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  • Barcodes and Bugs

    - by Tim Dexter
    A great mail from Mike at Browning last week. He has been through the ringer getting his BIP barcoding sorted out but he's now out of the woods. Here's the final result. By way of explanation, an excerpt from Mike's email:   This is an example of the GS1_128 carton shipping labels we are now producing with BIP in our web application for our vendors who drop ship products to our dealers. It produces 4 labels per printed page, in PDF format, on peel & stick label paper. Each label has a unique carton number, and a unique carton serial number in the SSCC-18 barcode. This example is for Cabelas (each customer has slightly different GS1-128 label format requirements – custom template for each - a pain!). I am using custom java encoders I wrote for the UPC and SSCC-18 barcodes, and a standard encoder (code128b) for the ShipTo zip barcode. Is there any way yet to get around that SUPER ANNOYING bug when opening the rtf template in MS Word, and it replaces my xsl code text in the barcode fields with gibberish??? Every time I open it I have to re-enter all the xsl code. Not only to be able to read & edit it, but also to get it to work in BIP (BIP doesn’t like the gibberish if I upload the template that has it). Mike's last point, regarding the annoying bug in the template builder, is one that I have experienced occasionally. The development team have looked at it and found it to be an issue with MSWord and not a plugin problem. That's all well and good but how can you get around it? Well, you can take advantage of the font mapping that BIP offers to get the barcodes into the PDF output. As many of you know, getting a barcode font to appear in the PDF output, you need employ the use of the xdo.cfg file in the template builder config directory.You would normally have an entry such as this:         <font family="Code 128" style="normal" weight="normal">        <truetype path="C:\windows\fonts\128R00.TTF" />       </font>to map a barcode font to get it to render in the PDF output when testing from the template builder plugin.   Mike's issue is only present when the formfield is highlighted with a barcode font. The other fields in the template are OK. What you can do to get around the issue is to bend the config entry to get around having to use the barcode font in the template at all. Changing the entry to something like:         <font family="Calibri" style="normal" weight="normal">        <truetype path="C:\windows\fonts\128R00.TTF" />       </font>   Note that we are mapping the Calibri; a humanly readable and non 'erroring' font in the template, to the code 128 barcode font. Where you used to highlight the field with the barcode in MSWord, you now use the Calibri font instead. At run time, BIP will go look for the Calibri font mapping and will drop in the Code128 font. Of course, Calibri is an example; you need to pick a font that you are not going to use any where else in the layout.

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  • CLR JIT Bugs Found During IKVM.NET Development

    "It is actually fairly common that people notice that things fail under retail but not debug and tend to blame code generation. While a code generation bug is possible, as a matter of statistics, it is not likely." -- Vance MorrisonDateCLRArchTypeDescription2010-06-12 v4 x64 Incorrect code Optimizer incorrectly propagates invariants.2010-06-04 v2, v4 x86 Crash ...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • System for registering bugs, enhancements and invoice them?

    - by Roland Bengtsson
    I am searching suggestions for improvements? Currently our team use Github Issues to register changes in our software. Sometimes our customers have requirements that we will invoice them for. So now we reqister the same issue again in CRM. Unfortunately, the workflow is not as smooth as Github Issues and most developers try to avoid CRM if possible. It also feels waste of time to register the same issue twice. Are there any suggestions for better workflow than this?

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  • Testing To Prevent Cascading Bugs

    - by jfrankcarr
    Yesterday, Twitter was hit with a "Cascading Bug" as described in this blog post: A “cascading bug” is a bug with an effect that isn’t confined to a particular software element, but rather its effect “cascades” into other elements as well. I've seen this kind of bug, on a smaller scale of course, on some projects I've worked on. They can be difficult to identify in dev/test environments, even within a test driven development environment. My questions are... What are some strategies you use, beyond the basic TDD and standard regression testing, to identify and prevent the potential trouble points that might only occur in the production environment? Does the presence of such problems indicate a breakdown in the software development process or simply a by-product of complex software systems?

