COMPUWARE
CHUCK
HOOVER
SERIES
Everything You Ever Wanted to
Know About DB2 Buffering
Table of Contents
DB2 Database Services
Basic Functions of the
Buffer Manager
Improvements V3 - V6
The Current Sub-System
Configuring & Tuning
DB2 Database Services
Basic Functions of the
Buffer Manager
Improvements V3 - V6
The Current Sub-System
Configuring & Tuning
DB2 Address Spaces
OS/390
IBM
Resource
Lock Manager
(IRLM)
DB2
DB2
System Services Database Services
Address
Address
Space
Space
Sort Work
Area
Allied Agent
Address
Space
RID
Sort Area
Log
Buffers
DB2
Log
BSDS
Buffers
DB2
Bootstrap
Data Set
BSDS
Virtual Buffer
Pool(s)
1.6 GB Max.
DB2
Database
DB2
Catalog
Directory
Distributed
Data Facility
Hiperpool(s)
EDM Pool
Locking Control
Elements
Optional
“Stuff”
IMS, CICS,
TSO, Batch
Applications
Stored
Procedure
Address
Space(s)
Data Spaces
DB2 Database Services
Application
Program
Relational
Buffer Manager Data Manager
Data System
(RDS)
DB2
Data- OS/390/DFP
base
Physical
4K Physical
Blocks
Blocks
(Pages)
on DASD
Logical
Records
Results Set Consisting
(Rows)
of Columns from
Within Indexes
& Table Spaces Multiple Rows from
Multiple Tables
Lock Manager,
Index Manager
and
Log Manager
Fetch Columns
from Rows
of Results
Table (Set)
DB2
Attach
Relational Data System
Application
Program
Relational
Data System
(RDS)
Qualified
Rows from
Data Manager
Optimizer for
Access Path
Selection
Stage Two
Predicates
Column
Movement
Join, Union
Logic
Sorting
Column and
Scalar Functions
Database Manager
Data Manager
Access Path
Navigation
GETPAGE
RELPAGE
Logical
Records
(Rows)
Within Indexes
WRITE and
Table Spaces
SET
PENDING
Lock Manager,
Index Manager
and
Log Manager
Data Page
Management
Index Page
Management
Page Space
Management
Work File
Management
Buffer Manager
Interface
Stage One
Predicates
DFP/VSAM
DB2
Database
DB2
Catalog
Directory
DB2
Database
OS/390/DFP
DB2
Database
DB2
Working
Storage
DB2 Buffer
Pool
Access Method
Logic
Device Error
Handling
Buffer Manager Major Functions
Buffer Manager
BP49
BP3
.
GETPAGE, RELPAGE,
SET WRITE PENDING
.
BP2
BP1
OS/390/DFP
BP0
4K Buffers
BP49
BP3
OS/390/ADMF
.
Data Set
OPEN / CLOSE
Buffer/Cache
Management
Read
Engines
Write
Engines
DFP / DASD
Interface
Hiperspace
Management
.
BP2
BP1
BP0
MVPG
V3 With
Hiperpools
8K Buffers
BP49
BP3
.
.
BP2
BP1
BP0
16K Buffers
OS/390/XES
V4 With
Data Sharing
BP49
BP3
.
.
BP2
BP1
BP0
32K Buffers
Coupling
Facility
Communication
DB2 Database Services Flow
Buffer Manager Data Manager
Relational
Data System
(RDS)
Application
Program
Fetch Cursor
DECLARE ... CURSOR FOR
SELECT (20 COLUMNS)
FROM CUSTOMER
WHERE SC1 = :HV1
AND SC2 = :HV2
AND SC3 = NSC1
DB2 Database Services Flow
Relational
Buffer Manager Data Manager
Data System
GETPAGE
. . . . . . . . . . . . . . . . .(RDS)
....
OBID X PAGE 2
(OBID X PAGE 2)
Application
Program
Fetch Cursor
Row 1
Row 2
Row 3
Row 4
Row 5
Row 6
OBID X PAGE 3
Row 3
Row 4
Fetch Cursor
Row 6
RELPAGE (OBID X PAGE 2)
GETPAGE (OBID X PAGE 3)
Row 1
Row 1
Row 2
Row 2
Row 6
Row 6
RELPAGE (OBID X PAGE N)
Return Code +100
Process Columns
from Page 3 Row 1
Fetch Cursor
Process Columns
from Page N Row 6
Fetch Cursor
GETPAGE
Page in
Virtual Buffer Pool?
Yes
Empty Buffer
in VBP?
Yes
Buffer Pool
Hit
Find Least-Recently-Used
Buffer in VBP
Move L-R-U Buffer
Contents to HP?
No
Write L-R-U Buffer
Contents to Hiperpool
Steal L-R-U Buffer
for Requested Page
Page in
Hiperpool?
Move Page to Virtual
Buffer Pool - Hiperpool Hit
Free Buffer in Hiperpool
Post LRU Chain
and Return
No
Read Page From
Disk - BP Miss
Buffer Pool Organization
Control
Information
and L-R-U
Anchor Points
Hash Table
Virtual Buffer Pool N
Buffer Headers
Please GETPAGE
OBID X Page Y
Look-Aside Hash Search
Hash Table
Which
Pool?
Buffer Headers
Data Manager
P(3)
= 0.14038
P(5)
= 0.17547
P(<=5) = 0.61596
P(>10) = 0.00284
Hashing
Algorithm
“Miss”
OBID Y
Page N
OBID Z
Page B
OBID T
Page B
OBID W
Page Q
OBID X
Page G
Repeat Logic for
Hiperpool (if one exists) Stop if DB2 V2.R3 (VBP Miss)
L-R-U* Buffer Chaining
For Locating
For Caching
Hash Table
Control Information
and L-R-U Anchor Points
Most Recent Sequential
Least Recent Sequential (STEAL)
Most Recent Random (HOT)
Least Recent Random (COLD)
OBID Y
Page N
OBID Z
Page B
OBID X
Page E
OBID Y
Page F
OBID W
Page G
OBID T
Page B
OBID X
Page D
OBID Z
Page D
OBID Y
Page H
OBID W
Page Q
OBID X
Page C
OBID Z
Page H
OBID X
Page A
OBID X
Page G
OBID W
Page E
OBID Y
Page E
OBID Y
Page C
OBID X
Page B
OBID X
Page I
OBID Z
Page B
* Least-Recently-Used
Buffer Aging and Stealing
Random GETPAGE Calls for Page Set X1 Page P1
tn
t0
Random
Synchronous
Disk Read
Page P1
Page Set X1
on Disk
Virtual Buffer Pool
Overlay
LeastRecentlyUsed Page
With Target
of Current
GETPAGE
Call
Random
Synchronous
Disk Read
Page P1
From Time t0 to Time tn
Eight GETPAGE Calls
Two synchronous disk reads
Overlaid with new page once
Nine L-R-U chain modifications
Buffering Versus Caching
Buffer: Something that reduces the shock of impact
An area to store data temporarily
Batch or Sequential Process
Buffer Set “A”
Input
“Flat”
File
Fill
Buffer
Set
“A”
Batch Program Waits
Output
“Flat”
File
Buffering Versus Caching
Buffer: Something that reduces the shock of impact
An area to store data temporarily
Batch or Sequential Process
Buffer Set “A”
Input
“Flat”
File
Fill
Buffer
Set
“B”
Batch Program Reads and Processes
Logical Records in Buffer Set “A”
and Writes Updated Logical
Records in Buffer Set “C”
Buffer Set “B”
Buffer Set “C”
Output
“Flat”
File
Buffering Versus Caching
Buffer: Something that reduces the shock of impact
An area to store data temporarily
Batch or Sequential Process
Buffer Set “A”
Input
“Flat”
File
Fill
Buffer
Set
“A”
Buffer Set “D”
Batch Program Reads and Processes Write
Buffer
Logical Records in Buffer Set “B”
Set
and Writes Updated Logical
“C”
Records in Buffer Set “D”
Buffer Set “B”
Buffer Set “C”
Output
“Flat”
File
Buffering Versus Caching
Buffer: Something that reduces the shock of impact
An area to store data temporarily
Batch or
Sequential
Process
DB2
Table
Space
Read
Engine
Write
Engine
Virtual
Buffer
Pool
DB2 Index Probe
Buffer Manager
Index X PAGE 2
Key X1
Key X2
Key X3
Key X4
Key X5
Key X6
NLPage N1
NLPage N2
NLPage N3
NLPage N4
NLPage N5
NLPage N6
Index X PAGE N5
Key X40 Leaf Pg L40
Key X42 Leaf Pg L42
Key X44 Leaf Pg L44
Key X46 Leaf Pg L46
Key X48 Leaf Pg L48
Key X50 Leaf Pg L50
Index X PAGE L44
Key X422
Key X425
Key X429
Key X433
Key X437
Key X440
RID X422
RID X425
RID X429
RID X433
RID X437
RID X440
Table Space X PG Y
Data Manager
Relational Data System
(RDS) SELECT...
GETPAGE (Index X Page 2)
.............................
