Post on 30-Dec-2015
transcript
2
WHAT IS PERFORMANCE TUNING? A combination of identifying and
reacting to performance problems– Proactively preventing such problems from
occurring
Key responsibility for Oracle DBAs– Ensures that service levels are being met– Avoids costly hardware upgrades
3
Why is performance tuning important? ‘At the core of business logic, and at the
core of business data for most production applications, is a relational database management system” – Ray Paquet of Gartner, July, 2002
No access = no data = no business– Includes poor performance, missed SLA’s
4
MAJOR CAUSES OF PROBLEMS Poorly tuned application code: SQL &
PL/SQL Contention for internal Oracle
Resources: locks, latches buffers IO bottlenecks Inadequate hardware resources
5
Procrastination? Only when the application and
RDBMS is tuned can the possibility of adding hardware be considered
– Don Burleson
– Number one resolution to performance issues in past three years was to upgrade hardware, add memory and add disk.
– Problems still persist!
6
Health CheckBest Practices? Where are the most common problems
past and present? How do I resolve those problems? How much benefit can I get from fixing the
problems identified? How much effort is involved in resolution? What can I do to prevent future issues?
7
‘Tuning Methodology’ Best Practices Identify issues happening now
– Resolve quickly
Find problems in the past – Resolve methodically
How to prevent future occurrences– Set Goals
‘What and How to tune’
8
APPLICATION TUNINGResolutions The greatest and most common
performance gains are attained through SQL tuning
A relative effort is modifying improper parameter settings
Just as important is resolving management of database space and data layout
10
Step 1: Optimize the Application Workload Effectively use the Oracle Optimizer
– Set optimizer mode to: RULE, COST or CHOOSE
Optimize SQL Statements– Set Optimizer initialization parameters– Determine SQL Code needs optimization– SQL Coding Best Practices– PL/SQL coding Best Practices
11
Step 2: Reduce Contention Identify and reduce Latch contention Identify and reduce Lock contention Optimize Redo Log configuration Reduce other internal contention
12
Identify and reduce Latch contention Types of Latches in the SGA that suffer most contention:
– Buffer Cache Latches, caused by:• SQL statements with very high logical or physical I/O, due to
unselective indexes (large index range scans) or many full table scans. • DBWR not keeping up with the dirty workload, which forces the
foreground process to hold the latch longer looking for a free buffer. • Undersized buffer cache.
– Library Cache Latches• Misses on this latch occur when SQL is executed at very high rates.
There is little you can do to reduce the load on this latch, although using private rather than public synonyms (or even direct object
references such as OWNER.TABLE) can help. • Use bind variables in your code
13
Identify and reduce Lock contention
Often caused in the application code and Data model:– Code for Concurrent use– Index Foreign Key relations– Reduce Ad-Hoc querying– Try to reduce Updates
14
Optimize Redo Log configuration
Use Fast disks – avoid RAID 5, use 0+1 or Filesystem level
replication
Multiplex Your RedoLogs Use NOLOGGING table operations Use multiple Disks for different Group
members Adjust Log Buffer size
15
Reduce Shared Pool contention Rewrite SQL Pin PL/SQL objects or SQL cursor objects in the shared
pool, use the DBMS_SHARED_POOL.KEEP Fully qualify tables and objects with the schema owner
name. This will eliminate some reparsing requirements. Increase the shared pool size when shared cursors are
being flushed out Decrease the shared pool size when the application
does not use bind variables and when cursors are not shared and reused.
16
Reduce Shared Pool contention continued
consider setting the parameter cursor_sharing = force (first available in 8.1.6). When this parameter is set, Oracle replaces embedded literal values with bind variables prior to parsing the statement, to avoid additional hard parses for SQL statements that differ only by literal values.
Add cursors to stored procedures/packages. Stored procedures/packages can be pinned in the shared pool, which prevents them from being flushed and subsequently reparsed.
Use the same bind variable length and array size in SQL statements. When an SQL statement with different bind variable lengths is used throughout an application, it cannot be shared.
17
Step 3: Physical IO Optimization
Tune Sorting parameters (Sort_Area) Tune SQL (avoid Full Table Scans) Reduce Row Chaining and Migration Balance IO Increase number of datafile devices Implement OFA Increase DB Block size
18
Step 4: Consider Best Practices Tune Top Down
– Start with Network, IO, Instance and Database design before tuning SQL
Set Benchmarks– Identify some SQL statements, and rerun them as test– Identify and monitor critical modules
Quantify the problem and the expectations. Make sure there is not some problem with the
infrastructure, get everyone involved. Involve the developers in your tuning efforts.
19
Understand all the features of the database you are using. Use as many standard Oracle provided functions as possible.
Learn how to generate and read execution plans.
Tune to reduce logical IO’s. Reducing the number of LIO’s will reduce both overall CPU usage as well as physical IO requirements. Generally, index usage will reduce LIO requirements, but sometimes the reverse it true.
Best Practices continued
20
Consider that sometimes writing PL/SQL can ultimately improve performance over SQL.
If you have lots of large queries doing full table scans, make sure that parallel query is configured correctly.
If Oracle is performing many hash joins, make sure the database parameters associated with hash joins (e.g. hash_area_size) are set correctly.
Best Practices continued
21
Quest Central Health Check A free service from Quest in which
our consultants use Quest Central Performance management to diagnose the health of your database
22
What does it do? Collects Metrics using PL/SQL packages at
a user defined interval Stores that information in a repository Allows you to run analysis against any
number of those stored collections Produces problems, recommendations,
solutions, reports, and goals for tuning
23
WHAT IS QUEST CENTRAL An integrated comprehensive
solution for Oracle DBAs– Real-time and Historical Diagnostics and
Analysis – Space Management – SQL Tuning– Database Administration