chapter 21 sga architecture and wait event
DESCRIPTION
Chapter 21 SGA Architecture and Wait Event. 2008. 07. 25. Summarized & Presented by Yeon JongHeum IDS Lab., Seoul National University. Primary Components of Oracle. System Global Area(SGA). Memory Structure of Instance Shared Pool Used to store the most recently executed SQL - PowerPoint PPT PresentationTRANSCRIPT
Chapter 21 SGA Architecture and Wait Event
2008. 07. 25.
Summarized & Presented by Yeon JongHeum
IDS Lab., Seoul National University
Copyright 2008 by CEBT
Primary Components of Oracle
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System Global Area(SGA)
Memory Structure of Instance
Shared Pool
Used to store the most recently executed SQL
Used to Most recently used data definitions
Database Buffer Cache
Stores copies of data block that have been retrieved from the data files
Redo Log Buffer Cache
Records all changes made to the database data blocks
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Shared Pool
Library cache
Contains statement text, parsed code, and execution plan
Data dictionary cache
Contains definitions for tables, columns, and privileges from the data dictionary tables
UGA
Session information for Oracle Shared Server user when large pool is not configured
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Library Cache
Used to store SQL statements and PL/SQL blocks to be shared by users
Managed by an LRU algorithm
Used to prevent statement reparsing
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Tuning Shared Pool
Shared Pool Size
SHARED_POOL_SIZE
SHARED_POOL_RESERVED_SIZE
V$SHARED_POOL_RESERVED
Wait Event
V$SESSION_WAIT or Statspack
Latch Free Wait Event
Library Cache Load Lock Wait Event
Library Cache Lock Wait Event
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Database Buffer Cache
Stores copies of data block and rollback block for caching that have been retrieved from the data files that server read
Enables great performance gains when you obtain and update data
Managed through a least recently used(LRU) algorithm
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Diagnostic Tools for DB Buffer Cache
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Latch of Database Buffer Cache
Cache Buffer Chain Latch
Guarantee buffer header serialize access(protect hash chain)
Processes need to acquire latch to get buffer header lock
Assign to each Hash Bucket
Cache Buffer LRU Chain Latch
Guarantee LRU list serialize access
Assign to each LRU List
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Tuning Database Buffer Cache
Sizing Database Buffer Cache
DB_CACHE_SIZE
DB_KEEP_CACHE_SIZE
DB_RECYCLE_CACHE_SIZE
Wait Event
Buffer Busy Wait Event
Free Buffer Wait Event
Local Write Wait Event
Buffer Dead Lock Wait Event
Direct Path Write Wait Event
Direct Path Read Wait Event
Write Complete Wait Event
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Redo Log Buffer
Processes copy redo entries from the user’s memory space to the redo log buffer for each DML or DDL statement
The redo entries contain the information necessary to reconstruct or redo changes made to the database by INSERT, UPDATE , DELETE CREATE, ALTER, or DROP operations.
Used for database recovery
Take up continuous, sequential space in the buffer
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Latch of Redo Log Buffer
Redo Copy Latch
Write log data to redo log buffer
Two times of CPU number
Redo Allocation Latch
Check and assign free spaces of redo log buffer to pro-cesses
Write log data order by time
Only one in the database
Redo Writing Latch
Write data of redo log buffer to redo log file by LGWR
Guarantee that only one LGWR executes
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Tuning Redo Log Buffer
Sizing the Redo Log Buffer
Adjust the LOG_BUFFER parameter
Default value : OS-specific, generally 500k
Wait Event
Log Buffer Space Wait Event
LGWR Wait For Redo Copy Wait Event
Log File Sequential Redo Wait Event
Log File Parallel Write Wait Event
Log File Single Write Wait Event
Log File Sync Wait Event
Log File Switch Completion Wait Event
Log File Switch(Check Incomplete) Wait Event
Log File Switch(Archive Needed) Wait Event
Log File Switch(Clear Log File) Wait Event
Switch Log File Command Wait Event
Redo Switch/Archive Wait Event
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