Table
Look-Up
Equal or Higher
GETPAGE (Index X Page N5)
Table
Look-Up
Equal or Higher
GETPAGE (Index X Page L44)
Table
Look-Up
Equal or Higher
GETPAGE (Table Space X Page Y)
Table Space X PG Y
Return Code 0
Application
Program
Index Caching
Cache: A place for storing provisions or valuables
for an extended period of time
Online or Random DB2 Process
DB2
Indexes
Index
Buffer
Pool
DB2 Buffer Manager Searches
Index B-Tree in Index Buffer Pool to
Locate RID of Target Row
in Table Space
Index Cache
Table
Space
Buffer
Pool
DB2
Table
Space
Synchronous I/O Buffers
GETPAGE INDEX X PAGE 2
GETPAGE INDEX X NLPAGE Y
GETPAGE INDEX X LPAGE Z
GETPAGE TABLE SPACE Q PAGE R
(3 GETPAGE Calls - 3 “Hits”)
(1 GETPAGE Call - 1 “Miss”)
Page Set x
Control
Information
Deferred Write Queue
Buffer Pool N Headers
Counter = 7
Oldest Modified Buffer
Newest Modified Buffer
6
1
5
4
2
3
Virtual Buffer Pool N
7
Write Engines
Page Set X
Control
Information
6
W
Counter = 2
Oldest Modified Buffer
Newest Modified Buffer
7
W
W
W
W
Virtual Buffer Pool N
DB2
Buffer
Manager
Asynchronous
Write
Engine
2
3
5
1
Address Span
<= 150 Pages
4
Page
Set
X
Deferred Write Engine Triggers
100
80
Abbreviated
Name
Full Name
Permitted
Range
IMTH
60
40
Immediate Write
Not
Threshold
Alterable
DWQT
Deferred Write
0-90%
Queue Threshold
VDWQT
Vertical Deferred
0-90%
Write Queue Threshold
20
0
Plus
- DB2 Checkpoint
- QUIESCE Command
- Data Set Close
- DB2 Shutdown
Default
Value
98%
50%
10%
Please RELPAGE Z
and GETPAGE A
Data Manager
Sequential Prefetch
Buffer Pool
X
Trigger
Pages
A
Y
Z
Asynchronous
Read
Engine
DB2
Page
Set
Sequential Prefetch - P Quantity
Prefetch Quantity (P)
Asynchronous
Read
Engine
4K Pools
No. of
ApplicaBuffers
tion
Utilities
in Pool Programs
8 to 223
224 to 999
> 999
8
16
32
16
32
64
DB2
Page
Set
32K Pools
No. of ApplicaBuffers
tion
Utilities
in Pool Programs
1 to 12
12 to 99
> 99
1
2
4
2
4
8
Sequential Detection
CUB
Prefetch Quantity (P)
T T T T
Plan A
Statement X
Index Probe
Plan B
Statement Y
Table Space
Scan with
Prefetch
CUB
T
T
CUB = Cursor Block
One per Open Cursor
"5-Out-of-8 Within P/ 2"
Trigger Page = (P/ 2) + 1
P
Asynchronous
Read
Engine
DB2
Page
Set
Asynchronous
Read
Engine
DB2
Page
Set
RID Pool
List Prefetch
Sorted
RIDs
P
Plan A
Statement X
Multiple
Index Access
T
Plan B
Statement Y
Table Space
Scan with
Prefetch
T
T
Asynchronous
Read
Engine
DB2
Page
Set
Asynchronous
Read
Engine
DB2
Page
Set
Buffer Inventory
Group Buffer Write
Pool Buffers Pending
Free Buffers
(Empty)
Uncommitted
Write Pending
(Changed Page)
Modified Pages
Hiperpool
Buffers
Invalid
Buffers
Free Buffers
(Empty)
Being Read
for Application Thread
by Data Manager
Active Buffers
(in Virtual Buffer Pool)
Virtual
Buffers
Invalid
Buffers
Version 4
With Data
Sharing
Free Buffers
(Empty)
Available (Stealable) Buffers
Buffer Status
Buffers
Page Being Write
Lock* Read Pending
Buffer
Status
Stealable
Description of Buffer and Contents
None
No
No
Contents can be overlaid or reclaimed
S or U
Yes
No
Non-Stealable Contents in use by Application Thread
X
Yes
Yes
Non-Stealable Contents in use and modified by Application.
Unit-of-recovery not yet committed.
X
No
Yes
Non-Stealable Contents modified by Application. Unit-ofrecovery not yet committed.
None
No
Yes
X
No
No
Non-Stealable Contents modified by Application. Unit-ofrecovery committed. Contents to be rewritten to
disk by asynchronous write engine.**
Contents modified by Application. Unit-ofStealable
recovery not committed. Contents have been rewritten to disk and can be overlaid or reclaimed.
* Assuming page-level locking by Application Thread.
** Buffer contents can be reclaimed and used by any application prior to being rewritten.
More Buffer Categories
Free Buffers
Random Buffers
Sequential
Buffers
* Sequential Prefetch
* Sequential Detection *
* DSNDB07 Work Files *
*
--ORDER BY
--GROUP BY
*
--UNION
--Merge Scan Joins
Index Probes
Index Look-Aside
Online Transactions Using
Small to Large Tables
Joins of Smaller Tables (or
Smaller Results Sets)
More Buffer Pool Thresholds
100
80
60
40
20
0
Abbreviated
Name
IMTH
Full Name
Immediate Write
Threshold
DWQT
Deferred Write
Queue Threshold
VDWQT
Data Set Deferred
Write Queue Threshold
DMTH
Data Manager
Threshold
SPTH
Sequential Prefetch
Threshold
VPSEQT Virtual Buffer Pool
Sequential Threshold
VPPSEQT
VBP Parallel
Sequential Threshold
Permitted
Range
Default
Value
Not
Alterable
0-90%
98%
0-90%
10%
Not
Alterable
0-100%
95%
0-100%
80%
0-100%
40%
50%
90%
Buffer Pools - Pre-Version 3
Expanded Storage
as Auxiliary Storage
Central
Storage
DBM1 Virtual
Address Space
B2
B1
Disk as Auxiliary Storage
A
Disk for
DB2 Object
Storage
A =DB2
B =OS/390
Monitoring Storage Utilization
DB2PM Systems Statistics:
Expanded
Storage
DB2
Hiperpool
OS/390 ESO
Hiperspace
DBM1 (Virtual
Buffer Pool)
“PAGE-INS REQ-READ” / time interval in seconds
OS/390 Virtual Storage Manager page-ins from auxiliary storage to
central storage per second to process DB2 data
“PAGE-INS REQ. FOR WRT” / time interval in seconds
OS/390 Virtual Storage Manager page-ins from auxiliary storage to
central storage per second to write DB2 updated data back
to DB2 disk page set
All page-ins and -outs should be between Central Storage and
Expanded Storage (Need help from OS/390 RMF Report*). If disk
paging is used, pool is too big or expanded storage is too small
If total PAGE-INS > 100 per second and expanded storage is available, implement
hiperpool (Try HP = 2 x VBP size)
Monitor DBM1 page movement between CS and ES - If “To ES” >> “To CS”
consider multiple buffer pools
* Paging Report from Program IFASMFDP Reporting on Type 70:79 Records
DB2 Version 3 Hiperpools
OS/390
IBM
DB2
Resource System
Lock
Services
Manager Address
(IRLM)
Space
DB2
Database
Services
Address
Space
Virtual
Buffer
Pools(s)
1.6 GB
Max.
Data
™ Hiperspace is a trademark of the IBM Corporation
Allied
Agent
Address
Space
OS/390
Hiperspaces™
2 GB
Max.
2 GB
Max.
2 GB
Max.
DB2 Hiperpool =
One to Four
OS/390 Hiperspaces
8 GB Max.
2 GB
Max.
Virtual Buffer Pool / Hiperpool
DB2
Indexes
DB2 Data Services
Address Space
(DBM1)
OS/390 / ESO Hiperspace(s)
HPn
VBPn
DB2
Table
Spaces
MVPG
Synchronous
Single Page
Movement
Disk
I/O
DB2
Catalog
Directory
DB2
Working
Storage
Virtual Buffer
Pool n
ADMF
Asynchronous
Multiple Page
Movement
Hiperpool n
Migration Sub-tasks
DB2 Data Services
Address Space (DBM1)
VBPn
Asynchronous
Migration
Sub-task
Virtual Buffer Pool n
SOURCE: L-R-U Unmodified Pages
OS/390 / ESO Hiperspace
OVERLAYS
HPn
Hiperpool n
TARGET: (1) Empty Pages
(2) L-R-U Pages
Virtual Buffer Pool / Hiperpool . . .
Expanded Storage
as Hiperspace
Expanded Storage
as Auxiliary Storage
B2
Disk as
Auxiliary
Storage
Disk for
DB2
Objects
B1
Central Storage
A2
Virtual Storage Address Spaces
A1
A =DB2
B =OS/390
Virtual Buffer
Pool n
Hiperpool n
A Hot Page - Efficient Caching
Random GETPAGE Calls for Page Set X1 Page P1
t0
tn
Virtual Buffer Pool
Hiperpool
Page P1
Page Set X1
on Disk
From Time t0 to Time tn
Eight GETPAGE Calls
One synchronous disk read
One ADMF page move to the hiperpool
One MVPG move to the virtual pool
Nine L-R-U chain modifications
A Cold Page - Inefficient Caching
t0
Random GETPAGE Calls for Page Set X1 Page P2
Minutes, Hours, Days??
tn
Virtual Buffer Pool
“Sent to Old
People’s
Home”
Page P2
Page P2
Hiperpool
Page Set X1
on Disk
“Sent to Old
People’s
Home”
Hiperpool
“Dies of
Old Age” From Time t to Time t
0
n
“Dies of
Old Age”
GETPAGE Calls
=2
VBP Hits “Reref Ratio” = 0 (0%)
Synchronous Reads = 2 (100%)
Hiperpool ADMF
= 2 (?)
Hiperpool Parameters
100
Abbreviated
Name
IMTH
80
DWQT
60
VDWQT
DMTH
40
SPTH
20
VPSEQT
VPPSEQT
0
HPSEQT
Full Name
Immediate Write
Threshold
Deferred Write
Queue Threshold
Data Set Deferred
Write Queue Threshold
Data Manager
Threshold
Sequential Prefetch
Threshold
Virtual Buffer Pool
Sequential Threshold
VBP Parallel
Sequential Threshold
Hiperpool Sequential
Steal Threshold
Permitted
Range
Default
Value
Not
Alterable
0-90%
98%
0-90%
10%
Not
Alterable
0-100%
95%
0-100%
80%
0-100%
40%
0-100%
80%
Plus CASTOUT = YES or CASTOUT = NO
50%
90%
"ALTER-able" Pools
1 DISPLAY BUFFERPOOL (BPX)
DETAIL (INTERVAL)
LSTATS
ALTER BUFFERPOOL (bpname)
VPSIZE (integer)
HPSIZE (integer)
VPSEQT (integer)
HPSEQT(integer)
VPPSEQT (integer)
DWQT (integer)
VDWQT (integer)
CASTOUT (YES | NO)
2 ALTER BUFFERPOOL (BPX)
VDWQT (2)
DB2 Online Pool Statistics
BUFFERPOOL NAME BPX, BUFFERPOOL ID X, USE COUNT 1
VIRTUAL BUFFERPOOL SIZE = 2500 BUFFERS
ALLOCATED
= 2500
TO BE DELETED
IN-USE / UPDATED
= 564
22.6%
HIPERPOOL SIZE
ALLOCATED
BACKED BY ES
= 5000 BUFFERS
CASTOUT
= 5000
TO BE DELETED
= 5000
Only One Page
Set Opened?
