Transcript Sys.dm_exec_sessions - Data Platform Knowledge Sharing Network

May 08 – 09 2012, Kongresshaus Berchtesgaden
SQL Server DMVs - Best of the Bunch.
Troubleshoot Your Data Platform Like
a Pro
@sqlmaster
Satya SK Jayanty
Director & Principal Architect
D BI A Solutions
About me

IT Experience
 Principal Architect & Consultant – D Bi A Solutions : Europe
([email protected])
 Been in the IT field over 20+ years (using SQL Server ver.4.2 onwards)

Publications
 Author: Microsoft SQL Server 2008 R2 Administration cookbook –
Packt Publishers (May 2011)
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Co-author for MVP Deep Dives Volume II – Manning Publications (October 2011)
Community Contributions
 SQL Server MVP since 2006
 Founder (SQLMaster) & blogs at www.sqlserver-qa.net (SQL Server Knowledge
Sharing Network)
 Contributing Editor & Moderator - www.sql-server-performance.com [SSP]
 Quiz Master & Blogger: www.beyondrelational.com & www.sqlservergeeks.com
 Active participation in assorted forums such as SSP, SQL Server Central, MSDN,
SQL Server magazine, dbforums etc.
www.sqlserver-qa.net
@sqlmaster
www.packtpub.com
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@sqlmaster
Agenda….
 None…!
 Nearly 300 DMVs to cover, not possible with 1 hour
presentation.
 Highlight most useful ones on the Data platform.
 DBA… Developers & Architects with relevant
privileges.
 Bound on permission levels.
 Playing through some code….
 Sharing on what I use on in my regular Consulting
engagements.
Where to start?
 SQL Server gets blame for every problem!
 Query running slow, connection timeout, unresponsive?
 Remember SP_WHO and SP_WHO2?
 Do you need third party tools?
 Think Performance/Monitoring…. Think DMVs
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SQL Server 2005 onwards… better way ahead
Most of the SQL Server Management Studio actions
DMV’s tour – long way to go
Implement recommended practices
Performance
Monitoring
Action
Monitor
Tuning Life Cycle
Analysis
Collect
Just a beginning…
 DMO – Dynamic Management Objects?
 …..no Distributed Management Objects!
 DMV – Dynamic Management Views
 DMF – Dynamic Management Functions
Permissions, if not SA
 VIEW SERVER STATE :: VIEW DATABASE STATE
2012
 Login :: User
 Now let us cover commonly used by DBAs.. Best of the bunch.
How do you pick best of the bunch?
Divide and Rule!
 Pick important problems in your data platform!
 Divide problem into 4: CPU, IO, Network & Memory
 Additionally query statistics to fine tune
 DMVs to offer helping hand on each of them.
 Sessions: Transactions
 Fragmentation: Index statistics, missing indexes
 Statistics: Waits, Query, Index usage
Sys.dm_os_wait_stats
 Wait stats – waiting for resource.
 To watch sum(time) and max(time)
 SQL2008 R2 consist 294 & now SQL2012 = 359
 Wait values to watch
 LOGMGR_QUEUE
 DBMIRROR_WORKER_QUEUE
 ONDEMAND_TASK_QUEUE
Sys.dm_os_wait_stats
 Resources
 Network: async network io (SQL2008+) & networkio
(SQL2000).
 Gets accumulated data…on resources.
Still waiting… Sys.dm_os_wait_stats
 CXPACKET & SOS_SCHEDULER_YIELD
 CPU is suffering
 Adding CPUs – rather reduce CPU intensive queries
 PAGEIOLATCH_*
 Hard disks & Disk IO is a problem
 Watch for other IO intensive processes on Windows
 Locking waits look for LCK_M_*
 Indicates transaction contention
 See whether non-SQL Server applications grabbing
resources
 So about wait tasks, now let’s see waiting tasks!
Sys.dm_os_waiting_tasks
 Good to get query specific performance problems
 Good one to capture blocking on instance
 Capture user sessions on query specific
 Join with dm_exec_sql_text gives sql_handle to get
handful statistics on problem
Sys.dm_exec_query_stats
 Gets cached query plans
 When used with sys.dm_exec_sql_text
sql_handle is best to obtain statistics
 To find if query is CPU bound then look for
total_worker time
 Best one to differentiate number of writes and reads
on database level
 SQL2012 – find queries returning large number of
rows
 total_rows, min_rows, max_rows and last_rows aggregate
row count columns.
Sys.dm_exec_sessions
 Session information – server scope view
 Extra information common criteria compliance
enabled, logon statistics displayed:
 last_successful_logon
 last_unsuccessful_logon
 unsuccessful_logons
 What’s new SQL2012: open_transaction_count
 removing the last of the reasons you ever needed to use:
• select * from sys.sysprocesses
Cardinalities..
From
To
On/Apply
Relationship
sys.dm_exec_sessions
sys.dm_exec_requests
session_id
One-to-zero or one-tomany
sys.dm_exec_sessions
sys.dm_exec_connectio session_id
ns
One-to-zero or one-tomany
sys.dm_exec_sessions
sys.dm_tran_session_tr session_id
ansactions
