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IBM Software Group
© 2008 IBM CorporationDISCO, Bicocca University, Milan – 11 Dec. 2008
DB2 for z/OS:Architecture and Functions
A ngelo S ironiE xecutive IT A rchitect IB M Ita lia S .p.A .
IBM Software Group | DB2 information management software
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The IBM Academic Initiative
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IBM Software Group | DB2 information management software
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Agenda
�z/System�z/Hardware
�z/OS
�DB2 for z/OS (V9)�Architecture�Memory Structure�Address Spaces Interaction�Subsystem (Re-)Start�DB Structures
�Concurrency Control & Locking�SQL Processing�DB2 Optimizer & Access Path Strategies�Buffer Pool Management�Query Parallelism�Logging�Autonomic Features�Security
®
IBM Software Group
© 2008 IBM CorporationDISCO, Bicocca University, Milan – 11 Dec. 2008
z/System Platform
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z/Hardware
� Also known as Mainframe
� Most recent incarnation
�z10 Family
� Z10 Major Characteristics
�4.4 Ghz Microprocessors
�Quad-core chips
�Max. Number of Core = 77
� User Core(*) = 64
� SAP (System Assist Processor) = 11
� Spare Core = 2
�Max. memory Size = 1.5 Tb
�Hardware Accelerators
� Cryptography
� Data Compression
� Decimal Floating Point arithmetic(*) Std., ICF, IFL, zIIP, zAAP
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Mainframe Evolution
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Mainframe Platform: The z/Architecture
Expanded Storage
MainStorage
CP
CP
Crypto
ETR… …
DynamicSwitch
DynamicSwitch
CU
…
…
…
…
Serial Channel Paths
CU CU
CU
Channel Subsystem
CU
CU…
CU …
CU …
…
………Parallel Channel Paths
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z/OS: Address Space Concept
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z/OS data
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®
IBM Software Group
© 2008 IBM CorporationDISCO, Bicocca University, Milan – 11 Dec. 2008
DB2 for z/OS
IBM Software Group | DB2 information management software
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DB2 for z/OS
�“Born” in 1983
�RDBMS for z System platform�Exploits the z platform
�Hybrid engine�Relational data
�ORDBMS extensions
�XML documents
�Parallel query engine
�Cluster support on Parallel Sysplex�Data Sharing architecture
�High Availability & Parallelism
�Distributed Data support
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Facts and Figures
� Used by:
– The top 56 banks in the world
– 23 of the top 25 U.S. retailers
– 9 of the top 10 global life/health insurance providers
� Performance, Performance, Performance
– Delivered the largest banking benchmark ever at the Bank of China, a record 9,445 transactions per second
– Supports the world’s largest known peak database workload - 1.1 billion SQL statements per hour at UPS
– The world’s largest known transaction processing database – 23.1 TB at the UK Land Registry
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DB2 for z/OS vs. DB2 for LUW Architecture
Subsystem DB2A
RDS Optimizer Lock Mgr.
Log Mgr. Buffer Mgr. I/O Mgrs.
Other Stor. I/O Buffers Log Buffers
DB2 Code & Storage Areas
Databases
DB2 Catalog
DB2 Directory
System
UserDB1
UserDBn
UserLog Files
LogncLog2
Log1
z/OS – OS/390
DB2 UDB Instance DB2A
Database-1
DB2 Catalog User Tables LogncLog2Log1
I/O Buffers Log Buffers
RDS Optimizer Lock Mgr.
Log Mgr. Buffer Mgr. I/O Mgrs.
DB2 Code & Storage Areas
DBM Storage Areas
Database-2
DB2 Catalog LogncLog2Log1
I/O Buffers Log Buffers
User Tables
Linux, Unix, Windows
DB2 for z/OS Architecture
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DB2 for z/OS: A z/OS Sub-system
ssnmWLMx
WLMManaged
StoredProcs.
ssnmWLMx
WLMManaged
StoredProcs.
ssnmWLMx
WLMManaged
Stored
Procs.
ssnmWLMx
WLMManaged
Stored
Procs.
