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elwoos
Master Smack Fu Yak Hacker

2052 Posts

Posted - 2006-03-31 : 10:52:29

I've recently been reading about latch waits. There is a lot of good stuff on the web but I wondered what people here thought about them. Microsoft suggest that if they are high you may have a problem [url]http://technet2.microsoft.com/WindowsServer/en/Library/9277f422-eb8c-4c14-89b5-9fe09f80fd191033.mspx[/url] but they don't indicate what constitutes a high value. FWIW mine appear to be around 1654.339 at a period of low - average use. For the same period my buffer cache hit ratio is 99.744%. The latter sounds pretty good to me but I'm not sure about the latch waits. Not sure it matters but this is SQL server 7!

I saw a suggestion that I should look at latch timeouts but can't see that option so have looked at Lock timeouts but am not sure which instance to pick

Any comments would be appreciated

thanks

steve

-----------

Oh, so they have internet on computers now!

schuhtl
Posting Yak Master

102 Posts

Posted - 2006-04-03 : 08:51:38

I recently had a Microsoft SQL Server Engineer onsite to do a SQL Server Health Check on several of our larger servers. I mentioned to the engineer that it would be great if there was some/better documentation regarding performance counter preferred values. As you know many of the counters have great descriptions of what they are supposed to measure but once you start measuring them you have no idea if the numbers are good or bad. I was told that within Microsoft many of the "experts" can't agree on a certain thresholds for every counter because it can make a big difference depending on the environment. They did pass along a document that the field engineer’s use as a starting point for most of the counters and this is what it has for SQL Server:Latches:

Object: - Server:Latches
Counter: - Average Latch Wait Time (ms)
Preferred Value: - < 300
Description and Threshold: - Average latch wait time (milliseconds) for latch requests that had to wait.

Jim77
Constraint Violating Yak Guru

440 Posts

Posted - 2006-04-03 : 11:02:17

That is interesting stuff any chance you could post any more default preferred starting point values please Schutl ?

schuhtl
Posting Yak Master

102 Posts

Posted - 2006-04-03 : 14:38:53

The information below is to be used as a guide. Just because the counters collected in your environment may be drastically different from those listed below does not mean that there is a problem. I am sure many of these could be debated but I find the information helpful and you can be the judge if it is useful in your environment(s). I am not the author of the content below so if you see something that you disagree with… don't blame me:)

Memory Bottleneck Analysis

Object: - Memory
Counter: - Available Mbytes
Preferred Value: - > 20MB
Description: -
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: - Paging File
Counter: - %Usage
Preferred Value: - < 70%
Description: - The peak usage of the Page File instance in percent.
Reference: - KB 889654

Object: - SQL Server: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.
Reference: -

Object: - SQL Server: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.
Reference: -

Object: - SQL Server: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.
Reference: -

Object: - SQL Server: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.
Reference: -

Object: - SQL Server: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.
Reference: -

Object: - SQL Server:Buffer Manager
Counter: - Free pages
Preferred Value: - > 640
Description: - Total number of pages on all free lists.
Reference: -

Object: - SQL Server:Buffer Manager
Counter: - Stolen pages
Preferred Value: - Varies. Compare with baseline
Description: - Number of pages used for miscellaneous server purposes (including procedure cache).
Reference: -

Object: - SQL Server: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.
Reference: -

Object: - SQL Server:Buffer Manager
Counter: - Target Server Memory(KB)
Preferred Value: -
Description: - Total amount of dynamic memory the server can consume.
Reference: -

Object: - SQL Server:Buffer Manager
Counter: - Total Server Memory(KB)
Preferred Value: -
Description: - Total amount of dynamic memory (in kilobytes) that the server is using currently
Reference: -

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
Reference: -

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.
Reference: -

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.
Reference: -

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.
Reference: -

Object: - SQL Server: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.
Reference: -

Object: - SQL Server: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.
Reference: -

Object: - SQL Server:Buffer Manager
Counter: - Free pages
Preferred Value: - > 640
Description: - Total number of pages on all free lists.
Reference: -