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  • Handling bugs, quirks, or annoyances in vendor-supplied headers

    - by supercat
    If the header file supplied by a vendor of something with whom one's code must interact is deficient in some way, in what cases is it better to: Work around the header's deficiencies in the main code Copy the header file to the local project and fix it Fix the header file in the spot where it's stored as a vendor-supplied tool Fix the header file in the central spot, but also make a local copy and try to always have the two match Do something else As an example, the header file supplied by ST Micro for the STM320LF series contains the lines: typedef struct { __IO uint32_t MODER; __IO uint16_t OTYPER; uint16_t RESERVED0; .... __IO uint16_t BSRRL; /* BSRR register is split to 2 * 16-bit fields BSRRL */ __IO uint16_t BSRRH; /* BSRR register is split to 2 * 16-bit fields BSRRH */ .... } GPIO_TypeDef; In the hardware, and in the hardware documentation, BSRR is described as a single 32-bit register. About 98% of the time one wants to write to BSRR, one will only be interested in writing the upper half or the lower half; it is thus convenient to be able to use BSSRH and BSSRL as a means of writing half the register. On the other hand, there are occasions when it is necessary that the entire 32-bit register be written as a single atomic operation. The "optimal" way to write it (setting aside white-spacing issues) would be: typedef struct { __IO uint32_t MODER; __IO uint16_t OTYPER; uint16_t RESERVED0; .... union // Allow BSRR access as 32-bit register or two 16-bit registers { __IO uint32_t BSRR; // 32-bit BSSR register as a whole struct { __IO uint16_t BSRRL, BSRRH; };// Two 16-bit parts }; .... } GPIO_TypeDef; If the struct were defined that way, code could use BSRR when necessary to write all 32 bits, or BSRRH/BSRRL when writing 16 bits. Given that the header isn't that way, would better practice be to use the header as-is, but apply an icky typecast in the main code writing what would be idiomatically written as thePort->BSRR = 0x12345678; as *((uint32_t)&(thePort->BSSRH)) = 0x12345678;, or would be be better to use a patched header file? If the latter, where should the patched file me stored and how should it be managed?

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  • Skype 4.2 crashes and bugs on 13.10

    - by Juhani Taylor
    I've installed Skype and it appears to work fine right up until the point where I try to call someone. If I try to video call someone then the programme freezes and I have to force quit. I've tried several 'solutions' I've found on various forums but none seem to work. Now, when I try to call the Echo service as a test to see if the bug's fixed, it seems to connect and start the non-video call, except that it's completely silent. No audio at all. Any help? It seems to be 2 separate issues: audio and generic crashing. Anyone come across these and found solutions?

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  • How To Deliberately Hide Bugs In Code (for use in a Novel I'm writing) [closed]

    - by Dennis Murphy
    I'm writing a novel in which an evil programmer wants to include subtle errors in his code that are likely to go unnoticed by his supervisor during a code review and unlikely to be caught by a compiler, yet cause damage at possibly random times when the program is executed by an end-user. I only need a couple of examples, which may be exotic but which have to be easily explainable to non-technical readers. Procedural or object-oriented examples would be equally helpful. (It's been a VERY long time since I've written any code.) Thanks for your help.

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  • Convert project without introducing bugs

    - by didietexas
    I have the C++ code of a exe which contains a UI and some process. My goal is to remove the UI so that I only have the process and to convert the exe into a dll. In order to do that, I am thinking of generating unit test before touching any code and then to do my modification and make sure the tests are not failing. The problem is that I am not sure if this is the best approach and if it is, is there a way to automatically generate unit test. BTW, I am using VS 2012. Do you have any guidance for me?

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  • Delphi 6 - Bugs disappear when I compile multiple times.

