Azure Method 1:  1. Add a Windows Azure Cloud Service to the existing solution                         2. Add WebRole Project in solution and select Existing Asp.Net project in it. Method 2: The other option would have been to create a new Cloud Service project and add the ASP.NET project (which you want to deploy on Azure) to it using -                    1. Solution | Add | Existing Project                    2. Add | Web Role Project in solution Converting Sql server database to SQL Azure - Step 1: Migrate the <Existing Application>.MDF Step 2: Migrate the ASP.NET providers Step 3: Change the connection strings More details can be found at http://blogs.msdn.com/jnak/archive/2010/02/08/migrating-an-existing-asp-net-app-to-run-on-windows-azure.aspx   Ritesh, D

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  • What's the progress on Haskell records?

    - by mmh
    Recently I stumbled once again on the issues of Haskells records, in particular the uniqueness of field names (it's a pain ...) I already read A proposal for records in Haskell from SPJ and Greg Morrisett but it's last update was 2003. Another paper Lightweight Extensible Records for Haskell from SPJ and Mark Jones is even older: It's from a Haskell workshop in 1999. Now I wonder if the process of giving Haskell new records made any progress. Does anybody know something about it or can point me to some further reading ?

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  • Ghost Records, Backups, and Database Compression…With a Pinch of Security Considerations

    - by Argenis
      Today Jeffrey Langdon (@jlangdon) posed on #SQLHelp the following questions: So I set to answer his question, and I said to myself: “Hey, I haven’t blogged in a while, how about I blog about this particular topic?”. Thus, this post was born. (If you have never heard of Ghost Records and/or the Ghost Cleanup Task, go see this blog post by Paul Randal) 1) Do ghost records get copied over in a backup? If you guessed yes, you guessed right. The backup process in SQL Server takes all data as it is on disk – it doesn’t crack the pages open to selectively pick which slots have actual data and which ones do not. The whole page is backed up, regardless of its contents. Even if ghost cleanup has run and processed the ghost records, the slots are not overwritten immediately, but rather until another DML operation comes along and uses them. As a matter of fact, all of the allocated space for a database will be included in a full backup. So, this poses a bit of a security/compliance problem for some of you DBA folk: if you want to take a full backup of a database after you’ve purged sensitive data, you should rebuild all of your indexes (with FILLFACTOR set to 100%). But the empty space on your data file(s) might still contain sensitive data! A SHRINKFILE might help get rid of that (not so) empty space, but that might not be the end of your troubles. You might _STILL_ have (not so) empty space on your files! One approach that you can follow is to export all of the data on your database to another SQL Server instance that does NOT have Instant File Initialization enabled. This can be a tedious and time-consuming process, though. So you have to weigh in your options and see what makes sense for you. Snapshot Replication is another idea that comes to mind. 2) Does Compression get rid of ghost records (2008)? The answer to this is no. The Ghost Records/Ghost Cleanup Task mechanism is alive and well on compressed tables and indexes. You can prove this running a simple script: CREATE DATABASE GhostRecordsTest GO USE GhostRecordsTest GO CREATE TABLE myTable (myPrimaryKey int IDENTITY(1,1) PRIMARY KEY CLUSTERED,                       myWideColumn varchar(1000) NOT NULL DEFAULT 'Default string value')                         ALTER TABLE myTable REBUILD PARTITION = ALL WITH (DATA_COMPRESSION = PAGE) GO INSERT INTO myTable DEFAULT VALUES GO 10 DELETE myTable WHERE myPrimaryKey % 2 = 0 DBCC TRACEON(2514) DBCC CHECKTABLE(myTable) TraceFlag 2514 will make DBCC CHECKTABLE give you an extra tidbit of information on its output. For the above script: “Ghost Record count = 5” Until next time,   -Argenis

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  • Ghost Records, Backups, and Database Compression…With a Pinch of Security Considerations

    - by Argenis
      Today Jeffrey Langdon (@jlangdon) posed on #SQLHelp the following questions: So I set to answer his question, and I said to myself: “Hey, I haven’t blogged in a while, how about I blog about this particular topic?”. Thus, this post was born. (If you have never heard of Ghost Records and/or the Ghost Cleanup Task, go see this blog post by Paul Randal) 1) Do ghost records get copied over in a backup? If you guessed yes, you guessed right. The backup process in SQL Server takes all data as it is on disk – it doesn’t crack the pages open to selectively pick which slots have actual data and which ones do not. The whole page is backed up, regardless of its contents. Even if ghost cleanup has run and processed the ghost records, the slots are not overwritten immediately, but rather until another DML operation comes along and uses them. As a matter of fact, all of the allocated space for a database will be included in a full backup. So, this poses a bit of a security/compliance problem for some of you DBA folk: if you want to take a full backup of a database after you’ve purged sensitive data, you should rebuild all of your indexes (with FILLFACTOR set to 100%). But the empty space on your data file(s) might still contain sensitive data! A SHRINKFILE might help get rid of that (not so) empty space, but that might not be the end of your troubles. You might _STILL_ have (not so) empty space on your files! One approach that you can follow is to export all of the data on your database to another SQL Server instance that does NOT have Instant File Initialization enabled. This can be a tedious and time-consuming process, though. So you have to weigh in your options and see what makes sense for you. Snapshot Replication is another idea that comes to mind. 2) Does Compression get rid of ghost records (2008)? The answer to this is no. The Ghost Records/Ghost Cleanup Task mechanism is alive and well on compressed tables and indexes. You can prove this running a simple script: CREATE DATABASE GhostRecordsTest GO USE GhostRecordsTest GO CREATE TABLE myTable (myPrimaryKey int IDENTITY(1,1) PRIMARY KEY CLUSTERED,                       myWideColumn varchar(1000) NOT NULL DEFAULT 'Default string value')                         ALTER TABLE myTable REBUILD PARTITION = ALL WITH (DATA_COMPRESSION = PAGE) GO INSERT INTO myTable DEFAULT VALUES GO 10 DELETE myTable WHERE myPrimaryKey % 2 = 0 DBCC TRACEON(2514) DBCC CHECKTABLE(myTable) TraceFlag 2514 will make DBCC CHECKTABLE give you an extra tidbit of information on its output. For the above script: “Ghost Record count = 5” Until next time,   -Argenis