IRL
M
ssnmMSTR
SystemServices
ssnmDBM1
RDS,Data &Buffer
Services
ssnmDIST
Distr.Data
Facility(DDF)
ssnmWLMx
WLMManaged
StoredProcs.
z/OS
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Memory Structure: DB2 Address Spaces (1 of 2)
� MSTR (System Services AS)�General Command processor
�Subsystem support
�Agent services manager
�Storage manager
�Message generator
� Initialization procedures
� Instrumentation facilities
�System parameter manager
�Recovery manager
�Recovery log manager
�Group manager
�Distributed transaction manager
� IRLM (Internal Resource Lock Manager AS)� Lock Manager
xxxxWLMx
WLM
Managed
Stored
Procs.
xxxxWLMx
WLM
Managed
Stored
Procs.
xxxxWLMx
WLM
Managed
Stored
Procs.
xxxxWLMx
WLM
Managed
Stored
Procs.
IRL
M
ssnmMSTR
System
Services
ssnmDBM1
RDS,
Data &
Buffer
Services
ssnmDIST
Distr.
Data
Facility
(DDF)
ssnmWLMx
WLM
Managed
Stored
Procs.
z/OS
� DBM1 (Database Manager AS)
�Service controller
�Data manager
� Large-object manager (LOBM)
�Data space manager
�Relational data system (RDS)
�Stored-procedures manager
�Utilities (work with associated code in an allied address space)
�Buffer manager
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Memory Structure: DB2 Address Spaces (2 of 2)
� DIST (Distributed Data Facility)
� DRDA (Distr. Relational Database Arch.) Support
� Data Communications Resource Manager (DCRM)
� Distributed Data Interchange Services (DDIS)
� Distributed Relational Data System Manager (DRDS)
� Distributed Transaction Manager (DTM)
� WLM (Workload Manager AS
for Stored Procedures)
�Stored Procedures
�External User-Defined Functions (UDF)
xxxxWLMx
WLM
Managed
Stored
Procs.
xxxxWLMx
WLM
Managed
Stored
Procs.
xxxxWLMx
WLM
Managed
Stored
Procs.
xxxxWLMx
WLM
Managed
Stored
Procs.
IRL
M
ssnmMSTR
System
Services
ssnmDBM1
RDS,
Data &
Buffer
Services
ssnmDIST
Distr.
Data
Facility
(DDF)
ssnmWLMx
WLM
Managed
Stored
Procs.
z/OS
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Allied Address Spaces
DBM1 MSTR IRLM
DIST
TSO
Batch
CICS
IMS
Stored Proc
WebSphere
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Programming Interfaces
� Developer communities
�COBOL, PL/I, C, C++,
�REXX™, APL2®, Assembler,
Fortran
�Java™ (JDBC / SQLJ)
�.NET (C#, VB .NET)
�PHP
�Perl
�Python
�Ruby on Rails
�Toad for DB2
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DB2 System Address Spaces Interaction
RelationalData System
Data/IndexManager
BufferManager
Log/RecoveryManager
LockManager
AttachmentFacility
IRLMMSTR
SPAS
SP/UDFExecution
DBM1
VSAM MediaManagerStorage
CICS
Trx. Server
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DB2 Subsystem Restart
DSNZ002I = DSNZINIT SUBSYSTEM V81A SYSTEMPARAMETERS LOAD MODULE NAME IS V81AZDSN
DSNY001I = SUBSYSTEM STARTING
DSNJ127I = SYSTEM TIMESTAMP FOR BSDS= 03.013 14:32:14.45DSNJ001I = DSNJW007 CURRENT COPY 1 ACTIVELOG DATA SET ISDSNAME=DSNC810.LOGCOPY1.DS02,STARTRBA=000001FF3000,ENDRBA=0000029CAFFFDSNJ001I = DSNJW007 CURRENT COPY 2 ACTIVELOG DATA SET ISDSNAME=DSNC810.LOGCOPY2.DS02,STARTRBA=000001FF3000,ENDRBA=0000029CAFFF
DSNJ099I = LOG RECORDING TO COMMENCE WITHSTARTRBA=00000265F000
S V81ADBM1
