Michael J. Swart

July 27, 2016

Do you Use CLR in SQL Server?

Filed under: Miscelleaneous SQL,SQLServerPedia Syndication,Technical Articles — Michael J. Swart @ 11:11 am

We don’t use CLR assemblies in SQL Server. For us, programming in the database means that maybe “you’re doing it wrong”. But there have been rare circumstances where I’ve wondered about what the feature can do for us.

For example, creating a CLR assembly to do string processing for a one-time data migration might be preferable to writing regular SQL using SQL Server’s severely limited built-in functions that do string processing.

Deployment Issues

I’ve always dismissed CLR as part of any solution because the deployment story was too cumbersome. We enjoy some really nice automated deployment tools. To create an assembly, SQL Server needs to be able to access the dll. And all of a sudden our deployment tools need more than just a connection string, the tools now need to be able to place a file where SQL Server can see it… or so I thought.

Deploy Assemblies Using Bits

CREATE ASSEMBLY supports specifying a CLR assembly using bits, a bit stream that can be specified using regular T-SQL. The full method is described in Deploying CLR Database Objects. In practice, the CREATE ASSEMBLY statement looks something like:

CREATE ASSEMBLY [MyAssembly]
FROM 0x4D5A900003000000040000... -- truncated binary literal
WITH PERMISSION_SET = SAFE

This completely gets around the need for deployments to use the file system. I was unaware of this option until today.

Your Experience

So what’s your experience? My mistaken assumptions kept me from evaluating CLR properly. I wonder if anyone is in the same position I was in and I wonder if this accounts for the low adoption in general of CLR in SQL Server. Answer this survey, Which option best describes you?


External Link to Survey Monkey survey.

Update July 29 Here are the answers so far:
CLRAnswers

July 20, 2016

Simplified Order Of Operations

Filed under: Miscelleaneous SQL,SQLServerPedia Syndication,Technical Articles — Michael J. Swart @ 8:00 am

I recently learned that when combining multiple operators in a SQL expression, AND has a higher precedence than OR but & has the same precedence as |. I expected the precedence rules for the logical operators to be consistent with the bitwise operators.

Even Stephen Sondheim seemed to struggle with this.

AND is Always Evaluated Before OR

SELECT 'TRUE' 
WHERE (1 = 1) OR (1 = 1) AND (1 = 0)
-- returns TRUE
 
SELECT 'TRUE' 
WHERE (1 = 0) AND (1 = 1) OR (1 = 1) 
-- returns TRUE

& and | are Evaluated Left To Right

SELECT 1 | 1 & 0
-- returns 0
 
SELECT 0 & 1 | 1
-- returns 1

Here Are The Official Docs

Here what Microsoft says about SQL Server’s Operator Precedence.

  1. ~ (Bitwise NOT)
  2. * (Multiply), / (Division), % (Modulo)
  3. + (Positive), – (Negative), + (Add), (+ Concatenate), – (Subtract), & (Bitwise AND), ^ (Bitwise Exclusive OR), | (Bitwise OR)
  4. =, >, <, >=, <=, <>, !=, !>, !< (Comparison operators)
  5. NOT
  6. AND
  7. ALL, ANY, BETWEEN, IN, LIKE, OR, SOME
  8. = (Assignment)

Practical Subset

I have a book on my shelf called Practical C Programming published by O’Reilly (the cow book) by Steve Oualline. I still love it today because although I don’t code in C any longer, the book remains a great example of good technical writing.

That book has some relevance to SQL today. Instead of memorizing the full list of operators and their precedence, Steve gives a practical subset:

  1. * (Multiply), / (Division)
  2. + (Add), – (Subtract)
  3. Put parentheses around everything else.

July 19, 2016

PASS Summit 2016: Developing High Concurrency Databases

Filed under: SQLServerPedia Syndication — Michael J. Swart @ 10:26 am

My session has been accepted!

Double Double excited

I’m excited that my talk Developing Highly Concurrent Databases got accepted as a session in this year’s PASS Summit in Seattle. This October.

You’ve heard the advice “write what you know”. I’ve applied that advice to my choice of topic. For the past nine years, I’ve worked for D2L, a fast growing company facing a higher volume of database activity year after year.

We built a system that has handled a peak load of over 50,000 transactions per second. And that’s without using In-Memory OLTP yet. Much of the talk will include lessons we’ve learned and things I wish we knew earlier.

Maybe I’ll see you there!

July 7, 2016

Prioritize This List of Issues (Results)

Filed under: Miscelleaneous SQL,SQLServerPedia Syndication,Technical Articles — Michael J. Swart @ 8:00 am

Earlier this week I asked people to help me out prioritizing a list of issues. I was surprised by the number of people who participated. I think I missed an opportunity to crowd-source a large part of my job by including my real issues.

Results

Thanks for participating. After the results started coming in, I realized that my question was a bit ambiguous. Does first priority mean tackle an issue first? Or does a higher numbered issue mean a higher priority? I clarified the question and took that into account for entries that picked sproc naming conventions as top priority.

Votes

The results were cool. I expected a variety of answers but I found that most people’s priorities lined up pretty nicely.

For example, even though I wrote a list of issues all with different severity, there were three issues that stood out as most critical: Corrupted databases, a SQL injection vulnerability and No automated backups. Keeping statistics up to date seemed to be the most important non-critical issue.

But there is one issue that I thought had a lot of variety, index fragmentation. I personally placed this one second last. I got a friend to take the survey and I got to hear him explain his choices. He wanted to tackle index fragmentation early because it’s so easily fixable. “It’s low hanging fruit right? Just fix it and move on.”

My friend also pointed out that this technique would work well as an interview technique. Putting priorities in an order is important but even better is that it invites so much discussion about the reasons behind the order.

Speaking of which, go check out Chuck Rummel’s submission. He wins the prize for most thorough comment on my blog.

My Priorities

Here they are:

  • Corrupted database – serving data is what databases are supposed to do
  • No automated backups – protect that data from disasters
  • A SQL injection vulnerability – protect the data from unauthorized users
  • Stale statistics – serve data efficiently
  • Cursors – a common cause of performance issues, but I’d want to be reactive
  • GUID identifiers – meh
  • NOLOCK hints – meh
  • Developers use a mix of parameterized SQL and stored procedures – It’s not a performance concern for me
  • Fragmented indexes – supposedly better performance?
  • Sprocs prefixed with “sp-” – aesthetics?

July 5, 2016

Prioritize This List of Issues

Filed under: Miscelleaneous SQL,SQLServerPedia Syndication,Technical Articles — Michael J. Swart @ 9:14 am

“One thing at a time / And that done well / Is a very good thing / As any can tell”

But life isn’t always that easy is it? I spend a lot of my workday juggling priorities. And I want to compare what I think to others. So I wrote a survey which explores the importance people place on different SQL Server issues. It’s easy to say avoid redundant indexes. But does it follow that it’s more important to clean up redundant indexes before rewriting cursors?

The List

Prioritize this list from greatest concern to least. So if an item appears above another item, then you would typically tackle that issue first.

  • Corrupted database
  • A SQL injection vulnerability
  • Stale statistics
  • Fragmented indexes
  • Developers use a mix of parameterized SQL and stored procedures
  • Sprocs prefixed with “sp_”
  • Cursors
  • GUID identifiers
  • NOLOCK hints
  • No automated backups

I want to hear what you think. Submit your prioritized list in the comments, or by using this survey: https://www.surveymonkey.com/r/MV9F9YT

I’ll be posting my own answers on Thursday, July 5, 2016.

Update: I’ve shared the results. Prioritize This List Of Issues (Results)

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