the self-managing database: automatic sga memory management tirthankar lahiri senior manager,...
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The Self-Managing Database: Automatic SGA Memory Management
Tirthankar Lahiri
Senior Manager, Distributed Cache & Memory Management
Oracle Corporation
Session id: 40091
Outline
Overview of Oracle Shared Memory (SGA) Introducing Automatic SGA Management Benefits Using the feature How Does it Work? Summary
SGA Overview
SGA: Oracle’s “Shared Global Area” Comprises multiple memory components
Java Pool
DatabaseBuffer Cache
Redo Log Buffer
Shared Pool
Large Pool
SGA
Fixed SGA
SGA Overview
In past releases: Separate parameters for SGA components
DB_CACHE_SIZESHARED_POOL_SIZELARGE_POOL_SIZEJAVA_POOL_SIZE
SGA Overview
Difficult to optimally set parameters Undersized component:
– Poor performance (excess IO, parses)– Out-of-memory errors (ORA-4031)
Oversized component: – Wastes memory – Configuring for the worst-case
SGA Overview
Oracle9i introduced SGA memory advisories:– Buffer Cache Advice (v$db_cache_advice)– Shared Pool Advice (v$shared_pool_advice)
Predicts performance for different sizes
Physical IOs
Buffer cache size
Buffer Cache Advice
SGA Overview
Advisories allow better sizing for components– Available out-of-the-box– Reduces trial and error– Recommendations based on actual workload– With Dynamic SGA:
Recommendations can be implemented online
Task of adjusting sizes still left to the DBA
Introducing Automatic SGA Memory Management
The Oracle Database 10g– Single parameter for total SGA size– Automatically sizes SGA components– Memory is transferred to where most needed – Uses workload information – Uses internal advisory predictions
Introducing Automatic SGA Memory Management
Single parameter for SGA size
DB_CACHE_SIZESHARED_POOL_SIZELARGE_POOL_SIZEJAVA_POOL_SIZE
Enable Automatic Shared Memory Management
SGA_TARGET
Introducing Automatic SGA Memory Management Set SGA_TARGET to the total SGA size
SGA_TARGET = 8G
Java Pool
DatabaseBuffer Cache
Redo Log Buffer
Shared Pool
Large Pool
SGA
Fixed SGA
Introducing Automatic SGA Memory Management
Four most commonly configured components are automatically sized:
– Shared Pool– Large Pool– Java Pool– Buffer Cache (DEFAULT buffer pool)
STATISTICS_LEVEL must be set to TYPICAL
Automatically adapts to workload changes
Maximizes memory utilization
Single Parameter makes it easier to use
Helps eliminate out of memory errors
Can help improve performance
Online
UsersLarge Batch
Jobs
Java Pool
Shared Pool
Large Pool
Buffer Cache
Shared Pool
Large Pool
Buffer Cache
Java Pool
Benefits of Automatic SGA Management
Using Automatic SGA Management: SGA_TARGET Parameter
Includes everything in the SGA:– Fixed SGA and other internal allocations– Automatically sized SGA components
Default buffer cache Shared pool Large pool Java pool
– Manual SGA components Log buffer Other caches (KEEP/RECYCLE, other blocksizes) Streams pool (new in 10g)
When SGA_TARGET is not set (or zero):– Auto-tuned parameters behave as in Oracle9i– Exception: SHARED_POOL_SIZE:
In Oracle10g internal startup overhead is included May need to increase value from Oracle9i Query to determine actual shared pool size in 9i Shared Pool Size automatically adjusted during
upgrade
SELECT SUM(bytes)FROM v$sgastatWHERE pool = 'shared pool';
Using Automatic SGA Management: Automatically Tuned Parameters
When SGA_TARGET is set:– Default values of auto-tuned
parameters is zero– A non-zero value is a lower bound
on the size of the component – Actual component size may be
higher
Using Automatic SGA Management: Automatically Tuned Parameters
Java Pool (1G)
Large Pool (1G)
Buffer Cache (3G)
Sg
a si
ze =
8G
Parameters: SGA_TARGET = 8GLARGE_POOL_SIZE = 1GSHARED_POOL_SIZE = 1G
Shared Pool (3G)
(Min size = 1G)
Using Automatic SGA Management: Determining the current component sizes
