1. SGA
Internals
Julian Dyke
Independent Consultant
Web Version
1 © 2005 Julian Dyke juliandyke.com

2. Agenda
 Introduction
 SGA
 Granules
 Fixed SGA
 Buffer Cache
 Shared Pool
 Permanent Areas
 Heaps
 Subheaps
 Library Cache
 Reserved Area
 Log Buffer
 Conclusion
2 © 2005 Julian Dyke juliandyke.com

3. Introduction
 Examples based on
 32 bit architecture
 Red Hat 2.1 AS
 Oracle 9.2.0.4
 Single (non-RAC) instance
 Examples affected by
 Oracle version
 Operating system
 Single instance / RAC
 Architecture (32/64)
 Parameters
3 © 2005 Julian Dyke juliandyke.com

4. Word Length
 Word length can be
 32 bit - 4 byte pointers
 64 bit - 8 byte pointers
 Also affects
 size of some integer variables e.g. int
 word alignment
 When moving from 32 bit to 64 bit Oracle recommends
doubling
 SHARED_POOL_SIZE
 SHARED_POOL_RESERVED_SIZE
 LARGE_POOL_SIZE
4 © 2005 Julian Dyke juliandyke.com

5. Double Linked Lists - Insertion
 Frequently used in SGA structures
 Each element includes pointers to next and previous elements
 Requires 8 bytes (32 bit systems) or 16 bytes (64 bit systems)
5000F430 55443080 55845C54 52175AC0
Head 5000F430
Tail 5000F430
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6. Double Linked Lists - Deletion
 Double linked lists are more efficient for
 insertion
 deletion
5000F430 55443080 55845C54 52175AC0
Head 55443080 55845C54 52175AC0 5000F430
Tail 52175AC0 5000F430 55443080 55845C54
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7. Memory Areas
08048000
 An Oracle process includes Executable
the following memory areas
0AAA28C0 PGA
Session Heap
 Executable
 PGA/Session Heap Shared
40000000 Libraries
 Shared Libraries
 SGA
50000000
 Stack SGA
584A4000
Stack
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8. Shared Memory
 Shared memory can be dumped to trace file using
$ sqlplus /nolog
SQL> CONNECT SYS/<password> AS SYSDBA
Connected
SQL> ORADEBUG SETMYPID
ORADEBUG SETMYPID
Statement processed
ORADEBUG IPC
SQL> ORADEBUG IPC
Information written to trace file
SQL> ORADEBUG TRACEFILE_NAME
/var/opt/oracle/admin/LX092001/udump/lx092001_ora_9824.trc
8 © 2005 Julian Dyke juliandyke.com

9. ORADEBUG IPC - Example
Area #0 `Fixed Size' containing Subareas 0-0
Total size 000000000006e5cc Minimum Subarea size 00000000
Area Subarea Shmid Stable Addr Actual Addr
0 0 163840 0x00000050000000 0x00000050000000
Fixed Area Subarea size Segment size
000000000006f000 0000000008800000
Area #1 `Variable Size' containing Subareas 1-1
Total size 0000000008000000 Minimum Subarea size 00400000
Area Subarea Shmid Stable Addr Actual Addr
Variable Area
1 1 163840 0x0000005006f000 0x0000005006f000
Subarea size Segment size
0000000008391000 0000000008800000
Area #2 `Redo Buffers' containing Subareas 2-2
Total size 00000000000a3000 Minimum Subarea size 00000000
Area Subarea Shmid Stable Addr Actual Addr
2 2 163840 0x00000058400000 0x00000058400000
Redo Buffers Subarea size Segment size
00000000000a3000 0000000008800000
Area #3 `skgm overhead' containing Subareas 3-3
Total size 0000000000001000 Minimum Subarea size 00000000
Area Subarea Shmid Stable Addr Actual Addr
3 3 163840 0x000000584a3000 0x000000584a3000
OS Specific Subarea size Segment size
0000000000001000 0000000008800000
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10. V$SGA
 Describes sizes of main components in SGA
 Used by SHOW SGA command in SQL*Plus
SELECT name, value FROM v$sga;
Name Value
Fixed Size 452044
Variable Size 83886080
Database Buffers 50331648
Redo Buffers 667648
 Based from X$KSMSD
 X$KSMSD derived from ksmstv_ (ksmst) in Fixed SGA
10 © 2005 Julian Dyke juliandyke.com