=
0
= YES
=
0
THRESHOLDS VP SEQUENTIAL
DEFERRED WRITE
=
=
RANDOM GETPAGE
SEQ. GETPAGE
DMTH HIT
= 260473 SYN READ I/O (R)
= 65536 SYN READ I/O (S)
=
0
= 15114
=
23
SEQUENTIAL PREFETCH REQUESTS
PAGES READ
=
=
=
SYS PAGES UPDATED
ASYNC WRITE I/O
= 87708 SYS PAGE WRITTEN
= 2411 SYNC WRITE I/O
= 13658
= 1820
DW HIT
NO WRITE ENGINE
=
=
= 1821
=
80 HP SEQUENTIAL
50 VERTICAL DEFERRED WRT =
80
20
Good!
35 PREFETCH I/OS
229
0 VERTICAL DWT HIT
0
229
Huh?
Expanded
Storage
OS/390 Paging in Pages per Second
OS/390 Paging Versus Pool Size
Paging
Disks
Auxiliary
Central
Storage
Storage
Virtual Storage
(Virtual Buffer Pool)
7,000
6,000
5,000
All Pages in
Virtual Buffer Pool
4,000
3,000
2,000
5,000 Pages in VBP
+ Excess in Hiperpool
1,000
0
0
20
40
60
Total Pool Size in Thousands of Pages
80
Performance Versus Pool Size
360
Stat
s
101
355
5,000 Pages in VBP
+ Excess in Hiperpool
350
345
All Pages in
Virtual Buffer Pool
340
335
.190
330
.185
325
Response Time in Seconds
Transactions per Second
365
.180
0
20
40
60
Total Pool Size in Thousands of Pages
80
.175
.170
All Pages in
Virtual Buffer Pool
.165
.160
.155
.150
5,000 Pages in VBP
+ Excess in Hiperpool
.145
.140
0
20
40
60
Total Pool Size in Thousands of Pages
80
OS/390 Paging vs. DB2 Hiperpool
Management
35
30
Total CPU Time
25
CPU
Time
Minimum at
2:1 HP:VBP
20
15
10
OS/390 Paging
CPU Time
DB2 CPU Time
5
0
0%
50%
100%
Percentage of 34,096 Page Pool in Hiperpool
Source: SHARE 83 Session 6418, "DB2 V3 User Experience With
Data Compression and Bufferpool Enhancements", R. Perih, Smith Barney
A DB2 Data Sharing Group
...
Coupling Facilities
OS/390
OS/390
Member
G001
Member
G002
Sysplex
Timers
OS/390
...
Member
G00n
DB2 Subsystem
Members
ESCON Channels & Switching
Shared
DFP
Shared
Data- Shared Cata- Shared
log Target &
base
DB2
Dist.DB2
CatalogLibraries
Directory
Shared Disk & Data Sets
Log
DB07
BSDS
for
ZPARMS
G001
of G001
Log
DB07
BSDS
for
ZPARMS
G002
of G002
...
Log
DB07
BSDS
for
ZPARMS
Gnnn
of Gnnn
Shared Disk But “Dedicated” Data Sets
Coupling Facility Functions
DB2
Member
M001
IRLM
GXM1
HP0
VBP0
HP1
VBP1
:
A Coupling Facility
Shared Communications
Area (SCA)
Group Shared Database
Locks
Buffer Pool Directories
Group Buffer Pool 0
Group Buffer Pool 1
:
DB2 Page Sets
on Shared Disk
DB2
Member
M002
IRLM
GXM2
HP0
VBP0
HP1
VBP1
:
Group Buffer Pools, Virtual Buffer Pools
& Hiperpools
Coupling Facility
System Communication Area
Group Locking Elements
DB2 Group A - Member C
DB2 Group A - Member B
DB2 Group A - Member A
Group Buffer
Pool N Directory
Group BP N
Local Cache
Vector
Page Registration
DB2 Group A - Member A
GBP N Directory
X.Y.Z
Q00
Reading
Database X
Page Set Y
Page Z
into
Buffer Q
Member A
VBP N
VBP N
Local Cache
Vector
Buffer
Q
GBP N Buffers
Database X
Page
Set Y
Page
Z
Cache Coherency
Member A
Member C
UOR 1:
S-Lock Page Z
GETPAGE Z (1st Read)
RELPAGE Z
COMMIT
Release S-Lock
UOR 2:
Group Buffer
Pool N
UOR 3:
S-Lock Page
GETPAGE Z
Page Is Invalid
Retrieve from GBP N (4)
RELPAGE Z
COMMIT
Release S-Lock
Virtual Buffer
Pool N
I
Local Cache
Vector
XI
3
X-Lock Page Z
GETPAGE Z (2nd Read)
SET WRITE PENDING
RELPAGE Z
COMMIT
Write Page Z to GBP (3)
Release X-Lock
4
Virtual Buffer
Pool N
1
2
Page Z
Database X Page Set Y
Local Cache
Vector
Cross-Member Invalidation
Member C
Virtual Pool N Vector
VVVVVVVVVVVVVVVVV
VVVVVVVVVVVVVVVVV
Hiperpool N Vector
Hiperpool N
Virtual Buffer
Pool N
GBPn Directory Entries
X1.Y1.Z1 Q1
X2.Y1.Z6 Q2
X1.Y2.Z3 0
X1.Y1.Z2 Q3
0
R1
R6
R3
S7
0
S2
S5
Group Buffer
Pool N
CHANGED X1.Y1.Z1
Member A
Virtual Pool N Vector
VVVVVV IVVVVVVVVVV
VVVVVVVVVVVVVVVVV
Hiperpool N Vector
System Administrator Decisions:
- Number of Pools and Buffers
- Number of Directory Entries
- Total Structure Size
Hiperpool N
Virtual Buffer
Pool N
I
Group Buffer Pool Caching
DB2
CREATE TABLESPACE
ALTER TABLESPACE
CREATE INDEX
ALTER INDEX
BUFFERPOOL bpname
CHANGED
GBPCACHE ALL
NONE (V6)
Casting Out to Disk
Member M00x
Triggering Events
Group Buffer
Pool n
1 - Group Buffer Pool
Checkpoint
2 - Exceed Group Threshold
3 - Exceed Class Threshold
4 - End Inter-DB2 R/W Interest
5 - “-STOP DATABASE”
Command
3
Private Buffer
for Member
2
4
1
Virtual Buffer
Pool n
Group Buffer Pool Duplexing
Coupling Facility X
Coupling Facility Y
System Communication Area
Group Locking Elements
DB2 Group A - Member C
PGBP N
Directory
SGBP N
Directory
DB2 Group A - Member B
DB2 Group A - Member A
I
I
Primary
Group BP N
I
I
I
I
Secondary
Group BP N
I
I
Local Cache
Vector
Local Cache
Vector
• Removes a single point-of-failure
• Overlapped movement of updated pages to both pools
• Secondary ready for immediate take over
• Updated pages rewritten to disk from primary
--secondary pages deleted if rewrite successful
• Excellent for VALUABLE READ/WRITE page sets
GETPAGE
Page in Virtual
Buffer Pool?
No
“GBPCACHE
ALL”?
No
Page in
Hiperpool?
A
No
Yes
Yes
Yes
Flagged as
Valid?
No
A
Flagged as
Valid?
No
Page in Group Yes
Buffer Pool?
No
Cache Miss - Sync. Group Buffer Pool
Disk Read - 15 ms Hit - 0.2 to 0.4 ms
Read Page from
Disk into VBP
Yes
Move Page from
GBP into VBP
Yes
Hiperpool Hit 0.04 ms
Move Page from
HP into VBP
Post LRU Chain and Return
Virtual Buffer
Pool Hit - 0 ms
Central
Storage
Only Storage
Supporting Instruction
Execution and
Input/Output
Operations
Auxiliary
Storage
Temporary Storage
for Address Space
Pages That Overflow
Central Storage
Logical Address
Space of 2 GB Max.
Virtual Storage
2 GB
OS/390
Address Spaces
for
System and
Application Program
Execution
Operating System
Nucleus, Virtual
Storage Management
and I/O Supervisor
Implemented
with a
Combination of
Expanded Storage
and Disk Storage
Processor Storage
Bipolar
Technology
HighSpeed
Processor
Cache
Central
Storage
2 GB
Max.
Addressable
at the
Bit Level
CMOS
Technology
Expanded
Storage
8 GB
Max.
Addressable
at the
4K Page Level
HighSpeed
Processor
Cache
Central
Storage
32 GB
Max.
