MSTechEd Europe 2012 Pre-Con: SQL Server Performance Tuning and Optimization - It all depends...

Yesterday I was at the Pre-conference Day at the MSTechEd Europe. I learned a lot during the session and tried to make some useful notes so I can use them for later reference. Specially the part on DMVs was very useful, I didn't use them before and certainly am checking them in the next weeks!

By Denny Cherry and Thomas LaRock

1. Identifying performance bottlenecks

Tools used:

- Performance Monitor

- Activity Monitor

- DB Tuning Advisor (DTA)

- Data collection

- Profiler

- SQLTrace

- Dynamic Management Views (DMVs)

- Extended Events (xEvents)

Blocking processes / wait events (running, runnable, waiting) aren't shown in Profiler (= SQLTrace + visualization). Those can be shown with the xEvents Wizard under Management in SSMS. Always tune it to your needs, never use a default (See PAL).

Summary:

- Define the problem

- Decide for tool with the best metrics and least (perf.) cost

- Consider the time needed to analyze

- It depends..

2. Index optimization

1. Indexing

- Started at design time

- Data types matter!

- Changes over time

- First line of defense for (quick) perf. Tuning

Do we have the right indexes?

- It depends..

- Follow best practices

- Use DMVs for missing indexes

- Focus on Logical IO (Inside SQL Server 2005: T-SQL Querying by Itzik Ben-Gan)

SQL Diagramming > table with highest selectivity of data

Index seek is better than Index scan.

If an index has only writes and no reads > delete the index

2. Execution Plans

Look for:

- Correlation with wait events

- Examine first operator (Select | Update | ..)

- Warnings (missing index)

- "More costly"  operators: LIKE > Spool uses tempdb

- "Fat fingers": thick arrows means lots of rows

- Looking at the #rows in

□ An index > update statistics

□ Hash match > input vs output rows (do nothing)

3. Filtered Indexes

An index with a filter (where clause), but no extended logic (e.g. OR)

4. ColumnStore Indexes

- Based on the xVelocity in-memory analytics engine (a.k.a. Vertipaq)

- CREATE COLUMNSTORE INDEX [COLUMNS]

- Downside: the table is read-only, workarounds:

□ Delete index > load data > create index

□ Use 2 tables, 1 read-only and 1 read/write table

3. Storage optimization

1. Table partitioning

- Reduce maintenance window

- Improve query response time

- Reduce recovery time

Create filegroups, a partition function and a scheme referencing the function.

Business (logic) knowledge is essential before starting partitioning!

When moving data: meta data (page headers) is updated

When deleting data: 

- Move partition to another table > then truncate (faster and save)

- Also getting data back that shouldn't be deleted is faster. Let the data stay in the other table for a few days before actually deleting it.

2. AlwaysOn (Enterprise feature)

- No need for shared storage

- Offload backups

- Scaling out read-only activity

4. Troubleshooting

- Are all queries running slow?

- Use xEvents with DMVs

- Is a subset of queries running slow?

- Use Executions plans with DMVs

Useful DMVs:

- Sys.dm_exec_query_stats

- Sys.dm_exec_query_plan

- Sys.dm_exec_cached_plans

STATISTICS IO ON

STATISTICS TIME ON

Using GO 10 after a SQL statement will execute the statement 10 times, useful when inserting data.

Resources mentioned can be found @ http://mrdenny.com/res/teched-2012-precon