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Category: Administration

Understanding Memory Grants

Published 2020-05-12 by Kevin Feasel

Taiob Ali walks us through the concept of memory grants:

DesiredMemory: Memory estimated to fit intermediate results in KB for the chosen degree of parallelism. If the query runs in serial mode, this is the same as SerialDesiredMemory.

(Amount needed to store all temporary rows in memory. This depends on the cardinality estimate, expected number rows and average size of row). This is called additional because a query can survive lack of such memory by storing part of temporary rows on hard disk. A query is not guaranteed to have the full amount if the total exceeds the preset limit.)

Read on for explanations of each of the elements in MemoryGrantInfo.

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Certificate Management with SQL Server 2019

Published 2020-05-12 by Kevin Feasel

Niko Neugebauer walks us through improvements in certificate management with SQL Server 2019:

If you have ever used them for connection encryption (TLS 1.2), you might have had some battles with the certificates, having to go into the registry to edit the thumbprint and if you doing a Failover Cluster or Availability Group installation – you would have to enjoy this operation on the multiple nodes. Not-so-very-user-friendly to say at least!
So many times, it would scare-off a non Server/Database Administrator or a junior Server/Database Administrator from trying those features.

Niko also mentions something very interesting about SQL Server Configuration Manager compatibility at the end of the post.

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Monitoring Azure Synapse Analytics SQL Pools with Power BI

Published 2020-05-12 by Kevin Feasel

Brett Powell has a pair of Power BI templates for monitoring Azure Synapse Analytics:

Upon clicking ‘Load’ you’ll either need to provide your credentials for this source (if you don’t have this data source saved from previous use) or the queries will execute and the following report pages will be available:

– Executions
– Waits
– Sessions
– Waits Detail
– Execution Detail
– Memory
– ExecutionDrillThrough (hidden)

Click through to see what the templates look like and how to obtain them.

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Change Tracking and Internal Tables

Published 2020-05-11 by Kevin Feasel

Tim Weigel continues a series on change tracking:

In my last post, I showed you how to configure change tracking at the table level and how to get configuration information about change tracking from the database engine. We looked at sys.change_tracking_databases and sys.change_tracking_tables, and looked at some sample scripts that present the information in a more readable format.

Before moving on to working with change tracking, I’d like to show you a little bit about how SQL Server handles change tracking data under the hood. Let’s take a few minutes to talk about sys.internal_tables, sys.dm_tran_commit_table, and sys.syscommittab. These aren’t objects that most DBAs interact with on a routine basis, but they’re useful for understanding how change tracking does what it does.

Click through to learn more about these internal tables.

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The Pains of Database Restoration

Published 2020-05-11 by Kevin Feasel

Stuart Moore covers some of the pains of database restoration in two posts. First, why dbatools’ Restore-DbaDatabase is a complicated as it is:

At first glance Restore-DbaDatabase looks like a slow lumberig complex beast. In reality it’s not that bad.

It’s the result of design decisions I took in wanting a solid versatile command that could cope with everything that people would want from it.

In this post, we’ll go through the main decisions/points of contention one by one

Stuart then covers the limitations of Restore-DbaDatabase:

Like all tools, Restore-DbaDatabase isn’t able to do everything that everyone wants it to. Certainly, at the moment I’d like it to write it’s own blog posts and fetch me a cold beer, but that doesn’t happen

A lot of the below isn’t complaining about people asking for features. If we can do it, we will, and we’re keen to make this work for as many people in as many situations as possible

But quite a few requests over the years have been non starters for a number of reasons.

Read them both; they’re part of Stuart’s 31 Days of Backup and Restore with dbatools series.

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Don’t Use sys.dm_hadr_cluster_members for Quorum Info

Published 2020-05-11 by Kevin Feasel

Sean Gallardy explains a limitation of sys.dm_hadr_cluster_members:

I’ve now run across a few different instances where the monitoring for quorum was done via this DMV. On the surface, it seems like nothing would be wrong with using the “number_of_quorum_votes” column to check on the members of the cluster and see their voting status. However, this isn’t quite the case… you see there are various mechanisms that influence whether or not a member (or witness) has a vote and these continue to be expanded in each version of WSFC.

