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Day: October 20, 2016

Flushing Change Tracking Internal Tables

Published 2016-10-20 by Kevin Feasel

Amit Banerjee mentions a new stored procedure for change tracking cleanup:

In SQL Server 2014 Service Pack 2 and above, we provided a new Stored Procedure, sp_flush_CT_internal_table_on_demand, to assist with Change Tracking cleanup. KB3173157 has more details. This stored procedure accepts a table name as parameter and will attempt to cleanup records from the corresponding change tracking internal table.  During the course of the deletion, it will print some verbose in the output window about the progress of deletion.

If automated change tracking cleanup works well enough for you, there’s no change; but if you’re struggling with that cleanup, this procedure might help.

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What Is DevOps?

Published 2016-10-20 by Kevin Feasel

Julia Evans looks at what DevOps means in practice:

I enjoyed reading this article about devops at Etsy. One of the really key things about this article is – there is no devops organization at Etsy. It’s about how developers and operations people work productively together! Also, it was a slow incremental migration towards different practices. They did not wake up one day and become devops. I think this is the first talk that used the term ‘devops’?

It’s also not about “everyone is a software developer” – one of the authors of this book, Katherine Daniels, is a senior operations engineer at Etsy at Etsy. I don’t know any of the details of her job, but my impression is that she has a lot of expertise in operations. It’s not like “make operations so easy that nobody has to an expert at it”. Of course you need people who know a ton about operations! Probably those people write software as part of their job?

One of the scariest realizations that I’m slowly coming to (other than “Information Technology is people!”) is the sheer number of overlapping dependencies in the tech world.  A bit earlier in my career, I felt like I could be “a SQL Server guy” and focus on that while not caring too much about the outside world.  It seems like saying that you want to be “just an X” has become more difficult at the margin, and DevOps is just one example of this:  keeping an edge means going broader about more things while still trying to dig deeper in relevant areas.  That’s a tough balancing act.

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RTVS 0.5

Published 2016-10-20 by Kevin Feasel

David Smith notes that R Tools for Visual Studio has hit version 0.5:

RTVS also makes it easy to run R code as a SQL Server 2016 stored procedure. (This is a great way to make share the results of R code with other database users while making use of the power of the database for R computations.) The new SQL R Stored Procedure file works with SQL Server R Services to create a stored procedure that embeds R code you create, edit and test within RTVS. This greatly simplifies the process of running R code within SQL Server 2016 as you can see below:

The RTVS team is making good progress.  If you passed on RTVS early on, it might be time to take another look.

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Phantom Reads

Published 2016-10-20 by Kevin Feasel

Wayne Sheffield discusses phantom reads:

Run both code scripts again (Code Script 1 first, and Code Script 2 within 10 seconds). This time, you will see that Code Script 2 completes immediately without being blocked, and when Code Script 1 finishes, it has spawned additional data in its result set. A phantom read in action.

If you want to hide from phantom reads completely, then you’ll need to use either the serializable or snapshot transaction isolation levels. Both of these have the same concurrency effects: No dirty reads, non-repeatable reads, or phantom reads. The difference is in how they are implemented: the serializable transaction isolation level will block all other transactions affecting this data, while the snapshot isolation level utilizes row versions to create connection-specific versions of the table for the transaction – all of these row versions will cause increased activity in the tempdb database. Let’s take a look at how the snapshot isolation level will eradicate the phantom reads. First off, we need to modify the database to accept this isolation level.

After reading Wayne’s post, if you want a more academic (i.e., less fun) read, you can also go back to the Microsoft Research isolation levels paper, which describes most of the isolation levels we have in place today for SQL Server.

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Temporary Stored Procedures

Published 2016-10-20 by Kevin Feasel

Jana Sattainathan discusses temporary stored procedures:

The real benefit of these procedures is when they contain lot of logic that you need on a temporary basis but do not want to clutter the existing stored procedure list. You could even have multiple temporary procedures that call each other. I would not go overboard with this. It is just a convenience.

I don’t often see these in use; when I’ve seen them, they’re in environments in which normal stored procedure create rights are locked down and you want to do something as a one-off (like testing an operation against production data).  In other words, those sketchy things that we don’t admit to each other that we do…

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BCP For UTF-8

Published 2016-10-20 by Kevin Feasel

Sanjay Mishra notes that SQL Server 2016 and 2014 SP2 support UTF-8 for BCP and BULK INSERT:

This requirement has been addressed in SQL Server 2016 (and backported to SQL Server 2014 SP2). To test this, I obtained a UTF-8 dataset from http://www.columbia.edu/~fdc/utf8/. The dataset is translation of the sentence “I can eat glass and it doesn’t hurt me” in several languages. A few lines of sample data are shown here:

(As an aside, it is entirely possible to load Unicode text such as above into SQL Server even without this improvement, as long as the source text file uses a Unicode encoding other than UTF-8.)

I ran into this problem before, where developers wanted to bulk load UTF-8 but had to settle for an inferior solution.

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Page Free Space On Heaps

Published 2016-10-20 by Kevin Feasel

Raul Gonzalez shows a case in which writing to a heap can be more efficient than writing to a clustered index:

Lots have been written, including myself, about the advantage and disadvantages of the different types of tables that exist in SQL Server, Clustered and Heaps.

Today I will again, because at the end of the day, a table is the most basic structure in a database and we need them to store the data, which is indeed the purpose of having a database, right?

Interesting reading.  Check it out.

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New Samsung Drives

Published 2016-10-20 by Kevin Feasel

Joe Chang looks at the Samsung 960 PRO SSD:

All the previous PCI-E x4 gen3 NVMe SSDs were rated between 2,000-2,500MB/s in large block read. The 960 Pro is rated for 3,500MB/s read. This is pretty much the maximum possible bandwidth for PCI-E x4 gen3. Each PCI-E gen3 lane is 8Gbit/s, but the realizable bandwidth is less. In earlier generation products, an upper bound of 800MB/s realizable per 8Gbit/s nominal signaling rate was typical.

Presumably there was a reason why every PCI-E x4 was in the 2000-2500MB/s bandwidth. It could be that these were 8-channel controllers and the NAND interface was 333-400MB/s. Even though 8 x 400MB/s = 3,200MB/s, it is expected that excess bandwidth is necessary on the downstream side. The could be other reasons as well, perhaps the DRAM for caching NAND meta-data. Intel had an 18-channel controller, which produced 2,400MB/s in the P750 line, and 2,800MB/s in the P3x00 line.

If you’re looking at a test lab server, this might be a good disk for you.

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