How Many Rows Have Changed?

Steve Jones, 2009-10-28

One of the things that I’ve asked DBAs, and I see asked often, is how much does your data change? That affects the transaction log sizes (and backups), the load on your server, possibly the tuning and specs you want to implement, etc. But most DBAs don’t have any clue what the change rate on their data is. Most probably can’t even tell you quickly what their data growth rate is.

The good ones can, and many of them either track it, or they do what I used to do: they monitor backup sizes and calculate an acceleration and velocity that assists them in proactively managing servers.

That accounts for growth, but what about changes? Very few DBAs know this, and it seems like it’s an advanced topic. I’ve never had a great, homegrown way to track this, and haven’t worried about it. Most of my systems could have weekly downtime, and I’d rebuild indexes, and statistics, during that time, so it wasn’t an issue.

The other day I was reading Kim Tripp’s blog because, well, it’s a good idea. She doesn’t post a lot, but when she does, it’s good stuff to know. In this post she talked about filtered indexes and statistics going stale quicker than expected. I’ll let you read it if you’re interested (you should be), but the interesting thing to me was her mentioning a way to know how many rows have changed.

In SQL Server 2000, there’s a value in sysindexes.rcmodctr that keeps track of how many rows have changed. This is used to note when to refresh statistics (it’s when 20% of the rows have changed).

In SQL Server 2005 and 2008, this is tracker per column, which may or may not be better. Read Kim’s explanation of that. However the values are in sysrowsetcolumns.rcmodified for SS2K5 and sysrscols.rcmodified for SS2K8.

That’s a handy piece of information for me to know. I can now easily track the number of rows that change daily, and then get some averages that might clue me in to the activity of the database. It’s not that this average means anything by itself, but if I know it, and then compare the last day’s change against the average, I’ll have some idea of the load on my server. Might help me diagnose issues, or let me know if the server if coming under more load.





Related content

Database Mirroring FAQ: Can a 2008 SQL instance be used as the witness for a 2005 database mirroring setup?

Question: Can a 2008 SQL instance be used as the witness for a 2005 database mirroring setup? This question was sent to me via email. My reply follows. Can a 2008 SQL instance be used as the witness for a 2005 database mirroring setup? Databases to be mirrored are currently running on 2005 SQL instances but will be upgraded to 2008 SQL in the near future.

Robert Davis


1,567 reads

Networking – Part 4

You may want to read Part 1 , Part 2 , and Part 3 before continuing. This time around I’d like to talk about social networking. We’ll start with social networking. Facebook, MySpace, and Twitter are all good examples of using technology to let…

Andy Warren


1,530 reads

Speaking at Community Events – More Thoughts

Last week I posted Speaking at Community Events – Time to Raise the Bar?, a first cut at talking about to what degree we should require experience for speakers at events like SQLSaturday as well as when it might be appropriate to add additional focus/limitations on the presentations that are accepted. I’ve got a few more thoughts on the topic this week, and I look forward to your comments.

Andy Warren


360 reads