How to Choose Between RCSI and Snapshot Isolation Levels

SQL Server offers two flavors of optimistic locking for traditional disk-based tables: Read Committed Snapshot Isolation (RCSI), and Snapshot Isolation. They are each great tools to reduce blocking and make applications faster, particularly in databases that have lots of tiny reads and writes that need to be quick, or mixed-use patterns (lots of little reads and writes + larger reporting queries).

Both isolation levels are available in SQL Server Standard Edition and Web Edition as well as Enterprise. That’s right, they’re cheap and easy. Each of them are controlled by database level settings, and default to disabled for new user databases when you install SQL Server and leave the default settings on the model database.

When should you pick one or the other? And when might you enable both?

Continue reading

The #1 Thing to Never Do to Fix a Performance Problem

Never, ever, disable backups to fix a performance problem.

If you’re not having a performance crisis, you might look at that sentence and say, “Wow, that’s super dumb! Who would ever do that?”

Well, a lot of people, actually. It’s pretty common.

Continue reading

Why ROWLOCK Hints Can Make Queries Slower and Blocking Worse in SQL Server

Sometimes when SQL Server gets slow, developers and DBAs find that the problem is blocking. After lots of work to identify the query or queries which are the blockers, frequently one idea is to add ROWLOCK hints to the queries to solve the problem or to disable PAGE locks on the table. This often backfires - here’s why.

Continue reading

Sliding Window Table Partitioning: What to Decide Before You Automate

Before you do all the work to map out a complex sliding window table partitioning scheme for your SQL Server tables, here’s the top five questions I’d think through carefully:

1) Do You Need Table Partitioning?

Some folks think they need partitioning for performance– but it really shines as a data management feature. Just because you’ve got tables with millions of rows in them doesn’t necessarily mean that partitioning will make queries faster. Make sure you’ve worked through traditional indexing and query re-writes first. Partitioning is lots of work, so don’t skip this question.

Continue reading

Does Query Store Regressed Queries View Catch Nasty Parameter Sniffing?

SQL Server 2016’s new Query Store feature has an option that looks for “regressed” query plans.

But does it catch “bad” parameter sniffing?

Continue reading

How to Find Missing Index Requests in Query Store

SQL Server 2016’s new Query Store feature makes it easier than ever for DBAs and developers to identify the most important queries to tune– and perhaps apply a quick fix by pinning an execution plan.

Continue reading

Useful Whitepapers for Planning SQL Server Migrations

Planning to move to new hardware for your SQL Server? Techniques like log shipping and database mirroring can be incredibly useful to make the change fast and painless– but you’ve got to pick the right techniques for your environment ahead of time, and know how to do a few things that aren’t in the GUI.

Here are some of my favorite whitepapers and resources to get you going.

Continue reading