Addressable
at the
Bit Level
But Can Only
Address up to
2 GB
OS/390 Data Spaces for DB2 Data Caching
DBM1
ESO
Address
Hiperspace
Space WRITE
Virtual
HiperBuffer
READ
pool
Pool
Move 4K-Pages
DBM1
MVCL A,B
MVCL C,D
OS/390
Data Space
Look-Aside
Pool
C
VBP
B
A
D
Can Address Data Space When in
“Access Register (AR) Mode”
 New way to configure virtual buffer pools
 Maximum of 128 x 2 gigabyte address spaces
(Eight times too big for current processors)
 Use subset of 32 gigabyte current maximum
 Watch for future processor and OS/390
announcements
Page Size and Pool Options
Virtual Pools
BP0 to BP49
BP8K0 to BP8K9
BP16K0 to BP16K9
BP32K to BP32K9
Hiperpools
HP0 to HP49
HP8K0 to HP8K9
HP16K0 to HP16K9
HP32K to HP32K9
Group Pools
GBP0 to GBP49
GBP8K0 to GBP8K9
GBP16K0 to GBP16K9
GBP32K to GBP32K9
Index page sets must have 4K page size
Sort work file may be either 4K or 32K page size
Must REORGanize to change page size (no ALTER command)
Use DROP CREATE or DSNTIAUL to convert
Everything still 4K physical blocks on disk
Uses for Larger Pages
Rows per Page
Row
Size
4K
8K
2K
3K
4K
5K
6K
7K
8K
2
1
1
-----
4
2
2
1
1
1
1
16K 32K
8
5
4
3
2
2
2
Improved Sequential Processing
Improved Volume Packing
16
10
8
6
5
4
4
Rows per Track
4K
8K
24
12
12
-----
24
12
12
6
6
6
6
16K 32K
24
15
12
9
6
6
6
24
15
12
9
7
6
6
Best Single Row Random
Processing
Group Buffer Pool Options
XRAY
BASE
INDEX
XRAY_BASE
GBP XPrimary
VBP X
GBP YPrimary
VBP Y
AUXILIARY
INDEX
XRAY
AUXILIARY
TABLE
VBP Z
GBPCACHE ALL
Any page accessed
by any member
copies into GBP
GBPCACHE CHANGED
Any page modified
by any member
copied into GBP
GBPCACHE NONE
Coupling facility used
for cross-validation
only - Write at commit
A Cold Page -- Efficient “Caching”
Random GETPAGE Calls for Page Set X1 Page P2
t0
tn
Smaller Virtual Buffer Pool
No Hiperpool
Buffer Stolen
and Overlaid
with Fresh Data
Page P2
Page Set X1
on Disk
Buffer Stolen
and Overlaid
with Fresh Data
Page P2
From Time t0 to Time tn
Two GETPAGE calls
Two synchronous disk reads
No L-R-U chain modifications (roundrobin algorithm)
DB2 Data Retrieval Hierarchy
External
(Physical)
I/O
Internal (Logical) I/O
Hiperpools
Expanded
Storage
Group
Buffer
Pools
Central
Storage
Virtual
Buffer
Pools
Central and
Auxiliary
Storage
SLOW
“The Best I/O
is NO I/O”
“The
Disk
Farm”
Disk -- The Original Concept
Request for
Random Access
Central
Channel Control
Storage
Unit
“Core”
3.Transfer
2.Rotate
1.Seek
Service Time =
1. Seek Time +
2. Rotational Latency +
3. Data Transfer
No Control Unit Storage
and Very Little Logic
Physical Volume
Flow of an External I/O
OS/39
0 DB2
Buffer
Manage
r
DFP
IOS
VSAM
Access
Metho
d
Input
Output
Supervisor
CHANNEL
Device Unit Channel Busy
Control Block Control Unit Busy
(UCB) Busy
Device Busy
QUEUING
PENDING
Delay
Delay
DISK
CONTROL
UNIT
CACHE
Search
and Data
Transfer
CONNECT
Time
Seek
Rotational
Position Sensing
DISCONNECT
Time
QUEUING Delay + PENDING Delay + CONNECT Time + DISCONNECT Time
= DISK RESPONSE TIME FOR EXTERNAL I/O
The Second Era
Small Cache Control Units
Basic
Microcode
< 64 MB of Cache Storage
Some (KB) Non-Volatile Storage
Goal:
• Faster Batch
Sequential Read
and Write
Using:
• Read-Ahead
Track Caching
• Write-Behind
Block Caching
Control Unit Read-Ahead / Write-Behind
OS/390
Access
Method
Channel
I/O Area
One Physical Block
OS/390
Access
Method
Channel
I/O Area
X Physical Blocks
Control
Unit
Cache Rest of
Storage Track
Control
Unit
Cache
Storage One Block
at a time
With Non-Volatile Storage
Disk Fast Write (DFW)
Three Types of Page Sets
Type 1
Type 2
Type 3
0400
0800
1200
1600
2000
Type 1 - High Access Activity All of the Time
Type 2 - High Access Activity Some of the Time
and Low Access Activity the Rest of the Time
Type 3 - Low Access Activity All of the Time
Incremental Improvements
Hardware
• More Cache Storage
• Multi-track Caching
• Cylinder Caching
• More Non-Volatile
Storage
Microcode
Goals:
• Bypass Cache
• Better Balance
• Record Cache (RC)
of Sequential vs.
Random Processing • Dynamic Cache
Management Extended
• Adapt to Dynamic
(DCME)
Access Patterns
The Current Era
Goals:
• Faster Batch
Sequential Read
and Write
• Channel Speed
Retrieval of
Cached Data
Larger Cache Control Units
Using:
• Cheap CMOS
Advanced
Storage
Microcode
• Sophisticated
Control Unit
>= 256 MB of Cache Storage
Management
More (MB) Non-Volatile Storage
• Data Compression
DB2 4K Page Read/Write Times
3380E 3380K 3380J 3390-3 3390-2 3390-1 U 2XP
Queuing
Pending
Disconnect
(Seek &
Rotation)
Connect
(Search &
Transfer)
Total
Read Hit
Ratio
Weighted
Average
?
?
25.3
?
?
24.3
?
?
20.3
?
?
22.1
?
?
19.6
?
?
16.6
?
?
11.7
1.4
1.4
1.4
1.0
1.0
1.0
0.4
26.7
25.7
21.7
23.1
20.6
17.6
12.1
---
---
---
20%
20%
20%
50%
26.7
25.7
21.7
18.6
16.7
14.3
6.1
Caching Efficiency
A. Random
GETPAGE Calls
193,239
VBP Hits
171,141
(A-B-C) 88.5%
Internal I/O External I/O
VBP Misses
22,098
(B+C)
B. Hiperpool
Hits
14,054 (7.3%)
DB2 System Statistics
Would
8,000 hits
be good
or bad?
Disk Cache
Controller
Hits ???
C. Synchronous
Reads
8,044 (4.2%)
Disk Reads
???
SMF 42-6 Records
SEQCACH Parameter versus Disk Microcode
DB2 SEQCACH *
BYPASS (Default)
Signal disk controller
to avoid caching for
DB2 read requests to
everything but sort work
files
SEQ (Optional)
Signal disk controller
to use caching for
- sequential prefetch
- dynamic prefetch
* BY SUBSYSTEM
Disk Controller
Microcoded Logic
Current
Cache
Hit Ratio** Range
Low
< 10%
Medium 10 to 55%
High
>55%
Action
Inhibit caching
Cache track
Cache cylinder
** BY PAGE SET
Santa Teresa Recommendations
OS/390 Options:
• Install Third Generation RAMAC Virtual Arrays
• Install as Much Disk Control Unit Cache Storage
as Possible
• Define Maximum Number of Virtual Disk Volumes (UCBs)
• Set Target of 50 - 80% Disk Cache Hit Ratio
• Ignore Access Arm Movement Analysis
DB2 Options:
• Install as Much Central Storage as Possible for DB2
Virtual Buffer Pools, Hiperpools and Group Buffer Pools
• Set Sequential Caching Parameter SEQCACH to SEQ
• Use DB2 Compression in Concert with Control Unit
Compression
• Use SnapShot for Fast Backup
“Until you can measure
something, and express
it in numbers, you have
only the beginning of
understanding.”
-- Lord Kelvin
DB2 Processing Cost Model
Buffer
Manager
Data
Manager
Relational Data
System (RDS)
Optimized Access Path
Indexes
-------------------
Index Entries
"Scanned"
Table
Spaces
________
________
________
________
________
________
________
________
Stage One ________
Qualified ________
Rows
________
Rows
"Scanned"
Rows
"Scanned"
RID and SORT
Work Areas
Temporary
Work Files
SELECT
With Host
Variables
Columns
from
Stage Two
Qualified
Rows
SELECT & FETCH Basic Cost Factors
Description of
Cost Factor
RDS
Data
Manager
Buffer
Manager
9,680
55
2,640
Number of Open/Fetch/Close Cursor Loops...................... NOFC
Number of Host Variables in Predicates............................ NHV
Number of Application Fetches (NQ2+1)........................... NF
Number of Pages Processed (GETPAGE Calls)............ .......................................................................... NP
Number of I/O Operations-Synchronous.....................................................................................................NIOS
Number of I/O Operations-Asynchronous..................................................................................................NIOA
Number of Rows Data Manager Examines ............................................................
Number of Search Arguments Evaluated at Stage 1*.............................................NRDME
Number of Rows Qualified at Stage 1..................................................................... NSA1*
Number of Data Columns Passed to RDS.............................................................. NQ1
NCR
Number of RID Pointer Sorts Initiated............................... NPSI
Number of RID Pointers Sorted......................................... NPS
Number of Search Arguments Evaluated at Stage 2........ NSA2
Number of Column Functions Evaluated.......................... NCF
Number of Rows Qualified at Stage 2.............................. NQ2
Number of Data Sorts Initiated.........................................
NSI
Number of Rows Sorted................................................... NRS
Number of Sort Work File Pages Processed................... NSWP
Number of Data Columns Passed to Application............
NCA
Class 2 Accounting Trace Factor
Path
Length
2,420
7,260
42,240
92
75
440
22
20,000
440
75
176
440
40,000
880
4,840
33
660
* Arguments used in index probes should not be counted
Table Space Scan Estimation
Application
Program
SELECT (20 COLUMNS)
FROM CUSTOMER
WHERE SC1 = :HV1
AND SC2 = :HV2
AND SC3 = NSC1
Columns
Returned
Optimized Access Path = Table Space Scan
NSA1
NRDME
NQ1
NCR
50,000
Rows
571,429
NSA1 Pages
NRDME
NQ1
NCR
20,000
Columns
RDS:
NOFC = 1
NHV
=2
NF
= 1,001
NSA2 = 1 x NQ1
NQ2
= 1,000*
NCA = 20 x
NQ2
Buffer
Manager
Data
Manager
Relational Data
System (RDS)
DATA MANAGER:
NSA1 = 2 x NRDME
NRDME= 20,000,000
NQ1
= 50,000*
NCR
= 21 x NQ1
BUFFER MANAGER:
NP
= 571,429
NIOS
=0
NIOA = 17,858
NP
NIOS
NIOA
History
Table with
20,000,000
100-byte rows
Sequential
Prefetch
17,858
Channel
Programs
Disk Model
= 3390-3
Disk Cache
= Turned Off
Blocks to Read = 571,429
at 35 rows per page
Buffers
> 1,000
Type of I/O
= Asynchronous
Asynchronous = 1,143 Sec.
Read Time
or 19 Min.
* Analyst’s Best “Guess”
CPU Cost of Table Space Scan
Database Services Address Space
Data
Buffer
RDS Manager Manager
Factor Factor Factor
NOFC
NHV
NF
NRDME
NSA1
NQ1
NCR
Path
Times
Performed Length
0.0%
0.0%
0.0%
571,429
0
17,858
2,420 1,382,858,180
7,260
0
42,240
754,321,920
19.7%
Number of Rows Examined
Number of Search Arguments Evaluated at Stage 1
Number of Rows Qualified at Stage 1
Number of Data Columns Passed to RDS
20,000,000
2*20,000,000
50,000
21*50,000
92 1,840,000,000
75 3,000,000,000
440
22,000,000
22
23,100,000
26.2%
42.7%
0.3%
0.3%
Number of Search Arguments Evaluated at Stage 2
Number of Rows Qualified at Stage 2
Number of Data Columns Fetched by Application
1*50,000
1,000
20*1,000
75
440
33
3,750,000
440,000
660,000
0.1%
0.0%
0.0%
1,003
660
661,980
0.0%
Number of Pages Processed (GETPAGE Calls)
Number of Synchronous I/O Operations
Number of Asynchronous I/O Operations
1
2
1,001
9,680
55
2,640
CPU
Load
9,680
110
2,642,640
Number of Open/Fetch/Close Cursor Loops
Number of Host Variables in Predicates
Number of Application Fetches (NQ2+1)
NP
NIOS
NIOA
NSA2
NQ2
NCA
Description
%Contribution
10.7%
System Services Address Space
Class 2 Accounting Trace Factor
Total Processor Path Length:
7,030,444,510 100.0%
Elapsed ("Wall Clock") Time
9021-711 CPU Time = 119.2 sec.