Some components not yet auto-tuned– Other buffer caches (Keep/Recycle)– Multiple blocksize caches– Streams Pool
Their parameters are user-specified Precisely control the sizes of their
components
Using Automatic SGA Management: Manually Tuned Parameters
Using Automatic SGA Management:Manually Tuned Parameters
When SGA_TARGET is set:– Total size of manual parameters is subtracted– Balance is given to the auto-tuned components
Keep Cache(1G)
Parameters:SGA_TARGET = 8GDB_KEEP_CACHE_SIZE = 1G
Auto Tuned Components (7G)
SharedPool
Large Pool
Default Cache
Java Pool
Initialization parameter values:
Querying V$PARAMETER
SGA_TARGET = 8G DB_CACHE_SIZE = 0JAVA_POOL_SIZE = 0LARGE_POOL_SIZE = 0SHARED_POOL_SIZE = 0
SELECT name, value, isdefault FROM v$parameterWHERE name like '%size';
Using Automatic SGA Management Using v$parameter
Enabling Automatic SGA Management
Using Automatic SGA Management : Resizing SGA_TARGET
SGA_TARGET is dynamic Can be increased till SGA_MAX_SIZE Can be reduced till some component reaches
minimum size Change in value of SGA_TARGET affects
only automatically sized components
Using Automatic SGA Management : Resizing SGA_TARGET
SGA_MAX_SIZE=10G
SGA_TARGET=9G
DatabaseBuffer Cache
DatabaseBuffer Cache
Redo Log Buffer
Large Pool
SGA_TARGET = 8G
Fixed SGA
Shared Pool
Java Pool
SGA_TARGET = 0 disables auto-tuning– Auto parameters set to current component sizes– SGA size as a whole is unaffected
Parameters:
sga_target = 8G
shared_pool_size=1G
Parameters:
sga_target = 0
db_cache_size = 4G
shared_pool_size = 2G
large_pool_size = 512M
java_pool_size = 512M
sga size = 8G
sga size = 8G
SGA_TARGET=0
Disabling Automatic SGA Management
SGA_TARGET = 8G
Java Pool
DatabaseBuffer Cache
Redo Log Buffer
Large Pool
SGA
Fixed SGA
Shared Pool
actual size = 2G
SHARED_POOL_SIZE=1G
Using Automatic SGA Management Resizing Auto Tuned Parameters
• Results in component resize only if new value > current size• Otherwise silently changes the minimum size
Manual parameter resize affects the tunable portion of the SGA
Using Automatic SGA Management Resizing Manually Set Parameters
Parameters:SGA_TARGET = 8GDB_KEEP_CACHE_SIZE = 1G
KeepCache(1G)
Auto Tuned Components (7G)
SharedPool
Large Pool
Default Cache
Java Pool
Parameters:SGA_TARGET = 8GDB_KEEP_CACHE_SIZE = 2G
KeepCache(2G)
Auto Tuned Components (6G)
How Does It Work?SGA Background Process
Background SGA Memory
Broker
Tracks component size
and pending resize
Coordinates sizing of SGA components
Based on workload information Captures statistics periodically in
background Uses the different memory advisories Memory is moved to where most needed No need to configure parameters for the
worst-case
How Does It Work?Basic SGA Tuning Principles
How Does It Work?Persistence of auto-tuned values
If server parameter file (spfile) is used:– Component sizes saved across shutdowns– Saved values used to bootstrap component sizes– Avoids having to relearn optimal values
For this reason use of spfile is recommended with Automatic SGA Management
Conclusions
Relieves the administrator from manually configuring the SGA
Internal algorithm adjusts based on workload No need to configure for the worst-case Simple usage model
Next Steps…. Recommended sessions
– The Self-Managing Database : Proactive Space and Schema Object Management (Thurs, Sept 11, 8 AM)
– The Self-Managing Database : Automatic Health Monitoring (Thurs, Sept. 11, 11 AM)
– The Invisible Oracle : Deploying Oracle Database in Embedded Environment (Wed, Sept. 10, 4:30 PM)
Recommended demos and/or hands-on labs– Oracle Database 10g : Manage the Oracle Environment Hands-
On Lab– Campground Demo : “The Self-Managing Database: Memory
Management”
Relevant web sites to visit for more information– http://otn.oracle.com/products/manageability/database/
content.html
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Thank you.
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