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Author: Kevin Feasel

SQL On Linux Connectivity

Slava Murygin troubleshoots connectivity issues with SQL Server on Linux:

After you enter SA password you have to get “vNext” version of your SQL Server.
If you did not get the correct response you might have following problems:
I)   Wrong SA password. To fix it, just re-configure SQL Server.
II)  SQL Server Tools are not installed.
III) Typo. Check your syntax.

The troubleshooting process is a bit different from SQL Server on Windows, but it’s still pretty straightforward.

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Avoiding Percent Growth

Angela Henry has a script to tame percent growth on database files:

I decided I needed to do something else other than just send an email notification, I needed to take corrective action when it occurred.  So I wrote a little stored procedure that will take the ALTER DATABASE statement as a parameter, parse it and take the appropriate corrective action. 

Simple enough, right?  Now I just need to add the call to my newly created stored procedure in my server level trigger and we are good to go.  But wait, you can’t ALTER a database within an ALTER DATABASE statement (don’t believe me? Use this as a learning exercise to see what happens when you try).  So what could I do?  There are several things you could do, but I chose to create a table that could hold this newly created ALTER DATABASE statement and insert the record there.  Then I created a SQL Agent job that runs once every hour and reads that table and executes any entries it finds, then deletes them after successfully executing.

Read the whole thing, including the disclaimer.

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Powershell Defaults

Michael Sorens has some time-saving defaults for Powershell:

Besides setting up some convenient shortcuts for use with built-in cmdlets, for developers it is also handy to be able to work some magic with your own custom cmdlets. In my shop, for example, we have one module containing a couple dozen cmdlets, many of which use a common parameter, Mode. This Mode parameter varies from client to client, but for any single client, every cmdlet working on their data needs to use the same value of Mode. So I have to add -Mode hist-0010-dev.test onto each cmdlet I am using, which gets very tiring/annoying very quickly. You could, of course, put that value into a variable and then just use, e .g. -Mode $myMode, which is less typing, but if less is better, then no typing at all is better still.

There are a lot of tips in this article, so take some time with it.

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10,000 R Packages

David Smith notes that CRAN is now up to 10,000 packages:

Having so many packages available can be a double-edged sword though: it can take some searching to find the package you need. Luckily, there are some resources available to help you:

  • MRAN (the Microsoft R Application Network) provides a search tool for R packages on CRAN.

  • To find the most popular packages, Rdocumentation.org provides a leaderboard of packages by number of downloads. It also provides lists of newly-released and recently-updated packages.

R is a big language; having good heuristics for figuring out where to find appropriate packages is extremely important.

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LOGMGR_RESERVE_APPEND

Paul Randal explains an uncommon wait stat:

Last week I was sent an email question about the cause of LOGMGR_RESERVE_APPEND waits, and in Monday’s Insider newsletter I wrote a short explanation. It’s a very unusual wait to see as the highest wait on a server, and in fact it’s very unusual to see it at all.

It happens when a thread is generating a log record and needs to write it into a log block, but there’s no space in the log to do so. The thread first tries to grow the log, and if it fails, and the database is in the simple recovery mode, then it waits for 1 second to see if log clearing/truncation can happen in the meantime and free up some space. (Note that when I say ‘simple recovery mode’, this also included a database in full or bulk_logged, but where a full backup has not been taken – i.e. the database is operating in what’s called pseudo-simple.)

Read on for more details and a repro script.

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Azure Functions: Contact Form

Eli Weinstock-Herman explains how to use Azure Functions to create dynamic content on an otherwise-static page:

My personal website is a static site: 100% HTML, JS, and CSS files with no server-side processing. I have custom code that pulls data from a variety of sources and builds updated versions of the files from templates, which are then deployed to the host. I do this to move the CPU latency of building the pages to my time, instead of charging it to visitors on each page hit. While I have a host, a strategy like this means I could also choose to host for free via github or similar services.

So there’s a great benefit to the reader and our wallet, but no server-side execution makes things like contact forms trickier. Luckily, Azure Functions or AWS Lambda can be used as a webhook to receive the form post and process it, costing nothing near nothing to use (AWS and Azure both offer a free tier for 1M requests/month and 400,000 GB-seconds of compute time).

Eli has a working example in the post, which I recommend checking out.

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Memory-Optimized Table Warnings

Robert Davis looks at messages in the error log related to memory-optimized tables:

The server on which we are running in-memory OLTP is a really hefty server with 128 logical cores and 1.5 TB of RAM (1.4 TB allocated to SQL Server). We are limiting in-memory’s memory usage with Resource Governor, which also makes it easy to see how much it is using. Needless to say, even with a limited percentage of 1.4 TB of RAM is still a lot of memory. The highest I have seen in-memory usage for this one database reach at peak activity levels is ~43 GB. In production, when the heavy in-memory OLTP processes complete, I see the system reclaim the in-memory buffers pretty quickly, though not completely. During a normal day, I often see the in-memory memory usage hovering between 1 and 3 GB even when there is virtually no traffic.

When testing in-memory on a dev server that only I was using before deploying to production, I noticed that the memory usage would stay at whatever high level it reached. This makes me believe that in-memory buffers are cleaned up and reclaimed as needed, and if not needed, they just hang around as in-memory buffers. And it appears that some of the buffers end up hanging around. Perhaps they wouldn’t if the server was memory starved. I have not tested that theory.

It’s a conjecture, but seems pretty solid.  Also worth reiterating is that they’re warnings, not errors.

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Troubleshooting Connectivity Errors

The CSS SQL Server Engineers have a guide for solving connectivity issues:

In addition to providing a quick checklist of items that you can go through, the doc provides step by step troubleshooting procedures for the following error messages:

  • A network-related or instance-specific error occurred while establishing a connection to SQL Server

  • No connection could be made because the target machine actively refused it

  • SQL Server does not exist or access denied

  • PivotTable Operation Failed: We cannot locate a server to load the workbook Data Model

  • Cannot generate SSPI context

  • Login failed for user

  • Timeout Expired

  • The timeout period elapsed prior to obtaining a connection from the pool

Click through for the guide.  It’s in choose-your-own-adventure format, though without nice graphics.

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Caching KPI Reports

Kathi Kellenberger discusses caching in SQL Server Reporting Services KPI reports:

Because these reports automatically show the data, the reports show cached data only. Imagine if hundreds or even thousands of report users brought the web portal page up each day causing the KPI reports to hit the database even when the report user was not interested in seeing the KPI reports at that time. That is why Microsoft decided to use cached data only in these reports.

When the data changes, the KPI report will continue to show the same information unless you configure a cache refresh plan on the dataset. Follow these instructions so that the KPI data will refresh on a scheduled basis.

Read on for a step-by-step guide on how to set up caching.

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