Tuesday, October 2, 2012
What is Algebrizer
What is Algebrizer(in SQL 2000 Normalizer in 2005/8 Algebrizer)
Algebrizer is a process in query execution, which starts its work after Parser. Once the parser finds query syntax correct, it passes it to the algebrizer. Here start work of algebrizer:
• Algebrizer is responsible for objects and columns names (which you have provided in query or which are being referenced by your query) verification. For example if wrong name for a table is typed in a query, then its algebrizer’s duty to verify and generate an error.
• Algebrizer also identifies all data types which are being processed for a given query.
• Algebrizer verify that GROUP BY and aggregate columns are placed in right place or not. For example if you write following query and just Ctrl+F5 (just to parse). No error will be generated. But when you will press F5 (execute it). After Parsing, algebrizer will work and return an error.
sys.dm_exec_query_optimizer_info Is DMV which provide the query optimizer information
A. Viewing statistics on optimizer execution
What are the current optimizer execution statistics for this instance of SQL Server?
SELECT * FROM sys.dm_exec_query_optimizer_info;
B. Viewing the total number of optimizations
How many optimizations are performed?
SELECT occurrence AS Optimizations FROM sys.dm_exec_query_optimizer_info
WHERE counter = 'optimizations';
C. Average elapsed time per optimization
What is the average elapsed time per optimization?
SELECT ISNULL(value,0.0) AS ElapsedTimePerOptimization
FROM sys.dm_exec_query_optimizer_info WHERE counter = 'elapsed time';
D. Fraction of optimizations that involve subqueries
What fraction of optimized queries contained a subquery?
SELECT (SELECT CAST (occurrence AS float) FROM sys.dm_exec_query_optimizer_info WHERE counter = 'contains subquery') /
(SELECT CAST (occurrence AS float)
FROM sys.dm_exec_query_optimizer_info WHERE counter = 'optimizations')
AS ContainsSubqueryFraction;
Wednesday, March 14, 2012
Logical Reads in SQL Server 2008
Logical Reads count can be get by using follwoing ways
Below are the ways to check logical Reads:
1. set statistics io on
2. sys.dm_exec_query_Stats by executing the below statement we can find detailed info about reads/writes select * from sys.dm_exec_query_Stats
3. SQL Profiler: by executing the sql profiler on that database we can find out logical reads.. there are some other SQL DMV/F which also help us to get logical reads...
Summary Info:
Logical Reads : Reading Data pages from Cache
Physical Reads : Reading Data pages from Hard Disk
Buffer Cach Hit Ratio: logical reads – physical reads)/logical read * 100%
note: Buffer cach hit ratio can be easily found using performance moniter...
Detailed Info: Logical Reads: Logical read indicates total number of data pages needed to be accessed from data cache to process query.
It is very possible that logical read will access same data pages many times, so count of logical read value may be higher than actual number of pages in a table. Usually the best way to reduce logical read is to apply correct index or to rewrite the query.
Physical Reads Physical read indicates total number of data pages that are read from disk. In case no data in data cache, the physical read will be equal to number of logical read. And usually it happens for first query request. And for subsequent same query request the number will be substantially decreased because the data pages have been in data cache.
Buffer Cash Hit Ratio Buffer hit ratio will be calculated based on these two kinds of read as the following formula: (logical reads – physical reads)/logical read * 100%.
The high buffer hit ratio (if possible to near 100%) indicates good database performance on SQL Server level.
So use information from physical read and buffer hit ratio to measure performance in server level and logical read to measure individual query level Execess of the Logical Reads tends high memory Usage
There are some ways by which we can Reduce Logical Reads:
1. Improper/Useless/Insufficient Indexes: Indexes should be build on the basis of data access or retrieval process if any of the indexes is build on the columns which are not used in a query will leads to High Logical reads and will degrade the performance while reads and writing the data....
2.Poor Fill Factor/Page Density: Page use should should not be very less. otherwise large number of page will be used for small amount of data which will also leads to High Logical Reads....
3.Wide Indexes: Indexing on the large number of columns will leads to high logical reads....
4. Index scanning: if query is leads to index scanning on the table then logical reads will be high...
Below are the ways to check logical Reads:
1. set statistics io on
2. sys.dm_exec_query_Stats by executing the below statement we can find detailed info about reads/writes select * from sys.dm_exec_query_Stats
3. SQL Profiler: by executing the sql profiler on that database we can find out logical reads.. there are some other SQL DMV/F which also help us to get logical reads...
Summary Info:
Logical Reads : Reading Data pages from Cache
Physical Reads : Reading Data pages from Hard Disk
Buffer Cach Hit Ratio: logical reads – physical reads)/logical read * 100%
note: Buffer cach hit ratio can be easily found using performance moniter...
Detailed Info: Logical Reads: Logical read indicates total number of data pages needed to be accessed from data cache to process query.
It is very possible that logical read will access same data pages many times, so count of logical read value may be higher than actual number of pages in a table. Usually the best way to reduce logical read is to apply correct index or to rewrite the query.
Physical Reads Physical read indicates total number of data pages that are read from disk. In case no data in data cache, the physical read will be equal to number of logical read. And usually it happens for first query request. And for subsequent same query request the number will be substantially decreased because the data pages have been in data cache.
Buffer Cash Hit Ratio Buffer hit ratio will be calculated based on these two kinds of read as the following formula: (logical reads – physical reads)/logical read * 100%.
The high buffer hit ratio (if possible to near 100%) indicates good database performance on SQL Server level.
So use information from physical read and buffer hit ratio to measure performance in server level and logical read to measure individual query level Execess of the Logical Reads tends high memory Usage
There are some ways by which we can Reduce Logical Reads:
1. Improper/Useless/Insufficient Indexes: Indexes should be build on the basis of data access or retrieval process if any of the indexes is build on the columns which are not used in a query will leads to High Logical reads and will degrade the performance while reads and writing the data....