11. Shared Global Area
 Contains
 Fixed SGA
 Buffer Pool
 Shared Pool Oracle 7.0 and above
 Large Pool Oracle 8.0 and above
 Java Pool Oracle 8.1.5 and above
 Streams Pool Oracle 10.1 and above
 Redo buffers
 Buffer Pool includes
 Default cache
 Keep and Recycle cache Oracle 8.0 and above
 2K, 4K, 8K, 16K and 32K cache Oracle 9.0.1 and above
11 © 2005 Julian Dyke juliandyke.com

12. Granules
 Introduced in Oracle 9.0.1
 SGA divided into granules
 In Oracle 9.2 granule size dependent on SGA_MAX_SIZE
 4 mb SGA_MAX_SIZE <= 128 mb
 16 mb SGA_MAX_SIZE > 128 mb
 If SGA_MAX_SIZE not set explicitly then defaults to sum of
individual pool parameters
 SGA_MAX_SIZE cannot be dynamically modified
12 © 2005 Julian Dyke juliandyke.com

13. Granules
 Pool parameters rounded up to nearest granule
 Each pool occupies one or more granules
 Different buffer caches held in separate granules
 First "granule" contains
 Fixed SGA
 Granule directory
 Heap headers
 Last "granule" contains
 Guard pages
 Redo buffer
 Operating system specific overhead
 Remaining space unused
13 © 2005 Julian Dyke juliandyke.com

14. Granules
SGA_MAX_SIZE = 128M 4M Fixed SGA 4M
DB_CACHE_SIZE = 48M Free 16M
JAVA_POOL_SIZE = 20M
LARGE_POOL_SIZE = 12M Buffer Pool 48M
SHARED_POOL_SIZE = 20M
128M Java Pool 20M
Large Pool 12M
Shared Pool 32M
Note – shared pool size
automatically increased Redo Buffer 4M
from 20M to 32M 4M
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15. Granule Operations
 The following pools can be dynamically resized
Pool Parameter Version
Shared Pool SHARED_POOL_SIZE 9.0.1 and above
Default DB_CACHE_SIZE 9.0.1 and above
2K DB_2K_CACHE_SIZE 9.0.1 and above
4K DB_4K_CACHE_SIZE 9.0.1 and above
8K DB_8K_CACHE_SIZE 9.0.1 and above
16K DB_16K_CACHE_SIZE 9.0.1 and above
32K DB_32K_CACHE_SIZE 9.0.1 and above
Keep DB_KEEP_CACHE_SIZE 9.0.1 and above
Recycle DB_RECYCLE_CACHE_SIZE 9.0.1 and above
Large Pool LARGE_POOL_SIZE 9.2.0 and above
Java Pool JAVA_POOL_SIZE 10.1 and above
 Streams pool cannot be dynamically resized in Oracle 10.1
15 © 2005 Julian Dyke juliandyke.com

16. Granule Views
 The following views support dynamic memory management
 Introduced in Oracle 9.2
 V$SGA_DYNAMIC_COMPONENTS
 V$SGA_DYNAMIC_FREE_MEMORY
 V$SGA_CURRENT_RESIZE_OPS
 V$SGA_RESIZE_OPS
 Not always reliable
 Introduced in Oracle 10.1
 V$SGAINFO
16 © 2005 Julian Dyke juliandyke.com

17. X$KSMGE
Introduced in Oracle 9.2
Describes individual granules Granule ID
ADDR RAW(4) 0 Free
2 Shared Pool
INDX NUMBER 3 Large Pool
INST_ID NUMBER 4 Java Pool
5 Buffer Pool
GRANNUM NUMBER
GRANTYPE NUMBER INVALID (Free)
ALLOCATED
GRANSTATE VARCHAR2(16)
GRANFLAGS NUMBER Granule Address
LOCALITY NUMBER
Granule Size
BASEADDR RAW(4)
GRANSIZE NUMBER Next granule ID
GRANNEXT NUMBER
Previous granule ID
GRANPREV NUMBER
17 © 2005 Julian Dyke juliandyke.com

