The document discusses direct access to Oracle's shared memory (SGA) using C code. It describes the main regions of the SGA, how information is used automatically and by queries, and reasons for direct access such as reading hidden information or during database hangs. It outlines examining the SGA contents through externalized X$ tables, with most structures in the SGA not directly visible. The document provides a procedure to summarize waits from the V$SESSION_WAIT view by mapping it to the underlying X$KSUSECST table fields and offsets.

1. Oaktable
 Jonathan Lewis and ORACLE_TRACE
 Oracle_Trace crashes my Database
 I start the SGA attach by searching every offset
 Anjo Kolk says James Morle wrote a program using
x$ksmmem
 I show James my first draft using x$ksmmem
 James is baffled by why I'm hard coding offsets
 James says the offsets are in some X$ table
 I search, turn up a mail by Jonathan Lewis on x$kqfco
 Goldmine – all the offsets
 Thanks Mogens Nogard!
 Thanks to TomKyte's Decimal to Hex

3. http://oraperf.sourceforge.net

4. Direct Oracle SGA Memory
Access
Reading data directly from
Oracle’s shared memory segment
using C code
Wednesday, February 20, 2013

5. SGA on UNIX
SMON S nnn
D nnn P nnn
PMON
SGA CKPT
Redo Log
Shared Pool Database Buffer Cache Buffer
DBWR
ARCH
LGWR
oracle sqlplus Machine
Memory

6. SGA on NT
S nnn D nnn P nnn CKPT
SMON Machine
Shared Pool Database Buffer Cache
Redo Log
Buffer Memory
PMON
DBWR
LGWR ARCH oracle
Process Space sqlplus

7. What is the SGA
 Memory Cache
 Often Used Data
 Rapid Access
 Shareable
 Concurrently Access

8. SGA 4 main regions
 Fixed information
– Users info
– Database statistics
– X$dual
– etc
 Data block cache
 SQL cache ( library cache/shared pool)
 Redo log buffer

9. How is the SGA info Used?
 Automatically
– data blocks cached
– Log buffer
– Sql cache
– Updates of system and user statistics
 User Queries
– User info v$session
– System info v$parameter
– Performance statistics v$sysstat, v$latch, v$system_event
– Buffer cache headers, x$bh

10. Why Direct Access with C?
 Reading Hidden Information
– Sort info on version 7
– OPS locking info version 8
– Contents of data blocks (only the headers or visible in X$)
 Access while Database is Hung
 High Speed Access
– Sampling User Waits, catch ephemeral data
– Scan LRU chain in X$bh
– Statistically approximate statistics
 SQL statistics per user
 Low overhead

11. Database Slow or Hung
Often happens at the largest sites when cutting
edge support is expected.
 Shared Pool errors ORA 4031
 Archiver or Log file Switch Hangs
 Hang Bugs
 Library Cache Latch contention
 ORA-00379: no free buffers available in buffer
pool DEFAULT

12. Statistical Sampling
By Rapidly Sampling SQL statistics
and the users who have the statistics
open, one can see how much work a
particular user does with a particular
SQL statement

13. Low Overhead
 Marketing Appeal
 Clients are sensitive about their production
databases
 Heisenberg uncertainty affect – less overhead
less affect monitoring has on performance
which we are monitoring

14. SGA made visible through x$tables
 Most of the SGA is not visible
 X$KSMMEM Exception, Raw Dump of SGA
 Information Externalized through X$ tables
 Useful or Necessary information is Externalized
 Externalized publicly through V$ Tables

15. Machine Memory
0x80000000
SGA SGA

16. Buffer Cache
Graphic SGA
SGA
0x80000000
Fixed Area
Buffer Cache
Shared Pool
Log Buffer

17. Fixed Area
SGA X$KSUSECST- user waits
0x80000000
0x85251EF4

18. X$KSUSECST
170 Records
2328 bytes
0x85251EF4 Row 1 Row 2
Row 3 …

19. X$KSUSECST Record
One Record in X$KSUSECST
1276
2328 bytes

20. X$KSUSECST Fields
1276 1278 1280 1284 1288
Seq # Event # p1 p2 p3

21. Externalization of C structs: X$
tables
If Structure foo was externalized in a X$
SQL> describe x$foo
Column Name Type
------------------------------ --------
ADDR RAW(8)
INDX NUMBER
ID NUMBER
B NUMBER

