Posts by Kendra Little

Dropping an Offline Database in SQL Server

SQL Server
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When you drop a database in SQL Server, the files are normally removed from the file system right away. POOF! Hope you had a backup if you ran DROP DATABASE against the wrong instance. However, things are a little different if you take the database offline before you drop it. Consider the following code: Transact-SQL…
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The Hard Truth About Patching SQL Server Availability Groups (Hotfixes, Cumulative Updates, and Service Packs)

Whoa, be careful with that fix As a DBA, you’re responsible for identifying necessary updates to keep your SQL Servers healthy. Your business may have some mandates about the frequency of patches, but even if they don’t, you have a duty to look out for Cumulative Updates, Service Packs, and out of band hotfixes that can prevent…
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Failing over an Asynchronous Mirror in SQL Server (video)

Database Mirroring
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Will a long running open transaction block you from changing to synchronous mode and failing over to your SQL Server database mirror? Join Kendra to test performing a planned failover from an asynchronous database mirror. Brent Says: Often, when I’m working with developers, they’re totally surprised that SQL Server’s failover methods all break in-flight transactions. No matter…
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Testing ALTER INDEX REBUILD with WAIT_AT_LOW_PRIORITY in SQL Server 2014

One of the blocking scenarios I find most interesting is related to online index rebuilds. Index rebuilds are only mostly online. In order to complete they need a very high level of lock: a schema modification lock (SCH-M). Here’s one way this can become a big problem: An online index rebuild starts against a large index A…
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What is the PREEMPTIVE_DEBUG Wait in SQL Server?

SQL Server
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Recently we got an email asking for help from a DBA who was concerned about a high percentage of the PREEMPTIVE_DEBUG wait on a SQL Server. They were investigating poor performance and had searched the internet high and low and not found information on what this wait means. They were stumped. What to Do When You Find an Unusual…
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Read Committed Snapshot Isolation: Writers Block Writers (RCSI)

When learning how Read Committed Snapshot Isolation works in SQL Server, it can be a little tricky to understand how writes behave. The basic way I remember this is “Readers don’t block writers, writers don’t block readers, but writers still block writers.” But that’s not so easy to understand. Let’s take a look at a simple test…
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The Most Confusing Words, Phrases, and Acronyms in SQL Server

Humor
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Words are hard. Acronyms are even harder. Here’s the words that give me the most trouble when talking to people about SQL Server. And thanks to all my Twitter friends quoted here for their suggestions! Replication “I have a question about replication…” “Which kind? Transactional? Merge? Peer to Peer?” “Availability Groups.” Technically, the word “replication”…
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Rebuild or Reorganize? How to Set Up Index Maintenance in SQL Server (video)

SQL Server
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Index maintenance is confusing. Should you use maintenance plans or customized SQL Agent jobs? Join Kendra to learn the difference between index ‘rebuild’ and ‘reorganize’ commands, and how to avoid the pitfalls of maintenance plans in SQL Server. Interested in trying out sp_BlitzTrace™ yourself? Download it in our free SQL Server download pack. You can…
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Transactional Replication Architecture: Isolating Subscriber Tables

Replication
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The best part about transactional replication is that it’s flexible. And the worst thing about transactional replication is that it’s flexible. A poor replication configuration will cause you performance pains and increase your risks of development and administrative errors. Here’s one important design principle: isolate your replication subscriber tables from one another, and from non-subscriber tables.…
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SQL Server’s Cost Threshold for Parallelism

SQL Server
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“Should a query get to use more than one CPU core?” That’s an important question for your SQL Server. If you’re not sure what parallelism is, get started by exploring the mysteries of CXPACKET with Brent. He’ll introduce you to the the setting, ‘Cost Threshold for Parallelism’. Let’s test Cost Threshold for Parallelism I generate an estimated…
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What Changed Our Career Trajectories?

SQL Server
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Jeremiah has coffee at the PASS Summit We’re a group of specialists and teachers here at Brent Ozar Unlimited. But we didn’t start that way– we started out as engineers and developers. So what was it that changed our career trajectories? For each of us, we had a lot of smaller factors along the way, but…
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