2.Poor Fill Factor/Page Density: Page use should should not be very less. otherwise large number of page will be used for small amount of data which will also leads to High Logical Reads....
3.Wide Indexes: Indexing on the large number of columns will leads to high logical reads....
4. Index scanning: if query is leads to index scanning on the table then logical reads will be high...
Deprecated Features in SQL Server 2012 Denali
Deprecated Features in SQL Server 2012 Denali
1. Old style join are no more supported like *= and =*
2. Compute and Compute by are no more supported
3. Added Restriction in Usage of Raiserror
RAISERROR in the format RAISERROR integer 'string' is discontinued
4. Fastfirstrow query hint is no more supported
5. Databaseproperty function is no more supported
6. 32-bit Address Windowing Extensions (AWE) and 32-bit Hot Add memory support are discontinued
7. SQL Mail is no more supported
8. sp_dboption is no more supported
9. with append clause on trigger is no more supported
10. I. sp_configure 'user instance timeout'
II. sp_configure 'user instances enabled'
11. 80 Compatibility level is not supported
12. 1. RESTORE DATABASE WITH DBO_ONLY
2. RESTORE LOG WITH DBO_ONLY
13. The Active Directory Helper service and the related components has been removed
sp_ActiveDirectory_Obj
sp_ActiveDirectory_SCP
sp_ActiveDirectory_Start
14. SQL Server 2012 Denali does not support SQL Server Distributed Management Objects (SQL-DMO) any more. SQL Server Management Objects (SMO) is the recommended alternative
15. SQL Server 2012 (Denali) no more supports the following backup commands.
BACKUP DATABASE WITH PASSWORD
BACKUP LOG WITH PASSWORD
BACKUP DATABASE WITH MEDIAPASSWORD
BACKUP LOG WITH MEDIAPASSWORD
16. SQL Server 2012 Denali does not support VIA protocol any more
Use TCP instead of VIA protocol
17. The ability for users to create new remote servers by using sp_addserver is discontinued. sp_addserver with the 'local' option remains available. Remote servers preserved during upgrade or created by replication can be used
18. sp_dropalias
19. The version parameter of PWDCOMPARE representing a value from a login earlier than SQL Server 2000 is discontinued
20. System table sys.database_principal_aliases is no more available
21. Xevent
databases_data_file_size_changed, databases_log_file_size_changed
eventdatabases_log_file_used_size_changed
locks_lock_timeouts_greater_than_0
locks_lock_timeouts
22. Set Options SET DISABLE_DEF_CNST_CHK is no more available
23. Data types text ,ntext,Image are no more avaiableData types
Data Transformation Services (DTS)
Support for migrating or running Data Transformation Services (DTS) packages has been discontinued in this release. The following DTS functionality has been discontinued.
• DTS runtime
• DTS API
• Package Migration Wizard for migrating DTS packages to the next version of Integration Services
• Support for DTS package maintenance in SQL Server Management Studio
• Execute DTS 2000 Package task
• Upgrade Advisor scan of DTS packages.
Execute DTS 2000 Package Task
The Execute DTS 2000 Package task has been discontinued.
To know the details about depreciated features in SQL Server 2012 Denli
Check below link:
http://msdn.microsoft.com/en-us/library/ms143729(v=sql.110).aspx
1. Old style join are no more supported like *= and =*
2. Compute and Compute by are no more supported
3. Added Restriction in Usage of Raiserror
RAISERROR in the format RAISERROR integer 'string' is discontinued
4. Fastfirstrow query hint is no more supported
5. Databaseproperty function is no more supported
6. 32-bit Address Windowing Extensions (AWE) and 32-bit Hot Add memory support are discontinued
7. SQL Mail is no more supported
8. sp_dboption is no more supported
9. with append clause on trigger is no more supported
10. I. sp_configure 'user instance timeout'
II. sp_configure 'user instances enabled'
11. 80 Compatibility level is not supported
12. 1. RESTORE DATABASE WITH DBO_ONLY
2. RESTORE LOG WITH DBO_ONLY
13. The Active Directory Helper service and the related components has been removed
sp_ActiveDirectory_Obj
sp_ActiveDirectory_SCP
sp_ActiveDirectory_Start
14. SQL Server 2012 Denali does not support SQL Server Distributed Management Objects (SQL-DMO) any more. SQL Server Management Objects (SMO) is the recommended alternative
15. SQL Server 2012 (Denali) no more supports the following backup commands.
BACKUP DATABASE WITH PASSWORD
BACKUP LOG WITH PASSWORD
BACKUP DATABASE WITH MEDIAPASSWORD
BACKUP LOG WITH MEDIAPASSWORD
16. SQL Server 2012 Denali does not support VIA protocol any more
Use TCP instead of VIA protocol
17. The ability for users to create new remote servers by using sp_addserver is discontinued. sp_addserver with the 'local' option remains available. Remote servers preserved during upgrade or created by replication can be used
18. sp_dropalias
19. The version parameter of PWDCOMPARE representing a value from a login earlier than SQL Server 2000 is discontinued
20. System table sys.database_principal_aliases is no more available
21. Xevent
databases_data_file_size_changed, databases_log_file_size_changed
eventdatabases_log_file_used_size_changed
locks_lock_timeouts_greater_than_0
locks_lock_timeouts
22. Set Options SET DISABLE_DEF_CNST_CHK is no more available
23. Data types text ,ntext,Image are no more avaiableData types
Data Transformation Services (DTS)
Support for migrating or running Data Transformation Services (DTS) packages has been discontinued in this release. The following DTS functionality has been discontinued.
