Chapter 9 Overview  Reasons to monitor SQL Server  Performance Monitoring and Tuning  Tools for Monitoring SQL Server  Common Monitoring and Tuning Tasks

Reasons to Monitor SQL Server  Minimize application or query response time  Maximize volume of transactions processed

Performance Tuning Strategies  Optimize Response time  Requires knowledge of the application, the Environment and users requirements and activities  Optimize throughput  Requires knowledge of how SQL Server handles data access concurrency and interaction with Windows 2000

Performance Tuning  Tune Client Application: Rewrite queries that limit searches Create useful indexes Minimize lock contention, avoid deadlocks Use stored procedures that reduce contention and increase concurrency. Offload data and only process from Server when appropriate

 Tune Database:  refine logical design – check to see if it is normalized to reduce redundancy; in exceptional circumstances de-normalize to reduce joins required  refine physical design – add or modify indexes, distribute files across drives, … Performance Tuning Approaches

 Tune SQL Server:  evaluate storage design – distribute data files across drives, de-fragment data and indexes  Tune Hardware configuration:  add memory, faster processor, faster hard drives Performance Tuning (ctd)

Establish Performance Baseline Determine baseline value of key factors influencing database performance Workload: volume of server activity Throughput: total number of queries in a given time period System resources: physical capacity of computer hardware Optimization : application and database design Contention: competition for the data records

SQL Server Monitoring Tools Windows 2000 Event Viewer Windows System Monitor with SQL Server Current Activity window in Enterprise Manager Transact SQL Tools SQL Profiler SQL Query Analyzer

Common Monitoring tasks 1.System level monitoring ( use W2000 Event Viewer or Windows System Monitor) for: Hardware Operating System Application 2. SQL Server specific monitoring (use EM, Transact SQL, or SQL Profiler) for: SQL Server activity Data consistency 3. Query performance (use Query Analyzer, SQL Profiler or Index Tuning wizard)

Windows Event Viewer  Windows 2000 Event Viewer displays error, warning and information messages in logs  Logs include: Windows Application log Windows System log Windows Security log

Windows Performance System Monitor Windows Performance System Monitor can measure: SQL Server I/O SQL Server Memory usage SQL Server User connections SQL Server Locking Replication Activity

Enterprise Manager Current Activity Enterprise Manager’s Current Activity window displays: 1.SQL Server Process Information  by process ID  by object 2. Locks, blocking and deadlocks information  System Administrator can take actions to inform users or terminate processes

Locking A lock is used to indicate that a user has some dependency on a resource Lock prevents other users to perform operations on the resource that would adversely affect the dependencies of the user owning the lock Locks are managed internally by system software and are acquired and released based on actions taken by the user.

Lock Modes There are several lock modes: shared, update, exclusive, intent, and schema lock mode indicates the level of dependency the connection has on the locked object SQL Server controls how the lock modes interact. For example, an exclusive lock cannot be obtained if other connections hold shared locks on the resource.

Lock Granularity Levels of lock of granularity: locks can be acquired on rows, pages, keys, ranges of keys, indexes, tables, or databases SQL Server dynamically determines the appropriate level at which to place locks for each Transact-SQL statement. Level at which locks are acquired can vary for different objects referenced by the same query; for example 1table may be very small and have a table lock applied, while another, larger table may have row locks applied.

Locking Each instance of SQL Server ensures that locks granted at one level of granularity respect locks granted at another level. For example, if UserA attempts to acquire a share lock on a row, but if UserB has an exclusive lock at the page or table level, UserA is blocked from acquiring locks until the lock held by UserB is freed.

Lock Contention If a connection needs a lock that conflicts with a lock held by another connection, the connection attempting to acquire the lock is blocked until: the conflicting lock is freed and the connection acquires the lock it requested the time-out interval for the connection expires. There is no default time-out interval but some applications set a time-out interval to prevent an indefinite wait locks are granted on a first-come, first-serve basis as the preceding connections free their locks.

Transact SQL Tools System stored procedures: sp_who: Current SQL Users and processes sp_lock: Active locks, as well as blocking and deadlock information sp_monitor: SQL Server statistics such as total processing time, number of reads and writes, and connection

SQL Profiler SQL Profiler provides you with the ability to trace server and database activity including login, user and application activity. You can capture the data to a table, file, or Transact SQL statement for further analysis. Strategy:  Choose event to Monitor  Choose trace Criteria  Choose data to capture  Group data meaningfully

SQL Query Analyzer Query Analyzer can be used to track and display: Query execution plan Server trace Server side statistics Client side statistics Query Analyzer’s Index Tuning Wizard can also be used.

Common Monitoring Requirements Information that is commonly monitored includes: Memory use Threads and Processor Use Hard disk input/output Locks Inefficient Queries

Memory Use Monitoring Memory Available Bytes  Monitors number of bytes available for use by processes to execute  This value should always be more than 5000 KB. Low value indicates shortage of physical memory. Memory: Pages/Sec  Monitors number of pages read from and written to hard disk  Counter should never be consistently greater than 0.

Threads and Processor Use Monitoring Processor: % processor time  Monitors percentage of time that processor is busy processing non-idle threads  Counter should be less than 90. System: Processor Queue Length  Monitors number of threads waiting for processor time  Counter should not be consistently > 2.

Threads,Processor Use Monitoring(ctd) Processor: % User time  Monitors percentage of time processor spends executing user processes(including SQL Server)  Can indicate if other processes are affecting SQL Server operations

Hard Disk I/O Monitoring  Physical Disk: %Disk time  Monitors percentage of time that the hard disk services read/write request. Should be less than 90.  Physical Disk: Avg. Disk Queue length  Monitors average number of read/write requests that are queued. Should not be more than 2 times the number of spindles.

Hard Disk I/O Monitoring (ctd)  Physical Disk: Disk Reads/see  Monitors rate of read operations. This counter should be consistently less than the capacity of your hard disk subsystem.  Physical Disk: Disk writes/see  Monitors rate of write operations. This counter should be constantly less than the capacity of hard disk subsystem.

Locks Monitoring  Deadlocks:  Automatically detected and killed  Blocking Locks:  Administrator intervention required  Managing Locks:  Use Windows System Monitor, SQL Profiler, EM or SP.

Query Monitoring  Identify Query Performance  Use SQL Profiler, traces and Stored procedure  Investigate and Improve Causes of Poor Query Performance  Causes may include network, memory, out-of-date statistics, indexes, inefficient query structure.