DSNR001I = RESTART INITIATEDDSNR003I = RESTART...PRIOR CHECKPOINTRBA=000002656090DSNR004I = RESTART...UR STATUS COUNTSIN COMMIT=0, INDOUBT=0,INFLIGHT=1, IN ABORT=0, POSTPONEDABORT=0DSNR007I = RESTART...STATUS TABLE
T CON-ID CORR-ID AUTHID PLAN S URID DAY TIME
------- ------- ------ -------- - ------------- --- --------
B TSO SYSADM SYSADM DSNESPRR F 003C20AC0141 042 04:35:54
Log Init Current Status Rebuild (CSR)
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DB2 Subsystem Restart
DSNI029I = DSNIFLAI THE FAST LOG APPLY PROCESS IS ACTIVE AND THE AVAILABLE
V81ADBM1 STORAGE IS 00000000 BYTES
DSNI028I = DSNIFLAF THE NUMBER OF QUALIFIED LOG RECORDS READ DURING THE FAST LOG APPLY PROCESS IS 45AND THE NUMBER OF FAST LOG APPLY BUFFERS PROCESSED ARE 1
DSNR005I = RESTART...COUNTS AFTER FORWARD RECOVERY IN COMMIT=0, INDOUBT=0
DSNR018I = RESTART...BACKWARDRECOVERY PROCESSED FROM RBA 00000265DE5B TO RBA 000002658912
DSNR006I = RESTART...COUNTSAFTER BACKWARD RECOVERYINFLIGHT=0, IN ABORT=0,POSTPONED ABORT=0
Forward Recovery Backward Recovery
End Restart
DSNR002I = RESTART COMPLETED
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DB Structures: Overview
�Database�A DB2 Catalog entry
�A collection of physical objects
�Table space�A collection of datasets (files) for storing one or more
Tables
�Table
� Index�B-tree structure and associated Index space
� Index space�A collection of datasets (files) for storing an Index
�View
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Data Structures in DB2
Storage group Physical DISK devices
Database
Table space
Table
Index
Logical concept
Physical data sets
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DB Structures: Table Space
�Simple�One or more table per table space�Individual pages may contain rows from multiple tables�Deprecated in latest DB2 Release (DB2 for z/OS V9)
�Segmented�One or more table per table space�Segments allocated to single table�Segment size (pages) = a multiple of 4 btw. 4 and 64
�Partitioned�Single-table table space� Multiple partitions (files) by data-values range�Indexes can be partitioned or not
�Universal�Both Segmented & Partitioned
� Partition by growth
� Partition by range
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Data & Index Compression
� Data Compression
�Defined at the table space level
�Using the Ziv-Lempel algorithm
�Requires a compression dictionary to be built
�Based on the CMPSC hardware instruction
� Newer generation of z processors implement instructions directly in
circuits (instead of microcode), yielding lower overhead. Instruction design favors decompression over compression.
�Reduce disk space, channel and memory occupancy
� Index Compression
�New in DB2 V9
�Not using Ziv-Lempel algorithm nor a compression dictionary
�Prefix compression used, instead
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Concurrency & Integrity: Locking
� DB2 for z/OS provides comprehensive locking to ensure data integrity
� Locks are used on a variety of data objects, including
�Rows
�Pages
�Tables
�Table space segments
�Table space partitions
�Entire table spaces
�Databases
� Locking granularity affected by
�DBA chosen LOCKSIZE on Database objects
�Application chosen ISOLATION Level
� Lock Escalation
N.B. No locking on Indexes – Latching used, instead.