9672-RX5 CPU Time = 211.1 sec.
1,143 sec. =
Asynchronous Disk Read Time
0
200
400
600
800 1,000 1,200
Time, in Seconds
~ 19 Minutes
DB2 I/O Model for Retrieval
Parallel Sysplex
Coupling Facility
Group
Buffer
Pools
IBM
3390
Models 1,
2 and 3
IBM 3990
Cached
Controller
Cache
Storage
Asynchron.
Read
Engines
IBM
RAMAC
VA
Cache
Storage
Virtual
Buffer
Pools
Buffer Manager
Expanded
Storage (ES)
OS/390
Paging Disk
Aux. Storage
(AS)
OS/390
Paging
Aux.
Storage
(AS)
DB2
ESO
Hiperpools
DBM1
Address Space
Virtual Storage
(2 GB)
Data Manager
Central
Storage (CS)
DB2 Retrieval Times
In
In Replace In AS
On Disk
In Hiper- In
In
ES Page in on In Disk
RanVBP pool GBP CS as AS CS
Disk Cache Seq.
Pref Seq. dom
Y
Y
Y
Y
N
N
Y
Y
N
N
N
N
* 3390 Model 1
N
Y
Y
N
Y
Y
N
N
N
N
Y
Y
N
N
N
N
Y
N
A
V
O
I
D
!!!
Y
N
N
N
Y
Y
Y
Elapsed Relative
Time* Speed
0
40 mic.
75 mic.
0
40
75
40 mic.
75 mic.
40
75
300 mic.
300 mic.
300
300
980 mic. 980
1.7* mil. 1,700
8.1* mil. 8,100
17.6* mil. 17,600
DB2 Retrieval Times
In
In Replace In AS
On Disk
In Hiper- In
In
ES Page in on In Disk
RanVBP pool GBP CS as AS CS
Disk Cache Seq.
Pref Seq. dom
Y
Y
Y
Y
N
N
Y
Y
N
N
N
N
N
Y
Y
N
Y
Y
N
N
N
N
Y
Y
N
N
N
N
* 3390 Model 1
Y
N
A
V
O
I
D
!!!
Y
N
N
N
Y
Y
Y
Elapsed Relative
Time* Speed
0
40 mic.
75 mic.
0
40
75
40 mic.
75 mic.
40
75
300 mic.
300 mic.
300
300
980 mic. 980
1.7* mil. 1,700
8.1* mil. 8,100
17.6* mil. 17,600
Sum of all working sets is
too big for your central storage (CS)
and expanded storage (ES)
DB2 I/O Model for Writing
IBM
3390
Models 1,
2 and 3
IBM
RAMAC
VA
Cache
Storage
IBM 3990
Cached
Controller
Cache
Storage
NonVolatile
Storage
(NVS)
DBM1
Address Space
Virtual Storage
Asynchronous
Write Engines
Virtual
Buffer
Pools
Synchronous
Write
Buffer Manager
Paging Disk
Auxiliary
Storage (AS)
Expanded
Storage (ES)
Asynchronous Deferred Write:
Best Case: 32 consecutive pages on disk
or Writing to NVS
Worst Case: 1 page in aux. storage
Santa Teresa Skip-Sequential (Min. Seek)
Synchronous Write:
Rare -- Sign of Very Hot Pages
Central
Storage (CS)
= 2 ms
= 2 ms
= 60 ms
= 4 ms
= 20 ms
Sizing - Proactive or Reactive?
Virtual Buffer
Pool(s)
1.6 GB Max.
Hiperpools
8 GB Max.
Group Buffer
Pool(s)
? GB Max.
A. Total Buffer Pool Size (in Megabytes) =
40 +(Processor “M-Value” / 10)
Given an IBM 9672-R15 (5th generation CMOS @ 112 MIPS)
Pool Size = 40 + (2710/10) = 311 megabytes (about 76,000 pages)
B. Total Buffer Pool Size (in Megabytes) =
40 + (Transactions per Second * 10)
Assuming 95 transactions per second
Pool Size = 40 + (95 * 10) = 990 megabytes (about 242,000 pages)
NOTE: 10 megabytes per transaction = 2,500 pages!
Source: SG24-2244 DB2 for OS/390 Capacity Planning
GETPAGE Rates vs. Buffer Pool Size
800
GETPAGEs per Second
700
600
500
400
20
MB
Pool
Size
300
200
40
MB
Pool
Size
100
0
8
9
10
11
12
13
14
15
16
Hour of the Day
Source: SHARE 76 Session I468, "A Systems Perspective of
Subsystem Performance", Tom Birmingham, IBM WSC
80
MB
Pool
Size
System Characteristics
vs. Buffer Pool Size
140
120
20 MB
40 MB
80 MB
132.1
112.2
100
100
100
100
100
91.8
88.3
76.5
80
72.1
60
40.6
40
28.7
20
0
GETPAGEs
During
Prime Shift
No. of
Synchronous
Reads
CPU per
GETPAGE
Transaction
Response
Time
Source: SHARE 76 Session I468, "A Systems Perspective of
Subsystem Performance", Tom Birmingham, IBM WSC
Key Statistics for Sizing
Pool
Too
Small
DM Threshold Hits
Synchronous Writes
OS/390 Disk Pages/Second
GETPAGEs/Second
Synchronous Reads
CPU/GETPAGE
Transaction Response Time
Pool
is
Optimal
for Users
Pool
Too
Large
DB2PM Version 3 Statistics Report - Long
BP0
GENERAL
QUANTITY
--------------------------------------------- ---------------CURRENT ACTIVE BUFFERS
71
UNAVAIL.BUFFER-VPOOL FULL
0
BP0 READ OPERATIONS
QUANTITY /MINUTE
----------------------------------------------- ---------------- ------------GETPAGE REQUEST
6134602
153.4K
GETPAGE REQUEST-SEQUENTIAL 5941363 D 148.8K
193239
4831.76
A GETPAGE REQUEST-RANDOM
NUMBER OF DATA SETS OPENS
0
SYNCHRONOUS READS
8570
214.28
SYNCHRON.
READS-SEQUENTIAL
526
13.15
G
MAX NUMBER OF ALLOC.BUFFERS
0
8044
201.13
BUFFERS ALLOCATED - VPOOL
10001 C SYNCHRON. READS-RANDOM
BUFFERS ALLOCATED - HPOOL
20000
GETPAGE PER SYN.READ-RANDOM
24.0
HPOOL BUFFERS BACKED
20000
SEQUENTIAL PREFETCH REQUEST
70375
1759.66
SEQUENTIAL PREFETCH READS
51850
1296.46
DFHSM MIGRATED DATA SET
0
PAGES
READ
VIA
SEQ.PREFETCH
1597717
39.9K
DFHSM RECALL TIMEOUTS
0
S.PREF.PAGES READ/S.PRF.READ
30.8
HPOOL EXPANS. OR CONTRACT.
0
LIST PREFETCH REQUESTS
168
4.20
VPOOL EXPANS. OR CONTRACT
0
LIST PREFETCH READS
11
0.28
VPOOL OR HPOOL EXP.FAILURE
0
PAGES READ VIA LIST PREFTCH
60
1.50
L.PRF.PAGES READ/L.PREF.READ
5.5
GETPAGE OPERATIONS-FAILED
0
DYNAMIC PREFETCH REQUESTED.
320
8.00
CONCUR.PREF.I/O STREAMS-HWM
0
DYNAMIC
PREFETCH
READS
77
1.93
PREF.I/O STREAMS REDUCTION
0
PAGES READ VIA DYN.PREFETCH
1815
45.38
PARALLEL QUERY REQUESTS
0
D.PRF.PAGES
READ/D.PRF.READ
23.6
PARALL.QUERY REQ.REDUCTION
0
PREF.QUANT.REDUCED TO 1/2
0
PREF.DISABLED-NO BUFFER
0
0.00
PREF.QUANT.REDUCED TO 1/4
0
PREF.DISABLED-NO READ ENG
0
0.00
B SYNC.HPOOL READ
ASYN.HPOOL READ-WITHOUT ADM
HPOOL READ(NO ADM) - FAILED
ASYN.HPOOL READ-WITH ADM
HPOOL READ(ADM) - FAILED
14054
351.41
6781 F 169.55
0
0.00
240138 E 6004.43
0
0.00
Buffer Pool Hit Ratio
Batting Average = Number of Safe Hits / Times at Bat
Buffer Pool Hit Ratio = (A - C) / A
No. of Times Page Found in Buffer Pool
No. of GETPAGE Calls
Random Hit Ratio =
(193,239 - 8,044) / 193,239
= 0.958
Sequential Hit Ratio =
(5,941,363 - 526) / 5,941,363 = 0.99991
Caching Efficiency
A. RANDOM
GETPAGEs
193,239
VBP0
171,141
Hits
(A-B-C)
VBP0
Misses
22,098
B+C
B. HP0
14,054
Hits
C. BP
Misses
8,044
88.56%
7.27% (or 63.60%)
4.16%
D. SEQUENTIAL
GETPAGEs
5,941,363
VBP0
VBP0
5,693,918 Misses
247,445
Hits
(D-E-F-G)
E+F+G
95.84%
4.15% (or 99.78%)
0.01%
E+F. HP0 G. BP
246,919 Misses
526
Hits
“Just Make the Pool Bigger”
100%
90%
Third 1,000 Only
Gains 3% More
80%
Second 1,000
Buffers Only
Gains 8% More
Hit Ratio
70%
60%
50%
Investment in
First 1,000 Buffers
Delivers 78% Hits
40%
30%
20%
10%
0%
2,000
4,000
6,000
8,000
Size of Pool
Obviously can waste “Virtual Storage”
Waste of central and expanded storage
Places extra burden on OS/390 Virtual Storage Manager
May force OS/390 paging to auxiliary disk storage
Random Hit Ratio vs. Coverage
100%
Random Hit Ratio
80%
90% Buffer Pool Hits
at 10% Coverage
60%
40%
DB2 / IMS -TM
Transaction Processing Benchmark
Avg. GETPAGE at 10% Coverage =
(0.90 * 0.0) + (0.10 * 17.6) = 1.76 ms
20%
0%
0%
10%
20%
30%
40%
50%
60%
% Database Covered by Buffer Pool
Source: ZZ05-0462 IBM WSC Tech. Bulletin: MVS/ESA and Data in Memory Performance Studies
Average GETPAGE Time vs. Coverage
Random Hit Ratio
GETPAGE Time
25 ms
Random Hit Ratio
RAMAC VA
3390-1
3390-2
3390-3
20 ms
15 ms
GETPAGE Time
at 10% Coverage (90% Hits)
RAMAC VA = 1.58 ms
3390-1
= 1.76 ms +11.4%
3390-2
= 2.06 ms +30.4%
3390-3
= 2.31 ms +46.2%
10 ms
5 ms
0 ms
0%
5%
10%
15%
20%
% Database Covered by Buffer Pool
Random Hit Ratio Versus “Coverage”
Hit Ratio for Random GETPAGEs
100%
High Random Access
to Small Working
Set of Pages
80%
60%
40%
100% Random Access
to All Pages in Page Set
20%
0%
0%
20%
40%
60%
80%
Size of Buffer Pool
Coverage =
Size of Page Set
100%
Hot Pages vs. Cold Pages
Pages Heavily Re-Used
“Resident Pages”
100%
Random Hit Ratio
80%
60%
Pages
With
Intermediate
Level
of
Re-Use
40%
20%
Pages With Very
Low Probability of Re-Use
“Transient Pages”
0%
0%
10%
20%
30%
40%
% Database Covered by Buffer Pool
50%
Classic Questions
How to Configure the Pool(s)?