22. SGA is One Large C Struct
struct foo
{
int id;
int A;
int B;
int C;
};
struct foo foo[N];

23. Struct C code
#include <stdio.h>
#include <fcntl.h>
#define N 20
/* structure definition: */
struct foo
{
int id;
int a;
int b;
int c;
};
/* end structure definition */

24. Struct Record
main(){
struct foo foo[20];
int fptr;
/* zero out memory of struct */
memset(foo,0,sizeof(foo));
foo[0].id=1; /* row 0 */
foo[0].a=12;
foo[0].b=13;
foo[0].c=13;

25. Struct Write to File
foo[1].id=2; /* row 1 */
foo[1].a=22;
foo[1].b=23;
foo[1].c=24;
/* write to file, simulate SGA */
if ((fptr = open("foo.out",O_WRONLY | O_CREAT,0777)) < 0 )
return -1;
write(fptr,foo,sizeof(foo));
return 0;
}

26. Simulate SGA with a File
write(fp,foo,sizeof(foo));

27. Simulate SGA with a File
Row 0 Row 1
ID A B C ID A …
0 1 3 4 6 8 bits
0 4
6 8
2 1
8 1
4 2
0 bytes
0 4 8 C
2 1
6 1
0 hex bytes
0 4 1 1 2
0 2
4 oct
0
Memory address 4 0 4
Increasing bytes

28. Struct File Contents
$ ./foo
$ ls -l foo.out
-rw-r--r-- joe dba 320 Feb 10 19:41 foo.out
int = 32 bits
Int = 4 bytes
20 entries * 4 int * 4 bytes/int = 320 bytes

29. od – octal dump
$ od -l foo.out
0000000 1 12 13 13
0000020 2 22 23 24
0000040 0 0 0 0
*
0000500

30. Struct File Contents
Address is in Hex
Column 2 is the ID
Column 3 is field A
Column 4 is field B
Column 5 is field C

31. X$ tables ?
 Ok, x$foo =~ foo[20]
 How do I get a list of x$ tables?
 Where is each X$ located?
 V$Fixed_Tables

32. V$Fixed_Table – list of X$ tables
SQL> desc v$fixed_table;
Name Null? Type
----------------------------------------- -------- -----------------
NAME VARCHAR2(30)
OBJECT_ID NUMBER
TYPE VARCHAR2(5)
TABLE_NUM NUMBER

33. Graphic: X$ Addresses
SGA
0x80000000
0x8????????
X$????

34. V$Fixed_Table
spool addr.sql
select
'select 'addr, ||''''||name||''''||' from ' || name ||' where
rownum < 2;'
from
v$fixed_table
where
name like 'X%'
/
spool off
@addr.sql

35. Example: finding the address
select
a.addr ,
'X$KSUSE'
from
X$KSUSE
where
rownum < 2 ;

36. X$ layout
6802B244 X$KSLEMAP
6802B7EC X$KSLEI
6820B758 X$KSURU
6820B758 X$KSUSE - v$session
6820B758 X$KSUSECST – v$session_wait
6820B758 X$KSUSESTA – v$session_stat
6820B758 X$KSUSIO
6826FBD0 X$KSMDD
6831EA0C X$KSRCHDL

37. What's in these X$ views
 V$ views are documented
 V$ views are based often on X$ tables
 The map from v$ to X$ is described in :
V$Fixed_View_Definition

38. V$Fixed_View_Definition
SQL> desc V$Fixed_View_Definition
Name Type
----------------------------------- --------------
VIEW_NAME VARCHAR2(30)
VIEW_DEFINITION VARCHAR2(4000)

39. Definition of V$Session_Wait
SQL> select
VIEW_DEFINITION
from
V$FIXED_VIEW_DEFINITION
where
view_name='GV$SESSION_WAIT';
VIEW_DEFINITION
-----------------------------------------------------------------------
select s.inst_id,s.indx,s.ksussseq,e.kslednam, e.ksledp1,s.ksussp1,s.ksussp1r,e.
ksledp2, s.ksussp2,s.ksussp2r,e.ksledp3,s.ksussp3,s.ksussp3r, decode(s.ksusstim,
0,0,-1,-1,-2,-2, decode(round(s.ksusstim/10000),0,-1,round(s.ksusstim/10000)))
, s.ksusewtm, decode(s.ksusstim, 0, 'WAITING', -2, 'WAITED UNKNOWN TIME', -1, '
WAITED SHORT TIME', 'WAITED KNOWN TIME') from x$ksusecst s, x$ksled e where bit
and(s.ksspaflg,1)!=0 and bitand(s.ksuseflg,1)!=0 and s.ksussseq!=0 and s.ksussop
c=e.indx