Click through for a short history lesson as well as some good advice on how accurately to get this information.

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The Value of Negative Identity Values

Published 2020-05-07 by Kevin Feasel

Randolph West explains why you might start at MIN(INT) for an identity integer column:

A quick(er) post this week, in response to Greg Low’s blog post from a few weeks ago titled “Don’t start identity columns or sequences with large negative values.”

Greg writes that you shouldn’t use large negative values in a table, because… it’s hard to read them, I guess? And also they don’t compress well.

I disagree … to a degree. Dang, words are hard. Anyway, when I design a table I create what’s called a surrogate key as my primary key, which is a value that is intended for the table to uniquely identify a row so that it participates in relational activities like joins and foreign keys in an efficient way. In other words the identity column is not for me, it’s for the database engine. I don’t need to worry about what row a value has. I choose the data type for that identity column based on the estimated number of rows, not whether I can memorize that a [StatusID] of 5 means something. Magic numbers are bad, mmmkay?

I don’t mind using negative values, especially for things like queue tables where the rows are ephemeral. The identity values may be harder to read, but as Randolph points out, in those types of cases, you aren’t really reading the values anyhow.

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Workload Classification with Resource Governor in Azure Synapse Analytics

Published 2020-05-05 by Kevin Feasel

Niko Neugebauer keys in on an interesting addition to Azure Synapse Analytics:

Given that we can specify 5 different parameters (USER MEMBERNAME, ROLE MEMBERNAME, WLM_LABEL, WLM_CONTEXT, START_TIME/END_TIME) – there must be a prioritisation mechanism in order to decide which condition gets selected. This mechanism is called Parameter Weighting in Azure Synapse and it assigns the following weight to each of those parameters:
USER = 64
ROLE = 32
WLM_LABEL = 16
WLM_CONTEXT = 8
START_TIME/END_TIME = 4
meaning that if the Workload Classifier fits into the timeframe START_TIME/END_TIME, WLM_LABEL & ROLE – it will receive 52 points = 4 + 16 + 32,
while a different Workload Classifier that fits into WLM_CONTEXT & USER will get 72 points = 8 + 64, thus will prevail and will be selected over the first Workload Classifier.

Azure Synapse Analytics (including when it was known as SQL Data Warehouse) has had some resource governor-related things I’ve wanted in the box product for a while, including labels (which are better than using application name).

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Queries Using tempdb: a Whodunit

Published 2020-05-05 by Kevin Feasel

Dave Bland shares a database detective story with us:

To find the culprit, we tracked down an old informant named sp_who2.  At first he had no comment, but we knew he had some information that could help us, so we kept after him.  Finally, he grew tired of us and gave us something just to make us go away. He said we needed to talk to his associate sysproccesses.  At first this guy was hard to find, but we located him sitting at a table.  He wasn’t really doing anything, just sitting there. So we approached him and sat down to see if we can get what we are looking for.  He also had no comment and referred us to his lawyer, sys.dm_exec_sessions.  After some searching, we were able to catch up with him at the DMV and he was not in a good mood.  He gave up some information, just not exactly what we are looking for.

Dave shows how we can figure out who created a specific temp table (a global temp table, in this case), the query that account used to create the temp table, and the time the temp table was created.

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Deleting Packages from the SSIS Catalog

Published 2020-05-05 by Kevin Feasel

Mala Mahadevan performs important cleanup work:

I will be blogging on a few things I learn on my journey to SSIS expertise. This is the first one. This came about as a result of wanting to delete a few packages from ssis catalog. We do not use these packages any more, and I wanted to clean them out from the project which resides on a few servers. I looked into a few ways of doing it.

Click through for three methods, including an in-depth discussion of the third (and least obstructive).

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