    - by Daisetsu
    My Delphi installation has been going downhill for the past few months. It seems though that every so often when I build a release it has strange errors in it which are resolved if I build, then compile, then build, compile, etc. I've talked to another developer who thinks that this is a compiler error. This sort of degrading performance over time has happened on other computers to us too. What does stack overflow think could be the problem.

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  • Managing records of bugs and notes

    - by Jim
    Hi. I want to create a knowledgebase for a piece of software. I'd also like to be able to track bugs and common points of failure in that application. Linking knowledgebase articles to bug records would be a real boon, as would the ability to do complex queries for particular articles and bugs on the basis of tags or metadata. I've never done anything like this before, and like to install as little as possible. I've been looking at creating a wiki with Wiki On A Stick, and it seems to offer a lot. But I can't make complex queries. I can create pages that list all 'articles' with a particular single tag, but I can't specify multiple tags or filters. Is there any software that can help? I don't want to spend money until I've tried something out thoroughly, and I'd ideally like something that demands little-to-no installation. Are there any tools that can help me? If something could easily export its data, or stored data in XML, that would be a real plus too. Otherwise, are there any simple apps that allow me to set up forms for bugs, store data as XML then query and process that XML on demand? Thanks in advance.

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  • Bugzilla - How to setup MTA that will receive Gmail to create bugs

    - by JRock
    I have been looking for a while on setting up an MTA for bugzilla to receive bugs via email and am not really seeing any detailed guides. Currently I am using gmail as the outbound smtp for messages, but I do not have a solution for the receiving of emails as bugs. I am assuming I would setup an MTA and it would grab down the emails and then bugzilla would read them somehow. I am unsure of this process/a solution for this; Any detailed help or direction would be great. Distro: Ubuntu 11.10

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  • Bug Repository

    - by goldenmean
    Hello, Is there any opensource or public domain repository of bugs where one can see the various bugs, symptoms of those bugs, and their fixes. The bugs could be from any part of the code, OS, GUI, device drivers etc. I guess if at there is anything like this, it might be from some open source development initiative like Linux Kernel Development, or some other Opensource project. Is there anything like this available online? It would be a vluable inputs to developers and testers all alike. wishes, -Ajit

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  • Oracle SQL Developer v3.2.1 Now Available