Object: - SQL Server:Buffer Manager
Counter: - Stolen pages
Preferred Value: - Varies. Compare with baseline
Description: - Number of pages used for miscellaneous server purposes (including procedure cache).
Reference: -

Object: - SQL Server: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.
Reference: -

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.
Reference: -

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.
Reference: -

Object: - Process (sqlservr)
Counter: - %Processor Time
Preferred Value: - < 80%
Description: -
Reference: -

Object: - Process (sqlservr)
Counter: - %Privileged Time
Preferred Value: - < 30% of %Processor Time (sqlservr)
Description: - Note: Divide the value by number of processors
Reference: -

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
Reference: -

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
Reference: -

Object: - SQLServer:Access Methods
Counter: - Full Scans / sec
Preferred Value: - < 1
Description: - If we see high CPU then we need to invistigate this counter, otherwise if the full scan are on small tables we can ignore this counter. Values greater than 1 or 2 indicates that we are having table / Index page scans. We need to analyze how this can be avoided.
Reference: -

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).
Reference: -

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.
Reference: -

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.
Reference: -

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.
Reference: -

Object: - SQLServer:General Statistics
Counter: - Logins/sec
Preferred Value: - < 2
Description: - > 2 per second indicates that the application is not correctly using connection pooling.

Reference: -

Object: - SQLServer:General Statistics
Counter: - Logouts/sec
Preferred Value: - < 2
Description: - > 2 per second indicates that the application is not correctly using connection pooling.
Reference: -

Object: - SQLServer:SQL Statistics
Counter: - Batch Requests/Sec
Preferred Value: - < 1000
Description: - Over 1000 batch requests per second indicate a very busy SQL Server.
Reference: -

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
Reference: -

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.
Reference: -

Object: - SQL Server:Latches
Counter: - Average Latch Wait Time (ms)
Preferred Value: - < 300
Description: - Average latch wait time (milliseconds) for latch requests that had to wait.
Reference: -

Transaction Management

Object: - SQL Server:Locks
Counter: - Number of Deadlocks/sec
Preferred Value: - < 1
Description: - The number of lock requests that resulted in a deadlock.
Reference: -

Object: - SQL Server: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.
Reference: -

Object: - SQL Server: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.
Reference: -

spirit1
Cybernetic Yak Master

11752 Posts

Posted - 2006-04-03 : 15:23:46

Kristen, sticky this!

Go with the flow & have fun! Else fight the flow

Blog thingie: [URL="http://weblogs.sqlteam.com/mladenp"]

elwoos
Master Smack Fu Yak Hacker

2052 Posts

Posted - 2006-04-04 : 03:18:27

Schutl that's great, thanks for providing that

steve

-----------

Oh, so they have internet on computers now!

eyechart
Master Smack Fu Yak Hacker

3575 Posts

Posted - 2006-04-04 : 03:41:19

that was a unbelievably excellent post. That should go in a blog ASAP.

-ec

eyechart
Master Smack Fu Yak Hacker

3575 Posts

Posted - 2006-04-04 : 03:42:53

quote:
Originally posted by schuhtl
They did pass along a document that the field engineer’s use as a starting point for most of the counters and this is what it has for SQL Server:Latches:

Schuhtl,

Can you pass along the title of that doc? I would like to request it from our TAM.

Again, thanks for the great post(s).

-ec

Jim77
Constraint Violating Yak Guru

440 Posts

Posted - 2006-04-04 : 04:12:43

what a super post

thank you muchly.

Kristen
Test

22859 Posts

Posted - 2006-04-04 : 06:32:24

"Kristen, sticky this!"

Consider it done!

Great post schuhtl, Thanks.

Kristen

bogey
Posting Yak Master

166 Posts

Posted - 2006-07-12 : 14:59:49

Any news on getting that document. We are evaluating Idera Diagnostic MGR and there are alot of numbers being displayed.

schuhtl
Posting Yak Master

102 Posts

Posted - 2006-07-12 : 15:22:35

bogey,

There is no "official" document... I was given a spreadsheet and I posted everything that the spreadsheet contained. What counter(s) are you looking for that are not listed?

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