• DTS runtime
• DTS API
• Package Migration Wizard for migrating DTS packages to the next version of Integration Services
• Support for DTS package maintenance in SQL Server Management Studio
• Execute DTS 2000 Package task
• Upgrade Advisor scan of DTS packages.
Execute DTS 2000 Package Task
The Execute DTS 2000 Package task has been discontinued.
To know the details about depreciated features in SQL Server 2012 Denli
Check below link:
http://msdn.microsoft.com/en-us/library/ms143729(v=sql.110).aspx
Tuesday, March 13, 2012
DeadLocks in SQL Server
Dead Lock: when two transactions are holding resources and both of them require before completion.
Once the dead lock situation is detected lock manager make one of the transactions as victim for rollback and raise error 1205 which is captured/handled properly
we can check Dead Lock , Blocking and Locking processes using bleow:
1. sp_who
2. sp_who2
3. select * from sys.sysprocesses
4. select * from Sys.dm_tran_locks
5. Using activity montor(in sql server 2008 only)
6. Using SQL Server Profiler(using template TSQL_Locks)
7. sp_lock
8. select * from master.dbo.syslockinfo
Once the dead lock situation is detected lock manager make one of the transactions as victim for rollback and raise error 1205 which is captured/handled properly
we can check Dead Lock , Blocking and Locking processes using bleow:
1. sp_who
2. sp_who2
3. select * from sys.sysprocesses
4. select * from Sys.dm_tran_locks
5. Using activity montor(in sql server 2008 only)
6. Using SQL Server Profiler(using template TSQL_Locks)
7. sp_lock
8. select * from master.dbo.syslockinfo
Locks and Dead Lock in SQL Server
Locks and Dead Lock in SQL Server 2008:
SQL Server uses locking and blocking mechanism to maintain data consistency in multiuser environment. Lock Manager is the SQL Server Internal governing body to handle locking scenarios like:
1. Determine Appropriate lock to be acquire/Release on resource
2. How much time will retain the lock
3. Decide when processes are allowed to modify data so that reads should be consistent
4. I. When SQL Server started with lock set to 0,lock manager allocate 2 percent of the memory allocated for SQL Server for an initial pool of lock structure(SQL 2000)
II. When SQL Server started with lock set to 0,lock manager allocate appropriate percent of the memory allocated for SQL Server for an initial pool of l 2500 lock structure(SQL 2005) as soon as lock pool is exhausted lock manager request for additional memory
III. The dynamic lock pool does not acquire more than 60 percent of the memory allocated to the Database Engine. After the lock pool has reached 60 percent of the memory acquired by an instance of the Database Engine, or no more memory is available on the computer, further requests for locks generate an error
5. Resolve Dead locks
6. compatibility between locks
SQL Server has seven different locking modes and three different lock types:
Locking modes are:
1. Shared locks(S): placed on resource for read operation and compatible for other shared and update lock except exclusive lock. When repeatable read or locking hint is used then shared lock is retained till duration of the transaction otherwise shared lock released as soon as read is completed
Equation: S on S = OK, S on U = OK, S on X = WAIT
2. Update Lock(U): placed on resource where shared lock is required and need to upgrade to exclusive lock. one transaction can acquire update lock on resource once the modification is required on resource update lock upgrade to exclusive lock
Equation: U on S = OK, U on U = WAIT, U on X = WAIT
3. Exclusive Lock(X): placed on resource for data modification and not compatible with any other type of lock .only nolock hint and read uncommitted isolation level overrides exclusive lock functionality.
Equation: X on S = WAIT, X on U = WAIT, X on X = WAIT
4. Intent(IS,IX,SIX):placed on resource to improve performance and locking efficiency by placing at high level i.e. table level
5. Schema(Sch-M,Sch-S):Sch-M is placed on resource while schema modification like while adding column to a table and Sch-S are placed on object/resource while query are being compiled or executed.
Equation: Sch-M Block all other operations until lock is released
Sch-S Locks are not compatible with Sch-M Locks
6. Bulk Update(BU):Placed on resource for Bulk insert and update of the data, these locks allow multiple bulk insert threads to access table but does not allow other processes to access the table,BU locks is enable by using TABLOCK hint or by using sp_tableoption for table lock for bulk load table option.
7. Key Range: Placed on the range of rows to protect against phantom insertion/deletion in a record set accessed by transaction, these locks are used by transaction using SERILIZABLE transaction isolation level.
These three different lock mode can be acquire at Row, Page, Table level and scope
Up to session, transaction, and cursor.
Dead Lock: when two transactions are holding resources and both of them require before completion.
Once the dead lock situation is detected lock manager make one of the transactions as victim for rollback and raise error 1205 which is captured/handled properly.
SQL Server uses locking and blocking mechanism to maintain data consistency in multiuser environment. Lock Manager is the SQL Server Internal governing body to handle locking scenarios like:
1. Determine Appropriate lock to be acquire/Release on resource
2. How much time will retain the lock
3. Decide when processes are allowed to modify data so that reads should be consistent
4. I. When SQL Server started with lock set to 0,lock manager allocate 2 percent of the memory allocated for SQL Server for an initial pool of lock structure(SQL 2000)
II. When SQL Server started with lock set to 0,lock manager allocate appropriate percent of the memory allocated for SQL Server for an initial pool of l 2500 lock structure(SQL 2005) as soon as lock pool is exhausted lock manager request for additional memory
III. The dynamic lock pool does not acquire more than 60 percent of the memory allocated to the Database Engine. After the lock pool has reached 60 percent of the memory acquired by an instance of the Database Engine, or no more memory is available on the computer, further requests for locks generate an error
5. Resolve Dead locks
6. compatibility between locks
SQL Server has seven different locking modes and three different lock types:
Locking modes are:
1. Shared locks(S): placed on resource for read operation and compatible for other shared and update lock except exclusive lock. When repeatable read or locking hint is used then shared lock is retained till duration of the transaction otherwise shared lock released as soon as read is completed
Equation: S on S = OK, S on U = OK, S on X = WAIT
2. Update Lock(U): placed on resource where shared lock is required and need to upgrade to exclusive lock. one transaction can acquire update lock on resource once the modification is required on resource update lock upgrade to exclusive lock
Equation: U on S = OK, U on U = WAIT, U on X = WAIT
3. Exclusive Lock(X): placed on resource for data modification and not compatible with any other type of lock .only nolock hint and read uncommitted isolation level overrides exclusive lock functionality.