    - by thatjeffsmith
    Oracle SQL Developer version 3.2.1 is now available. I recommend that everyone now upgrade to this release. It features more than 200 bug fixes, tweaks, and polish applied to the 3.2 edition. The high profile bug fixes submitted by customers and users on our forums are listed in all their glory for your review. I want to highlight a few of the changes though, as I recognize many of you lack the time and/or patience to ‘read the docs.’ That would include me, which is why I enjoy writing these kinds of blog posts. I’m lazy – just like you! No more artificial line breaks between CREATE OR REPLACE and your PL/SQL In versions 3.2 and older, when you pull up your stored procedural objects in our editor, you would see a line break inserted between the CREATE OR REPLACE and then the body of your code. In version 3.2.1, we have removed the line break. 3.1 3.2.1 Trivia Did You Know? The database doesn’t store the ‘CREATE’ or ‘CREATE OR REPLACE’ bit of your PL/SQL code in the database. If we look at the USER_SOURCE view, we can see that the code begins with the object name. So the CREATE OR REPLACE bit is ‘artificial’ The intent is to give you the code necessary to recreate your object – and have it ‘compile’ into the database. We pretty much HAVE to add the ‘CREATE OR REPLACE.’ From now on it will appear inline with the first line of your code. Exporting Tables & Views When exporting data from your tables or views, previous versions of SQL Developer presented a 3 step wizard. It allows you to choose your columns and apply data filters for what is exported. This was kind of redundant. The grids already allowed you to select your columns and apply filters. Wouldn’t it be more intuitive AND efficient to just make the grids behave in a What You See Is What You Get (WYSIWYG) fashion? In version 3.2.1, that is exactly what will happen. The wizard now only has two steps and the grid will export the data and columns as defined in the visible grid. Let the grid properties define what is actually exported! And here is what is pasted into my worksheet: "BREWERY"|"CITY" "3 Brewers Restaurant Micro-Brewery"|"Toronto" "Amsterdam Brewing Co."|"Toronto" "Ball Brewing Company Ltd."|"Toronto" "Big Ram Brewing Company"|"Toronto" "Black Creek Historic Brewery"|"Toronto" "Black Oak Brewing"|"Toronto" "C'est What?"|"Toronto" "Cool Beer Brewing Company"|"Toronto" "Denison's Brewing"|"Toronto" "Duggan's Brewery"|"Toronto" "Feathers"|"Toronto" "Fermentations! - Danforth"|"Toronto" "Fermentations! - Mount Pleasant"|"Toronto" "Granite Brewery & Restaurant"|"Toronto" "Labatt's Breweries of Canada"|"Toronto" "Mill Street Brew Pub"|"Toronto" "Mill Street Brewery"|"Toronto" "Molson Breweries of Canada"|"Toronto" "Molson Brewery at Air Canada Centre"|"Toronto" "Pioneer Brewery Ltd."|"Toronto" "Post-Production Bistro"|"Toronto" "Rotterdam Brewing"|"Toronto" "Steam Whistle Brewing"|"Toronto" "Strand Brasserie"|"Toronto" "Upper Canada Brewing"|"Toronto" JUST what I wanted And One Last Thing Speaking of export, sometimes I want to send data to Excel. And sometimes I want to send multiple objects to Excel – to a single Excel file that is. In version 3.2.1 you can now do that. Let’s export the bulk of the HR schema to Excel, with each table going to it’s own workbook in the same worksheet. Select many tables, put them in in a single Excel worksheet If you try this in previous versions of SQL Developer it will just write the first table to the Excel file. This is one of the bugs we addressed in v3.2.1. Here is what the output Excel file looks like now: Many tables - Many workbooks in an Excel Worksheet I have a sneaky suspicion that this will be a frequently used feature going forward. Excel seems to be the cornerstone of many of our popular features. Imagine that!

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  • Why are some bugs I'm affected by and subscribed to missing in my launchpad bug list?

    - by joschi
    I have a long list of bugs in my launchpad account but some bugs I set to being affected by and being subscribed to are not showing up in that list. Even when I change the options of bugs to show I don't get these bugs.First I thought these were bugs being set to 'wishlist' but some of them are showing up in the list. Does anyone else know that he/she is subscribed to a bug he/she doesn't find in his bug list? And maybe there's also someone who knows how to fix this.

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  • MERGE Bug with Filtered Indexes

