1. Microsoft ASP.NET Connections
Plan Guides
Jeremy Lowell
Data Realized
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2. Microsoft ASP.NET Connections
Agenda
Who is it for?
Why do they exist?
What is it?
Query processing
Query Plans
Plan Guides
Demo
Why do they exist? Remember 6.5 to 7.0
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3. Microsoft ASP.NET Connections
Overview
Plan Guides
Why?
Increased complexity in database environments today
Linq to SQL
C.O.T.S. implementations
Commercial-off-the-shelf
Proactive vs. Reactive
Who?
Database Administrators
Database & BI Developers
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4. Microsoft ASP.NET Connections
Plan Guides
What are they?
Plan Guides can be used to optimize the performance of queries when you cannot or do not want to change the text of the query directly.
Plan guides can be useful when a small subset of queries in a database application deployed from a third-party vendor are not performing as expected.
Plan guides influence optimization of queries by attaching query hints or a fixed query plan to them. -- Microsoft
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5. Microsoft ASP.NET Connections
Query Plans
Query Processing
Many ways to get data from the source :: linq to sql, ad-hoc, prepared, cots implementations etc….
*** SQL server will always look to the cache store before generating a new plan.
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6. Microsoft ASP.NET Connections
Query Plans
Creation
One note of importance::
SQL Server uses the optimal access plan, but query optimization is limited by what is possible.
Meaning… Even a great optimizer can’t always make poor code run efficiently.
Optimizer
Evaluates
Keys
Indexes
Clustered
Non-clustered
Cardinality (selectivity)
Quantity of data
Statistics
Etc…
Generates Query Plan
Execution context (parameter variables)
Stores Query Plan in Cache
This is where it gets FUN!
Known as Procedure Cache, Statement Cache, Plan Cache etc…
When a query plan is created….
Optimizer will evaluate the plan and take many things into account when it does that.
They include keys, indexes etc….
PAUSE!!!! Questions!!!
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7. Microsoft ASP.NET Connections
Query Plans
Cache
Hard to “see” the cache in memory on a server…
dbcc proccache
num proc buffs num proc buffs used num proc buffs active proc cache size proc cache used proc cache active
num proc buffs
Total number of pages used by all entries in the procedure cache.
num proc buffs used
Total number of pages used by all entries that are currently being used.
num proc buffs active
For backward compatibility only. Total number of pages used by all entries that are currently being used.
proc cache size
Total number of entries in the procedure cache.
proc cache used
Total number of entries that are currently being used.
proc cache active
For backward compatibility only. Total number of entries that are currently being used.
Updates will be available at _06/ASP_Connections

8. Microsoft ASP.NET Connections
Query Plans
Cache
DMV’s
SELECT cacheobjtype,objtype, sum(refcounts) as TotalRefcounts, sum(usecounts) as TotalUseCounts from sys.dm_Exec_Cached_plans
group by cacheobjtype,objtype
cacheobjtype objtype TotalRefcounts TotalUseCounts
Parse Tree View
Compiled Plan Proc
Compiled Plan Trigger
Extended Proc Proc
Compiled Plan Adhoc
Parse Tree UsrTab
Compiled Plan Prepared
Parse Tree Check
Refcounts
Number of cache objects that are referencing this cache object.