40. The Fields in X$ tables
 OK, I've picked an X$
 I've got the starting address
 Now, how do I get the fields?

41. X$KQFTA
 Kernel Query Fixed_view Table
 INDX use to find column information
 KQFTANAM X$ table names

42. X$KQFCO
 Kernel Query Fixed_view Column
 KQFCOTAB Join with X$KQFTA.INDX
 KQFCONAM Column name
 KQFCOOFF Offset from beginning of the row
 KQFCOSIZ Columns size in bytes

43. X$KSUSECST Fields
1276 1278 1280 1284 1288 Address
Seq # Event # p1 p2 p3
2 2 4 4 4 BYTES

44. SGA Contents in Resume
In resume:
Oracle takes the C structure defining the
SGA and maps it onto a shared memory
segment
Memory address Increasing
0x800000
0
Fixed SGA Buffer Redo Library
Cache Buffer Cache
Oracle provides access to some of the SGA
contents via X$ tables

45. **** Procedure *****
1. Choose a V$ view
2. Find base X$ Tables for v$ view
3. Map X$ fields to V$ fields
4. Get address of X$ table in SGA
5. Get the size of each record in X$ table
6. Get the number of records in X$ table
7. Get offsets for each desired field in X$ table
8. Get the base address of SGA

46. 1) V$SESSION_WAIT Example
 List of all users waiting
 Detailed information on the waits
 Data is ephemeral
 Useful in Bottleneck diagnostics
 High sampling rate candidate
 Event 10046 captures this info
Good table for SGA sampling

47. V$SESSION_WAIT Description
SQL> desc v$session_wait
Name Type
----------------------------------------- --------------------------
SID ,NUMBER
SEQ# ,NUMBER
EVENT ,VARCHAR2(64)
P1TEXT ,VARCHAR2(64)
P1 ,NUMBER
P1RAW ,RAW(4)
P2TEXT ,VARCHAR2(64)
P2 ,NUMBER
P2RAW ,RAW(4)
P3TEXT ,VARCHAR2(64)
P3 ,NUMBER
P3RAW ,RAW(4)
WAIT_TIME ,NUMBER
SECONDS_IN_WAIT ,NUMBER
STATE ,VARCHAR2(19)
)

48. V$SESSION_WAIT Short
SQL> desc v$session_wait
Name Type
---------------------------- -------------
SID NUMBER
SEQ# NUMBER
EVENT VARCHAR2(64)
P1 NUMBER
P2 NUMBER
P3 NUMBER)

49. V$FIXED_VIEW_DEFINITION
Gives mappings of V$ views to X$ tables
SQL> select
VIEW_DEFINITION
from
V$FIXED_VIEW_DEFINITION
where
view_name='V$SESSION_WAIT‘;

50. V$SESSION_WAIT View Definition
VIEW_DEFINITION
---------------------------------------------------------------------
select
s.inst_id,
s.indx,
s.ksussseq,
e.kslednam,
e.ksledp1,
s.ksussp1,
s.ksussp1r,
e.ksledp2,
s.ksussp2,
s.ksussp2r,
e.ksledp3,
s.ksussp3,
s.ksussp3r,
round(s.ksusstim / 10000),
s.ksusewtm,
decode(s.ksusstim, 0, 'WAITING', -2, 'WAITED UNKNOWN TIME',
-1, 'WAITED SHORT TIME', 'WAITED KNOWN TIME')
from
x$ksusecst s,
x$ksled e
where
bitand(s.ksspaflg,1)!=0 and
bitand(s.ksuseflg,1)!=0 and
s.ksussseq!=0 and
s.ksussopc=e.indx

51. View Definition Short
VIEW_DEFINITION
---------------------------------------------------------------------
select
s.indx,
s.ksussseq,
e.kslednam,
s.ksussp1,
s.ksussp2,
s.ksussp3
from
x$ksusecst s,
x$ksled e
where
s.ksussopc=e.indx