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Concurrency Control: Locking
� Lock Modes & Granularity
�Table, Partition, Table space
� IS – Intent Share
� IX – Intent Exclusive
� S – Share
� U – Update
� X – Exclusive
� SIX – Share with Intent Exclusive
�Page, Row
� S - Shared
� U - Update
� X - Exclusive
NoNoNoX
NoNoYesU
NoYesYesS
XUSLock ModeLock Modes
Compatibility
Matrix
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DB2 Isolation Level
�UR - Uncommitted Read�For read only queries, no record locking
�Will see uncommitted changes by other transactions
�CS - Cursor Stability�Locks and unlocks the row or page, where the application is
positioned
�Guaranteed to only return data which was committed at the time of the read
�RS - Read Stability�Will keep all qualifying rows locked until the transaction is
completed
�Does release locks on rows that do not satisfy query predicates
�RR - Repeatable Read�Will lock all rows visited and keep locks until the transaction is
completed
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SQL Processing: Static SQL
�Usually used for batch and transactional applications
�Data structures and query semantics know at coding time
�Bound once at program preparation time (before or even long before execution time)�CPU savings
�Easier security control
�Dynamic re-optimization available
�Coding example�EXEC SQL SELECT NAME INTO :custname
FROM CUSTOMERS
WHERE ID = :custid
�Java example: SQLJ
host variable
host variable
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SQL Processing: Dynamic SQL
� Usually used for Query & Reporting, and Business Intelligence applications
� Used when data structures and/or query semantics unknown before execution
� Statement built / stored into program area
� Bound at execution time � Re-bound before each execution unless cached (usage of parameter
markers required)
� Caching reduces CPU consumption
� Dynamic re-optimization still available
� Example (w. parameter marker)� SELECT NAME
FROM CUSTOMERS
WHERE ID = ?
� Dynamic SQL interfaces: ODBC (.Net), JDBC (Java)
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Application Packages and Plans
� Application Package�Contains control structures that DB2 uses when it runs
SQL statements
� Control Structure = operational form of an SQL statement
�Generated at program BIND time
�Each package derived from a single source program
�Supports Versioning & Switch-back
�Packages are grouped into Collections
� Application Plan�Relates an application process to a local DB2 instance
�Contains a list of package names (and/or Collection names)
�Execution requires specific authorization
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Access Path Major Strategies� Join Methods�NLJ – Nested Loop Join�MS – Merge Scan�HJ – Hybrid Join�SJ – Star Join
� Data Access�Relation Scan / Partition Scan�No-matching Index Scan�Matching Index Scan�Index Screening
� Index access may / may not involve table access
�Multiple Index Usage (Union / Intersection)
� I/O Methods�Synchronous Read�Pre-fetch�Dynamic Pre-fetch�List Pre-fetch
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Retrieving Access Path Information
� EXPLAIN statement
�Dynamic Execution
�Accepts Parameter markers
�Applies to single SQL query at a time
�Access Path info stored into PLAN_TABLE and two optional tables
� EXPLAIN Option of BIND Command
�For Static SQL queries
�Applies to all queries in module
�Access Path info stored into PLAN_TABLE and two optional tables
� EXPLAIN data in Perf. Trace records
�Applies to Dynamic SQL Queries
�Proper Perf. Trace must be enabled
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Analyzing Access Path
� Access Path graph display� Using Visual Explain
� Similar to function available on DB2 for LUW
� Tabular representation in set of tables� Most relevant info in PLAN_TABLE
� Example
QRY QBL PL TAB AC MTCH ACCESS IX SORT SORC J
NO KNO NO MTH TNAME CARD NO TY COLS NAME O UJOG UJOG T
---+---+--+---+------+---------+---+--+----+---------+--+----+----+-
100 1 1 0 CAMPG 61 3 I 2 IX_CM1 N NNNN NNNN
1 2 1 PERS 2,051,585 5 I 0 IX_CRM_1 N NNNN NNNN
1 3 1 PERSIN 324,769 2 I 2 IX_PE1 N NNNN NNNN
1 4 1 CONTA 327,645 1 I 1 IX_CON_3 N NNNN NNNN
1 5 1 PHNE 39,005 6 I 3 IX_PH_2 N NNNN NNNN L
1 6 3 - 0 0 N NNNN NNYN
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Query Parallelism
�For Dynamic SQL
�Enabled / disabled by SET CURRENT DEGREE statement
�Applies to queries subsequently prepared
�For Static SQL
�Enabled / disabled by DEGREE option of BIND
�Applies to all queries in application program
�Characteristics
�Final decision up to DB2
�Type of parallelism (CPU or I/O) chosen by DB2
�Degree of parallelism chosen by DB2
�Installation can set max. degree
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Buffer Pools
� Created in the DB2 DBM1 AS when first dataset opened� Deleted when all referenced data sets are closed
� Different page size of buffer� 4, 8, 16, 32 KB
� Table space and BP association is done with SQL� CREATE / ALTER TABLESPACE or INDEX
