Category: T-SQL Tuesday

Rob Farley talks about an issue with heaps:

What I found was that the list of IDs was being stored in a table without a clustered index. A heap. Now – I’m not opposed to heaps at all. Heaps are often very good, and shouldn’t be derided. But you need to understand something about heaps – which is that they’re not suited to tables that have a large amount of deletes. Every time you insert a row into a heap, it goes into the first available slot on the last page of the heap. If there aren’t any slots available, it creates a new page, and the story continues. It doesn’t keep track of what’s happened earlier. They can be excellent for getting data in – and Lookups are very quick because every row is addressed by the actual Row ID, rather than some key values which then require a Seek operation to find them (that said, it’s often cheap to avoid Lookups, by adding extra columns to the Include list of a non-clustered index). But because they don’t think about what kind of state the earlier pages might be in, you can end up with heaps that are completely empty, a bunch of pointers from page to page, with header information, but no actual rows therein. If you’re deleting rows from a heap, this is what you’ll get.

This guy’s heap had only a few rows in it. 8 in fact, when I looked – although I think a few moments later those 8 had disappeared, and were replaced by 13 others.

But the table was more than 400MB in size. For 8 small rows.

Read the whole thing, including Rob’s reluctance to post on this topic.

Andy Yun had the task of cleaning up test accounts:

Monday morning came along and as scheduled, our Production DBAs executed my script before start of business. 30 minutes later, the frantic calls started to reach us. Seems some of our clients could no longer “make widgets!” Accounts that they needed to route data were gone! My manager and I looked at one another in horror – we were only deleting internal accounts!!! We didn’t hesitate and immediately had our Prod DBAs back out the change with my backout script, before the rest of the United Stated started business. The backout was executed immediately and all was back to normal, but business folks were pissed and wanted to know what happened.

It was good foresight to have a backout script.

Matt Gordon has the roundup for T-SQL Tuesday 87:

Finally, as a first time host, I was obviously hoping that this topic would garner some responses, but you never know until you hit that post button whether you’ve selected something of interest to the community or not. Thankfully, this month’s topic picked up views from over 20 countries and over 20 blog responses. The list (with a brief post-by-post commentary from me) is below. Happy reading and thanks again for reading/writing/participating!

Read on for the full list of respondents.