CHECKDB (Part 3): What does CHECKDB really do? (2 of 4)

In the previous post of this series, I covered the system table checks that have to be done before anything else can be checked by CHECKDB. Now that I’ve described pages, extents, IAM chains/allocation units and the major allocation bitmaps, in this post I’ll cover the allocation checks. 1. Primitive checks of critical system tables(Part 1…)… Read more

Checksum in SQL2005

Page checksum is new feature in SQL2005 that provides you a stronger mechanism than torn-page to detect any corruptions in IO path. Here are some details and scenarios   PAGE CHECKSUM:   Between the time a database page is written to the disk and subsequently read by SQL Server, it may get corrupted for reasons… Read more

Why is the NULL bitmap in a record an optimization?

I’ve had some questions sent in comments and I wanted to reply to some of them using a post so others who aren’t subscribed to the comment sections can see the answers.   Wesley Backelant said: I was wondering what exactly you mean by “this allows an optimization when reading columns that are NULL”.  Could you elaborate… Read more

Fragmentation (part 3): What are extents?

(Ok – another flight – another blog post. This time its Boston back to Seattle. The three of us who’d come over for the training course upgraded to 1st Class on Alaska for the flight back (great value at $100 for a 6-hour flight) and so there’s oodles of room for laptops, newspapers, and long… Read more

Fragmentation (part 2): What are pages?

(Boston continues its reputation – with me at least – for great seafood – calamari and pan-seared fresh halibut this evening. Yum! I was tempted to get on the T – Boston’s subway system – and see what’s happening downtown but with no jacket I’d get wet. So, instead I’ll be boring and geeky and… Read more

Fragmentation (part 1): What are records?

This blogging thing sucks you in, doesn’t it? Not content with having an ongoing series on disaster recovery and CHECKDB (with another 6 and 25 more posts planned respectively), I’m starting a new series on fragmentation. This will begin from first principles and work up, in approximately 18 posts over the next few months. The… Read more