� Buffer management� Services Data Mgr. and Index Mgr. get page requests
� Locates a page in the buffer pool
� If not found, loads page from DASD to buffer pool
� Returns the address of page to DM or IM
� Deferred write pages to DASD
� Manages buffer pools usage
� Page latch for page integrity
� Data set management� Open and close
� Pre-format disk space
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Buffer Pools Management Strategy
� Search
�Hashing table
� Replace
�Least recently used (LRU)
�Most recently used (MRU)
�First-in-first-out (FIFO)
� Write
�Deferred write
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Buffer Pools Management Queues
Buffer manager
Hash table
DS1 DS2 DS3
Deferred write queue
LRU chain head
LRU chain tailSLRU chain head
SLRU chain tail
Buffer pools
Table or Indexspace
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Logging Overview
� The DB2 log�used to register data changes and other significant DB2 events
� DB2 uses the log to �Recover database objects
�Rollback transactions
�Perform restart recovery
�Record certain diagnostic data
� Major log record types include�System checkpoint records
�Unit of Recovery (UR) control records: e.g. Begin UR, commit
�Database undo/redo records
�Database Exception Table records
� Exception states, e.g. LPL, RECP, STOPped, etc.
�Pageset control records – e.g.
� Pageset/Partition open/close
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Logging Overview
Dual Copy recommended for
�BSDS
�Active Logs
�Archive Logs
Output Log Buffers
Threshold (user defined)
Reusable
BSDSAutomatic
Offload
Reusable
Notreus.
Notreus. Active
Logs
Archive
Logs
Input Log Buffers
Data Before/After Image
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Anatomy of the Log
� Output buffers
�In MSTR virtual memory
�All log records written initially to the output buffers
�Size and write thresholds user-controlled
� Input buffers�In MSTR virtual memory
�Used when DB2 needs to read back records from active/archive logs
� Active log�Most recently written log records – written when
� Application Commits � Output Buffers threshold reached� Database write� System checkpoint
� Archive log�Contains log records "offloaded" from the active logs
� Bootstrap Dataset (BSDS)�Contains control information needed to manage logging / recovery
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Active Log� Must reside on DISK
�Anywhere from 2 to 93 active log datasets
�Max size per dataset = 4GB
� Used in "wrap around" mode. Dataset reused when archived
� Can have dual copies, Copy1/Copy2
�Highly recommended for availability reasons
� DB2 switches to next active log dataset when:
�Space in current active log dataset has been exhausted
�I/O error forces a "truncate and switch"
�ARCHIVE LOG command ("truncate and switch")
� An active log dataset can have one of five possible states:
�NEW: newly added dataset that has yet to be formatted�REUSABLE: new dataset, or dataset that has been offloaded
�NOTREUSABLE: dataset full but not yet offloaded
�STOPPED: DB2 has taken this dataset offline due to errors�TRUNCATED: not full due to I/O error or ARCHIVE LOG
command
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Active Log Offload
� Offload is the process of copying an active log dataset to an archive log dataset
� Offload is initiated by one of the following events:
�When the active log dataset has filled (normal case)
�When the last available active log dataset is 75% full, plus increments of 5% thereafter
�When an I/O error on the active forces truncation
�When the ARCHIVE LOG command is issued
� DISPLAY LOG command can be used to monitor offload activity
� Information about the dataset written to BSDS when offload completes
�Inventory wraps such that oldest entry is deleted automatically
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DB2 for z/OS Autonomic Features
�DB2 Base Autonomic Features
�Deep integration with z/OS WLM
� WLM-managed Stored Procedures AS
� WLM-managed I/O priority
� WLM-managed Buffer pools size
�Dynamic IX Creation for query processing (in-memory WF)
�DB2 Optimization Service Center (OSC)
�New no-charge offering
�Available via web download
�Additional Autonomic Features
�Included into DB2 Optimization Expert for z/OS (OE)
�New OTC (one Time Charge) offering
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DB2 OSC / OE Features
YesAccess Path Advisor
YesWorkload Query Advisor
YesQuery Advisor
YesWorkload Index Advisor
YesQuery Index Advisor
YesYesProfile based Monitoring
YesYesWorkload Statistics Advisor
YesYesQuery Statistics Advisor
YesYesVisual Plan Hint
YesYesAccess Plan Graph
YesYesQuery Formatter, Annotation
Yes
Optimization Service Center
YesQueries from Cache, Catalog
Optimization Expert
Function
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Security: Basics� Can be managed inside or outside DB2
�Inside DB2 using GRANT / REVOKE SQL statements
�Outside DB2 using OS-based security tool (IBM RACF, CA ACF2, etc.)