Equation: X on S = WAIT, X on U = WAIT, X on X = WAIT
4. Intent(IS,IX,SIX):placed on resource to improve performance and locking efficiency by placing at high level i.e. table level
5. Schema(Sch-M,Sch-S):Sch-M is placed on resource while schema modification like while adding column to a table and Sch-S are placed on object/resource while query are being compiled or executed.
Equation: Sch-M Block all other operations until lock is released
Sch-S Locks are not compatible with Sch-M Locks
6. Bulk Update(BU):Placed on resource for Bulk insert and update of the data, these locks allow multiple bulk insert threads to access table but does not allow other processes to access the table,BU locks is enable by using TABLOCK hint or by using sp_tableoption for table lock for bulk load table option.
7. Key Range: Placed on the range of rows to protect against phantom insertion/deletion in a record set accessed by transaction, these locks are used by transaction using SERILIZABLE transaction isolation level.
These three different lock mode can be acquire at Row, Page, Table level and scope
Up to session, transaction, and cursor.
Dead Lock: when two transactions are holding resources and both of them require before completion.
Once the dead lock situation is detected lock manager make one of the transactions as victim for rollback and raise error 1205 which is captured/handled properly.
Wednesday, January 11, 2012
SQL Server Bottleneck Analysis Guidelines
SQL Server Bottleneck Analysis Guidelines
Memory Bottleneck Analysis 2
Disk Bottleneck Analysis 4
Processor Bottleneck Analysis 6
Overall SQL Server Bottleneck Analysis 8
Transaction Management 9
Key performance counters 10
Memory Bottleneck Analysis
Object: - Memory
Counter: - Available Mbytes
Preferred Value: - > 20MB
Reference: - KB 889654
Object: - Memory
Counter: - Free System Page Table Entries
Preferred Value: - > 7000
Description: - Free System Page Table Entries is the number of page table entries not currently in use by the system. If < 7000, consider removing /3GB.
Reference: - KB 311901
Object: - Memory
Counter: - Pages/Sec
Preferred Value: - < 50
Description: - Pages/sec is the rate at which pages are read from or written to disk to resolve hard page faults. This counter is a primary indicator of the kinds of faults that cause system-wide delays.
Reference: - Monitoring and Tuning Your Server
Object: - Memory
Counter: - Pages Input/Sec
Preferred Value: - < 10
Description: - Pages Input/sec is the rate at which pages are read from disk to resolve hard page faults.
Reference: - KB 889654
Object: - Paging File
Counter: - %Usage
Preferred Value: - < 70%
Description: - The amount of the Page File instance in use in percent.
Reference: - KB 889654
Object: - SQLServer:Buffer Manager
Counter: - Page Life Expectancy
Preferred Value: - > 300
Description: - This performance monitor counter tells you, on average, how long data pages are staying in the buffer. If this value gets below 300 seconds, this is a potential indication that your SQL Server could use more memory in order to boost performance.
Object: - SQLServer:Buffer Manager
Counter: - Lazy Writes/Sec
Preferred Value: - < 20
Description: - This counter tracks how many times a second that the Lazy Writer process is moving dirty pages from the buffer to disk in order to free up buffer space. Generally speaking, this should not be a high value, say more than 20 per second or so. Ideally, it should be close to zero. If it is zero, this indicates that your SQL Server's buffer cache is plenty big and SQL Server doesn't have to free up dirty pages, instead waiting for this to occur during regular checkpoints. If this value is high, then a need for more memory is indicated.
Object: - SQLServer:Buffer Manager
Counter: - Page reads/sec
Preferred Value: - < 90
Description: - Number of physical database page reads issued. 80 – 90 per second is normal, anything that is above indicates indexing or memory constraint.
Object: - SQLServer:Buffer Manager
Counter: - Checkpoint Pages/Sec
Preferred Value: - This value is relative, it varies from server to server, we need to compare the average to a base line capture to tell if the value is high or low.
Description: - When a checkpoint occurs, all dirty pages are written to disk. This is a normal procedure and will cause this counter to rise during the checkpoint process. What you don't want to see is a high value for this counter over time. This can indicate that the checkpoint process is running more often than it should, which can use up valuable server resources. If this has a high figure (and this will vary from server to server), consider adding more RAM to reduce how often the checkpoint occurs, or consider increasing the "recovery interval" SQL Server configuration setting.
Object: - SQLServer:Buffer Manager
Counter: - Page writes/sec
Preferred Value: - < 90
Description: - Number of physical database page writes issued. 80 – 90 per second is normal, anything more we need to check the lazy writer/sec and checkpoint counters, if these counters are also relatively high then, it’s memory constraint.
Object: - SQLServer:Buffer Manager
Counter: - Free pages
Preferred Value: - > 640
Description: - Total number of pages on all free lists.
Object: - SQLServer:Buffer Manager
Counter: - Stolen pages
Preferred Value: - Varies. Compare with baseline
Description: - Number of pages used for miscellaneous server purposes (including procedure cache).
