Nah, the plan can be the same for lots of different executions. If it doesn't recompile, regardless of parameters passed, you'll see the same plan used over & over. It's...

So, a hardware change and then behavior changed? When you say right before, you mean several days, several hours, or they pretty much coincide?

We had the experience once where backups slowed down and the problem was a switch going bad. It didn't evidence itself for any other process except our SQL Server backups....

And to understand the performance degradation, capture the execution plan of the query, once when it's running well, and once when it's running badly. Compare those to understand the changes....

Are you backing up to the same disk where all the data is? Are you backing up to the disk where the OS or is? Are you backing up across...

In the end, most SQL Server problems come down to the queries. I'd suggest setting up some kind of query monitoring. Since you're posting in the 2019 forum, the best...

To my knowledge, the only book specifically on this topic was written back in 2008 or so (looking it up, seems the book got updated in 2012). However,

Oh please. We don't have to list all the times we screwed up do we? My list is going to take a long time to compile. I think I'll have...

Grant - its likely to be Solar EMP rather than Solar Radiation - look up carrington event.

.. and the Sun HAS been behaving in an unpredictable manner this Solar...

Thanks.  Can you comment on Query store, Forced a good plan with query store and left query store on to capture all. So far the server is operating well....

If you're rebuilding the indexes, then don't update the statistics. An index rebuild updates the statistics with a full scan. You don't need to run that after a rebuild.

Wait, are we talking parameters or variables as stated in the original question? They're different and result in differences in estimated row counts.

You've already received the scoop on parameters. The...

Option 2 is probably the way to go. Cross database dependencies are very difficult to deal with in SSDT. I always found I had to do a certain amount of...

Nothing is immediately leaping out. Have you checked the database consistency recently? Anything in your error logs?

Hardware.

Since you're not in any way filtering data, the only solution is great big giant hardware. Spend lots of money and this will go faster.

Now, you could look at possibly...