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Minimally logged operations
Today, we’re going to look at which database operations can be performed with what’s known as “minimal logging”, which can result in a cosiderable performance boost. Included is a quick overview of...
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HASH JOIN deep-dive
Among the three different types of join operators used by SQL Server, the HASH JOIN does some of the hardest work. It scales pretty well and is very suitable for parallel processing. As such, it can be...
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Blocking/non-blocking aggregate operators
Some database operations can be performed in distinctly different manners, with different impacts on query performance. One important example of such an operation is calculating an aggregate. In this...
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Inline variable assignment in UPDATE statements
Ok, here’s a brain-twister. Not only can you assign values to a column in an UPDATE statement using variables, but you can assign values to variables as well. It’s really not as complicated as it may...
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Partitioned views over table partitioning
Today, we’re going to be looking at a kind of poor-mans’s-partitioning, using a view to union records from multiple tables. We’ll also take a look at when you would want this type of solution, some...
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Parallel execution, part 2
Continuing on last week’s post on parallelism, here’s part two, where we take a closer look at when parallel plans are considered and what you can do to either force or prevent a query from running...
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Parallel execution, part 3
In the two previous parts of this series, we’ve looked at how parallelism works, how you can control it, and how it affects your query (and server) performance in different environments. In this, the...
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Joining two SCD2 tables
A number of OLTP systems store dimension data in SCD2-like tables in order to retain all the revisions whenever the dimension information changes. In certain situations, you may come across a need to...
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Segment and Sequence Project
For windowed functions, SQL Server introduces two new operators in the execution plan; Segment and Sequence Project. If you’ve tried looking them up in the documentation, you’ll know that it’s not...
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Median and percentile in T-SQL
Back in 2014 I wrote a blog post on how to calculate a median value using the NTILE window function. It’s far from the best performing solution there is, but it worked on SQL Server 2008, before the...
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Catching circular references in parent-child structures
A popular form of organizing dimensions is in parent-child structures, also known as “unbalanced” or “ragged” dimensions, because any branch can have an arbitrary number of child levels. There are many...
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Key Lookup without an output column?
Performance tuning the other day, I was stumped by a query plan I was looking at. Even though I had constructed a covering index, I was still getting a Key Lookup operator in my query plan. What I...
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Encrypting SQL Server connections with Let’s Encrypt certificates
Encrypting your SQL Server’s TDS connections should be high on your list of things to do if you’re concerned with the privacy of your data. This often boils down to one big problem: can you get a valid...
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Grouping dates without blocking operators
It’s not entirely uncommon to want to group by a computed expression in an aggregation query. The trouble is, whenever you group by a computed expression, SQL Server considers the ordering of the data...
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Operations that need a serial plan
Some operations in SQL Server will turn your entire query plan serial (single-threaded), others will just reserve a so-called “serial zone”. I read up on this stuff a number of years ago (including a...
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Calculating invoice settlements with window functions
I’ve solved this puzzle a number of times, but I’ve never really been quite happy with the result. It was either too slow, too much code, too hard to understand. So here’s a fresh take at computing...
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Consolidating grouped transactions into evenly sized batches
I recently worked with a large set of accounting transactions. I needed to split those rows into multiple logical batches, but each batch had to be logically consistent – among other things, those...
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A “shock absorber” pattern for high-performance data ingestion
It’s almost like a myth – one that I’ve heard people talk about, but never actually seen myself. The “shock absorber” is a pretty clever data flow design pattern to ingest data where a regular ETL...
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Optimizing a string split and search
We’re no strangers to doing things in T-SQL that would perhaps be more efficient in a procedural language. Love it or hate it, a T-SQL solution is easier in some situations, like my sp_ctrl3 procedure...
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T-SQL template parser
Just for the heck of it, I scratched together a template parser for T-SQL . The usage of this function is similar to the STRING_SPLIT() function, except instead of splitting a string by a delimiter...
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