52. 2) V$SESSION_WAIT Based on
X$KSUSECT
VIEW_DEFINITION
---------------------------------------------------
-
select
indx,
ksussseq,
ksussopc,
ksussp1,
ksussp2,
ksussp3
from
x$ksusecst

53. Equivalent SQL Statements
select select
indx, sid
ksussseq, seq#
ksussopc, event
ksussp1, p1
ksussp2, p2
ksussp3 p3
from from
x$ksusecst v$session_wait )
Note: x$ksusecst. Ksussopc is the event #
x$ksled.kslednam is a list of the event names where
x$ksled.indx = x$ksusecst. ksussopc

54. 3) V$ to X$ Field Mapping

55. 4) Get base SGA address for X$ table
Find the location of X$KSUSECST in the SGA
SQL> select addr from x$ksusecst where rownum < 2
ADDR
--------
85251EF4

56. 5) Find the Size of Each Record
SQL> select
((to_dec(e.addr)-to_dec(s.addr))) row_size
from
(select addr from x$ksusecst where rownum < 2) s,
(select max(addr) addr from x$ksusecst where rownum < 3) e ;
ROW_SIZE
----------------
2328

57. 6) Find the Number of Records in the
structure
SQL> select count(*) from x$ksusecst ;
COUNT(*)
--------------
170

58. Get Offsets for Each Desired Field in X$ table
SQL> select c.kqfconam field_name,
c.kqfcooff offset,
c.kqfcosiz sz
from
x$kqfco c,
x$kqfta t
where
t.indx = c.kqfcotab and
t.kqftanam='X$KSUSECST'
order by
offset
;

59. X$KQFTA - X$ Tables Names
List of X$ tables
 INDX use to find column information
 KQFTANAM X$ table names
To get Column information join with X$KQFCO
X$KQFTA.INDX = X$KQFCO.KQFCOTAB

60. X$KQFCO – X$ Table Columns
List of all the columns in X$ Tables
 KQFCOTAB Join with X$KQFTA.INDX
 KQFCONAM Column name
 KQFCOOFF Offset from beginning of the row
 KQFCOSIZ Columns size in bytes

61. Field Offsets
FIELD_NAME OFFSET SZ
------------------------------ ---------- ----------
ADDR 0 4
INDX 0 4
KSUSEWTM 0 4
INST_ID 0 4
KSSPAFLG 1 1
KSUSSSEQ 1276 2
KSUSSOPC 1278 2
KSUSSP1 1280 4
KSUSSP1R 1280 4
KSUSSP2 1284 4
KSUSSP2R 1284 4
KSUSSP3 1288 4
KSUSSP3R 1288 4
KSUSSTIM 1292 4
KSUSENUM 1300 2
KSUSEFLG 1308 4

62. What are all the fields at OFFSET 0?
These are all calculated values and not stored
explicitly in the SGA.
ADDR memory address
INDX record number, like rownum
INST_ID database instance ID
KSUSEWTM calculated field

63. Unexposed Fields
What happens between OFFSET 1 and 1276?
• Unexposed Fields
• Sometimes exposed elsewhere, in our case
• V$SESSION
• V$SESSTAT

64. Fields at Same Address
Why do some fields start at the same address?
KSUSSP1
KSUSSP1R
Are at the same address
Equivalent of
V$SESSION_WAIT.P1
V$SESSION_WAIT.P1RAW
These are the same data, just exposed as
Hex
Decimal

65. 7) Offsets of Fields

66. 8) Get Base SGA Address
SQL> select addr from x$ksmmem where
rownum < 2
ADDR
--------------
80000000

67. Results X$KSUSECST

68. Machine Memory
0x80000000
SGA SGA

69. Fixed Area
SGA X$KSUSECST- user waits
0x80000000
0x85251EF4

70. X$KSUSECST
170 Records
2328 bytes
0x85251EF4 Row 1 Row 2
Row 3 …

71. X$KSUSECST Record
One Record in X$KSUSECST
1276
2328 bytes

72. X$KSUSECST Fields
1276 1278 1280 1284 1288
Seq # Event # p1 p2 p3

73. Attaching to the SGA
 UNIX System Call “shmat”
To attach to shared memory Unix as a system
call
void *shmat( int shmid,
const void *shmaddr,
int shmflg );

74. ID and Address arguments to “shmat”
The arguments are:
 shmid – shared memory identifier specified
 shmaddr – starting address of the shared memory
 shmflg - flags
The argument shmflg can be set to SHM_RDONLY . To
avoid any possible data corruption the SGA should only
be attached read only.
The arguments shmid and shmaddr need to be set to
Oracle’s SGA id and address.

