There have been a large number of posts made regarding the interaction between full database backups and the log chain (like this one). However there still seems to be a lot of confusion around regarding how they interact. I doubt I can clear up the confusion with yet… Read more

A while back I wrote up a short introductory overview of Genetic Algorithms. Just for the shear, absolute fun of it, I thought I’d implement a basic genetic algorithm within SQL Server and use it to solve a form of the knapsack problem.

Now first a few comments… Read more

This one comes up a lot on the forums, often as advice given…

“You should use integers for the key rather than strings. The joins will be faster.”

It sounds logical. Surely integers are easier to compare than large complex strings. Question is, is it true?

This is going to… Read more

I was guest presenter on last week’s Quest Pain of the Week presentation. The presentation is available for download from Quest. This is a roundup of the questions from the presentation. (I have edited some of the questions for spelling, grammar and readability)

Q: Why do you have to wait… Read more

I see a lot of advice that talks about the clustered index been the best index for use for range queries, that is queries with inequalities filters, queries that retrieve ranges of rows, as opposed to singleton queries, queries that retrieve single rows (including, unfortunately, a Technet article).

I… Read more

It’s looking like it’s going to be a busy year.

It’s only January and I already have three presentations lined up for the first quarter of the year.

• On the 10^th February I’m presenting on database corruption for Quest’s Pain of the Week webcast. I’m not Paul Randal,…

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This is going to be a quick one…

I keep seeing forum code (and production code) that includes the DISTINCT in IN or EXISTS subqueries. The rationale is given either as a performance enhancement or as necessary for correct results.

Is it necessary or useful? Only one way to find… Read more

One last post on execution plans and Profiler (at least for now)

When trying to check a query’s execution plan, the display execution plan option of Management Studio is usually adequate, however there are occasions where it’s either not feasible to run the query from Management Studio or the particular… Read more

I heard this one over at SSC a while back. “Avoid IF statements in stored procedures as they result in recompiles”

Ok, it sounds reasonable, if the optimiser optimises for the execution path taken on first execution it’ll have to go back and optimise the other paths when they are… Read more

I’ve looked at cache hit and miss events and at the cache insert and remove events. The only cache-monitoring event (of current interest) left is the recompile event.

There are two recompile events available in Profiler in SQL 2008

• SP:Recompile under Stored Procedures
• SQL:StmtRecompile under T-SQL

Which to use when? Read more

SELECT @@Version

Microsoft SQL Server “Denali” (CTP1) – 11.0.1103.9 (X64)

I’ve been playing with the CTP for a few days (with absolutely no documentation) and there are a few fun and interesting things that I found. These may not be earth-shattering changes, but they are interesting, and I don’t doubt… Read more

So, it’s the second Tuesday of the month again, and it’s time for T-SQL Tuesday again. This month it’s hosted by Sankar Reddy and the topic is “Misconceptions in SQL Server”

I thought I’d tackle a trio of table variable myths and partial truths.

Table Variables are memory-only

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Or “If one index is good, surely many indexes (indexes? indices? indi?) will be better”

This is a question that comes up very often on the forums. Something along the lines of:

I have a query with multiple where clause conditions on a table. Should I create one…

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Or “Plan cache monitoring – insert and remove”

Previously I took a look at the CacheHit and CacheMiss events to see how they behave and how to identify what’s been searched for in the cache. in this follow up, I want to take a similar look at the… Read more

Or “Monitoring plan cache usage”

For people interested in the details of how SQL is using and reusing execution plans, there are some useful events in profiler for watching this in detail, under the Stored procedure group:

• SP:CacheMiss
• SP:CacheInsert
• SP:CacheHit
• SP:CacheRemove
• SP:Recompile
• SP:StmtRecompile

Additionally there’s the SQL:StmtRecompile event… Read more

Short answer: No

I keep seeing this come up on various forums when people ask what makes a database go suspect or what could have caused their database to be marked suspect. I can almost guarantee when that question comes up, one or more people will answer ‘missing files’. That… Read more

On the first day of DBA hell, the server gave to me
A database with damaged system tables and no good backups (1)

On the second day of DBA hell, the server gave to me
Two databases with widespread corruption, no backups (1, 2)

On… Read more

Over the last several months I’ve had a look at IN, Exists, Join and their opposites to see how they perform and whether there’s any truth in the advice that is often seen on forums and blogs advocating replacing one with the other.

Previous parts of this series can be… Read more

And to wrap up the miniseries on IN, EXISTS and JOIN, a look at NOT EXISTS and LEFT OUTER JOIN for finding non-matching rows.

For previous parts, see

• In vs Exists
• In vs Inner Join
• Not in vs Not Exists

I’m looking at NOT EXISTS and LEFT OUTER JOIN, as… Read more

Or “Shot gun query tuning”

There have been a fair few forums questions in recent months asking for help in removing index scans, loop joins, sorts or other, presumed, slow query operators. There have been just as many asking how to replace a subquery with a join or… Read more