    - by Paul White
    A MERGE statement can fail, and incorrectly report a unique key violation when: The target table uses a unique filtered index; and No key column of the filtered index is updated; and A column from the filtering condition is updated; and Transient key violations are possible Example Tables Say we have two tables, one that is the target of a MERGE statement, and another that contains updates to be applied to the target.  The target table contains three columns, an integer primary key, a single character alternate key, and a status code column.  A filtered unique index exists on the alternate key, but is only enforced where the status code is ‘a’: CREATE TABLE #Target ( pk integer NOT NULL, ak character(1) NOT NULL, status_code character(1) NOT NULL,   PRIMARY KEY (pk) );   CREATE UNIQUE INDEX uq1 ON #Target (ak) INCLUDE (status_code) WHERE status_code = 'a'; The changes table contains just an integer primary key (to identify the target row to change) and the new status code: CREATE TABLE #Changes ( pk integer NOT NULL, status_code character(1) NOT NULL,   PRIMARY KEY (pk) ); Sample Data The sample data for the example is: INSERT #Target (pk, ak, status_code) VALUES (1, 'A', 'a'), (2, 'B', 'a'), (3, 'C', 'a'), (4, 'A', 'd');   INSERT #Changes (pk, status_code) VALUES (1, 'd'), (4, 'a');          Target                     Changes +-----------------------+    +------------------+ ¦ pk ¦ ak ¦ status_code ¦    ¦ pk ¦ status_code ¦ ¦----+----+-------------¦    ¦----+-------------¦ ¦  1 ¦ A  ¦ a           ¦    ¦  1 ¦ d           ¦ ¦  2 ¦ B  ¦ a           ¦    ¦  4 ¦ a           ¦ ¦  3 ¦ C  ¦ a           ¦    +------------------+ ¦  4 ¦ A  ¦ d           ¦ +-----------------------+ The target table’s alternate key (ak) column is unique, for rows where status_code = ‘a’.  Applying the changes to the target will change row 1 from status ‘a’ to status ‘d’, and row 4 from status ‘d’ to status ‘a’.  The result of applying all the changes will still satisfy the filtered unique index, because the ‘A’ in row 1 will be deleted from the index and the ‘A’ in row 4 will be added. Merge Test One Let’s now execute a MERGE statement to apply the changes: MERGE #Target AS t USING #Changes AS c ON c.pk = t.pk WHEN MATCHED AND c.status_code <> t.status_code THEN UPDATE SET status_code = c.status_code; The MERGE changes the two target rows as expected.  The updated target table now contains: +-----------------------+ ¦ pk ¦ ak ¦ status_code ¦ ¦----+----+-------------¦ ¦  1 ¦ A  ¦ d           ¦ <—changed from ‘a’ ¦  2 ¦ B  ¦ a           ¦ ¦  3 ¦ C  ¦ a           ¦ ¦  4 ¦ A  ¦ a           ¦ <—changed from ‘d’ +-----------------------+ Merge Test Two Now let’s repopulate the changes table to reverse the updates we just performed: TRUNCATE TABLE #Changes;   INSERT #Changes (pk, status_code) VALUES (1, 'a'), (4, 'd'); This will change row 1 back to status ‘a’ and row 4 back to status ‘d’.  As a reminder, the current state of the tables is:          Target                        Changes +-----------------------+    +------------------+ ¦ pk ¦ ak ¦ status_code ¦    ¦ pk ¦ status_code ¦ ¦----+----+-------------¦    ¦----+-------------¦ ¦  1 ¦ A  ¦ d           ¦    ¦  1 ¦ a           ¦ ¦  2 ¦ B  ¦ a           ¦    ¦  4 ¦ d           ¦ ¦  3 ¦ C  ¦ a           ¦    +------------------+ ¦  4 ¦ A  ¦ a           ¦ +-----------------------+ We execute the same MERGE statement: MERGE #Target AS t USING #Changes AS c ON c.pk = t.pk WHEN MATCHED AND c.status_code <> t.status_code THEN UPDATE SET status_code = c.status_code; However this time we receive the following message: Msg 2601, Level 14, State 1, Line 1 Cannot insert duplicate key row in object 'dbo.#Target' with unique index 'uq1'. The duplicate key value is (A). The statement has been terminated. Applying the changes using UPDATE Let’s now rewrite the MERGE to use UPDATE instead: UPDATE t SET status_code = c.status_code FROM #Target AS t JOIN #Changes AS c ON t.pk = c.pk WHERE c.status_code <> t.status_code; This query succeeds where the MERGE failed.  The two rows are updated as expected: +-----------------------+ ¦ pk ¦ ak ¦ status_code ¦ ¦----+----+-------------¦ ¦  1 ¦ A  ¦ a           ¦ <—changed back to ‘a’ ¦  2 ¦ B  ¦ a           ¦ ¦  3 ¦ C  ¦ a           ¦ ¦  4 ¦ A  ¦ d           ¦ <—changed back to ‘d’ +-----------------------+ What went wrong with the MERGE? In this test, the MERGE query execution happens to apply the changes in the order of the ‘pk’ column. In test one, this was not a problem: row 1 is removed from the unique filtered index by changing status_code from ‘a’ to ‘d’ before row 4 is added.  At no point does the table contain two rows where ak = ‘A’ and status_code = ‘a’. In test two, however, the first change was to change row 1 from status ‘d’ to status ‘a’.  This change means there would be two rows in the filtered unique index where ak = ‘A’ (both row 1 and row 4 meet the index filtering criteria ‘status_code = a’). The storage engine does not allow the query processor to violate a unique key (unless IGNORE_DUP_KEY is ON, but that is a different story, and doesn’t apply to MERGE in any case).  