Dmv's & Performance Monitor in SQL Server

DMVs And Performance Monitor
in SQL Server
By
Zeba Tabassum

Agenda
Definition
DMVs Type
DMVs Category
Disadvantage Of DMVs
Performance Monitor
Counters

DMV’s
Definition
Dynamic management views and functions return server state information
that can be used to monitor the health of a server instance, diagnose
problems, and tune performance.
Prior to SQL Server 2005, we had several system tables(for example
sysprocesses, syslockinfo etc.) to monitor the state of the system. Though
these system tables are still available in SQL Server 2005 and in later versions
but SQL Server 2005 introduced whole new set of Dynamic Management
Views

DMV’s Type
There are two types of dynamic management views:-
• Server-scoped DMV’s They reside in master database and provide SQL
Server instance wide information. To access these DMV we need to have
SELECT permission on the objects and VIEW SERVER STATE permission on
the server.
• Database-scoped DMV’s They reside in each database and provide
database wide information. To access these DMV we need to have SELECT
permission on the objects and these require VIEW DATABASE STATE
permission on the database.

Listing DMVs
SELECT name AS DMV_Name,
[type] AS DMV_Type,
type_desc
FROM sys.system_objects
WHERE name LIKE 'dm_%'
ORDER BY name
SELECT count(*) TotalDMVCount
FROM sys.system_objects
WHERE name LIKE 'dm_%'

Dmv's & Performance Monitor in SQL Server

DMVs
The most frequently used DMV sections are:
• Database
• Execution
• IO
• Index
• SQL operating system

Database DMVs
Sys.dm_db_log_space_usage
sys.dm_db_partition_stats
sys.dm_db_file_space_usage
Sys.dm_db_task_space_usage

Database DMVs
SELECT TOP 3 object_name(object_id) AS objname,
in_row_data_page_count,
in_row_reserved_page_count,
used_page_count,
reserved_page_count,
row_count
FROM sys.dm_db_partition_stats
GO

Execution Related DMVs
• sys.dm_exec_connections
• sys.dm_exec_sessions
• sys.dm_exec_requests
• sys.dm_exec_cached_plans
• sys.dm_exec_query_plans
• sys.dm_exec_sql_text
• sys.dm_exec_query_stats

SELECT session_id,
login_name,
last_request_end_time,
cpu_time
FROM sys.dm_exec_sessions
WHERE session_id >= 61
GO

SELECT connection_id,
session_id,
client_net_address,
auth_scheme
FROM sys.dm_exec_connections
WHERE session_id >= 61

I/O Related DMV’s
• sys.dm_io_virtual_file_stats
• sys.dm_io_pending_io_requests
• sys.dm_io_cluster_shared_drives

I/O Related DMV’s
--Shows I/O stats for (data and log files) and virtual files no. of read and write
SELECT *
FROM sys.dm_io_pending_io_requests
GO
SELECT TOP 5 db_name(database_id) DataBaseName,
file_id,
num_of_reads,
num_of_writes
FROM sys.dm_io_virtual_file_stats(NULL, NULL)

Index Related DMVs
• sys.dm_db_index_physical_stats
• sys.dm_db_index_usage_stats
• sys.dm_db_index_operational_stats
• sys.dm_db_missing_index_details
• sys.dm_db_missing_index_groups
• sys.dm_db_missing_index_group_stats
• sys.dm_db_missing_index_columns

Index Related DMVs
--- Returns system_scansCounts with different date and objects
fragmentation of index operations. --
DECLARE @DBName VARCHAR(50)='testnew'
DECLARE @dbid BIGINT-- Database DB Id
SET @dbid=DB_ID(@DBName)
SELECT @DBName AS DataBaseName,
system_scans,
last_system_scan
FROM sys.dm_db_index_usage_stats
WHERE database_id = @dbid

Index Related DMVs
SELECT @DBName AS DataBaseName,
object_id,
avg_fragmentation_in_percent,
fragment_count
FROM sys.dm_db_index_physical_stats (@dbid, NULL, NULL, NULL, NULL)
WHERE database_id = @dbid
AND fragment_count > 0

Operating System Related DMVs
• sys.dm_os_performance_counters
• sys.dm_os_schedulers
• sys.dm_os_nodes
• sys.dm_os_waiting_tasks
• sys.dm_os_wait_stats

---Returning cached page count for each database
SELECT COUNT(*)AS cached_pages_count,
db_name(database_id) AS database_name,
database_id
FROM sys.dm_os_buffer_descriptors
WHERE database_id NOT IN ( 32767, 4, 2, 1,3, 5 )
GROUP BY db_name(database_id),
database_id
ORDER BY cached_pages_count DESC;
GO

--How memory is used overall on the server, and how much memory is
available
SELECT total_physical_memory_kb,
available_physical_memory_kb,
total_page_file_kb,
system_memory_state_desc
FROM
sys.dm_os_sys_memory

Disadvantages
• The biggest disadvantage in my opinion is the data in the DMVs is reset
upon SQL restart. So if you are trying to do trending type of reports, you'll
need to capture this DMV data on a regular basis to a DW somewhere.
DMV data is not guaranteed to be accurate at the time of retrieval. They
are updated asynchronously.

