The Wiert Corner – irregular stream of stuff

Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for the ‘Database Development’ Category

Delphi hinting directives: deprecated, experimental, library and platform

Posted by jpluimers on 2014/10/01

I’ve been experimenting with the Delphi hinting directives lately to make it easier to migrate some libraries to newer versions of Delphi and newer platforms.

Hinting directives (deprecated, experimental, library and platform) were – like the $MESSAGE directive – added to Delphi 6.

Up to Delphi 5 you didn’t have any means to declare code obsolete. You had to find clever ways around it.

Warnings for hinting directives

When referring to identifiers marked with a hinting directive, you can get various warning messages that depend on the kind of identifier: unit, or other symbol. Read the rest of this entry »

Posted in Apple Pascal, Borland Pascal, DEC Pascal, Delphi, Delphi 2005, Delphi 2006, Delphi 2007, Delphi 2009, Delphi 2010, Delphi 6, Delphi 7, Delphi 8, Delphi XE, Delphi XE2, Delphi XE3, Delphi XE4, Development, Encoding, FreePascal, ISO-8859, ISO8859, Java, Lazarus, MQ Message Queueing/Queuing, Reflection, Software Development, Sybase, Unicode, UTF-8, UTF8 | 1 Comment »

TSQL: showing database level and server level permissions

Posted by jpluimers on 2014/06/12

A few short scripts checking out the cause for TFS Integration Tools refuses to start despite an admin being able to create a TEST database. Read the rest of this entry »

Posted in Database Development, Development, SQL Server, SQL Server 2008, SQL Server 2008 R2, SQL Server 2012 | Leave a Comment »

The C language specification describes an abstract computer, not a real one – The Old New Thing – Site Home – MSDN Blogs

Posted by jpluimers on 2014/04/09

Interesting read:

The C language specification describes an abstract computer, not a real one – The Old New Thing – Site Home – MSDN Blogs.

In other words: any language that merges null behaviour in the underlying storage will have a problem somwehere.

So if you want to have true nullable types, your null flag should be stored outside the underlying storage.

The .NET framework 2 and up, most database management systems and many other environment support that.

But most languages don’t support it for pointer types. So there will be portions of address spaces either inaccessible, or only accessible when skipping the null pointer checks.

Note that the thread above contains some very interesting bits, for instance this one:

Matt 28 Mar 2013 5:58 PM #

@MarkY “Dereferencing null is undefined?  Cool!  I thought it was guaranteed to crash, just like a false assertion or something.  So crashing is the OS guarantee, not the language guarantee apparently.”

Nope. It’s not an OS guarantee either. The OS won’t ever normally allocate memory at address zero, but there’s nothing to stop you telling it to. Try doing “VirtualAlloc(1, 4096, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE)” on your pre-Windows8 machine.

In fact, this is the reason why null-dereferences in kernel mode are often exploitable as elevation of privilege attacks. The null-page is mappable and within the user-addressable region of memory, so if the kernel dereferences a null pointer, it reads attacker controllable data.

And btw, this is the reason why on Linux and Windows8+ you can’t map the null-page.

–jeroen

via: The C language specification describes an abstract computer, not a real one – The Old New Thing – Site Home – MSDN Blogs.

Posted in .NET, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, Borland C++, Borland Pascal, C, C#, C# 2.0, C# 3.0, C# 4.0, C# 5.0, C++, C++ Builder, Database Development, Delphi, Development, Pascal, Quick Pascal, Software Development, Turbo Pascal, VB.NET, VB.NET 10.0, VB.NET 11.0, VB.NET 8.0, VB.NET 9.0 | Leave a Comment »

Venn Diagrams of SQL Join queries (via: Data Visualization – Google+)

Posted by jpluimers on 2014/04/08

Some great venn diagrams of SQL JOINs via Data Visualization – Google+ of which I wish they were PNG:

Thanks to that link, I found the original article and images by C.L. Moffat!

Click on the image to view a larger version.

–jeroen Read the rest of this entry »

Posted in Access, Database Development, DB2, Development, Firebird, InterBase, MySQL, OracleDB, PostgreSQL, SQL, SQL Server, SQL Server 2000, SQL Server 2005, SQL Server 2008, SQL Server 2008 R2, SQL Server 2012, SQL Server 7 | Leave a Comment »

SQL Server: when your database is in “Recovery Pending” mode

Posted by jpluimers on 2014/03/31

With SQL Server, when your database is in “Recovery Pending” mode don’t just start blindingly search google, but sit down as you might be causing more damage doing so.

After sitting down, read these two posts by Paul Randal | SQLskills.com from his SQL Server Corruption series:

  1. Search Engine Q&A #4: Using EMERGENCY mode to access a RECOVERY PENDING or SUSPECT database.
  2. SQL Server EMERGENCY mode repair.

Then think about it before acting.

Though the simplest cause for “Recovery Pending” might be that a disk spin-up was slow, or a disk became full (and everything might just be dandy after the disk is available and there is enough room on it), make sure you read the above posts first before relying on the simple causes.

–jeroen

Posted in Development, Software Development, SQL Server, SQL Server 2005, SQL Server 2008, SQL Server 2008 R2, SQL Server 2012, SQL Server 2014 | Tagged: , , | Leave a Comment »

 
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