This strict rule applies regardless of the fact that if all changes were applied, there would be no unique key violation (row 4 would eventually be changed from ‘a’ to ‘d’, removing it from the filtered unique index, and resolving the key violation). Why it went wrong The query optimizer usually detects when this sort of temporary uniqueness violation could occur, and builds a plan that avoids the issue.  I wrote about this a couple of years ago in my post Beware Sneaky Reads with Unique Indexes (you can read more about the details on pages 495-497 of Microsoft SQL Server 2008 Internals or in Craig Freedman’s blog post on maintaining unique indexes).  To summarize though, the optimizer introduces Split, Filter, Sort, and Collapse operators into the query plan to: Split each row update into delete followed by an inserts Filter out rows that would not change the index (due to the filter on the index, or a non-updating update) Sort the resulting stream by index key, with deletes before inserts Collapse delete/insert pairs on the same index key back into an update The effect of all this is that only net changes are applied to an index (as one or more insert, update, and/or delete operations).  In this case, the net effect is a single update of the filtered unique index: changing the row for ak = ‘A’ from pk = 4 to pk = 1.  In case that is less than 100% clear, let’s look at the operation in test two again:          Target                     Changes                   Result +-----------------------+    +------------------+    +-----------------------+ ¦ pk ¦ ak ¦ status_code ¦    ¦ pk ¦ status_code ¦    ¦ pk ¦ ak ¦ status_code ¦ ¦----+----+-------------¦    ¦----+-------------¦    ¦----+----+-------------¦ ¦  1 ¦ A  ¦ d           ¦    ¦  1 ¦ d           ¦    ¦  1 ¦ A  ¦ a           ¦ ¦  2 ¦ B  ¦ a           ¦    ¦  4 ¦ a           ¦    ¦  2 ¦ B  ¦ a           ¦ ¦  3 ¦ C  ¦ a           ¦    +------------------+    ¦  3 ¦ C  ¦ a           ¦ ¦  4 ¦ A  ¦ a           ¦                            ¦  4 ¦ A  ¦ d           ¦ +-----------------------+                            +-----------------------+ From the filtered index’s point of view (filtered for status_code = ‘a’ and shown in nonclustered index key order) the overall effect of the query is:   Before           After +---------+    +---------+ ¦ pk ¦ ak ¦    ¦ pk ¦ ak ¦ ¦----+----¦    ¦----+----¦ ¦  4 ¦ A  ¦    ¦  1 ¦ A  ¦ ¦  2 ¦ B  ¦    ¦  2 ¦ B  ¦ ¦  3 ¦ C  ¦    ¦  3 ¦ C  ¦ +---------+    +---------+ The single net change there is a change of pk from 4 to 1 for the nonclustered index entry ak = ‘A’.  This is the magic performed by the split, sort, and collapse.  Notice in particular how the original changes to the index key (on the ‘ak’ column) have been transformed into an update of a non-key column (pk is included in the nonclustered index).  By not updating any nonclustered index keys, we are guaranteed to avoid transient key violations. The Execution Plans The estimated MERGE execution plan that produces the incorrect key-violation error looks like this (click to enlarge in a new window): The successful UPDATE execution plan is (click to enlarge in a new window): The MERGE execution plan is a narrow (per-row) update.  The single Clustered Index Merge operator maintains both the clustered index and the filtered nonclustered index.  The UPDATE plan is a wide (per-index) update.  The clustered index is maintained first, then the Split, Filter, Sort, Collapse sequence is applied before the nonclustered index is separately maintained. There is always a wide update plan for any query that modifies the database. The narrow form is a performance optimization where the number of rows is expected to be relatively small, and is not available for all operations.  One of the operations that should disallow a narrow plan is maintaining a unique index where intermediate key violations could occur. Workarounds The MERGE can be made to work (producing a wide update plan with split, sort, and collapse) by: Adding all columns referenced in the filtered index’s WHERE clause to the index key (INCLUDE is not sufficient); or Executing the query with trace flag 8790 set e.g. OPTION (QUERYTRACEON 8790). Undocumented trace flag 8790 forces a wide update plan for any data-changing query (remember that a wide update plan is always possible).  Either change will produce a successfully-executing wide update plan for the MERGE that failed previously. Conclusion The optimizer fails to spot the possibility of transient unique key violations with MERGE under the conditions listed at the start of this post.  It incorrectly chooses a narrow plan for the MERGE, which cannot provide the protection of a split/sort/collapse sequence for the nonclustered index maintenance. The MERGE plan may fail at execution time depending on the order in which rows are processed, and the distribution of data in the database.  Worse, a previously solid MERGE query may suddenly start to fail unpredictably if a filtered unique index is added to the merge target table at any point. Connect bug filed here Tests performed on SQL Server 2012 SP1 CUI (build 11.0.3321) x64 Developer Edition © 2012 Paul White – All Rights Reserved Twitter: @SQL_Kiwi Email: [email protected]

