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Month: September 2016

Memory And Storage

Published 2016-09-23 by Kevin Feasel

Glenn Berry has a nice post on current and near-future memory and storage technologies:

Over the past couple of years, we have seen the introduction and increasing usage of NVM Express (NVMe) PCIe SSDs based on existing NAND flash technology. These typically have latencies in the 50-100 microsecond range. They also use the newer, much more efficient NVMe protocol and the PCIe interface, giving much better performance than older SAS/SATA SSDs using the old AHCI protocol.

Currently, Hewlett Packard Enterprise (HPE) is selling 8GB NVDIMM modules for their HPE Proliant DL360 Gen9 servers and HPE Proliant DL380 Gen9 servers. These modules have 8GB of DRAM which is backed by 8GB of flash for $899.00, which is pretty expensive per gigabyte. These two-socket servers have 24 memory slots that each support up to 128GB traditional DDR4 DIMMs. Any slots you use for NVDIMM modules won’t be available for regular memory usage. You can use a maximum of 16 memory slots for NVDIMM usage, which gives you a maximum capacity of 128GB. You must use Intel Xeon E5-2600 v4 series processors in order to get official NVDIMM support. Micron is scheduled to release larger capacity 16GB NVDIMMs in October of 2016.

Read the whole thing.

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Creating Partitioned Views

Published 2016-09-23 by Kevin Feasel

Erik Darling describes partitioned views:

Hooray. Now you have to type less.

Partitioned views don’t need a scheme or a function, there’s no fancy syntax to swap data in or out, and there’s far less complexity in figuring out RIGHT vs LEFT boundaries, and leaving empty partitions, etc. and so forth. You’re welcome.

A lot gets made out of partition level statistics and maintenance being available to table partitioning. That stuff is pretty much automatic for partitioned views, because you have no choice. It’s separate tables all the way down.

Partitioned views, AKA SQL Server 2000 partitioning.  I think my favorite use case for them today is to serve as a combination of hot data in a memory-optimized table and cold data on disk.

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WOxCompliant Update

Published 2016-09-23 by Kevin Feasel

Chris Bell has an updated version of his WOxCompliant:

What changed?

  1. I fixed an issue that would cause a continual loop to occur and hang the script indefinitely. With this fix, my tests are returning results in just seconds now!

  2. Corrected various typos and details in the results

  3. If you had xp_Cmdshell active before the script, it used to turn it off at the end for compliance. Now the script checks and leaves it active if you had it active. It will still notify you of the results though

This is one of my favorite third-party scripts for configuring a database.

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Levenshtein Distances

Published 2016-09-22 by Kevin Feasel

Peter Coates provides an extremely fast estimate of Levenshtein Distance:

If your application requires a precise LD value, this heuristic isn’t for you, but the estimates are typically within about 0.05 of the true distance, which is more than enough accuracy for such tasks as:

  • Confirming suspected near-duplication.

  • Estimating how much two document vary.

  • Filtering through large numbers of documents to look for a near-match to some substantial block of text.

The estimation process is pretty interesting.  Worth a read.

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XGBoost

Published 2016-09-22 by Kevin Feasel

Koos van Strien moves from Python to R to run an xgboost algorithm:

Note that the parameters of xgboost used here fall in three categories:

  • General parameters

    • nthread (number of threads used, here 8 = the number of cores in my laptop)

  • Booster parameters

    • max.depth (of tree)
    • eta

  • Learning task parameters

    • objective: type of learning task (softmax for multiclass classification)
    • num_class: needed for the “softmax” algorithm: how many classes to predict?

  • Command Line Parameters

    • nround: number of rounds for boosting

Read the whole thing.

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TCP Chimney Offloading

Published 2016-09-22 by Kevin Feasel

Wayne Sheffield offers advice on TCP Chimney Offloading:

With all of these changes to the OS, which setting should we use for SQL Server? In general, for all of these operating systems, I recommend that TCP Chimney Offload be disabled – because you can see odd connectivity problems in any other state. Notice in the above quote that Microsoft says that this feature is best used for applications with long-lived connections that transfer large amounts of data – hopefully your OLTP database is performing lots of short-lived connections and they are not transferring large amounts of data (if they are, I can help you with that!).

Definitely worth a read.

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HDP 2.5 Sandbox

Published 2016-09-22 by Kevin Feasel

The Hortonworks Data Platform 2.5 sandbox is now available:

GET STARTED IN 4 STEP

1) Download HDP Sandbox as a VM image(VMware and Virtualbox or Docker
2) Setup and Start the VM image.
3) Try a Sandbox tutorial, check out the list of free tutorials, or jump directly into an Hello to HDP hands-on tutorial.
4) Need more help? Visit the Hortonworks Community Connection(HCC) and interact directly with the community and our development team.

It looks like they’ve bumped up the RAM requirements to 8 GB and have added new tutorials.

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Specifying Columns In Entity Framework

Published 2016-09-22 by Kevin Feasel

Richie Rump shows how to limit the number of columns returned in an Entity Framework query:

This one’s a bit more tricky but let’s walk through it. We’re getting data from the Posts table where the Tags column equals “<sql-server>” and selecting every column from both the Posts and PostTags tables. We can tell because there are no specified properties in the Select. Even though this statement looks more complex it’s only three lines and looks somewhat like a SQL statement. But it’s really a LINQ (Language Integrated Query) statement, specifically a LINQ to Entities statement. This LINQ statement will be translated into this SQL statement:

Read the whole thing.

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SSAS Timezone Conversions

Published 2016-09-22 by Kevin Feasel

Meagan Longoria notes that last processed date is UTC but the Properties page is local time:

The datetime returned by this query is in UTC. My query returns 9/19/2016 7:43:03 PM.

If I go into the properties of my SSAS database, I can see this same info, but the timezone conversion has already been done for me (this server is in Central time zone).

I think that on net, that’s the best way to do it:  store everything in UTC and use the presentation layer to convert those to local times.

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SQL Server 2014 SMO And TruncateData

Published 2016-09-22 by Kevin Feasel

Max Trinidad finds a version inconsistency in SMO:

Hum! I just found out that in SQL Server 2014 (SP2 installed), while migrating from SQL Server 2005, one of my PowerShell script (I’ve been using for a long time) that uses SMO to truncate tables. But, when running it against a SQL Server 2014 database, I’m getting an error:

“..this property is not available on SQL Server 2014.”

For mi surprise, I ran the same PowerShell script against SQL Server 2016 and it works fine.

That seems rather odd.  If this affects you, vote up his UserVoice item.

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