18. Granule Dumps
 Granules can be dumped using
ALTER SESSION SET EVENTS
‘immediate trace name granulelist level <level>’
 where <level> is
Heap Level
Null Granule 255
Home Granule 511
Shared Pool 767
Large Pool 1023
Java Pool 1279
Buffer Cache 1535
18 © 2005 Julian Dyke juliandyke.com

19. Fixed SGA
 Area containing all fixed variables
 Contains pointers to all other structures in SGA
 Variable name, type, address and size
determined when Oracle executable is linked
 Located at start of first granule of SGA
50000000
Fixed SGA
5001D9E8 Granule Directory
5001DF50
Heap Headers
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20. X$KSMFSV
 Externalises name, type, address and size of all variables in
fixed SGA
Name
ADDR RAW(4)
INDX NUMBER Type
INST_ID NUMBER
Address
KSMFSNAM VARCHAR2(64)
KSMFSTYP VARCHAR2(64) Size
KSMFSADR RAW(4)
KSMFSSIZ NUMBER
 SGA can be dumped using
ORADEBUG FIXEDSGA
20 © 2005 Julian Dyke juliandyke.com

21. Global Area Dumps
 Global areas can be dumped using
ALTER SESSION SET EVENTS
‘immediate trace name global_area level <level>’
 where <level> is
Heap Level
PGA 1
SGA 2
PGA + SGA 3
UGA 4
PGA + UGA 5
SGA + UGA 6
PGA + SGA + UGA 7
 More detail is included at levels 0x08 0x10 0x18 (OR)
21 © 2005 Julian Dyke juliandyke.com

22. X$KSMMEM
 Externalises contents of all locations in the SGA
Address
ADDR RAW(4)
INDX NUMBER
INST_ID NUMBER
Value
KSMMMVAL RAW(4)
 Does not work on Windows platforms
22 © 2005 Julian Dyke juliandyke.com

23. Buffer Cache
51400000 DB_CACHE_SIZE = 48M
51800000 DB_BLOCK_SIZE = 8192
51C00000  Buffer Cache includes 12 x 4M granules
52000000  Each granule contains 500 buffers
52400000  Buffer Cache contains 6000 buffers
52800000
Block Buffers Per
52C00000 Size Granule
53000000
4mb 16mb
53400000
53800000 2048 1875 7503
4096 979 3916
53C00000
8192 500 2002
54000000
16384 253 1012
32768 127 509
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24. Buffer Headers
 Each buffer has a buffer header
 In 9.2.0.4 buffer headers are 188 bytes
 Buffer headers are stored in same granule as buffers
 Buffer headers include
 Replacement list
 Hash list
 Pointer to buffer
Buffer
Headers
Buffers
Granule
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25. X$BH
 Externalises buffer headers
ADDR RAW(4)
Hash List Address
INDX NUMBER
INST_ID NUMBER Block Size
HLADDR RAW(4)
BLSIZ NUMBER Hash List
NXT_HASH RAW(4)
Replacement List
PRV_HASH RAW(4)
NXT_REPL RAW(4) Tablespace#
PRV_REPL RAW(4)
Absolute File Number
TS# NUMBER
FILE# NUMBER Relative File Number
DBARFIL NUMBER Block Number
DBABLK NUMBER
OBJ NUMBER Object ID
BA RAW(4) Buffer Address
CR_SCN_BAS NUMBER
25 © 2005 Julian Dyke juliandyke.com