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  • Cardinality Estimation Bug with Lookups in SQL Server 2008 onward

    - by Paul White
    Cost-based optimization stands or falls on the quality of cardinality estimates (expected row counts).  If the optimizer has incorrect information to start with, it is quite unlikely to produce good quality execution plans except by chance.  There are many ways we can provide good starting information to the optimizer, and even more ways for cardinality estimation to go wrong.  Good database people know this, and work hard to write optimizer-friendly queries with a schema and metadata (e.g. statistics) that reduce the chances of poor cardinality estimation producing a sub-optimal plan.  Today, I am going to look at a case where poor cardinality estimation is Microsoft’s fault, and not yours. SQL Server 2005 SELECT th.ProductID, th.TransactionID, th.TransactionDate FROM Production.TransactionHistory AS th WHERE th.ProductID = 1 AND th.TransactionDate BETWEEN '20030901' AND '20031231'; The query plan on SQL Server 2005 is as follows (if you are using a more recent version of AdventureWorks, you will need to change the year on the date range from 2003 to 2007): There is an Index Seek on ProductID = 1, followed by a Key Lookup to find the Transaction Date for each row, and finally a Filter to restrict the results to only those rows where Transaction Date falls in the range specified.  The cardinality estimate of 45 rows at the Index Seek is exactly correct.  The table is not very large, there are up-to-date statistics associated with the index, so this is as expected. The estimate for the Key Lookup is also exactly right.  Each lookup into the Clustered Index to find the Transaction Date is guaranteed to return exactly one row.  The plan shows that the Key Lookup is expected to be executed 45 times.  The estimate for the Inner Join output is also correct – 45 rows from the seek joining to one row each time, gives 45 rows as output. The Filter estimate is also very good: the optimizer estimates 16.9951 rows will match the specified range of transaction dates.  Eleven rows are produced by this query, but that small difference is quite normal and certainly nothing to worry about here.  All good so far. SQL Server 2008 onward The same query executed against an identical copy of AdventureWorks on SQL Server 2008 produces a different execution plan: The optimizer has pushed the Filter conditions seen in the 2005 plan down to the Key Lookup.  This is a good optimization – it makes sense to filter rows out as early as possible.  Unfortunately, it has made a bit of a mess of the cardinality estimates. The post-Filter estimate of 16.9951 rows seen in the 2005 plan has moved with the predicate on Transaction Date.  Instead of estimating one row, the plan now suggests that 16.9951 rows will be produced by each clustered index lookup – clearly not right!  This misinformation also confuses SQL Sentry Plan Explorer: Plan Explorer shows 765 rows expected from the Key Lookup (it multiplies a rounded estimate of 17 rows by 45 expected executions to give 765 rows total). Workarounds One workaround is to provide a covering non-clustered index (avoiding the lookup avoids the problem of course): CREATE INDEX nc1 ON Production.TransactionHistory (ProductID) INCLUDE (TransactionDate); With the Transaction Date filter applied as a residual predicate in the same operator as the seek, the estimate is again as expected: We could also force the use of the ultimate covering index (the clustered one): SELECT th.ProductID, th.TransactionID, th.TransactionDate FROM Production.TransactionHistory AS th WITH (INDEX(1)) WHERE th.ProductID = 1 AND th.TransactionDate BETWEEN '20030901' AND '20031231'; Summary Providing a covering non-clustered index for all possible queries is not always practical, and scanning the clustered index will rarely be optimal.  Nevertheless, these are the best workarounds we have today. In the meantime, watch out for poor cardinality estimates when a predicate is applied as part of a lookup. The worst thing is that the estimate after the lookup join in the 2008+ plans is wrong.  It’s not hopelessly wrong in this particular case (45 versus 16.9951 is not the end of the world) but it easily can be much worse, and there’s not much you can do about it.  Any decisions made by the optimizer after such a lookup could be based on very wrong information – which can only be bad news. If you think this situation should be improved, please vote for this Connect item. © 2012 Paul White – All Rights Reserved twitter: @SQL_Kiwi email: [email protected]

