Go Along, Get Along
This is a somewhat complicated topic. There’s not a great TL;DR here, but I don’t want anyone to walk away from this post thinking that parallelism or indexes are “bad”.
What I do want to show …
Category: Spills
Spills Week: Exchange Spill Excruciation
Many Have Entered, Few Have Left
For some background on Exchange Spills, check out this Great Post™ by Joe.
The root of this demo was trying to show people silly things about CTEs, how TOP can fence things off…
Spills Week: Hash Join Humiliation
Thirsty Thursday
If you’ve made it this far, you’ve learned a few things:
- Not all spills are worth trying to fix
- The more columns you select, the worse spills get
- The larger your string datatypes are, the worse spills get
Spills Week: Hash Match Aggravation
Quite Different
Hash spills are nothing like sort spills, in that even with (very fast) disks, there’s no immediate benefit to breaking the hash down into pieces via a spill.
In fact, there are many downsides, especially when memory is …
Spills Week: When Sort Spills Start To Matter
Imbalance
In yesterday’s post, we looked at a funny situation where a query that spilled was about 5 seconds faster than one that didn’t.
Here’s what the query looked like:
SELECT x.PostId
FROM (
SELECT v.PostId,
ROW_NUMBER() OVER ( … Spills Week: When Sort Spills Might Not Matter
Pre-faced
Every post this week is going to be about spills. No crazy in-depth, technical, debugger type stuff.
Just some general observations about when they seem to matter more for performance, and when you might be chasing nothing by fixing …