26. Shared Pool
56400000 Shared Pool includes
 Permanent Area
56800000
 Segmented Arrays
56C00000  Library Cache
57000000  Row Cache
 Reserved Area
57400000
57800000 Shared Pool occupies
 8 x 4M granules = 32M
57C00000
 SHARED_POOL_SIZE = 20M
58000000
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27. V$SGASTAT
 Describes sizes of individual components in SGA
SELECT pool, name, value FROM v$sgastat;
Pool Name Value
fixed sga 452044
buffer cache 50331648
log buffer 656384
shared pool enqueues 51680
shared pool sessions 91656
shared pool library cache 1480240
shared pool dictionary cache 1614976
shared pool free memory 19746760
large pool free memory 12582912
java pool free memory 20971520
27 © 2005 Julian Dyke juliandyke.com

28. Permanent Areas
 Allocated at instance startup 56400000
 Contain structures such as
 processes 56800000
 sessions
56C00000
 segmented arrays
SELECT ksmchptr, ksmchsiz 57000000
FROM x$ksmsp
WHERE ksmchcls = 'perm';
57400000
Address Size
57800000
5641F000 3967868
5681F000 2718736 57C00000
56AB6C10 905116
56C1F00 4063188 58000000
5701F000 4067328
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29. Sessions
 Array of sessions stored in shared pool permanent area
 Allocated at instance startup
 Number of elements specified by SESSIONS parameter
 In Oracle 9.2 each element is 2412 bytes
 Session array externalised by
 X$KSUSE
 General information
 Used by V$SESSION
 X$KSUSESTA
 Statistics
 Used by V$SESSTAT
 X$KSUSECST
 Current Waits
 Used by V$SESSION_WAIT
29 © 2005 Julian Dyke juliandyke.com

30. Sessions
ksusga_
struct ksusg
Array of X$KSUSE X$KSUSESTA X$KSUSECST
Pointers V$SESSION V$SESSTAT V$SESSION_WAIT
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31. Segmented Arrays
 Used to store arrays of objects
 Array too large to fit in granule
 Array may grow dynamically
 Objects using segmented arrays include
 enqueues (locks)
 enqueue resources (resources)
 transactions
 transaction branches
 Segmented arrays managed recursively by segmented array
 Segmented arrays externalised in X$KSMDD
31 © 2005 Julian Dyke juliandyke.com

32. Segmented Arrays
Segmented Call
Arrays
Segmented
Array
Segmented
Enqueues
Array Segmented
Header Array
Segmented
Array Enqueue
Header Resources
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33. X$KSMDD
 Externalises segmented array headers Name of array
ADDR RAW(4)
INDX NUMBER
INST_ID NUMBER
NAME VARCHAR2(30)
ELEMENTS_CHUNK NUMBER
ITEMS_PT NUMBER
INITENTRIES NUMBER
NUMENTRIES NUMBER Number of
chunks
CURENTRIES NUMBER
NUMCHUNKS NUMBER
Address of parent
ELEMSIZE NUMBER heap
FLAGS NUMBER
HEAP RAW(4)
SECONDARY RAW(4)
33 © 2005 Julian Dyke juliandyke.com

34. Heaps
 A heap consists of one or more extents
 Each heap extent occupies a single granule
 Each extent contains one or more chunks
 Each heap has a header containing
 list of used chunks
 list of free chunks
Heap Extent 0 Extent 1 Extent 2
Header
Free List Chunks
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35. Extent
Chunks Extent
Header
 Chunks contain Chunk
 header Header
 body
Chunk
Body
 Size of chunk header
dependent on chunk type
 16 bytes <= size <= 32 bytes
 Chunks chained through extent
 Chunks can be
 permanent
 recreatable
 freeable
 free
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36. X$KSMSP
 Externalises chunks in the shared pool Description of chunk type
Address of chunk
ADDR RAW(4)
Size including header
INDX NUMBER
INST_ID NUMBER Class
●Perm
KSMCHIDX NUMBER ●Recreate
KSMCHDUR NUMBER ●Freeable
●Free
KSMCHCOM VARCHAR2(16) ●R-Free
KSMCHPTR RAW(4) ●R-Freeable
KSMCHSIZ NUMBER Type (recreate only)
●0x18 - KGL Handle
KSMCHCLS VARCHAR2(8) ●0x24 - Fixed Allocation
KSMCHTYP NUMBER ●0x74 - KQR PO
●0x80 - KQR SO
KSMCHPAR RAW(4) ●0xFFF - Extended header
Address of parent
36 © 2005 Julian Dyke juliandyke.com