UseCounts
Number of times this object has been used since it has existed in cache
Cacheobjtype
Type of object in cache
Ojbtype
To get a count of the number of compiled plans –
View, Proc, Trigger, Proc (extended), Adhoc, Prepared, Check, UsrTab
Updates will be available at _06/ASP_Connections

9. Microsoft ASP.NET Connections
Query Plans
Cache
DMV’s
Return attributes for a specific plan
SELECT plan_handle, refcounts, usecounts, size_in_bytes, cacheobjtype, objtype FROM sys.dm_exec_cached_plans; GO SELECT attribute, value, is_cache_key FROM sys.dm_exec_plan_attributes(<plan_handle>);
Set options
SELECT plan_handle, pvt.set_options, pvt.sql_handle FROM ( SELECT plan_handle, epa.attribute, epa.value FROM sys.dm_exec_cached_plans OUTER APPLY sys.dm_exec_plan_attributes(plan_handle) AS epa WHERE cacheobjtype = 'Compiled Plan' ) AS ecpa PIVOT (MAX(ecpa.value) FOR ecpa.attribute IN ("set_options", "sql_handle")) AS pvt;
Optimizer info
select * from sys.dm_exec_query_optimizer_info
Memory breakdown of all cached complied plans
SELECT plan_handle, ecp.memory_object_address AS CompiledPlan_MemoryObject,
omo.memory_object_address, pages_allocated_count, type, page_size_in_bytes
FROM sys.dm_exec_cached_plans AS ecp JOIN sys.dm_os_memory_objects AS omo
ON ecp.memory_object_address = omo.memory_object_address
OR ecp.memory_object_address = omo.parent_address
WHERE cacheobjtype = 'Compiled Plan’ order by page_size_in_bytes desc
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10. Microsoft ASP.NET Connections
Query Plans
Cache
DMV’s
SELECT st.text, cp.usecounts, cp.size_in_bytes, cp.cacheobjtype, cp.objtype from sys.dm_exec_cached_plans cp
cross apply
sys.dm_exec_sql_text(cp.plan_handle) st order by cp.usecounts desc
Sql_text usecounts size_in_bytes cacheobjtype objtype
create procedure [dbo]… Compiled Plan Proc
CREATE PROC [dbo]… Compiled Plan Proc
CREATE PROC [dbo]… Compiled Plan Proc
CREATE PROCEDU [db Compiled Plan Proc
CREATE FUNC [dbo]… Compiled Plan Proc
nvarch… Compiled Plan Prepared
int)SELECT [t0].[… Compiled Plan Prepared
sys.dm_exec_sql_text(cp.plan_handle)
Imagine the possibilities!!
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11. Microsoft ASP.NET Connections
Query Plans
Cache
Top 10 ….
Physical Reads
select top 10 substring(st.text, (qs.statement_start_offset/2) + 1, ((case statement_end_offset when -1 then datalength(st.text) else qs.statement_end_offset end - qs.statement_start_offset)/2) + 1) as statement_text, *
from sys.dm_exec_query_stats qs cross apply sys.dm_exec_sql_text(qs.sql_handle) st
where execution_count > 1 and dbid = 5 order by total_physical_reads desc
Max Physical Reads
order by max_physical_reads desc
Max Logical Reads
Order by max_logical_reads desc
Max Logical Writes
Order by max_logical_writes desc
Total Elapsed time
Max Elapsed time
Etc….
Updates will be available at _06/ASP_Connections

12. Microsoft ASP.NET Connections
Query Plans
Cache
Things to look for :
Determine if the adhoc or dynamic statements are generating plans that are re-used, or in this case, not being re-used.
select Count (*), refcounts, usecounts, objtype, left(text,50) from sys.dm_Exec_cached_plans cross apply sys.dm_exec_sql_text(plan_handle)
where cacheobjtype = 'Compiled Plan’ and objtype = 'Adhoc' and usecounts = 1
group by refcounts, usecounts, objtype, left(text,50) order by 1 desc
Count Refcount Usecount objtype sql – first 50 characters….
Adhoc Select DISTINCT TOP 100 W…………..
Adhoc SELECT TOP 1000 W……….
Adhoc select distinct top v.W………
Means that there are 4811 plans for three nearly identical statements
Significant memory required for caching plans
Finite amount of cache for plans
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13. Microsoft ASP.NET Connections
Query Plans
Cache
Life of…
Execution cache is re-cycled based on age, usage and statistics they are dependent upon
Engine will not always choose “best” plan; rather it will find a balance between the best plan and one quick to create and easy to maintain.
The algorithms to match new SQL statements to existing, unused execution plans in the cache require that all object references be fully qualified. For example, the first of these SELECT statements is not matched with an existing plan, and the second is matched:
SELECT * FROM Contact
SELECT * FROM Person.Contact
Execution plan is marked for de-allocation from cache when the following is true:
The memory manager requires memory and all available memory is currently being used.
The age field for the object is 0.
The object is not currently referenced by a connection.
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14. Microsoft ASP.NET Connections
Query Plans
Cache
Recompile
Use Profiler to determine reason: BOL has great explanations.