One-to-zero or one-tomany
sys.dm_exec_sessions
sys.dm_exec_cursors(se session_id CROSS APPLY One-to-zero or one-tossion_id | 0)
OUTER APPLY
many
sys.dm_exec_sessions
sys.dm_db_session_spa session_id
ce_usage
One-to-one
Sys.dm_exec_requests
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Similar to SP_WHO2 and active requests are resulted
No need DBCC INPUTBUFFER (still lives in SQL2012)
Good to get blocking chain
Find backup & restore operation look into
percent_complete column
 No need to look into sysprocesses catalog view as
 sys.dm_exec_sessions,
sys.dm_exec_sessions and
sys.dm_exec_requests are best ones.
Index usage statistics
 Identify the used and unused indexes
 How to track about all indexes and heaps on the
database?
 Best to run number of times (busy and calm) in
benchmarking the performance.
 …mix and match with missing indexes.
sys.dm_db_index_physical_stats
 Remember DBCC SHOWCONTIG … forget about it!
 Returns fragmentation statistics .
 Helpful to obtain how often indexes need to be
rebuilt based on how frequently they become
fragmented.
 Tables with frequent insert/update/delete
operations.
 Best to run number of times (busy and calm) in
benchmarking the performance
 …mix and match with missing indexes.
sys.dm_db_index_physical_stats
 What to look for…
 avg_fragmentation_in_pct for logical for indexes and
extent fragmentation for heaps.
 Shows information index_id=0, HEAP & index_id=1,
Clustered Index
 Based on the fragmentation level schedule the REBUILD &
REORG operations.
• ALTER INDEX … REORGANIZE
• ALTER INDEX … REBUILD
• ALTER INDEX … REBUILD ALL
Good to use
SORT_IN_TEMPDB &
improve the contiguity
of index extents. OFF
by default
Still on…
 To use:
Select * from sys.dm_db_index_physical_stats
(db_id(),OBJECT_ID(‘dbo.person'),NULL,NULL,NULL)
 Scan depth used:
 LIMITED – faster and default
 SAMPLED – 1% of leaf pages
 DETAILED – heavy IO operation
 Statistics are fine, how about obtain missing indexes
information.
Missing Indexes feature
 To start with:
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sys.dm_db_missing_index_columns
sys.dm_db_missing_index_group_stats
sys.dm_db_missing_index_groups
sys.dm_db_missing_index_details
 Good with INCLUDE columns -- suggestions
 Only non-clustered indexes (no spatial indexes)
 Statistics are retained until index is rebuilt or service
is restarted.
 Use it wisely…. Don’t over use
sys.dm_db_index_usage_stats
 Finds index access information
 Eliminate built-in indexes OBJECTPROPERTY([object_id], 'IsMsShipped') = 0
 What to look
That index
hasn’t
been used
for:
at all!
 0 or no values:
• user_lookups,
• user_seeks,
Ouch, index
• user_scans (read operations)
hurts
 Value > seeks and scans
• user_updates
Other handy ones…
 Lock pages enabled
 sys.dm_os_process_memory
 Long running SQLCLR queries (type=E_TYPE_USER)
 sys.dm_os_workers & sys.dm_clr_tasks
 FT catalogs population
 sys.dm_fts_active_catalogs &
sys.dm_fts_index_population
 AUTO page repair history
 sys.dm_db_mirroring_auto_page_repair
What’s new and enhanced …SQL2012
 sys.dm_server_memory_dumps
 Memory dump information
 sys.dm_exec_query_stats
 4 new columns to troubleshoot long running queries
 sys.dm_server_services
 Use to report status information about services
 sys.dm_server_registry
• Returns 1 row per registry key
What else….
 sys.dm_os_windows_info
 Returns operating system information
 sys.dm_os_volume_stats
 operating system volume (directory) on which the
specified databases and files are stored
 Operating system volume (directory)
 sys.dm_os_volume_stats mix with sys.database_files to
obtain total space & available space for DB files:
SELECT database_id, f.file_id, volume_mount_point,
total_bytes, available_bytes FROM sys.database_files
AS f CROSS APPLY
sys.dm_os_volume_stats(DB_ID(f.name), f.file_id);
SYSMON Counters
Replaces sys.sysperfinfo catalog view.
 If the installation instance of SQL Server fails to display the
performance counters of the Windows operating system,
 sys.os_performance_counters
 Over 250+ “SQL Server:” specific counters (SQL2008 R2 &
SQL2012)
 Good to get PERFMON counters information (instantly)
 VIEW SERVER STATE is necessary
 Find deprecated features used in code
 [sqlinstance]:Deprecated Features object
Words of advice….
Make sure you perform B&B
 Baseline & Benchmarking
 Systems resource usage
 Capacity planning
 Read the free e-book, How to Become an Exceptional
DBA
 DBA checklist
 http://www.simple-talk.com/sql/databaseadministration/brads-sure-dba-checklist/
 http://www.sqlserver-qa.net knowledge sharing
network.
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End slide if you need one
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