75. Finding Oracle SGA’s ID and
Address
Use ORADEBUG to find the SGA id
SQL> oradebug setmypid
Statement processed.
SQL> oradebug ipc
Information written to trace file.

76. Finding Trace File
SQL> show parameters user_dump
NAME VALUE
----------------------- --------------------------------
user_dump_dest /u02/app/oracle/admin/V901/udump
SQL> exit
$ cd /u02/app/oracle/admin/V901/udump
$ ls -ltr | tail -1
-rw-r----- usupport dba Aug 24 18:01 v901_ora_23179.trc

77. Finding SHMID in Trace File
$ vi v901_ora_23179.trc
…
Total size 004456c Minimum Subarea size 00000000
Area Subarea Shmid Stable Addr Actual Addr
0 0 34401 0080000000 0080000000
…

78. Attaching to the SGA
Shmid 34401
Shmaddr 0x80000000
Shmflg SHM_RDONLY
The SGA attach call in C would be:
Shmat(34401, 0x80000000, SHM_RDONLY);
This call needs to be executed as a UNIX user who has
read permission to the Oracle SGA

79. C Code Headers
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <errno.h>
#include "event.h"
event.h is for translating the event #s into event
names

80. Events.h
Spool events.h
select 'char event[][100]={' from dual;
select '"'||name||'",' from v$event_name;
select ' "" };' from dual;
spool off

81. Define Base Addresses and Sizes
/* SGA BASE ADDRESS */
#define SGA_BASE 0x80000000
/* START ADDR of KSUSECST(V$SESSION_WAIT) */
#define KSUSECST_ADDR 0x85251EF4
/* NUMBER of ROWS/RECORDS in KSUSECST */
#define SESSIONS 150
/* SIZE in BYTES of a ROW in KSUSECST */
#define RECORD_SZ 2328

82. Define Offsets to Fields
#define KSUSSSEQ 1276 /* sequence # */
#define KSUSSOPC 1278 /* event # */
#define KSUSSP1R 1280 /* p1 */
#define KSUSSP2R 1284 /* p2 */
#define KSUSSP3R 1288 /* p3 */

83. Set Up Variables
main(argc, argv)
int argc;
char **argv;
{
void *addr;
int shmid;
int shmaddr;
void *current_addr;
long p1r, p2r, p3r;
unsigned int i, seq, tim, flg, evn;

84. Attach to SGA
/* ATTACH TO SGA */
shmid=atoi(argv[1]);
shmaddr=SGA_BASE;
if (
(void *)shmat(
shmid,
(void *)shmaddr,
SHM_RDONLY)
== (void *)-1 ) {
printf("shmat: error attatching to SGAn");
exit();
}

85. Set Up Sampling Loop
/* LOOP OVER ALL SESSIONS until CANCEL */
while (1) {
/* set current address to beginning of Table */
current_addr=(void *)KSUSECST_ADDR;
sleep(1);
printf("^[[H ^[[J"); /* clear screen */
/* print page heading */
printf("%4s %8s %-20.20s %10s %10s %10s n",
"sid", "seq", "wait","p1","p2","p3");

86. Loop over all Sessions
for ( i=0; i < SESSIONS ; i++ ) {
seq=*(unsigned short *)((int)current_addr+KSUSSSEQ);
evn=*(short *) ((int)current_addr+KSUSSOPC);
p1r=*(long *) ((int)current_addr+KSUSSP1R);
p2r=*(long *) ((int)current_addr+KSUSSP2R);
p3r=*(long *) ((int)current_addr+KSUSSP3R);
if ( evn != 0 ) {
printf("%4d %8u %-20.20s %10X %10X %10X n",
i, seq, event[evn] ,p1r, p2r,p3r
);
}
current_addr=(void *)((int)current_addr+RECORD_SZ);
}
}
}

