Winnowing Down WhoIsActive Data

Kendra Little shows how to use temporary objects to pare down the results of sp_whoisactive for later storage:

I used the @schema parameter to have sp_WhoIsActive generate the schema for the table itself. Full instructions on doing this by Adam are here.

Since I care about tempdb in the case of this example, I used @output_column_list to specify that those columns should come first, followed by the rest of the columns.

I also elected to set @get_plans to 1 to get query execution plans if they’re available. That’s not free, and they can take up a lot of room, but they can contain a lot of helpful info.

This is a very useful guide, and also read the linked documentation for sp_whoisactive; there’s a huge amount of goodness in that one procedure.

Indirect Checkpoint And Non-Yielding Scheduler Problems

Parikshit Savjani has a post describing an issue you might experience with indirect checkpoint post SQL Server-2012:

One of the scenarios where skewed distribution of dirty pages in the DPList is common is tempdb. Starting SQL Server 2016, indirect checkpoint is turned ON by default with target_recovery_time set to 60 for model database. Since tempdb database is derived from model during startup, it inherits this property from model database and has indirect checkpoint enabled by default. As a result of the skewed DPList distribution in tempdb, depending on the workload, you may experience excessive spinlock contention and exponential backoffs on DPList on tempdb. In scenarios when the DPList has grown very long, the recovery writer may produce a non-yielding scheduler dump as it iterates through the long list (20k-30k) and tries to acquire spinlock and waits with exponential backoff if spinlock is taken by multiple IOC routines for removal of pages.

This is worth taking a close read.

Bacpacing In Azure

Derik Hammer shows how to use a bacpac file to deploy an existing database to Azure SQL Database:

The recommended method for working with Azure is always PowerShell. The Azure portal and SSMS are tools there for your convenience but they do not scale well. If you have multiple databases to migrate, potentially from multiple servers, using PowerShell will be much more efficient. Scripting your Azure work makes it repeatable and works towards the Infrastructure as Code concept.

In this demonstration, the below steps will be used.

  1. Export the bacpac file to a local directory with sqlpackage.exe.

  2. Copy the bacpac to Azure Blob Storage with AzCopy.exe

  3. Use the PowerShell AzureRM module and cmdlets to create an Azure SQL Database from the bacpac file.

Derik shows the point-and-click way as well as the Powershell way.

Self-Analysis Of SQL Server Dump Files

Arun Sirpal walks through the SQL Server Diagnostics preview:

Notice the region to upload – If you are using a work machine I would suggest getting authorisation. The great thing here is that this is GDPR compliant.

Once ready hit the upload button, it goes through 3 phases. Upload, Analysis and a recommendation.

It sends your dump files to an external service, which is important enough to point out.  If you want more details on the product, Rony Chatterjee has a FAQ.

PoshBot

Warren Frame shows off ChatOps with PoshBot:

We’re going to cover the basics to get up and running with PoshBot:

  • Create a Slack bot
  • Create a PoshBot configuration
  • Run PoshBot as a service
  • Write a PoshBot plugin
  • Use PoshBot

This might seem like a lot of work, but the configuration and service are a one time thing – Writing plugins is just like writing PowerShell functions and modules!

One of my mad scientist co-workers has put together a similar bot and it tells our DBA team how servers are doing.  It’s quite useful for system reconnaissance, particularly when all you have is a phone and a trouble ticket.

Wiggle Room Files

David Klee shows one tactic for running out of disk space, in this case on an ESXi host:

Sometimes this task is harder than it sounds. If your SAN is out of space, or the SAN management tools are out of your control, you could be stuck.

But… follow a simple trick to give yourself that last little bit of wiggle room in the event that a snapshot fills a datastore.

Add a large text file to the root of the datastore that you can delete if you need headroom! I know it sounds too simple… but it’s simple and effective.

Filed under “old but good.”

Performance Comparison: Comparing Column Differences

Shane O’Neill has a column difference showdown:

The original post for this topic garnered the attention of a commenter who pointed out that the same result could be gathered using a couple of UNION ALLs and those lovely set-based EXCEPT and INTERSECT keywords.

I personally think that both options work and whatever you feel comfortable with, use that.

It did play on my mind though of what the performance differences would be…what would the difference in STATISTICS IO, TIME be? What would the difference in Execution Plans be? Would there even be any difference between the two or are they the same thing? How come it’s always the things I tell myself not to forget that I end up forgetting?

This may not be the most important thing to test, but it does show you a technique.

Interesting SQL Server GitHub Repos

Denis Gobo links to five interesting GitHub repos:

dbatools

dbatools is a free PowerShell module with over 200 SQL Server administration, best practice and migration commands included.

GitHub Repo is here: https://github.com/sqlcollaborative/dbatools

Also make sure to visit their website: https://dbatools.io/

Read on for the other four.

Switching In Identity Columns

Kenneth Fisher shows a way of working around the difficulty of adding an identity column to an existing table:

A friend had an interesting problem today. A really big table (multiple millions of rows) and no primary key. He then ran into an issue where he had to have one. The easiest thing is to create a new int column with an identity column right? Unfortunately in this case because of the size of the table, the log growth on adding an identity column was too much. So what to do?

Well, it would be nice if we could add an int column, populate it in chunks, then make it an identity column. Unfortunately, you can’t add identity to an existing column.

Read on for the answer.

Using Buffer Pool Extension

William Wolf talks about Buffer Pool Extension:

With this feature, SQL Server will extend the Buffer Pool Cache to non-volatile(ssd) storage.  This will alleviate the I/O contention of mechanical disks by augmenting memory.  The BPE uses the SSD as memory extension rather than disk.  This feature can be used with standard and enterprise, but would provide noticeable benefits for Standard Edition.  According to books online, the BPE size can be up to 32 times(Enterprise) or 4 times(Standard Edition) the value of max_server_memory, but the recommended ratio is 1:16 or less.

By utilizing this option, we can alleviate some memory pressure.  To demonstrate this for me was a litte difficult at first. My laptop, as most newer laptops, has a SSD. So I plugged in a SATA hard drive externally and moved my database there for testing. If the database files are already on SSD, adding BPE may not give much benefit as the memory from BPE would write to SSD as well.

Buffer Pool Extension did end up in the Hall of Shame, but scenarios like Wolf describes exist, and in those scenarios, BPE could be a viable third-best option.

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