Sql server troubleshooting

SQL Server Troubleshooting and Performance Monitoring
And throw in some performance tuning for giggles

Intro
Stacy Hein
Database Guy

Start with the Basics
Start with the tools you know
Logs, Logs, Logs
Performance Monitor
Some tools you might not know
Traces
Profiler Traces
Execution plans
Toad or other third party applications

Why do performance monitoring?
Goes hand-in-hand with troubleshooting
Identify bottlenecks (CPU, Memory, SQL queries, etc.)
Planning (capacity management, end-of-life, etc.)
Identify server/instance configuration issues
Base-lining your servers
Should start troubleshooting the SQL Server before the client says there is an issue.

The Usual Suspects
Memory
Processor
Disk
Database instance configuration
Queries
Maintenance

Performance Counters
Remember that performance counters should not be taken individually. Get the whole story.
Most thresholds are dependent on the system and application.
Ignore spikes. Sustained thresholds are the only ones that count.

Memory
A good place to start generally.
64 bit has helped with both memory and processor bottlenecks.
More is good – always.

Memory Performance Counters
Memory: Available Bytes
Key counter especially when used with others.
Memory: Pages / sec
Hard page faults – going to disk to get it.
VMM goes to pagefile to retrieve.
Above 20 suggests possible memory issue.
Memory: Page Faults / Sec
Sum of hard an soft page faults

Memory Performance Counters
Page File: % Usage
Also useful with the other counters.
Some rules for the pagefile
Move from system disk
Put on more than one drive if possible
Make it 2 times the size of the physical RAM in the server

Processor Performance Counters
Processor:% Processor Time
Total processing time for non-idle thread
80-90% means need processor
Processor: %User Time
Total time used for executing user processes (e.g. SQL)
System: Processor Queue
Over 2 = bad
Consider how many cores and divide total by number of cores

Disk Performance Counters
Physical disk
PhysicalDisk: Avg. Read Queue Length Should be less than 2
PhysicalDisk: Avg. Write Queue Length Should be less than 2
PhysicalDisk: % Disk Time more than 50% indicates a bottleneck

Disk Performance Counters
Logical Disk
SQL Server:BufferManager:Page reads/sec
SQL Server reading pages from disk. If you are near your hardware maximums for this counter tune your database by adding indexes, redesign queries, etc.
SQL Server:BufferManager:Page writes/sec
SQL Server writing pages to disk. If you are near your hardware maximums for this counter tune your database by adding indexes, redesign queries, etc.

Networking Performance Counters
Network Interface Bytes Total/sec
Network Interface Bytes Sent/sec
Network Interface Bytes Received/sec
Network Interface Current Bandwidth5
Don’t usually have a networking issue that is not the cable, the NIC, or route/rule issues.

Dynamic Management Views and Functions
Can get performance counter data from these.
Is a snapshot not continuous
Common ones used
sys.dm_os_performance_counters
sys.dm_os_sys_info
sys.dm_os_wait_stats
sys.dm_io_virtual_file_stats - function

Trace Flags
Used in determining deadlocks (in this case anyway)
1204
Reports deadlock information formatted by each node involved in the deadlock
1222
formats deadlock information, first by processes and then by resources
Use DBCC TRACEON to set

Profiler is your Friend
Can execute and capture trace information for all transactions running on SQL server instance.
Can isolate transactions you need to capture.

Database Instance Configuration
Can affect server performance
Examples
Memory settings, processor affinity settings, affinity masks, AWE setting (for 32 bit instances), etc.
If you are going to change your settings, understand the instances role

Instance Roles
High Write Instance
The database and log disk should be RAID 10 and separated on different physical volumes.
The logical and physical model of the database is important. High write tables should be on their own partitions. This is also be true for very large, clustered indexes.
Tempdb should be on its own RAID 10 partition and should have one data file for each core dedicated to SQL Server.
Although disk is usually the primary issue with a high write system, put as much RAM as you can in this system.

Instance Roles
High Read Instance (Reporting?)
Memory, Memory, Memory is the most important component to a read-intensive system. The more you have the more that can be accessed in memory and not read from disk.
Tempdb should be on its own RAID 10 partition and should have one data file for each core dedicated to SQL Server. If you are doing massive reads, you are probably doing calculations for reporting. This operations are handled in tempdb now in SQL Server 2005 and forward.
Although memory is the key to a system that does massive read operations, if you can afford it, make the database and log file partitions RAID 10 for when you would need to access them.

Instance Roles
If your system is a hybrid the defaults should work for the server. If not, tweak design and system settings as necessary careful to consider what the instance might be processing (i.e. more reads or more writes).

Other Keys to Troubleshooting
Understand the data and applications on the instance
The physical and logical design of the database coupled with the system setting will go far in establishing a high performing instance/server.
Well designed queries are also

Tuning Queries
Execution Plans
Profiler
Third party apps
Toad for SQL Server

Tuning Queries
Rules for code creation
Use procedures for the repetitive queries
Avoid cursors
Reduces the use of temp tables
Return only the rows an app needs
Set NOCOUNT ON
Use the schema when naming the object
Do all DDL at top of procedures
Use ANSI JOIN language
Look for ANSI SET commands in your code

Maintenance
Database maintenance is key to mitigating some performance problems.
Backups for obvious reasons
Index fragmentation can cause issues for the server.
Two options DBCC DBREINDEX and DBCC INDEXDEFRAG
UPDATE STATISTICS - depends on your application.
Be careful there is a performance trade off for recompiling queries.

Maintenance is a key component to the preventative side of server support.

Sql server troubleshooting

by Nathan Winters on May 20, 2010

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