� Privileges
�Collection
�Database
�Function / Procedure
�Package / Plan
�Schema
�Sequence
�System
�Table / View
�Type / JAR (e.g. SQLJ)
�Use
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Security: DB2 Trusted Context & DB2 Role
�DB2 Trusted Context
�Allows a unique set of privileges to be associated with an application preventing the misuse of privileges when not accessing through the trusted context
�Example:
� User Paul is allowed to retrieve information from
PERSONNEL table only when accessing DB2 from a
specified Host Name or IP Address
�DB2 Role
�A role is a object that can be granted any authority or privilege
�A role is only associated with a DB2 process when the application is associated with a trusted context
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DB2 Trusted Context & DB2 Role: Example
CREATE ROLE CTXROLE ;
CREATE TRUSTED CONTEXT CTX1
BASED UPON CONNECTION
USING SYSTEM AUTHID ADMIN1
DEFAULT ROLE CTXROLE
WITH ROLE AS OBJECT OWNER
ATTRIBUTES (ADDRESS ‘9.67.40.219’)
ENABLE ;
GRANT DBADM TO CTXROLE ;
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Multilevel Security
� Security Policy
�a set of laws, rules and practices that regulate how an organization manages, protects and distributes its sensitive data
�Used by the system to decide whether a particular subject can access a particular object
� Multilevel Security (MLS)
�A security policy that allows the classification of data and users based on a system of hierarchical security levels combined with a system of non-hierarchical security categories
�Has two primary goals
1.Controls must prevent unauthorized individuals from accessing
information at a higher classification than their authorization (read up)
2.Controls must prevent individuals from declassifying information(write down)
�Hierarchy established in the security server (i.e. IBM RACF)
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Multilevel Security: Example
426Z3BLUE
19834I4INDIGO
183U5VIOLET
11994Q6BLUE
112U7RED
653G8ORANGE
239874R9RED
1375W10YELLOW
2351B2
1985A1
Conf_InfoValueIDSEC_LABEL
RAINBOW
SUNSET GREEN PASTEL
RED ORANGE YELLOW BLUE INDIGO VIOLET
SallySECLABEL=‘RAINBOW’
JoeSECLABEL=‘SUNSET’
SUNSET
Sam PASTEL
SECLABEL=‘PASTEL’
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References (available on the Web)
[1] K.E. Plambeck et al., Development and Attributes of z/Architecture, IBM
J. RES. & DEV. VOL. 46 NO. 4/5 July/September 2002
[2] Paul Roger et al., ABCs of z/OS System Programming Volume 10, IBM
Redbook SG24-6990-03
[3] D.J. Haderle, R.D. Jackson, IBM Database 2 Overview, IBM Systems Journal, Vol. 23, No. 2, 1984 (original paper written shortly after DB2 Announcement)
[4] Paolo Bruni & al., DB2 9 for z/OS Technical Overview, IBM Redbook SG24-7330
[5] DB2 for z/OS Documentation (e.g. SC18-9847 Introduction to DB2 for
z/OS) available from
http://www-01.ibm.com/software/data/db2/zos/library.html
[6] Redbooks on z/OS and DB2 for z/OS available from
www.redbooks.ibm.com
[7] The IBM Academic Initiative (Italia) – Pls. visit Internet page at
http://www-304.ibm.com/jct01005c/university/scholars/it/scholars_program.html