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  • What are the main differences between SRV records and TXT records?

    - by Chris Adams
    Hi there, I'm trying to consolidate domain names for the servers I look after to just use one panel instead of 3 or 4, and one thing stopping me is that the provider I originally wanted to move them to only lets me the following kinds of records: A MX NS CNAME TXT The first four I understand, but I'm not sure about the relationship (if any) between SRV records and TXT records. Can I use TXT records in the place of SRV records? They both seem to be general text records to just point at a particular server without needing to specify a particular protocol, so it doesn't sound like a totally unreasonable assumption, but I'd rather check here before I break something. If I can only set the above records, does that mean I'm essentially unable to so any SRC record redirecting? Thanks!

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  • Adding Column to a SQL Server Table

    - by Dinesh Asanka
    Adding a column to a table is  common task for  DBAs. You can add a column to a table which is a nullable column or which has default values. But are these two operations are similar internally and which method is optimal? Let us start this with an example. I created a database and a table using following script: USE master Go --Drop Database if exists IF EXISTS (SELECT 1 FROM SYS.databases WHERE name = 'AddColumn') DROP DATABASE AddColumn --Create the database CREATE DATABASE AddColumn GO USE AddColumn GO --Drop the table if exists IF EXISTS ( SELECT 1 FROM sys.tables WHERE Name = 'ExistingTable') DROP TABLE ExistingTable GO --Create the table CREATE TABLE ExistingTable (ID BIGINT IDENTITY(1,1) PRIMARY KEY CLUSTERED, DateTime1 DATETIME DEFAULT GETDATE(), DateTime2 DATETIME DEFAULT GETDATE(), DateTime3 DATETIME DEFAULT GETDATE(), DateTime4 DATETIME DEFAULT GETDATE(), Gendar CHAR(1) DEFAULT 'M', STATUS1 CHAR(1) DEFAULT 'Y' ) GO -- Insert 100,000 records with defaults records INSERT INTO ExistingTable DEFAULT VALUES GO 100000 Before adding a Column Before adding a column let us look at some of the details of the database. DBCC IND (AddColumn,ExistingTable,1) By running the above query, you will see 637 pages for the created table. Adding a Column You can add a column to the table with following statement. ALTER TABLE ExistingTable Add NewColumn INT NULL Above will add a column with a null value for the existing records. Alternatively you could add a column with default values. ALTER TABLE ExistingTable Add NewColumn INT NOT NULL DEFAULT 1 The above statement will add a column with a 1 value to the existing records. In the below table I measured the performance difference between above two statements. Parameter Nullable Column Default Value CPU 31 702 Duration 129 ms 6653 ms Reads 38 116,397 Writes 6 1329 Row Count 0 100000 If you look at the RowCount parameter, you can clearly see the difference. Though column is added in the first case, none of the rows are affected while in the second case all the rows are updated. That is the reason, why it has taken more duration and CPU to add column with Default value. We can verify this by several methods. Number of Pages The number of data pages can be obtained by using DBCC IND command. Though, this an undocumented dbcc command, many experts are ok to use this command in production. However, since there is no official word from Microsoft, use this “at your own risk”. DBCC IND (AddColumn,ExistingTable,1) Before Adding the Columns 637 Adding a Column with NULL 637 Adding a column with DEFAULT value 1270 This clearly shows that pages are physically modified. Please note, a high value indicated in the Adding a column with DEFAULT value  column is also a result of page splits. Continues…

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  • Synthetic database records

    - by michipili
    Assume we are getting some statistics from a customer which we analyse and we send our comments to the customer. Now, the customer tells us that the statistic they computed between January and March are based on a wrong methodology and sends us corrected series. We want perform analysis with the wrong and with the correct set of data, which are huge and only differ from January to March. Therefore, we need something like synthetic database records implementing the following logic: synthetic[1] = wrong_data synthetic[2] = correct_data between Januar and March, wrong_data otherwise With this, we can easily perform our analyses on synthetic records. Should such synthetic records be implemented in the application logic or on the side of the database? What are common pitfalls of such an implementation?

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