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Archive for August, 2012

September Chicago SQL Server User Group Meeting

August 22, 2012 1 comment

Chicago SQL Server User Group Logo
The September meeting of the Chicago SQL Server User Group will be Thursday, September 13th at the Microsoft Technology Center. If you are interested in attending, you can RSVP from the CSSUG Home Page. You can register for the group as well and receive information about upcoming meetings and group news.

A new section has been added to the home page for member blogs, and new posts to those blogs will be tweeted under the #chisql hash tag. If you are registered for the group and are interested in having your blog added, send your blog address here or post it in the comments here.

Finally, we are looking for presenters for future meetings. If you would like to present, post in the comments or send an e-mail to me here.

Categories: CSSUG, PASS, SQL Server Tags: ,

Database Corruption on the Principal AND the Mirror

August 15, 2012 Leave a comment

Over the past year, I’ve read a number of Paul Randal’s (b|t) blog posts regarding database corruption. I knew he had corrupt databases available for download at sqlskills.com, but I’d never found time to look at them.

That changed last week when the newest member of my team, Nick Schwab (b|t), was looking at mirroring. He asked about Automatic Page Repair, specifically what would happen if a page was corrupted on the principal and the mirror at the same time. I told him I did not know and asked him to run some tests.

Using these instructions from Kendra Little’s (b|t) blog, Nick was set to start corrupting pages.

Here is what he found. If the page was corrupted on the principal and was read from disk, the initial attempt would error but Automatic Page Repair would be triggered and subsequent access attempts would succeed. If a page was corrupted on the mirror, SQL Server would take no action until a role switch occurred and the page was read from disk on the new principal. At that point Automatic Page Repair would kick in.

That brings us to Nick’s question. If the same page was corrupted on both the principal and the mirror, Automatic Page Repair would pull the mirror copy of the page over and still fail on corruption. I understand that the possibility of this happening in a live environment is extremely small, but it is worth keeping in mind for mirrored applications. At the least, it is a good argument for having a restore strategy (see Myth Number 30-30 here).

Many thanks to Kendra and Paul for making this information available at their blogs.

The August Chicago SQL Server User Group Meeting

August 10, 2012 Leave a comment

Last night was the August meeting of the Chicago SQL Server User Group. It was the second meeting Aaron Lowe and I have run. Ira Whiteside of Melissa Data was kind enough to sponsor the meeting and was scheduled to present. Unfortunately, Ira ran into car problems on the way down and could not make it. In Ira’s absence, Aaron and I decided that we would each do a presentation. Aaron presented on Writing Professional Database Code, which was excellent. Statement terminators and version control for database code are two of Aaron’s suggestions I will bring back to my team.

I started off the meeting with a short presentation introducing Adam Machanic’s sp_whoisactive. If you do any troubleshooting of SQL Server issues, sp_whoisactive is a tool you should be using. It consolidates data from sp_who2, sys.dm_exec_requests and a number of other DMOs to give you a quick and complete picture of how each process is performing on your system. You can pull the execution plan for each process and have the option to generate deltas for a number of metrics over a period of time. The best part about the procedure is that it is free for download. The fact that Adam Machanic provides the code for free is a testament to the strength of the SQL Server community.

If you live in the Chicago area and are not registered for the user group, you can do so here. You will receive e-mail notification for upcoming meetings. We are looking for group members to present at upcoming meetings. If you are interested, you can e-mail me here. I hope to see you at an upcoming meeting.

Categories: CSSUG, DMO, sp_whoisactive Tags: ,