Messing With Statistics

Erik Darling shows how to fake stats:

One thing I’ve found is that the inflated counts don’t seem to change anything for Identities, or Primary Keys. You’ll always get very reasonable plans and estimates regardless of how high you set row and page counts for those. Regular old clustered indexes are fair game.

Some really interesting things can start to happen to execution plans when SQL thinks there’s this many rows in a table. The first is that SQL will use a rare (in my experience) plan choice: Index Intersection. You can think of this like a Key Lookup but with two nonclustered indexes rather than from one nonclustered index to the clustered index.

This is very useful when you don’t have many rows in dev, can’t put many rows in dev, and can’t restore a stats-only database from prod.

More On String Splitting

Aaron Bertrand has a follow-up post on STRING_SPLIT():

So here, the JSON and STRING_SPLIT methods took about 10 seconds each, while the Numbers table, CLR, and XML approaches took less than a second. Perplexed, I investigated the waits, and sure enough, the four methods on the left incurred significant LATCH_EX waits (about 25 seconds) not seen in the other three, and there were no other significant waits to speak of.

And since the latch waits were greater than total duration, it gave me a clue that this had to do with parallelism (this particular machine has 4 cores). So I generated test code again, changing just one line to see what would happen without parallelism:

There’s a lot going on in that post, so I recommend checking it out.

IT Pro Cloud Essentials Program

Kevin Feasel

2016-04-22

Cloud

Grant Fritchey talking about a new Microsoft program:

You need to start working on adding Azure knowledge to your skill set. If you have access to an MSDN license, getting into Azure is easy because of the credits available. However, not everyone works for a company that provides MSDN or has purchased a license. In that case, getting into Azure, just for testing and learning could be expensive (I frequently “spend” $150/month with my MSDN credits). However, Microsoft is very serious about getting everyone moved into this space. They’ve launched a new free program called IT Pro Cloud Essentials. Not only does it give you Azure credit, but you also get access to O365, another set of skills and understanding you need to acquire.

Also check out their Visual Studio Dev Essentials program.  Its Azure credit is only $25 a month, but offers you SQL Server 2014 (and will offer 2016) Developer Edition.

Finding Nested Stored Procedures

Michael J. Swart has a script to find nested stored procedures:

Adventureworks seems just fine to me. Only four instances of procedures calling procedures. I looked at the database I work with most. Hundreds of procedures (representing 15% of the procedures) call other procedures. On the other end of the spectrum is Stackoverflow. I understand that they don’t use stored procedures at all.

Check out the comments for more notes.

Truncating Log Files

Sean McCown has a script to truncate log files:

I want to show you a great piece of code to truncate and shrink all your log files. The biggest question you always ask is why should you shrink your log files? It’s been drilled into everyone’s head that shrinking log files is bad because you can cause too many VLFs, and of course there’s the zeroing out that happens when they grow.
OK, so let’s answer that question. There are a couple reasons you’d want to shrink all the files to a small size.

Regularly shrinking log files in production isn’t a particularly great thing, but as Sean points out, there are valid reasons for doing this.

ENCRYPTION_SCAN Locks

Suresh Kandoth explains ENCRYPTION_SCAN in a non-TDE scenario:

There are three types of operations that acquire lock with the resource_type of DATABASE and resource_subtype of ENCRYPTION_SCAN:

– Encryption scan performed during TDE enable/disable

– Bulk Allocations that happen as part of bcp/bulk insert/select-into/index operations, etc

– Sort spills that are done as part of sort operators in the query plan

These locks are taken to serialize operations like bulk allocations and sorts with encryption scan.

Read the whole thing.  It looks like this isn’t by itself a significant issue, but it is interesting to see this lock type against a database without TDE.

Field And Record

Kevin Feasel

2016-04-21

Naming

Michael Swart introduces Field & Record magazine:

I’m definitely a descriptivist. Language is always changing and if a word or phrase gets adopted widely enough, it is no longer “wrong” (whatever that means).

So when I hear “Field” and “Record” they’re acceptable to me. But if I’m explaining something, I don’t want to distract from the thing I’m saying. And from that point of view, I try to use “Row” and “Column” because I don’t know anyone who blinks at those terms.

Entity and Attribute or bust.  That’s my philosophy.

Scientific Notation

Andy Mallon digs into one scenario in which you shouldn’t assume how ISNUMERIC behaves:

Someone posted to #sqlhelp on Twitter, asking the following: “Wondered if anyone could enlighten me as to why ISNUMERIC(‘7d8’) returns 1?”

Sure enough, SELECT ISNUMERIC('7d8') returns a 1.

Great answer and explanation, and his advice to use TRY_CONVERT() for 2012 and up is spot-on.

Installing ODBC Drivers

Kevin Feasel

2016-04-21

Linux

Steph Locke shows how to install the SQL Server ODBC drivers in Ubuntu:

Did you know you can now get SQL Server ODBC drivers for Ubuntu? Yes, no, maybe? It’s ok even if you haven’t since it’s pretty new! Anyway, this presents me with an ideal opportunity to standardise my SQL Server ODBC connections across the operating systems I use R on i.e. Windows and Ubuntu. My first trial was to get it working on Travis-CI since that’s where all my training magic happens and if it can’t work on a clean build like Travis, then where can it work?

Now I can create R functionality that can reliably depend on SQL Server without having to fallback to JDBC. A definite woohoo moment!

Thanks to Steph for putting together this script.

Restoration Options

Richie Lee covers the WITH RECOVERY, WITH NORECOVERY, and WITH STANDBY database restoration options:

Similar to NORECOVERY except that the database will accept read only connections. To do this any uncommitted transactions in the backup will be rolled back and stored in a transaction undo file (tuf.) Whilst users are running queries against the database no further restores can continue until all queries are complete (though this is not the case with log shipping.) When the next restore occurs, those uncommitted transactions in the tuf file will be rolled forward and the next log is restored.

Diving into STANDBY mode was quite helpful.  I’ve never needed to restore a database into standby mode, but could see it being useful for bringing back deleted records.

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