1z0-042 Oracle database 10g workshop. Learn by presentation series. Oracle sga in nutshell. Oracle dba training courseware.

1. DBAMETRIX Solutions
Present
Oracle SGA in a Nutshell

2. DBA Learn by Presentation
series
 DBA learning by presentation offered by
DBAMETRIX Solutions.
 This all presentations have been prepared by
Gitesh P Trivedi.
 Gitesh Trivedi has work excellent 14 years
experience in DBA field and as consultant faculty.
 For more details please contact to
www.dbametrix.com or gitesh@dbametrix.com or
giteshtrivedi@yahoo.com

3. What is SGA
 SGA called as Shared Global Area
 It populates in Oracle’s memory region
 Size of SGA depends on Granule
distribution
 Sometime it also called as Shared Memory
Area
 It populates when Oracle database started

4. Sub Components of SGA
SGA
Buffer Cache Log Buffer Shared Pool Java Pool Stream Pool Large Pool
Dictionary Cache Library Cache Control Structure
Shared SQL Area Locks
Latches
Execution Plan
Parse Tree
Private Area
Persistent Area
Runtime Area

5. Parameters of SGA
 Db_cache_size (Buffer Cache)
 Log_buffer (Log Buffer)
 Shared_pool_size (Shared Pool)
 Java_pool_size (Java Pool)
 Large_pool_size (Large Pool)
 Stream_pool_size (Stream Pool)

6. What is granules
 With dynamic SGA, the unit of allocation is
called a granule
 Allocation of SGA components, as unit of
granule
 Granule size is determined by total SGA
size
 We can check size of granule from
v$sgainfo dynamic view

7. Size of Granules
 It depends on operating system and kernel bit version.
 In Oracle 9i, if SGA is smaller than 128 MB than size of
granule is 4MB. If more than 128MB than size of granule
is 16MB.
 From Oracle 10g, if SGA is smaller than 1GB than size of
granule is 4MB and bigger for 16MB.
 For 32bit Windows platform if SGA is bigger than 128MB
than size of granule is 8MB
 Expanding size of component of SGA depends on
multiple of Granule size

8. SGA Structure
Dict Cache Lib Cache
Buffer Cache Log Buffer Con Str
Sort Ext Pool Shared Pool
Stream Pool Java Pool Large Pool

9. Database Buffer Cache
 For fetching data, Oracle first check in Buffer Cache.
 If no found data in Buffer Cache then Oracle fetch data
from disk and copy in Buffer Cache for avoiding
unnecessary disk I/O.
 3 types of Buffers available in Buffer Cache.
 Those are free buffers, pinned buffers and dirty buffers.
 When Oracle don’t find room for pinning new buffers
then dirty buffers are flushed and written in to disk.
 For managing these all buffers, Oracle utilizes a least
recently used algorithm for flushing buffers in Disk.

10. Type of Buffer Cache
 Multiple Buffer Cache
 DEFAULT Buffer Cache db_cache_size
 KEEP Buffer Cache db_keep_cache_size
 RECYCLE Buffer Cache
db_recycle_cache_size
 Non standard Buffer Cache also available
with parameter db_nK_cache_size where n is
2,4,8,16,32.
 In Oracle 8i and prior version parameter was
db_block_buffers

11. How Buffers work
All are free Buffers in Buffer Cache

12. How Buffers work
Pinned Buffers in
Buffer Cache
Free Buffers in Buffer Cache

13. How Buffers work
Pinned Buffers
Free Buffers
Dirty Buffers

14. How Buffers work
No free Buffers available, all occupied.

15. How Buffers work
Now free Buffers
available
Dirty Buffers flushed to disk

16. Log Buffers
 Redo log buffer is circular buffer that hold
data of changes in database.
 Each redo entries contain data about
dml/ddl operations.
 It is usable to reconstruct data from redo
entries.
 Periodically Log Writer process writes data
from redo log buffer to disk.

17. How Log buffer works
LGWR flushes data from buffer
to disk Log Buffer
Redo Redo Redo
Log Log Log
group 1 group 2 group 3

18. Shared Pool
 Information of data dictionary views and privileges
stores in Dictionary Cache.
 Explain plans, Cursors, Bind variables, store
procedures store in Library Cache.
 Lock and Latches store in Control structure.
 Sort Extent Pool contains mapping of sort segment
and sorting information.
 There is no separate parameter for any sub
components.
 Parameter of Shared Pool is shared_pool_size.

19. How Shared Pool works
Raw Cache Library Cache
Control
Structure
Sort extent Pool
Tracking sort
segment Stores
Contains dictionary cursors, Hold locks &
data, privileges, PL/SQL latches
system data

20. Managing Shared Pool
 Shared pool can be flushed using “alter system
flush shared_pool” command.
 While flushing shared pool, all objects wipe off
and cursors become invalidate. Oracle reparse
all cursors after reuse.
 If object pinned using dbms_shared_pool.keep,
would never flush (after using above command).
 Default size of shared pool is 8 MB in 32 bit
platform and 64 MB in 64 bit platform.

21. Large Pool
 It contains I/O of server process
 It contains memory of Backup & Restore
operations
 It contains memory for shared server process
(mts configuration)
 It contains parallel server process and buffers
 There is no LRU algorithm to manage request in
Large Pool
 Parameter is large_pool_size

22. Java Pool
 It handles Java related memories
 It contains Java class, definitions and JVM components
 It handles request for session specific java code
 In Oracle 8i can be disable, but from Oracle 9i it can't
due to dependencies like feature of data warehousing
(SYS.DBMS_CDC_PUBLISH), export and import etc
 It determines from following query from database
 SELECT name, bytes FROM V$SGASTAT WHERE pool =
'java pool';
 Parameter is java_pool_size

23. Stream Pool
 It uses allocation of memory of stream
buffers
 If size is greater than 0, then allocates
stream in pool. If size is 0 then memory
will be allocated in shared pool
 Parameter is stream_pool_size

24. SGA_TARGET (Oracle 10g and
higher version)
 Introduce in 10g as Automatic Shared
Memory Management.
 If set nonzero value then Oracle
automatically determine and adjust SGA size.
 Oracle re-distribute memory allocation when
found change of workload.
 For re-organization of SGA size, responsible
background process is called MMAN (Memory
Manager).

25. Components of SGA_TARGET
 Buffer Cache (default)
 Log Buffer
 Shared Pool
 Stream Pool
 Java Pool
 Large Pool
 Manual allocation of buffer pools (keep & recyle)
 Manual allocation of Non-standard Buffer Cache
((controlled by DB_nK_CACHE_SIZE, n = {2, 4, 8,
16, 32})

26. New Automatic Memory
Management in Oracle 11g
 New parameters memory_target and
memory_max_target are introduced.
 Whole instance memory automatically managed using
these parameters.
 It overrides sga_target and pga_target.
 If both set then it will be treated as lower bound of
memory of same region.
 Memory_target is dynamic and memory_max_target is
static parameter.
 V$memory_target_advice dynamic view for more
reference and guidance of same new feture.

27. Oracle SGA in Nutshell
Presented by Gitesh P Trivedi
DBAMETRIX Solutions
www.dbametrix.com