Changes made to a table or view referenced by the query (ALTER TABLE and ALTER VIEW). Changes to any indexes used by the execution plan. Updates on statistics used by the execution plan, generated either explicitly from a statement, such as UPDATE STATISTICS, or generated automatically.
Dropping an index used by the execution plan.
An explicit call to sp_recompile.
Large numbers of changes to keys (generated by INSERT or DELETE statements from other users that modify a table referenced by the query).
For tables with triggers, if the number of rows in the inserted or deleted tables grows significantly.
Executing a stored procedure using the WITH RECOMPILE option.
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15. Microsoft ASP.NET Connections
Query Plans
Cache
Parameterization
Simple (Default)
SQL 2k – known as Auto-Parameterization
Enables the engine to better match queries and their plans
SQL Server parameterizes a relatively small set of queries
Example :
SELECT * FROM AdventureWorks2008.Production.Product WHERE ProductSubcategoryID=1;
This query will be parameterized by the engine at compile time.
SELECT * FROM AdventureWorks.Production.Product WHERE ProductSubcategoryID = 4;
This query will use the same plan.
More complex statements may not be parameterized.
Statements which reference more than one table.
Delete or update with a from clause
Many more …
Forced
Under the default behavior of simple parameterization, SQL Server parameterizes a relatively small class of queries.
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16. Microsoft ASP.NET Connections
Query Plans
Cache
Parameterization
Forced Parameterization
Forces all statements to be parameterized.
Any literal value will be parameterized with many exceptions.
Xquery, Cursors, ANSI_PADDING or ANSI_NULLS set to OFF.
The TOP, TABLESAMPLE, HAVING, GROUP BY, ORDER BY, OUTPUT...INTO, or FOR XML clauses of a query; Statements that reference variables, ETC….
Alter Database <name> SET parameterization FORCED / SIMPLE
Decreases compilations – increases concurrency
Quite a few “does this”, “does not do this” set’s of rules.
Ensure that you test it on your unique situation and reference the link above.
-- Forced PARAMETERIZATION
Very powerful option – Take heed to test this thoroughly. Works great for some things, not so great for others.
Reference BOL for all of the “does this”; “does not do this” set of rules…. Too many to get into during this session.
However, you can specify that all queries in a database be parameterized, subject to certain limitations, by setting the PARAMETERIZATION option of the ALTER DATABASE command to FORCED.
Doing so may improve the performance of databases that experience high volumes of concurrent queries by reducing the frequency of query compilations.
Segue :::
PLAN GUIDES
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17. Microsoft ASP.NET Connections
Plan Guides
Creation
Context
OBJECT Plan Guide
Stored proc’s, UDF’s, Triggers (dml), CTE’s, etc…
SQL Plan Guide
t-sql statements (dynamic, ad-hoc, prepared etc…)
Template Plan Guide
Standalone queries that parameterize to a specified form.
These can OVERRIDE the parameterization setting.
The PARAMETERIZATION database option is SET to FORCED, but there are queries you want compiled according to the rules of simple parameterization.
The PARAMETERIZATION database option is SET to SIMPLE (the default setting), but you want forced parameterization to be attempted on a class of queries. (
Many ways to get data from the source :: linq to sql, ad-hoc, prepared, cots implementations etc….
SQL server will always look to the cache store before generating a new plan.
Updates will be available at _06/ASP_Connections

18. Microsoft ASP.NET Connections
Plan Guides
Demo
Create an object plan guide
Disable the Plan Guide
Enable the Plan Guide
Drop the Plan Guide
View the Plan Guides
Create a SQL plan guide
Create a Template plan guide
Create a SQL plan guide using XML_SHOWPLAN
Create a Plan guide against an existing query plan.
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19. Microsoft ASP.NET Connections
Plan Guides
Profiler
Capture event
SQL:BatchStarting
Extract event data to a file ** Open in Notepad
Must be exact spacing
Exception is to escape ‘ ‘s
Demo …
Validation
Performance category >> Plan_Guide_Successful & Plan_Guide_Unsuccessful
Perfmon
Guided Plan Executions/sec & MisGuided Plan Executions/sec
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20. Microsoft ASP.NET Connections
Questions
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21. Your Feedback is Important
Microsoft ASP.NET Connections
Your Feedback is Important
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Contact:
Updated Slides – Page 1 of the schedule guide
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