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  • Deliberately adding bugs to assess QA processes

    - by bgbg
    How do you know that as many bugs as possiblle have been discovered and solved in a program? Couple of years ago I have read a document about debugging (I think it was some sort of HOWTO). Among other things, that document described a technique in which the programming team deliberately adds bugs into the code and passes it to the QA team. The QA process is considered completed when all the deliberately known bugs have been discovered. Unfortunately, I cannot find this document, or any similar one with description of this trick. Can someone please point me to such a document?

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  • How to get useful feedback/bug reports from users

    - by Mikael Eliasson
    I'm sure most webmasters have recived a mail like this: Creating [insert item here] is not working! When you check it out there is no general problem with the function but rather the user has discovered an edge case. Almost every mail I get is like this and in the long run it gets a bit annoying to always have to ask the user for more information. Is there anything I can do to get my users provide more useful feedback? Right now I have a mailto: for the webmaster mail in the page footer. I was thinking of changing this so that they have to report through a form on the site. Anyone got any experience with this? Do you get better/more reports by having a feedback form instead of giving the users the email?

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  • Apple New Year alarm bug cause

    - by StasM
    As many people know, Apple has a bug in their iPhone that prevented alarms from going off at 1st and 2nd of January 2011. What is strange is how that bug might happen - i.e., as far as I know this bug happens in all timezones and nobody is switching off DST on Jan 1st, so it's not timezone or DST-related. Also, Jan 1st seems to be nothing special as a UNIX timestamp, so something like sign change or integer overflow can't be the reason. It is highly improbably that alarm code has something like if(date == JANUARY_1_2011 || date == JANUARY_2_2011) turn_alarms_off(); - that would be a sabotage and not a bug. So the question is - could you imagine and describe a bug that would cause the alarm to fail exactly at Jan 1st and 2nd everywhere while letting it work otherwise, without specifically referring to those exact dates? Of course, if somebody knows the real cause, that would be a definite answer, but if nobody knows it - I think it is interesting to think what might be the cause of such strange bug.

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