87. Output
$ sga_read_session_wait 34401
sid seq wait p1 p2
p3
0 40582 pmon timer 12C 0 0
1 40452 rdbms ipc message 12C 0 0
2 43248 rdbms ipc message 12C 0 0
3 24706 rdbms ipc message 12C 0 0
4 736 smon timer 12C 0 0
5 88 rdbms ipc message 2BF20 0 0
8 178 SQL*Net message from 6265710 1 0

88. Pitfalls
 Byte Swapping
 32 bit vs 64 bit
 Multiple Shared Memory Segments
 Segmented Memory
 Addresses are "unsigned int"
 Misaligned Access

89. Little Endian vs Big Endian
 Is low byte values first or high byte values first ?
 a byte is 8 bits
– 00000000-11111111 bits,0 – 31 dec, 0x0 - 0xFF hex
 Big Endian is "normal" , highest bit first
 In ascii, the word "byte" is stored as
– b = 62, y = 79, t = 74, e = 65
 echo 'byte' | od -x
– b y t e
– 62 79 74 65
 Little Endian, ie byte swapped (Linux, OSF, Sequent, ? )
– y b e t
– 79 62 65 74

90. Byte Swap Example
Short = 2 bytes ie 16 bits
Goal, get the flag in the "second" byte
#ifdef __linux
uflg=*(short *)((int)sga_address)>>8;
#else
uflg=*(short *)((int)sga_address);
#endif

91. Byte Swap
Big Endian:
00 00 00 00 00 00 00 01
Little Endian
00 00 00 01 00 00 00 00
Solution, push the value over 8 places, to the
right,
ie >>8

92. 64 bit vs 32 bit
 SQL> desc x$ksmmem
Name Type
------------------------------------- ---------
ADDR RAW(4)
INDX NUMBER
INST_ID NUMBER
KSMMMVAL RAW(4)
-> 32 bit
Raw(8) -> 64 bit

93. Segmented Memory
x$ksuse – can be dis-contiguous
Work around:
select 'int users[]={' from dual;
select '0x'||addr||',' from x$ksuse;
select '0x0};' from dual;

94. Misaligned Access
 Some platforms seg fault when addressing
misaligned bytes, need to read in even bytes or
units of 4 bytes depending on platform
1 2 3 4 5 6 7 8

95. x$ksusecst Record: What's Missing?
One Record in X$KSUSECST
??? ???
1276
2328 bytes

96. Select Addr from X$? where Rownum<
2;
6802B244 X$KSLEMAP
6802B7EC X$KSLEI
6820B758 X$KSURU
6820B758 X$KSUSE – v$session
6820B758 X$KSUSECST – v$session_wait
6820B758 X$KSUSESTA – v$sesstat
6820B758 X$KSUSIO
6826FBD0 X$KSMDD
6831EA0C X$KSRCHDL

97. x$ksuse Record Contains
x$ksusecst
One Record in X$Ksusecst
v$session v$sesstat v$session_wait v$session
236 1276
2328 bytes
x$ksusesta x$ksusecst
x$ksuse

98. Getting v$sesstat addresses
select '#define '||
upper(translate(s.name,' :-()/*''','________'))||' '||
to_char(c.kqfcooff + STATISTIC# * 4 )
from
x$kqfco c,
x$kqfta t,
v$statname s
where
t.indx = c.kqfcotab
and ( t.kqftanam='X$KSUSESTA' ) and c.kqfconam='KSUSESTV'
and kqfcooff > 0
order by
c.kqfcooff
/

99. User Drilldown Query: 4 joins
select
w.sid sid,
w.seq# seq,
w.event event,
w.p1raw p1,
w.p2raw p2,
w.p3raw p3,
w.SECONDS_IN_WAIT ctime,
s.sql_hash_value sqlhash,
s.prev_hash_value psqlhash,
st.value cpu
from
v$session s,
v$sesstat st,
v$statname sn,
v$session_wait w
where
w.sid = s.sid and
st.sid = s.sid and
st.statistic# = sn.statistic# and
sn.name = 'CPU used when call started' and
w.event != 'SQL*Net message from client'
order by w.sid;

100. Other Fun Stuff
The next example is output from an SGA
program that follows the LRU of the Buffer
Cache
The program demonstrates the
• insertion point of LRU
• cold end of LRU
• hot end of the LRU
• Full Table Scan Insertion Point

101. LRU HOT

102. LRU COLD