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Day: March 24, 2016

NUMA With Few Cores

Published 2016-03-24 by Kevin Feasel

Denny Cherry asks and answers the question of how many NUMA nodes we should use on a server with a large amount of RAM but relatively few cores:

For this example, let’s assume that we have a physical server with 512 Gigs of RAM and two physical NUMA nodes (and two CPU sockets). We have a VM running in that machine which has a low CPU requirement, but a large working set. Because of this we have 4 cores and 360 Gigs of RAM presented to the VM.

The answer is not trivial, making this an interesting question.

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Database In Recovery

Published 2016-03-24 by Kevin Feasel

James Anderson had a database which would drop into In Recovery mode a few times throughout the day:

The database in question wasn’t stuck in recovery, it would slip in and out of the status throughout the day. Normally, I would only ever expect to see a database in recovery during a restore or after a service restart. Once recovery is complete, I would not expect to see the database slip into ‘in recovery’ again. I especially wouldn’t expect a database to keep slipping in and out of recovery.

The answer is a true head-slapper.  Whose head, I’ll leave up to you…

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Optimizing OR Clauses

Published 2016-03-24 by Kevin Feasel

Daniel Hutmacher looks at different ways of optimizing queries with multiple conditionals and different parameters:

The SQL Server query optimizer can find interesting ways to tackle seemingly simple operations that can be hard to optimize. Consider the following query on a table with two indexes, one on (a), the other on (b):

SELECT a, b
FROM #data
WHERE a<=10 OR b<=10000;

The basic problem is that we would really want to use both indexes in a single query.

We get to see a few different versions of the query as well as the execution plans which result.

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Using The OUTPUT Clause

Published 2016-03-24 by Kevin Feasel

Steve Jones shows how to use the OUTPUT clause with an INSERT statement:

I got asked a question about the OUTPUT clause recently and realized I didn’t remember the syntax. I’ve rarely used this, so I had to look it up and thought this would be a good basic post.

The idea with OUTPUT is that the data from the inserted and deleted tables can be output from the INSERT statement, outside of your triggers. This is the same data, but you can access it in the insert.

The format is

INSERT xxx OUTPUT yyyy INTO @zzz VALUES (or SELECT) mmmm

If I had one thing I could change about OUTPUT, I’d like to be able to output directly into variables for those cases in which I know I’m only going to get one result (or maybe I only care about one arbitrary result in a set).

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Graphing CPU Utilization

Published 2016-03-24 by Kevin Feasel

Slava Murygin uses spatial data types to graph CPU utilization on a SQL Server instance:

That diagram provides you about 260 last minutes of Server CPU usage and measured in percents.

As you can see my SQL Server is mostly doing nothing and only during that blog-post writing in the last half and hour or so it is heavily running test scripts to over-utilize my CPU, but it still barely goes more than 60% of CPU (Blue line).

The Red line represents all other processes besides of SQL Server and you can tell if anything else from outside is impacting your performance.

Combined with Glenn Berry’s diagnostic queries, you could generate some quick analytics.  I’d still use R for anything more than slightly complicated, but this is great for those environments in which you don’t have good alternative tooling.

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