A Single Large Pool versus
Multiple, Not-So-Large?
Which Pages Sets in Which Pools?
Any Scientific Method to Help?
DB2 Capabilities
80 Virtual Buffer Pools, Hiperpools and
Group Buffer Pools
Dynamic Alter of Sizes and Thresholds
Dynamic Reassignment of Page Sets
Improved Statistical Display
Categories of Buffer Pool Statistics
Data Manager/Buffer Manager Trace
Synchronous Reads During Prime Shift
Synchronous Read Rate
27-Feb
28-Feb
1-Mar
2-Mar
3-Mar
4-Mar
5-Mar
1
4
15
Virtual Buffer Pool Number
16
Synchronous Reads During Night Shift
Synchronous Read Rate
27-Feb
28-Feb
1-Mar
2-Mar
3-Mar
4-Mar
5-Mar
1
4
15
Virtual Buffer Pool Number
16
Synchronous Read During Midnight Shift
Synchronous Read Rate
27-Feb
28-Feb
1-Mar
2-Mar
3-Mar
4-Mar
5-Mar
1
4
15
Virtual Buffer Pool Number
16
DB2
Key Page Set
Characteristics
Density of Access
Mode of Access
Size of Page Set
Rereferencing Pattern
Read-Only or Read/Write
Static or Erratic Behavior
A Tough Step
“We need to identify the
specific page sets
containing a high
percentage of pages with the
characteristic of being mainly
resident.”
“Once the page sets have been
identified......”
Two Basic Tracing Options
IFCID 6 - Start of Reading Page from Disk
IFCID 198 - GETPAGE, RELPAGE and
SET WRITE PENDING Calls to Buffer Manager
G-Series (IFCID 198 Trace)
• DBID
• OBID
• No. of Unique Pages Used
• GETPAGE Count for Object
• Virtual BP Hit Count
Data Manager
Buffer Manager Interface
All GETPAGE,
RELPAGE and Set
Write Pending Calls
~ 9,000 records
per second
G-Series
Random
GETPAGE
Calls
~ 3,400 records
per second for
“operational”
buffer pool*
Summarized
IFCID 198
Records
~ 900 records
per sample
10 Traces of One Minute Each
* For production page sets (no DB2 catalog, sort work files or decision support objects)
Time Sequence of IFCID Records
VBP Hit
GETPAGE Call (Write 198)
Flagged as Buffer Pool Hit
Possible Set Write Pending Call (Write 198) Time Interval T1
RELPAGE Call (Write 198)
Time Interval T2
HP Hit
GETPAGE Call (Write 198)
Flagged as Buffer Pool Miss
Possible Set Write Pending Call (Write 198)
RELPAGE Call (Write 198)
GBP Hit
GETPAGE Call (Write 198)
Flagged as Buffer Pool Miss
Possible Set Write Pending Call (Write 198)
RELPAGE Call (Write 198)
NOTE: No IFCID 6’s or 7’s are written--no I/O with hits.
Interarrival Rate of GETPAGE Calls
Random GETPAGE Calls for Page P2 of Page Set X1
t0
Seconds, Minutes, Hours?
tn
Virtual Buffer Pool
“Sent to Old
People’s
Home”
Page P2
“Sent to Old
People’s
Home”
Page P2
Hiperpool
Page Set X1
on Disk
Hiperpool
“Dies of
Old Age”
“Dies of
Old Age”
Number of
Pages Reread
Reread Interval
3,000
2,500
2,000
1,500
1,000
500
0
10K
1
20K
30K
2
40K
3
4
50K
R-Series (IFCID 6 Trace)
Buffer Manager
VSAM DFP Interface
R-Series
Start of Read
Page from Disk
~ 100 records
per second for
“operational” page sets
10 Traces of 10 Minutes Each
Summarized
IFCID 6
Records
• DBID
• OBID
• No. of Pages Read
• No. of Pages Reread
Time Sequence of IFCID Records
VBP, HP, GBP All Missed
GETPAGE Call (Write 198)
Flagged as Buffer Pool Miss
Write 6--Start of Disk I/O
Call DFP/VSAM
Time Interval T3
Posted by DFP/VSAM
Write 7--End of Disk I/O*
Possible Set Write Pending Call (Write 198)
RELPAGE Call (Write 198)
Downstream Analysis
G-Series
Summarized
IFCID 198
Records
R-Series
Summarized
IFCID 6
Records
Download
Microsoft
Excel
Microsoft
Access
10 G-Series Samples of GETPAGE Calls
250,000
200,000
Total GETPAGEs
150,000
1,542 Unique Page Sets Observed
100,000
50,000
GETPAGEs by Page Set
0
G01
G02
G03
G04
G05
G06
G07
G08
G09
G10
96 Page Sets Generated
90.1% of GETPAGE Calls
Total GETPAGEs
100,000
91 Well
Behaved
Consistent
Page Sets
Five
Inconsistent
Page Sets
1
G01
G02
G03
G04
G05
G06
G07
G08
G09
G10
Does the 80-20 Rule Apply?
100%
Cumulative Contribution to Total Workload
3
2
1
90%
4
80%
70%
115
60%
20% of
Page Sets
50%
10% of
Page Sets
40%
1 = ADPUs
30%
2 = GETPAGEs
20%
3 = VBP Hits
10%
4 = VBP Misses
0%
100
200
300
400
Size of Page Set
PAD = Page Access Density
= Random GETPAGEs per
Minute per Page
PAD
PAD
Distribution of PAD Values
100
1,459
90
80
70
No. of
Page
Sets
60
Cut-Off Point
57
Range: 0.1 to 3,413
Mean: 74.29
> 200 = 83 Page Sets
50
40
30
20
12
7
10
2 1 1 1 0 1 0 0 0 0 0 0 0 1
0
<=200
<=800
<=1,400
<=2,000
PAD Values
<=2,600
<=3,200
IAGPC - Inter-Arrival Time
1 : PAD = InterArrival Time of
GETPAGE Requests
for the “Average” Page
Given: PAD = 3,413 GETPAGEs per Minute per Page
IAGPC = 1 / PAD = 1 / 3,413
= 0.000293 Minutes Between GETPAGE Calls
for the “Average” Page
Rereferencing Pattern
“Hot” to “Cold” Access Density
Clustering Index:
One Root Page
86 Non-Leaf Pages
37,640 Leaf Pages
Table:
170,700 Data Pages
Page Type
= 1,000,000 GETPAGEs/Page
=
11,628 GETPAGEs/Page
=
27 GETPAGEs/Page
=
PAD
6 GETPAGEs/Page
IAGPC
Root
6,506.4 / min.
9.2 ms.
Non-Leaf
75.7 / min. 793.1 ms.
Leaf
0.173 / min. 5.79 sec.
Data
0.038 / min. 26.2 min.
But How About Tables?
New Mexico
Area Code
505
New York
City Area
Code 212
Identifying Objects of Interest
GETPAGE Calls
3
23,208
540
43
66
55
832,224
18,604
45
109,902
177
112,960
2,752
41
29,447
VBP Misses
34
883,636
2,254
392
29,649
0
0
0
0
0
LEGEND
No. of Page Sets
No. of GETPAGE Calls
Average Pages Used
Page Access Density
VBP Misses
4
102,655
215
477
126
45
29,652
86
345
1,148
Page Access Density
(PAD)
Identifying Objects of Interest
GETPAGE Calls
0.19%
1.96%
1.14%
0.04%
3.57%
67.60%
40.70%
58.47%
11.48%
10.00%
5.52%
15.67%
VBP Misses
2.20%
8.19%
43.22%
15.77%
LEGEND
% of Page Sets
% of Distinct Pages
% of GETPAGE Calls
% of VBP Misses
0.26%
0.78%
5.02%
0.07%
2.92%
0.31%
1.45%
0.61%
0.00%
0.00%
0.00%
Page Access Density
0.00%
(PAD)
LEGEND
Buffer Pool ID
No. of Page Sets
No. of VBP Pages
No. of Hiperpool Pages
No. of GETPAGE Calls
Average Pages Used
Page Access Density
VBP Misses
Uninteresting
BPZ
1,401
1,000
-0173,225
5,823
30
47,072
Buffer Pool Allocation
GETPAGE Calls
BPY
55
5,500
35,000
832,224
18,604
45
109,902
VBP Misses
BPX
86
2,500
5,000
1,039,151
3,095
336
30,989
Page Access
Density
(PAD)
DB2 Catalog
& Directory
BP0
?
1,000
4,000
?
?
?
?
DB2 Sort
BP1
?
2,000
-0?
?
?
?