Object: - SQLServer:Buffer Manager
Counter: - Buffer Cache hit ratio
Preferred Value: - > 90%
Description: - Percentage of pages that were found in the buffer pool without having to incur a read from disk.
Object: - SQLServer:Buffer Manager
Counter: - Target Server Memory(KB)
Preferred Value: -
Description: - Total amount of dynamic memory the server can consume.
Object: - SQLServer:Buffer Manager
Counter: - Total Server Memory(KB)
Preferred Value: -
Description: - Total amount of dynamic memory (in kilobytes) that the server is using currently
Disk Bottleneck Analysis
Object: - PhysicalDisk
Counter: - Avg. Disk Sec/Read
Preferred Value: - < 8ms
Description: - Measure of disk latgency. Avg. Disk sec/Read is the average time, in seconds, of a read of data from the disk.
More Info:
Reads or non cached Writes
Excellent < 08 Msec ( .008 seconds )
Good < 12 Msec ( .012 seconds )
Fair < 20 Msec ( .020 seconds )
Poor > 20 Msec ( .020 seconds )
Cached Writes Only
Excellent < 01 Msec ( .001 seconds )
Good < 02 Msec ( .002 seconds )
Fair < 04 Msec ( .004 seconds )
Poor > 04 Msec ( .004 seconds
Object: - PhysicalDisk
Counter: - Avg. Disk sec/Write
Preferred Value: - < 8ms (non cached) < 1ms (cached)
Description: - Measure of disk latency. Avg. Disk sec/Write is the average time, in seconds, of a write of data to the disk.
Object: - PhysicalDisk
Counter: - Avg. Disk Read Queue Length
Preferred Value: - < 2 * spindles
Description: - Avg. Disk Read Queue Length is the average number of read requests that were queued for the selected disk during the sample interval.
More Info:
< (2+ no of spindles) Excellent
< (2*no of spindles) Good
< (3* no of spindles) Fair
Reference - Whitepaper “Performance Monitoring in Windows 2003: Best Practices” by Ben W. Christenbury
Note: If the disk has say 20 disk and it is RAID 10 then no. of spindles = 20/2 = 10. If it is RAID 5 then the no. of spindles = no of disks = 20.
Object: - PhysicalDisk
Counter: - Avg. Disk Write Queue Length
Preferred Value: - < 2 * spindles
Description: - Avg. Disk Write Queue Length is the average number of write requests that were queued for the selected disk during the sample interval.
Object: - SQLServer:Buffer Manager
Counter: - Page reads/sec
Preferred Value: - < 90
Description: - Number of physical database page reads issued. 80 – 90 per second is normal, anything that is above indicates indexing or memory constraint.
Object: - SQLServer:Buffer Manager
Counter: - Page writes/sec
Preferred Value: - < 90
Description: - Number of physical database page writes issued. 80 – 90 per second is normal, anything more we need to check the lazy writer/sec and checkpoint counters, if these counters are also relatively high then, it’s memory constraint.
Object: - SQLServer:Buffer Manager
Counter: - Free pages
Preferred Value: - > 640
Description: - Total number of pages on all free lists.
Object: - SQLServer:Buffer Manager
Counter: - Stolen pages
Preferred Value: - Varies. Compare with baseline
Description: - Number of pages used for miscellaneous server purposes (including procedure cache).
Object: - SQLServer:Buffer Manager
Counter: - Buffer Cache hit ratio
Preferred Value: - > 90%
Description: - Percentage of pages that were found in the buffer pool without having to incur a read from disk.
Processor Bottleneck Analysis
Object: - Processor
Counter: - %Processor Time
Preferred Value: - < 80%
Description: - % Processor Time is the percentage of elapsed time that the processor spends to execute a non-Idle thread.
Object: - Processor
Counter: - %Privileged Time
Preferred Value: - < 30% of Total %Processor Time
Description: - % Privileged Time is the percentage of elapsed time that the process threads spent executing code in privileged mode.
Object: - Process (sqlservr)
Counter: - %Processor Time
Preferred Value: - < 80%
Object: - Process (sqlservr)
Counter: - %Privileged Time
Preferred Value: - < 30% of %Processor Time (sqlservr)
Description: - Note: Divide the value by number of processors
Object: - System
Counter: - Context Switches/sec
Preferred Value: - < 3000
Description: -
1500 – 3000 per processor Excellent – Fair
> 6000 per processor Poor
Upper limit is about 40,000 at 90 % CPU per CPU
NOTE: Remember to divide by number of processors
Object: - System
Counter: - Processor Queue Length
Preferred Value: - < 4 per CPU
Description: - For standard servers with long Quantums
<= 4 per CPU Excellent
< 8 per CPU Good
< 12 per CPU Fair
Object: - SQLServer:Access Methods
Counter: - Full Scans / sec
Preferred Value: - < 1
Description: - If we see high CPU then we need to investigate this counter, otherwise if the full scan are on small tables we can ignore this counter. Values greater than 1 or 2 indicate that we are having table / Index page scans. We need to analyze how this can be avoided.
Object: - SQLServer:Access Methods
Counter: - Worktables Created/Sec
Preferred Value: - < 20
Description: - Number of worktables created in tempdb per second. Worktables are used for queries that use various spools (table spool, index spool, etc).
Object: - SQLServer:Access Methods
Counter: - Workfiles Created/Sec
Preferred Value: - < 20
Description: - Number of work files created per second. Tempdb workfiles are used in processing hash operations when the amount of data being processed is too big to fit into the available memory. They may be able to reduce this number by making the queries more efficient by adding/changing indexes, adding additional memory, etc.