Performance Monitor
Performance Monitor, commonly referred to as PerfMon, is a Microsoft
Windows utility that allows us to capture :-
statistical information about the hardware environment, operating system,
and any applications that expose properties and counters.
We will learn how to use System Monitor to gather counters into counter
logs, which can be used to troubleshoot system and performance issues.

There are five major resource areas that can cause bottlenecks and affect
server performance:
physical disk,
memory,
process,
CPU, and
Network
If any of these resources are overutilized, your server or application can
become noticeably slow or can even crash.

Performance Counters
LogicalDisk% Free Space
This measures the percentage of free space on the selected logical disk drive.
Take note if this falls below 15 percent, you risk running out of free space for
the OS to store critical files. One obvious solution here is to add more disk
space.
PhysicalDisk% Idle Time
This measures the percentage of time the disk was idle during the sample interval. If
this counter falls below 20 percent, the disk system is saturated. You may consider
replacing the current disk system with a faster disk system.

Disk Counters
PhysicalDiskAvg. Disk Sec/Read :This measures the average time, in seconds,
to read data from the disk.
PhysicalDiskAvg. Disk Sec/Write:This measures the average time, in seconds,
it takes to write data to the disk.
PhysicalDiskAvg. Disk Queue Length :
This indicates how many I/O operations are waiting for the hard drive to
become available. If the value here is larger than the two times the number of
spindles, that means the disk itself may be the bottleneck.

Memory Counters
MemoryCache Bytes :This indicates the amount of memory being used for
the file system cache. There may be a disk bottleneck if this value is greater
than 300MB.
Memory% Committed Bytes in Use:This measures the ratio of Committed
Bytes to the Commit Limit—in other words, the amount of virtual memory in
use. This indicates insufficient memory if the number is greater than 80
percent. The obvious solution for this is to add more memory.

MemoryAvailable Mbytes:This measures the amount of physical memory, in
megabytes, available for running processes. If this value is less than 5 percent
of the total physical RAM, that means there is insufficient memory, and that
can increase paging activity. To resolve this problem, you should simply add
more memory.
MemoryPages per Second :This measures the rate at which pages are read
from or written to disk to resolve hard page faults. If the value is greater than
1,000, as a result of excessive paging, there may be a memory leak.

Processor Counters
Processor% Processor Time:This measures the percentage of elapsed time
the processor spends executing a non-idle thread. If the percentage is greater
than 85 percent, the processor is overwhelmed and the server may require a
faster processor.
Processor% User Time :This measures the percentage of elapsed time the
processor spends in user mode. If this value is high, the server is busy with
the application. One possible solution here is to optimize the application that
is using up the processor resources.
SystemProcessor Queue Length
This indicates the number of threads in the processor queue. The server
doesn't have enough processor power if the value is more than two times the
number of CPUs for an extended period of time.

Network Counters
Network InterfaceBytes Total/Sec :
This measures the rate at which bytes are sent and received over each
network adapter, including framing characters. The network is saturated if
you discover that more than 70 percent of the interface is consumed. For a
100-Mbps NIC, the interface consumed is 8.7MB/sec (100Mbps = 100000kbps
= 12.5MB/sec* 70 percent). In a situation like this, you may want to add a
faster network card or segment the network.
Network InterfaceOutput Queue Length:
This measures the length of the output packet queue, in packets. There is
network saturation if the value is more than 2. You can address this problem
by adding a faster network card or segmenting the network.

SQL Server Counters
SQLServer: General Statistics – User Connections
SQLServer: Memory Manager – Memory Grants Pending
SQLServer: SQL Statistics – Batch Requests/sec
SQLServer: SQL Statistics – Compilations/sec
SQLServer: SQL Statistics – Recompilations/sec
SQLServer:BufferManager - Buffer Cache hit ratio
This is the percentage of requests serviced by data cache. When cache is
properly used, this should be over 90%. The counter can be improved by
adding more RAM.
SQLServer:Databases,

SQL Server Counters
SQLServer:Exec Statistics,
SQLServer:General Statistics,
SQLServer:Latches,
SQLServer:Locks– Average Wait Time
This counter shows the average time needed to acquire a lock. This value needs to
be as low as possible.
SQLServer:MemoryManager– Target Server Memory (KB):
indicates how much memory SQL Server “wants”.
SQLServer:MemoryManager— Total Server Memory (KB):
Indicates how much memory SQL Server is actually using.
SQLServer:PlanCache
SQLServer:Access Methods – Full scans/sec:
higher numbers (> 1 or 2) may mean you are not using indexes and resorting to
table scans instead.

Dmv's & Performance Monitor in SQL Server

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