37. Heap Dumps
 Heaps can be dumped using
ALTER SESSION SET EVENTS
‘immediate trace name heapdump level <level>’;
 where <level> is
Heap Summary Detail
PGA 1 1025
SGA 2 2050
UGA 4 4100
CGA – Current Call 8 8200
CGA – User Call 16 16400
LGA – Large Pool 32 32800
37 © 2005 Julian Dyke juliandyke.com

38. Free List
 Heap free lists contain 255 buckets
 Each bucket contains double linked list to free chunks
 Bucket sizes increase in
 increments of 4 bytes - 16, 20, 24, 28, 32 ... 808, 812
 increments of 64 bytes - 876, 940, 1004 ... 3948, 4012
 then 4108, 8204, 16396, 32780, 65548
 Reduces fragmentation
38 © 2005 Julian Dyke juliandyke.com

39. Free List
 Example
Heap Header
16 24 byte chunks
20
Buckets
24
28 36 byte chunks
32
36
40
44
48
52
52 byte chunks
56
60
64
39 © 2005 Julian Dyke juliandyke.com

40. Subheaps
 Heaps can contain subheaps
 Objects can have up to 10 subheaps
 SQL statements include subheaps 0 and 6
 Subheaps consist of one or more extents
 Subheaps have heap headers
 Subheap header format similar to heap header format
 Only one freelist containing all free space
Extent 0 Extent 1 Extent 2
Subheap
Header
Free
List Chunk
40 © 2005 Julian Dyke juliandyke.com

41. Subheap Dumps
 In Oracle 9.0.1 and below to dump a subheap, first obtain the
address of the subheap and convert to decimal
0x56b95c0c = 1454988300
 For a summary dump use
ALTER SESSION SET EVENTS
‘immediate trace name heapdump_addr level 1454988300’;
 For a detailed dump add 1 to the address e.g.
ALTER SESSION SET EVENTS
‘immediate trace name heapdump_addr level 1454988301’;
 In Oracle 9.2 and above to dump the subheap summary use
ALTER SESSION SET EVENTS
‘immediate trace name heapdump_addr level 1, addr 0x56b95c0c’;
 For a detailed dump use
ALTER SESSION SET EVENTS
‘immediate trace name heapdump_addr level 2, addr 0x56b95c0c’;
41 © 2005 Julian Dyke juliandyke.com

42. Subheap Dumps
 Example - dump the SGA using
ALTER SESSION SET EVENTS ‘immediate trace name heapdump level 2’;
Chunk 56b94dc8 sz= 304 recreate "KGL handles " latch=0x56efd918
Chunk 56b94ef8 sz= 560 freeable "library cache " ds=0x56b95c0c
Chunk 56b95128 sz= 540 recreate "KQR PO " latch=(nil)
Chunk 56b95344 sz= 540 recreate "KQR PO " latch=0x56d719f4
Chunk 56b95560 sz=1116 freeable "KGLS heap " ds=0x56b96d1c
Chunk 56b959bc sz= 20 free " "
Chunk 56b959d0 sz= 560 recreate "library cache " latch=(nil)
ds 56b95c0c sz=1120 ct= 2
56b94ef8 sz= 560
Chunk 56b95c00 sz= 96 freeable "library cache "
 Dump subheap using
ALTER SESSION SET EVENTS
‘immediate trace name heapdump_addr level 1, addr 0x56b95c0c’;
42 © 2005 Julian Dyke juliandyke.com

