I will be giving a presentation in between Earthquakes and Hurricanes in Charlotte NC. this Wednesday the 31st of August on Understanding Indexes in SQL Server 2008. If you are in the area please drop by and say hello. You can find out more information and register for the event here. Andy

The following table summarizes the results from my last two blog entries, showing the CPU time used when performing 5 million clustered index seeks: In test 1, making the clustered index unique improved performance by around 40%. In test 2, making the same change reduced performance by around 70% (on 64-bit systems – more on that later).  ...

I had a discussion with a friend in Microsoft  IT this morning, and as we were evaluating some query plans we ran into more clustered index woes. Remember that clustered indexes affect the base table itself (which is why there can be only one) and are expensive to update. They are fantastic for reading data, but you need to carefully evaluate ...

Ola has a set of stored procedures to do maint operations, see http://ola.hallengren.com/. Ola has now updated them to support exclusions or inclusions of tables, indexes or even whole schemas from index rebuild/reorg. Check out http://ola.hallengren.com/Documentation.html#SelectingIndexes for info on how to define exclusions and ...

You know the answer already: It depends. But I often see some percentage value quoted and the point of this post is to show that there is no such percentage value. To get the most out of this blog post, you should understand the basic structure for an index, i.e. how the b+ tree look like. You should also understand the difference between a ...

I just read in a forum about a user who want to replikate a table, but the table doesn't have a PK. The table is pretty large, and having the table not available while adding the PK is undesireable. The table has a clustered index already, and there are other columns which are known to be unique (presence of unique indexes). What I ...

One of the questions I was asked recently while speaking at user groups, was regarding the order that jobs like rebuilding indexes or updating statistics should be performed as part of the database maintenance activities. Then I started writing this post about this topic on the weekend but was interrupted several times, including one of them to ...

Since I will be speaking about the Query Optimizer at the coming PASS Summit, I have been preparing my presentation and at the same time blogging about it. This time I will describe the Missing Indexes feature, seen from the point of view of the Query Optimizer.   We know that it is the job of the Query Optimizer to find an efficient ...

Let's start with some background on forwarding pointers: Forwarding pointers in heaps can be a mess to get rid of. A forwarding pointer happens when you modify a row so that the row doesn't fit on the same page anymore. SQL Server moves the row to a new page and leaves a forwarding pointer where the old row used to be. This means that ...

Everyone should know by now how really useful the DMVs dm_exec_query_stats, and dm_db_index_usage_stats and the associated DMFs for obtaining the SQL and XML plan: dm_exec_sql_text, dm_exec_query_plan, and dm_exec_text_query_plan. Of course it has been explained that dm_exec_query_stats is not a replacement for SQL Server Profiler and SQL Trace. ...