Object: - SQLServer:Access Methods
Counter: - Page Splits/sec
Preferred Value: - < 20
Description: - Interesting counter that can lead us to our table / index design. This value needs to be low as possible. If you find out that the number of page splits is high, consider increasing the fillfactor of your indexes. An increased fillfactor helps to reduce page splits because there is more room in data pages before it fills up and a page split has to occur.
Overall SQL Server Bottleneck Analysis
Object: - SQLServer:General Statistics
Counter: - User Connections
Preferred Value: -
Description: - The number of users currently connected to the SQL Server.
Object: - SQLServer:General Statistics
Counter: - Logins/sec
Preferred Value: - < 2
Description: - > 2 per second indicates that the application is not correctly using connection pooling.
Object: - SQLServer:General Statistics
Counter: - Logouts/sec
Preferred Value: - < 2
Description: - > 2 per second indicates that the application is not correctly using connection pooling.
Object: - SQLServer:SQL Statistics
Counter: - Batch Requests/Sec
Preferred Value: - < 1000
Description: - Over 1000 batch requests per second indicate a very busy SQL Server.
Object: - SQLServer:SQL Statistics
Counter: - SQL Compilations/sec
Preferred Value: - < 10% of the number of Batch Requests / sec
Description: - The number of times per second that SQL Server compilations have occurred. This value needs to be as low as possible. If you see a high value such as over 100, then it’s an indication that there are lots or adhoc queries that are running, might cause CPU
Object: - SQLServer:SQL Statistics
Counter: - SQL Re-Compilations/sec
Preferred Value: - < 10% of the number of SQL Compilations/sec
Description: - This needs to be nil in our system as much as possible. A recompile can cause deadlocks and compile locks that are not compatible with any locking type.
Object: - SQLServer:Latches
Counter: - Average Latch Wait Time (ms)
Preferred Value: - < 300
Description: - Average latch wait time (milliseconds) for latch requests that had to wait.
Transaction Management
Object: - SQLServer:Locks
Counter: - Number of Deadlocks/sec
Preferred Value: - < 1
Description: - The number of lock requests that resulted in a deadlock.
Object: - SQLServer:Locks
Counter: - Lock Requests/sec
Preferred Value: - < 1000
Description: - Number of requests for a type of lock per second. Lock requests/sec > 1000 indicates that the queries are accessing large number of rows; the next step is to review high read queries. If you also see high Avg. Wait time, then it’s an indication of blocking, then review the blocking script output.
Object: - SQLServer:Locks
Counter: - Average Wait Time (ms)
Preferred Value: - < 500
Description: - This is the average wait time in milliseconds to acquire a lock. Lower the value the better it is. If the value goes higher then 500, there may be blocking going on; we need to run blocker script to identify blocking.
Key performance counters
Buffer cache hit ratio
The buffer cache hit ratio is the percentage of pages found in the buffer cache without having to read from disk. A value of 90 percent or higher is desirable. If the value is 60 percent, you should add more memory until the value is consistently greater than 90 percent.
Page life expectancy
Have you ever checked out the page life expectancy counter in Performance Monitor's Buffer Manager object? SQL Server Books Online (BOL) says the page life expectancy value is the "number of seconds a page will stay in the buffer pool without references." So, a buffer that has a 300-second page life expectancy will keep any given page in memory in the buffer pool for 5 minutes before the buffer pool flushes the page to disk—unless a process references the page.
This counter can be helpful in determining whether you have a memory problem, giving you a reasonably accurate view of whether your server has memory pressure. According to Microsoft, 300 seconds is the minimum target for page life expectancy. If the buffer pool flushes your pages in less than 300 seconds, you probably have a memory problem. Looking at this value is particularly handy when your page life expectancy is significantly higher or lower than 300 seconds. For example, a customer recently asked me, "Do we need more memory?" I monitored the page life expectancy value for the customer's system, and the value didn't fall below 3000 seconds. That's quantifiable proof that more memory wouldn't help performance. Other customers have an average page life expectancy between 10 and 50 seconds, and they wonder why their servers are slow.
Memory Bottleneck Analysis 2
Disk Bottleneck Analysis 4
Processor Bottleneck Analysis 6
Overall SQL Server Bottleneck Analysis 8
Transaction Management 9
Key performance counters 10
Memory Bottleneck Analysis
Object: - Memory
Counter: - Available Mbytes
Preferred Value: - > 20MB
Reference: - KB 889654
Object: - Memory
Counter: - Free System Page Table Entries
Preferred Value: - > 7000
Description: - Free System Page Table Entries is the number of page table entries not currently in use by the system. If < 7000, consider removing /3GB.
Reference: - KB 311901
Object: - Memory
Counter: - Pages/Sec
Preferred Value: - < 50
Description: - Pages/sec is the rate at which pages are read from or written to disk to resolve hard page faults. This counter is a primary indicator of the kinds of faults that cause system-wide delays.
Reference: - Monitoring and Tuning Your Server
Object: - Memory
Counter: - Pages Input/Sec
Preferred Value: - < 10
Description: - Pages Input/sec is the rate at which pages are read from disk to resolve hard page faults.
Reference: - KB 889654
Object: - Paging File
Counter: - %Usage
Preferred Value: - < 70%
Description: - The amount of the Page File instance in use in percent.
Reference: - KB 889654
Object: - SQLServer:Buffer Manager
Counter: - Page Life Expectancy
Preferred Value: - > 300
Description: - This performance monitor counter tells you, on average, how long data pages are staying in the buffer. If this value gets below 300 seconds, this is a potential indication that your SQL Server could use more memory in order to boost performance.