43. Subheap Dumps
HEAP DUMP heap name="library cache" desc=0x576193c4
Extent 0 extent sz=0x224 alt=32767 het=16 rec=9 flg=2 opc=2
parent=0x5000002c owner=0x5761826c nex=(nil) xsz=0x224
EXTENT 0 addr=0x57615130
Chunk 57615138 sz= 312 perm "perm " alo=260
Chunk 57615270 sz= 76 freeable "kgltbtab "
Chunk 576152bc sz= 76 freeable "kgltbtab "
Extent 1 Chunk 57615308 sz= 76 freeable "kgltbtab "
EXTENT 1 addr=0x57616a88
Chunk 57616a90 sz= 512 perm "perm " alo=512
Extent 2 Chunk 57616c90 sz= 28 free " "
EXTENT 2 addr=0x57618254
Chunk 5761825c sz= 172 perm "perm " alo=172
Chunk 57618308 sz= 36 free " "
Free List Total heap size = 1288
FREE LISTS:
Bucket 0 size=0
Chunk 57616c90 sz= 28 free " "
Chunk 57618308 sz= 36 free " "
Total free space = 64
UNPINNED RECREATABLE CHUNKS (lru first):
PERMANENT CHUNKS:
Chunk 57615138 sz= 312 perm "perm " alo=260
Chunk 57616a90 sz= 512 perm "perm " alo=512
Chunk 5761825c sz= 172 perm "perm " alo=172
Permanent space = 996
43 © 2005 Julian Dyke juliandyke.com

44. X$KSMHP
 Externalises chunks in a subheap
ADDR RAW(4)
INDX NUMBER Address of data segment
INST_ID NUMBER
KSMCHDS RAW(4) Description of chunk type
KSMCHCOM VARCHAR2(16) Address of chunk
KSMCHPTR RAW(4)
KSMCHSIZ NUMBER Size including header
KSMCHCLS VARCHAR2(8) Class
KSMCHTYP NUMBER ●Perm
●Free
KSMCHPAR RAW(4)
KSMCHOWN RAW(4) Address of parent heap
44 © 2005 Julian Dyke juliandyke.com

45. X$KSMHP
SQL> SELECT COUNT(*) FROM x$ksmhp;
COUNT(*)
--------
SQL> SELECT COUNT(*) FROM
0
x$ksmhp;
0 rows
SQL> SELECT kglobhd6 FROM x$kglob
WHERE kglnaobj = 'SELECT SUM(c1) FROM t1'
AND kglhdadr != kglhdpar;
KGLOBHD6
--------
5755E798
SQL> SELECT COUNT(*) FROM x$ksmhp
WHERE ksmchds = HEXTORAW ('5755E798');
COUNT(*)
--------
1
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46. Library Cache
 Database objects
 Tables
 Views
 Packages
 Functions
 Shared cursors
 SQL statements
 Anonymous PL/SQL block
 Stored PL/SQL procedures and functions
 Java stored procedures
 Methods
46 © 2005 Julian Dyke juliandyke.com