R-Series Samples of Pages Read/Reread
80,000
70,000
60,000
50,000
40,000
Pages Read
30,000
Pages Reread
20,000
10,000
0
R01
R02
R03
R04
R05
R06
R07
R08
R09
R10
Top Page Sets for Disk Reads
100,000
Total Read
10,000
1,000
98 Well
Behaved
Consistent
Page Sets
100
10
Two Erratic
Inconsistent
Page Sets
1
R01
R02
R03
R04
R05
R06
R07
R08
R09
R10
Does the 80-20 Rule Apply?
100%
1
90%
2
Contribution to Total Workload
80%
3
134
70%
10% of
Page Sets
60%
20% of
Page Sets
50%
40%
1 = Reads
30%
2 = Rereads
20%
3 = Weighted Rereads
10%
0%
1
50
100
150
200
250
Number of Page Sets
300
350
400
Distribution of Read Values
100
1,813
90
80
Range: 1 to 113,940
Mean: 327
70
60
No. of
Page
Sets
50
40
30
35
23
20
6
10
2
3
0
3
3
1
0
2
1
2
5
0
<=2,000
<=4,000
<=6,000
<=8,000 <=10,000 <=12,000 <=14,000
No. of Reads
Distribution of Reread Values
100
1,785
90
80
70
No. of
Page
Sets
Range: 0 to 17,167
Mean: 48
60
52
50
40
30
22
20
10
6
6
8
3
2
4
4
1
2
2
0
1
0
<=200
<=400
<=600
<=800
<=1,000
No. of Rereads
<=1,200
<=1,400
Distribution of % Rereads
180
591
171
164
160
138 139
140
130
116
120
No. of
Page
Sets
Range: 0 to 61.12%
Mean: 14.68%
159
109
95
100
80
60
42
40
31
20
13
0
0
1
0
<=4%
<=16%
<=28%
<=40%
% of Rereads
<=52%
>60%
Distribution of Weighted Rereads
180
847 346
Range: 0 - 2,587
Mean: 8.69
160
147
140
120
No. of
Page
Sets
Mean Value
(224 Page Sets Above Average)
100
80
60
42
40
20
0
0
5
10
15
20
25
30
Weighted Re-reads
35
40
45
50
Identifying Objects of Interest
LEGEND
No. of Page Sets
Total Reads
Total Rereads
Reread Percentage
Weighted Rereads
Weighted Rereads
0
0
0
0.00%
0
10
6,011
172
2.86%
13
Reads
172
14,563
3,999
27.46%
1,296
157
525,839
77,685
14.77%
13,276
19
27,035
877
3.24%
64
72
14,649
3,441
23.49%
921
2
681
72
10.57%
8
Rereads
Identifying Objects of Interest
LEGEND
% of Total Page Sets
% of Total Reads
% of Total Rereads
% of Weighted Rereads
Weighted Rereads
9.06%
2.35%
4.39%
7.53%
0.00%
0.00%
0.00%
0.00%
0.53%
0.97%
0.19%
0.08%
Reads
8.27%
84.69%
85.20%
777.14%
1.00%
4.35%
0.96%
0.37%
3.79%
2.36%
3.77%
5.35%
0.11%
0.11%
0.08%
0.05%
Rereads
LEGEND
Buffer Pool ID
No. of Page Sets
No. of Reads
No. of Rereads
Reread Percentage
Weighted Rereads
VBP Size
Hiperpool Size
BPY1
1,499
65,868
6,051
9.18%
1,717
2,000
-0-
Buffer Pool Allocation
Weighted Rereads
BPX1
401
555,051
85,125
15.34%
15,493
5,000
30,000
Reads
Rereads
DB2 Catalog
& Directory
BP0
?
?
?
?
?
1,000
4,000
DB2 Sort
BP1
?
?
?
?
?
2,000
-0-
Comparison of Traces
G-Series
141 Page Sets
91.52% of
GETPAGE
Calls
74.96% of
VBP Misses
R-Series
401 Page Sets
90.02% of
Weighted
Rereads
Degree of Overlap
G NOT R
G AND R
G NOT R
Page Sets
GETPAGEs
Pages Used
PAD
VBP Misses
Wgtd. Rereads
No.
%
63
3.19
427,736 20.92
2,094
7.61
204.27
5,698
3.03
33
0.19
R NOT G
G AND R
No.
78
1,443,639
19,645
73.49
135,193
10,943
%
3.95
70.61
71.38
71.93
63.59
R NOT G
No.
323
104,979
3,165
33.17
29,580
4,550
%
16.35
5.13
11.50
15.74
26.44
Standalone
G-Series
R-Series
G-Series
Page Sets
GETPAGEs
Pages Used
PAD
VBP Misses
Wgtd. Rereads
No.
141
1,871,375
21,739
86.08
140,891
10,976
%
7.14
91.53
78.99
74.96
63.78
R-Series
No.
401
1,548,618
22,810
67.89
164,773
15,493
%
20.30
75.74
82.88
87.66
90.02
Ranking of Critical Page Sets
Object
ID
Weighted
Rereads
370.006
379.004
370.037
379.023
416.263
420.024
371.065
416.102
370.004
402.012
420.014
370.029
402.002
401.008
401.014
1. 2,587
2. 1,284
3. 805
4. 587
5. 498
6. 456
7. 441
8. 389
9. 315
10. 285
11. 238
12. 212
13. 204
14. 201
15.
185
VB Pool
Misses
1.
2.
3.
4.
9.
91.
24.
-14.
23.
173.
5.
22.
7.
6.
29,187
15,235
8,799
4,652
3,111
271
1,452
N/R
2,089
1,545
130
4,295
1,614
4,009
4,098
GETPAGE
Calls
1.
7.
4.
14.
11.
39.
15.
-53.
25.
175.
3.
35.
12.
13.
168,298
78,608
100,035
39,455
54,007
8,858
36,423
N/R
6,207
15,805
684
100,806
9,938
52,907
51,290
Page Access
Density (PAD)
281. 59.92
305. 56.29
122. 142.14
159. 103.02
967. 7.18
832. 11.69
42. 342.00
-N/R
396. 40.07
129. 130.94
379. 44.29
45. 307.62
182. 89.45
81. 210.20
87. 198.36
Erratic Page Sets
60%
50%
The Normal
Distribution
40%
30%
20%
97.72%
of
Population
10%
0%
-3.0
-2.3
-1.5
-0.8
0.0
0.8
Standard Deviation
Mean +
(2 x Standard
Deviation)
1.5
2.3
3.0
Summary of Buffer Configurations
Pool
BP0
BP1
BP2
BPX
BPY
BPZ
BPX’
BPY’
Original Set-Up
IFCID 6
VBP
HP
VBP
HP
Contents
Size
Size Size
Size
DB2 Catalog & Directory 1,000 4,000 1,000 4,000
Sort Work Files
2,000
0 2,000
0
All Operational Data
10,000
0
High GP and PAD
High VBP Misses
All Other Cold Page Sets
High Reread
5,000 30,000
All Other Cold Page Sets
2,000
0
Totals
13,000 4,000 10,000 34,000
IFCID 198
VBP
HP
Size
Size
1,000 4,000
2,000
0
2,500 5,000
5,500 30,000
1,000
0
12,000 39,000
“Industrial Strength” Analysis
- Michael Barnard
CGU Life, Kent, U.K.
“Reread Minimization”
- IBM Watson Research
Messers. Dan, Yu, Chung
“DBPMAA Algorithm”
- IBM Almaden Research
Drs. Levy and Morris
and Mr. Messinger
“Depth Distributions”
- IBM and Responsive Systems
“Buffer Pool Tool™”
™Trademark of Responsive Systems
Michael Barnard’s Approach
Goal: Minimize Rereads of Pages from Disk
1. Create DB2 table to save trace data
CREATE TABLE IFCID6
(POOL_ID CHAR(8)
NOT NULL,
DBID
SMALLINT
NOT NULL,
OBID
SMALLINT
NOT NULL,
PAGE
CHAR(6)
NOT NULL,
READTYPE CHAR(1)
NOT NULL)
2. Run DB2 trace for IFCID 6 records
DB2
Trace
RAW IFCID 6
Start Read I/O
Records
3. Run DB2PM report to format the IFCID 6 records
RAW IFCID 6
Start Read I/O
Records
DB2PM
Formatted
IFCID 6 Start
Read I/Os
Load and Summarize
4. Load report line items into DB2 table using the DB2 LOAD Utility*
LOAD DATA INDDN SYSREC00 REPLACE LOG NO
CONTINUEIF(118:120)=‘ACE’
INTO TABLE xxxxx.IFCID6 WHEN (80:83)=‘DBID’
(POOL_ID POSITION(108:115) CHAR(8),
DBID
POSITION(88:91)
INTEGER EXTERNAL,
OBID
POSITION(218:221) INTEGER EXTERNAL,
PAGE
POSITION(239:244) CHAR(6),
READTYPE POSITION(260:260) CHAR(1))
Formatted
IFCID 6 Start
Read I/Os
DB2 LOAD
DB2 Table
IFCID6
5. Run SQL query against table IFCID6 for re-read report
* Based on DB2PM report format with DB2 Version 4. Version 5’s record layout is different to accommodate LARGE table spaces.
The Buffer Pool Tool
Coupling
Facility Sizing
Estimator
Pool
Configuration
Simulator
DB2 Subsystem
DB2
Instrumentation
Facility
IFI Exit
Logic
DB2
Trace
IFCID 6,
7 & 198
Records
BPT
Analysis
Buffer Pool
Performance
Statistics
GETPAGE
by Page Set
Analysis
Buffer Pool Statistics
Statistics for Buffer Pool: BP0
Buffer size is.......................................…...............4K
Number of VP Buffers is....…...........10,000
VP sequential threshold is…...............80%
Number of HP Buffers is.......….................0
HP sequential threshold is......…..........80%
Hiper Space Castout is..............….........Yes * Application
Vertical Write Threshold...............….....10%
HIT RATIO
Horizontal Write Threshold............…....50%
Number of GETPAGEs........................….....2,379,499
Number of Sequential Access...1,429,246 60.1% of GETPAGEs
Number of Random Access..........709,940 29.8% of GETPAGEs
Number of RID_List.......................240,313 10.1% of GETPAGEs
Number of Random Misses..........277,488 77.1 Misses per Sec.
Number of Misses (others)...........149,291 41.5 Misses per Sec.