Object: - SQLServer:Buffer Manager
Counter: - Lazy Writes/Sec
Preferred Value: - < 20
Description: - This counter tracks how many times a second that the Lazy Writer process is moving dirty pages from the buffer to disk in order to free up buffer space. Generally speaking, this should not be a high value, say more than 20 per second or so. Ideally, it should be close to zero. If it is zero, this indicates that your SQL Server's buffer cache is plenty big and SQL Server doesn't have to free up dirty pages, instead waiting for this to occur during regular checkpoints. If this value is high, then a need for more memory is indicated.
Object: - SQLServer:Buffer Manager
Counter: - Page reads/sec
Preferred Value: - < 90
Description: - Number of physical database page reads issued. 80 – 90 per second is normal, anything that is above indicates indexing or memory constraint.
Object: - SQLServer:Buffer Manager
Counter: - Checkpoint Pages/Sec
Preferred Value: - This value is relative, it varies from server to server, we need to compare the average to a base line capture to tell if the value is high or low.
Description: - When a checkpoint occurs, all dirty pages are written to disk. This is a normal procedure and will cause this counter to rise during the checkpoint process. What you don't want to see is a high value for this counter over time. This can indicate that the checkpoint process is running more often than it should, which can use up valuable server resources. If this has a high figure (and this will vary from server to server), consider adding more RAM to reduce how often the checkpoint occurs, or consider increasing the "recovery interval" SQL Server configuration setting.
Object: - SQLServer:Buffer Manager
Counter: - Page writes/sec
Preferred Value: - < 90
Description: - Number of physical database page writes issued. 80 – 90 per second is normal, anything more we need to check the lazy writer/sec and checkpoint counters, if these counters are also relatively high then, it’s memory constraint.
Object: - SQLServer:Buffer Manager
Counter: - Free pages
Preferred Value: - > 640
Description: - Total number of pages on all free lists.
Object: - SQLServer:Buffer Manager
Counter: - Stolen pages
Preferred Value: - Varies. Compare with baseline
Description: - Number of pages used for miscellaneous server purposes (including procedure cache).
Object: - SQLServer:Buffer Manager
Counter: - Buffer Cache hit ratio
Preferred Value: - > 90%
Description: - Percentage of pages that were found in the buffer pool without having to incur a read from disk.
Object: - SQLServer:Buffer Manager
Counter: - Target Server Memory(KB)
Preferred Value: -
Description: - Total amount of dynamic memory the server can consume.
Object: - SQLServer:Buffer Manager
Counter: - Total Server Memory(KB)
Preferred Value: -
Description: - Total amount of dynamic memory (in kilobytes) that the server is using currently
Disk Bottleneck Analysis
Object: - PhysicalDisk
Counter: - Avg. Disk Sec/Read
Preferred Value: - < 8ms
Description: - Measure of disk latgency. Avg. Disk sec/Read is the average time, in seconds, of a read of data from the disk.
More Info:
Reads or non cached Writes
Excellent < 08 Msec ( .008 seconds )
Good < 12 Msec ( .012 seconds )
Fair < 20 Msec ( .020 seconds )
Poor > 20 Msec ( .020 seconds )
Cached Writes Only
Excellent < 01 Msec ( .001 seconds )
Good < 02 Msec ( .002 seconds )
Fair < 04 Msec ( .004 seconds )
Poor > 04 Msec ( .004 seconds
Object: - PhysicalDisk
Counter: - Avg. Disk sec/Write
Preferred Value: - < 8ms (non cached) < 1ms (cached)
Description: - Measure of disk latency. Avg. Disk sec/Write is the average time, in seconds, of a write of data to the disk.
Object: - PhysicalDisk
Counter: - Avg. Disk Read Queue Length
Preferred Value: - < 2 * spindles
Description: - Avg. Disk Read Queue Length is the average number of read requests that were queued for the selected disk during the sample interval.
More Info:
< (2+ no of spindles) Excellent
< (2*no of spindles) Good
< (3* no of spindles) Fair
Reference - Whitepaper “Performance Monitoring in Windows 2003: Best Practices” by Ben W. Christenbury
Note: If the disk has say 20 disk and it is RAID 10 then no. of spindles = 20/2 = 10. If it is RAID 5 then the no. of spindles = no of disks = 20.
Object: - PhysicalDisk
Counter: - Avg. Disk Write Queue Length
Preferred Value: - < 2 * spindles
Description: - Avg. Disk Write Queue Length is the average number of write requests that were queued for the selected disk during the sample interval.
Object: - SQLServer:Buffer Manager
Counter: - Page reads/sec
Preferred Value: - < 90
Description: - Number of physical database page reads issued. 80 – 90 per second is normal, anything that is above indicates indexing or memory constraint.
Object: - SQLServer:Buffer Manager
Counter: - Page writes/sec
Preferred Value: - < 90
Description: - Number of physical database page writes issued. 80 – 90 per second is normal, anything more we need to check the lazy writer/sec and checkpoint counters, if these counters are also relatively high then, it’s memory constraint.
Object: - SQLServer:Buffer Manager
Counter: - Free pages
Preferred Value: - > 640
Description: - Total number of pages on all free lists.
Object: - SQLServer:Buffer Manager
Counter: - Stolen pages
Preferred Value: - Varies. Compare with baseline
Description: - Number of pages used for miscellaneous server purposes (including procedure cache).
Object: - SQLServer:Buffer Manager
Counter: - Buffer Cache hit ratio
Preferred Value: - > 90%
Description: - Percentage of pages that were found in the buffer pool without having to incur a read from disk.
Processor Bottleneck Analysis
Object: - Processor
Counter: - %Processor Time
Preferred Value: - < 80%
Description: - % Processor Time is the percentage of elapsed time that the processor spends to execute a non-Idle thread.
Object: - Processor
Counter: - %Privileged Time
Preferred Value: - < 30% of Total %Processor Time
Description: - % Privileged Time is the percentage of elapsed time that the process threads spent executing code in privileged mode.