47. Library Cache
 For example
CREATE TABLE t1
(
c1 NUMBER,
c2 NUMBER,
c3 NUMBER,
c4 NUMBER
);
CREATE INDEX i1 ON t1 (c1);
CREATE INDEX i2 ON t1 (c3);
SELECT SUM(c2)
FROM t1
WHERE c3 = 42
AND c4 < 2004;
0 SELECT STATEMENT
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (BY INDEX ROWID) OF 'T1'
3 2 INDEX (RANGE SCAN) OF 'I2'
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48. Library Cache 512 x 1 word
pointers
Library Cache
Object Handle
256 x DLL
Heap headers
ksmgsg_ KGLHD
Library
struct kgsms Cache
KGLHD
KGLHD
KGLHD
512 x 256 =
131072 buckets
Anonymous
List
KGLHD KGLHD KGLHD KGLHD
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49. Library Cache Object - Parent
KGLHD KGLNA Parent
SELECT SUM (c2) FROM t1 Name
WHERE c3 = 42 AND c4 < 2004
KGLOB Parent
Object
Heap 0
Parent
Handle X$KGLOB Child
Handle
KGLHD
Child 1
16 x 1 word KGLHD
pointers Child 2
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50. Library Cache Object - Child
Child Statistics
Object Subheap
KGLHD etc
Header
KGLOB
Heap 0
Child Heap 6
Handle Subquery
Header
X$KGLOB Subheap
Header SELECT
Statement
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51. Library Cache - Statement
Subquery
Header
Explain SORT
Plan Operation
(AGGREGATE)
Explain
Plan Operation TABLE ACCESS (BY
INDEX ROWID)
Explain INDEX
Plan Operation
(RANGE SCAN)
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52. Sort (Aggregate)
Output SORT (AGGREGATE)
Columns
Expression
Function Expression
Op=SUM
Expression
Column Expression
Variable
Column Definition Column Alias
Obj =1234 Alias=C2
Col=2
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53. Table Access (By Index Rowid)
Output Predicate
Columns TABLE ACCESS (BY INDEX ROWID)
c4 < 2004
ROWID
Variable Expression Expression Condition
Column Definition Column Expression Expression
Obj =1234
Col=2
Variable Function Expression
Op=LT
Column Definition Table Alias Expression Expression
Obj =1234 Alias=T1
Col=ROWID
Column Expression Constant Expression
Variable Constant
Value=2004
Column Definition Column Alias
Obj =1234 Alias=C4
Col=4
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54. Index (Range Scan)
Output Predicate
Columns INDEX (RANGE SCAN) c3 = 42
Variable Expression Array
Column Definition Expression
Obj =1234
Col=ROWID
Function Expression
Op=EQ
Expression Expression
Column Expression Constant Expression
Variable Constant
Value=42
Column Definition Column Alias
Obj =1234 Alias=C3
Col=3
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55. Shared Pool Reserved Area
 Area of memory reserved for large contiguous requests for
memory
 Reduces fragmentation in shared pool
 Only used if no space available in shared pool
 Summarised in V$SHARED_POOL_RESERVED
 SHARED_POOL_RESERVED_SIZE
 specifies size of shared pool in bytes
 defaults to 5% of SHARED_POOL_SIZE
 _SHARED_POOL_RESERVED_PCT
 specifies percentage of shared pool to reserve
 defaults to 5%
 _SHARED_POOL_RESERVED_MIN_ALLOC
 specifies minimum chunk size e.g. 4400
55 © 2005 Julian Dyke juliandyke.com

56. X$KSMSPR
 Externalises address, size and class of all chunks in the
shared pool Comment
● free memory
ADDR RAW(4) ● reserved_stopper
INDX NUMBER
INST_ID NUMBER Address
KSMCHCOM VARCHAR2(16)
KSMCHPTR RAW(4) Size in bytes
KSMCHSIZ NUMBER
KSMCHCLS VARCHAR2(8) Class
●R-free
KSMCHTYP NUMBER ●R-freeable
KSMCHPAR RAW(4)
56 © 2005 Julian Dyke juliandyke.com

57. Shared Pool Reserved Area
56400000
SELECT ksmchcom,ksmchptr,ksmchsiz,ksmchcls
FROM x$ksmspr 56800000
ORDER BY ksmchptr;
56C00000
KSMCHCOM KSMCHPTR KSMCHSIZ KSMCHCLS
reserved_stopper 56400024 20 R-freeable 57000000
free memory 56400038 126900 R-free
reserved_stopper 5641EFEC 20 R-freeable 57400000
reserved_stopper 56800024 20 R-freeable
free memory 56800038 126900 R-free 57800000
reserved_stopper 5681EFEC 20 R-freeable
reserved_stopper 56C00024 20 R-freeable 57C00000
free memory 56C00038 126900 R-free
58000000
reserved_stopper 56C1EFEC 20 R-freeable
reserved_stopper 57000024 20 R-freeable
57 STOP 2005 Julian Dyke
© juliandyke.com

58. Log Buffer
58400000 Guard Page
LOG_BUFFER = 524288
 2 x 4K guard pages (DEADFACE)
 1288 x 512 byte blocks for redo
 Each 512 byte includes 16 byte header
 Usable redo = 1288 x 496 = 638848 bytes
Header - 16 bytes
Body - 496 bytes
584A2000
Guard Page
58 STOP 2005 Julian Dyke
© juliandyke.com

59. Thank you for your interest
For more information and to provide feedback
please contact me
My e-mail address is:
info@juliandyke.com
My website address is:
www.juliandyke.com
59 © 2005 Julian Dyke juliandyke.com