Not the one you like the least, or the one that requires the most work.
What’s the one that you can’t use because it’s just flat out busted?
For me, it’s SSMS’s Live Query Statistics, aka live query plans. The idea is so awesome – you click Query, Include Live Query Statistics, and then when you run queries, you get this awesome animated execution plan:
This is really useful when I’m troubleshooting long-running queries or procs, especially cases when I can’t wait long enough to get the full actual query plan, but I need to know where we’re hung up, which parts are taking the longest.
Except the live plan only shows the first statement in a batch. In the movie above, notice how I’ve got two queries in my batch. I hit execute, but then only the live query plan for the first query – the Users scan – shows up. Then the live query plan stops updating until the entire batch finishes. If you want to see the live plan for subsequent statements, you have to go into Activity Monitor – which you shouldn’t be using – and then go into active expensive queries. You can briefly see the live plan for whatever one statement happens to be running, but as the next statement starts, you have to jump through more hoops to see the next statement.
Except the percentages are misleading. The live plans show percentages on them, which makes it seem like it’s the percent complete for an operation, but it’s not. It’s the percentage of rows SQL Server found in various stages of the plan, compared to its original estimates for that operator. People see 1%, and they think that means it’s 1% done – but that part of the operation might actually be fully complete, but it just brought back less rows than SQL Server expected. Or they’ll see 100%, but the operator is still working – that’s just because SQL Server found some data, but it’s still churning away on that operator. I could go on and on.
Except the final results are wildly misleading. In the movie above, notice how the final plan shows three statements, not one: it shows the Users operation twice for some reason.
Except often, it doesn’t even work at all. Even if it’s the perfect use case – a single-statement query that takes forever – when I demo the feature, I have to explain, “Now what I’m about to do may not even work at all, so forgive me if I curse and then stop the query and then start it again, or jump over to Activity Monitor.” It doesn’t feel like I can predict success of it at all.
I really want to love Live Query Statistics, except…
What about you? What feature drives you crazy due to the bugs?
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