Object: - Process (sqlservr)
Counter: - %Processor Time
Preferred Value: - < 80%
Object: - Process (sqlservr)
Counter: - %Privileged Time
Preferred Value: - < 30% of %Processor Time (sqlservr)
Description: - Note: Divide the value by number of processors
Object: - System
Counter: - Context Switches/sec
Preferred Value: - < 3000
Description: -
1500 – 3000 per processor Excellent – Fair
> 6000 per processor Poor
Upper limit is about 40,000 at 90 % CPU per CPU
NOTE: Remember to divide by number of processors
Object: - System
Counter: - Processor Queue Length
Preferred Value: - < 4 per CPU
Description: - For standard servers with long Quantums
<= 4 per CPU Excellent
< 8 per CPU Good
< 12 per CPU Fair
Object: - SQLServer:Access Methods
Counter: - Full Scans / sec
Preferred Value: - < 1
Description: - If we see high CPU then we need to investigate this counter, otherwise if the full scan are on small tables we can ignore this counter. Values greater than 1 or 2 indicate that we are having table / Index page scans. We need to analyze how this can be avoided.
Object: - SQLServer:Access Methods
Counter: - Worktables Created/Sec
Preferred Value: - < 20
Description: - Number of worktables created in tempdb per second. Worktables are used for queries that use various spools (table spool, index spool, etc).
Object: - SQLServer:Access Methods
Counter: - Workfiles Created/Sec
Preferred Value: - < 20
Description: - Number of work files created per second. Tempdb workfiles are used in processing hash operations when the amount of data being processed is too big to fit into the available memory. They may be able to reduce this number by making the queries more efficient by adding/changing indexes, adding additional memory, etc.
Object: - SQLServer:Access Methods
Counter: - Page Splits/sec
Preferred Value: - < 20
Description: - Interesting counter that can lead us to our table / index design. This value needs to be low as possible. If you find out that the number of page splits is high, consider increasing the fillfactor of your indexes. An increased fillfactor helps to reduce page splits because there is more room in data pages before it fills up and a page split has to occur.
Overall SQL Server Bottleneck Analysis
Object: - SQLServer:General Statistics
Counter: - User Connections
Preferred Value: -
Description: - The number of users currently connected to the SQL Server.
Object: - SQLServer:General Statistics
Counter: - Logins/sec
Preferred Value: - < 2
Description: - > 2 per second indicates that the application is not correctly using connection pooling.
Object: - SQLServer:General Statistics
Counter: - Logouts/sec
Preferred Value: - < 2
Description: - > 2 per second indicates that the application is not correctly using connection pooling.
Object: - SQLServer:SQL Statistics
Counter: - Batch Requests/Sec
Preferred Value: - < 1000
Description: - Over 1000 batch requests per second indicate a very busy SQL Server.
Object: - SQLServer:SQL Statistics
Counter: - SQL Compilations/sec
Preferred Value: - < 10% of the number of Batch Requests / sec
Description: - The number of times per second that SQL Server compilations have occurred. This value needs to be as low as possible. If you see a high value such as over 100, then it’s an indication that there are lots or adhoc queries that are running, might cause CPU
Object: - SQLServer:SQL Statistics
Counter: - SQL Re-Compilations/sec
Preferred Value: - < 10% of the number of SQL Compilations/sec
Description: - This needs to be nil in our system as much as possible. A recompile can cause deadlocks and compile locks that are not compatible with any locking type.
Object: - SQLServer:Latches
Counter: - Average Latch Wait Time (ms)
Preferred Value: - < 300
Description: - Average latch wait time (milliseconds) for latch requests that had to wait.
Transaction Management
Object: - SQLServer:Locks
Counter: - Number of Deadlocks/sec
Preferred Value: - < 1
Description: - The number of lock requests that resulted in a deadlock.
Object: - SQLServer:Locks
Counter: - Lock Requests/sec
Preferred Value: - < 1000
Description: - Number of requests for a type of lock per second. Lock requests/sec > 1000 indicates that the queries are accessing large number of rows; the next step is to review high read queries. If you also see high Avg. Wait time, then it’s an indication of blocking, then review the blocking script output.
Object: - SQLServer:Locks
Counter: - Average Wait Time (ms)
Preferred Value: - < 500
Description: - This is the average wait time in milliseconds to acquire a lock. Lower the value the better it is. If the value goes higher then 500, there may be blocking going on; we need to run blocker script to identify blocking.
Key performance counters
Buffer cache hit ratio
The buffer cache hit ratio is the percentage of pages found in the buffer cache without having to read from disk. A value of 90 percent or higher is desirable. If the value is 60 percent, you should add more memory until the value is consistently greater than 90 percent.
Page life expectancy
Have you ever checked out the page life expectancy counter in Performance Monitor's Buffer Manager object? SQL Server Books Online (BOL) says the page life expectancy value is the "number of seconds a page will stay in the buffer pool without references." So, a buffer that has a 300-second page life expectancy will keep any given page in memory in the buffer pool for 5 minutes before the buffer pool flushes the page to disk—unless a process references the page.
This counter can be helpful in determining whether you have a memory problem, giving you a reasonably accurate view of whether your server has memory pressure. According to Microsoft, 300 seconds is the minimum target for page life expectancy. If the buffer pool flushes your pages in less than 300 seconds, you probably have a memory problem. Looking at this value is particularly handy when your page life expectancy is significantly higher or lower than 300 seconds. For example, a customer recently asked me, "Do we need more memory?" I monitored the page life expectancy value for the customer's system, and the value didn't fall below 3000 seconds. That's quantifiable proof that more memory wouldn't help performance. Other customers have an average page life expectancy between 10 and 50 seconds, and they wonder why their servers are slow.
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