Number of No_Reads...........................604 0.0% of GETPAGEs
Number of Hits............................1,952,116 82.0% of GETPAGES*
System HIT RATIO.............................................34.7%
Avg. Page Residency......................................1,250 Seconds
Report continues on next page
Buffer Pool Statistics
Continued from previous page
Number of Pages Read...........................1,553,174
Number of Sync Pages Read.................393,989
Number of SPref Pages Read.................999,889
Number of LPref Pages Read...................14,853
Number of DPref Pages Read.................144,443
Number of Read I/Os..................................442,966
Number of Sync Read I/Os.....................393,989
Number of SPref Read I/Os.......................32,127
Number of LPref Read I/Os.......................11,853
Number of DPref Read I/Os.........................4,997
Delay of Sync Read I/Os.................................14
Delay of SPref Read I/Os.................................36
Delay of LPref Read I/Os.................................43
Delay of DPref Read I/Os.................................44
Report continues on next page
431.5 Pages per Second
25.4% of Pages Read
64.4% of Pages Read
1.0% of Pages Read
9.3% of Pages Read
123.1 I/Os per Second
88.9% of Read I/Os
7.3% of Read I/Os
2.7% of Read I/Os
1.1% of Read I/Os
ms. average (Max. 249)
ms. average (Max. 250)
ms. average (Max. 249)
ms. average (Max. 243)
Buffer Pool Statistics
Continued from previous page
Number of Set Write Pending (Modifications)............170,158
Number of Pages Written............................73,624
Number of Sync Pages Written ...................100
Number of ASync Pages Written ............73,524
20.5 Pages per Sec
0.1% of Pages Written
99.9% of Pages Written
Number of Write I/Os..............…...................45,719
12.7 I/Os per Sec
Number of Sync Write I/Os...…......................100
0.2% of Write I/Os
Number of ASync Write I/Os......................45,619
.99.8% of Write I/Os
Delay of Sync Write I/Os....................................7 ms. average (Max. 66)
Delay of ASync Write I/Os..................................4 ms. average(Max. 231)
Average Number Pages/Async Write..............1.6 pages
Page Set Statistics
Statistics for Table Space.......................................DB2xx.TABLEyy
Number of GETPAGEs.................................690,589 29.0% of Pool’s GETPAGEs
Number of Sequential Access..................634,019 91.8% of GETPAGEs << Note
Number of Random Access........................56,570 8.2% of GETPAGEs
Number of RID_List Access.................................0 0.0% of GETPAGEs
Number of Random Misses.........................27,438
7.6 Misses per Sec
Number of Misses (others)..........................19,740
5.5 Misses per Sec
Number of No_Reads............................................0
0.0% of GETPAGEs
Number of Hits............................................643,411 93.2% of GETPAGEs
System HIT RATIO.............................................-1.9%
Average Page Residency......................................0 Seconds
Report continues on next page
Application
HIT RATIO
Page Set Statistics
Continued from previous page
Number of Pages Processed..........................704,258
Number of Sync Pages Read.........................27,938
Number of SPref Pages Read.......................654,078
Number of LPref Pages Read..................................0
Number of DPref Pages Read.........................22,242
195.6 Pages per Second
4.0% of Pages
92.9% of Pages
0.0% of Pages
3.2% of Pages
Number of Read I/Os.........................................49,414
Number of Sync Read I/Os...........................27,938
Number of SPref Read I/Os...........................20,735
Number of LPref Read I/Os....................................0
Number of DPref Read I/Os................................741
Delay of Sync Read I/Os.....................................21
Delay of SPref Read I/Os.....................................38
Delay of LPref Read I/Os.......................................0
Delay of DPref Read I/Os.....................................43
13.7 Read I/Os per Sec
56.5% of Read I/Os
42.0% of Read I/Os
0.0% of Read I/Os
1.5% of Read I/Os
ms. average (Max. 239)
ms. average (Max. 250)
ms. average (Max. 0)
ms. average (Max. 183)
Report continues on next page
Page Set Statistics
Continued from previous page
Number of Set Write Pendings (Modifications)..14,443 8.5% of pool SWPs
Number of Pages Written.....................................8,055
2.2 Pages per Sec.
Number of Sync Pages Written .... ...........................1 0.0% of Pages Written
Number of ASync Pages Written ........................8,054 100.0% of Pages Written
Number of Write I/Os.............................................4,833
1.3 I/Os per Sec.
Number of Sync Write I/Os........................................1
0.0% of Write I/Os
Number of ASync Write I/Os...............................4,832 100.0% of Write I/Os
Delay of Sync Write I/Os...........................................6 ms. average (Max. 6)
Delay of ASync Write I/Os.........................................4 ms. average (Max. 219)
Average Pages / Write I/O (Asynch).......................1.67
Simulation at the Buffer Pool Level
Forecast
Read
I/O Rate
Forecast
Application
Hit Ratio
Results of Simulation for Buffer Pool..................................BP0
Buffer Pool GETPAGE Total.......................................2,379,499
Pages in
Pool
10,000*
18,000
26,000
34,000
42,000
50,000
58,000
66,000
GETPAGEs
Used
2,362,768
2,349,204
2,322,343
2,294,862
2,267,584
2,233,613
2,171,257
2,160,792
* Baseline Verification
Forecast
BP Hits
1,971,692
2,049,084
2,067,504
2,070,271
2,064,701
2,044,257
1,995,045
1,991,388
Applic.
Hit Ratio
83.5 %
87.3 %
89.1 %
90.3 %
91.1 %
91.6 %
91.9 %
92.2%
Page Read Read I/O System
Rate
Rate
Hit Ratio
438.5/sec. 120.6/sec. 34.0%
382.8/sec. 95.0/sec. 42.6%
358.2/sec. 83.1/sec. 46.7%
338.2/sec. 75.1/sec. 49.9%
326.4/sec. 69.2/sec. 51.6%
322.3/sec. 66.3/sec. 52.5%
322.6/sec. 64.2/sec. 52.6%
315.8/sec. 62.1/sec. 53.6%
Simulation at the Page Set Level
Forecast
Application
Hit Ratio
Forecast
Read
I/O Rate
Results for Table Space..................................... DB2xx.TABLEyy
Page Set GETPAGE Total.................................690,589 ( 29.0% of BP GETPAGEs)
Pages in GETPAGEs No. of Applic. Wking Set Size Pages
Read System
Pool
Used
BP Hits Hit Ratio Avg.
Max. Read
I/Os Hit Ratio
10,000 689,218 661,803 95.6 % 3,277 8,607 198.5/sec. 13.8/sec. -2.1%
18,000 688,180 663,431 96.4 % 6,297 15,329 198.8/sec. 13.1/sec. -1.6%
26,000 686,874 664,066 96.7 % 9,537 21,855 201.2/sec. 12.8/sec. -1.2%
34,000 685,796 664,560 96.9 % 13,074 28,390 203.3/sec. 12.5/sec. -0.8%
42,000 685,025 665,323 97.1 % 16,815 34,939 204.8/sec. 12.2/sec. -0.5%
50,000 684,158 665,571 97.3 % 20,804 41,553 208.1/sec. 12.1/sec. -0.2%
58,000 680,175 662,784 97.4 % 25,196 48,298 213.6/sec. 12.0/sec. -0.1%
66,000 672,849 655,905 97.5% 29,344 54,684 211.9/sec. 11.9/sec. 0.0%
Heavy use of sequential prefetch causes
high application and low system hit ratio
Simulation at the Page Set Level
Forecast
Application
Hit Ratio
Forecast
Read
I/O Rate
Results for Table Space......................................DB2xx.TABLEzz
Page Set GETPAGE Total................................406,973 ( 17.1% of BP GETPAGEs)
Pages in GETPAGE No. of Applic.
Wking Set Size Pages Read System
Pool
Used
BP Hits Hit Ratio Avg.
Max. Read
I/Os Hit Ratio
10,000 405,845 302,693 74.6 % 2,352 6,653 85.3/sec. 31.0/sec. 25.4%
18,000 404,852 349,267 86.3 % 3,512 7,072 51.3/sec. 17.2/sec. 55.4%
26,000 402,225 363,294 90.3 % 4,312 8,501 39.6/sec. 12.5/sec. 66.0%
34,000 395,202 367,227 92.9 % 4,914 8,476 30.0/sec. 9.3/sec. 74.2%
42,000 385,542 364,811 94.6 % 5,341 8,643 24.2/sec. 7.1/sec. 78.9%
50,000 374,082 355,458 95.0 % 5,592 8,712 21.2/sec. 6.5/sec. 81.3%
This page set should not be in the same pool as
DB2xx.TABLEyy on the preceding page
Simulation - Large Random Object
Forecast
Application
Hit Ratio
Forecast
Read
I/O Rate
Results for Index Space........... ..............................DB2xx.INDEXxx
Page Set GETPAGE Total....................................559,377 ( 17.2% of BP GETPAGEs)
Pages in GETPAGE No. of Applic. Wking Set Size Pages
Read System
Pool
Used
BP Hits Hit Ratio Avg.
Max. Read
I/Os Hit Ratio
10,000
558,266 340,542 61.0 % 3,364
6,264 193.5/sec. 20.8/sec. 58.1%
18,000
557,425 345,046 61.8 % 7,249 10,112 194.6/sec. 19.9/sec. 58.5%
26,000
556,357 346,054 62.1 % 9,656 12,314 199.1/sec. 19.5/sec. 59.1%
34,000
555,494 348,850 62.8 % 13,513 15,965 201.6/sec. 18.9/sec. 59.7%
42,000
554,873 349,015 62.9 % 15,223 17,101 201.9/sec. 18.7/sec. 60.1%
50,000
554,159 349,674 63.1 % 16,174 18,096 202.8/sec. 18.4/sec. 60.5%
Very large, random and low rereference causes this profile....
Buffer Pool Tool Testimonial
GETPAGE Calls per second
Read I/Os per second
58%
Reduction
No. of VB Pools
No. of Hiperpools
Pages in HPs
1
0
7
0
7
3
5k
13.3% Reduction in DB2 Elapsed Time
6.7% Reduction in DB2 CPU Time
Over 2,000,000 I/Os per day eliminated
7
3
10k
7
3
15k
7
3
30k
$410,000 savings per years
Conclusions
DB2 buffer management is
• Sophisticated but understandable
• Designed for high-performance
• Keeping up with hardware economics
and capabilities
• Measurable and controllable
Questions?
Contact
Chuck Hoover
Compuware Corporation
(248) 737-7300 x-16249
chuck_hoover@compuware.com
or chuckhoovermi@aol.com
Chuck Hoover
Compuware Corporation
31440 Northwestern Highway
Farmington Hills, Michigan
MI 48334-2564
(248) 737-7300 Extension 16249
FAX: (248) 737-7513
E-mail: chuck_hoover@compuware.com
COMPUWARE
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