Time Travelling With DB2 10 For zOS

Time Travelling with DB2 10
for z/OS

The Information Management Specialists

Topics
• Introduction
• DB2 10 for z/OS Overview
• Temporal Data Support
• Early Experiences
• Further Reading
• Summary


Introduction
• Director and Principal Consultant at Triton Consulting
• 24 years DB2 experience, 19 as a consultant working with
customers in UK, Europe and the US
• IBM Gold Consultant since 1999
• IBM Information Champion
• Former IDUG (International DB2 User Group) President
• Author of IBM Redbooks, white papers and more recently
“flashbooks”


DB2 10 for z/OS
• Extensive beta program running throughout
2009/10, with customers from all around the world
• Generally available since October 2010
• Upgrade path provided from DB2 8 or DB2 9
• Many customers are currently planning their DB2 10
upgrades, to begin in the next 12-24 months
 DB2 8 for z/OS End of Support in April 2012


Top New Features
• CPU/Performance Improvements • In-memory object support
• Temporal Data • Optimiser enhancements
• Virtual Storage Enhancements • MEMBER CLUSTER for UTS
• High performance DBATs • Backup and recovery
• Security Extensions enhancements
• Improved Catalog Concurrency • Enhanced audit
• Access Path Management • Include additional index
columns
• pureXML enhancements
• Currently Committed semantics
• Enhanced SQL OLAP functions
• Automated statistics
• Skip Migration
• Dynamic schema change
enhancements • And many more….


Why Temporal Data?
• Most IT systems need to keep historical as well as current
information
• Industry regulations and competitive pressures are
prompting IT managers to maintain even more data for
longer periods of time
• Most warehousing / analytics applications require a
historical perspective of data
• Implementation requires lots of effort by DBA and
developer to design, test and implement
 Lots of “reinventing the wheel”


Why Temporal Data?
• DB2 10 provides this functionality as part of the database
engine – the first major RDBMS vendor to do so
 Improve DBAs and developer productivity
 Reduce errors in application code
 Reduce time-to-market for new applications
 Improve performance by driving function into the database
engine
 Improve application consistency
 Support compliance / audit requirements


Why Temporal Data?
• Solve common business problems
 Ensure that a customer only has one financial position at a
given time
 Was an insured covered for a procedure on a specific date?
► Was that information correct at the time the claim was processed?
 Establish prices for a catalog ahead of time, so that they
are completed before the change needs to be made
 Answer a customer complaint about an old bill
 … and many, many more


Temporal Data Concepts
• Temporal Table - a table that supports “data
versioning” to allow point-in-time queries to be
executed
 Multiple versions of each row are kept by DB2 as they
change over time
 Additional metadata is kept, recording the period in time
when a given version of the row was valid
 Contrast to traditional non-temporal (aka “snapshot”)
tables, where only the current version of a row is available
unless developer/DBA have taken additional steps to
support historical perspective


• Period – the time during which a given version of a row
is/was valid
 Period is defined by special start timestamp and end timestamp
columns in the temporal table
 Note that in current DB2 implementation start timestamp is
inclusive (>=), but end timestamp is not inclusive (<)
► Feature request to provide ZPARM and make this a site decision

CustNo … Start_TS End_TS
Period #1
123 … 2011-05-01 11:03 2011-05-26 23:51
123 … 2011-05-26 23:51 9999-12-31 23:59
Period #2


• System Temporal Table – a temporal table that uses
DB2 system-defined periods to record row history
 Associated with a DB2 system event (INSERT / UPDATE /
DELETE) against table – all changes captured
 DB2 automatically sets start and end timestamp for a
period
 History is maintained in a separate “history” table
 No gaps between periods – end timestamp of previous row
version = start timestamp of new version
 Useful for audit/compliance requirements
 Typically implemented by DBA

• Business Temporal Table – a temporal table that uses
business-defined periods to record row history
 Aka “application temporal”
 Associated with a business event such as a change of address
 Useful for tracking business events over time
 History is maintained in the base table
 Application has control over start and end timestamp for a
given period
► Can have gaps between periods
 Typically implemented by developer and DBA


• Bi-Temporal Table – a temporal table that supports
both business and system time periods
 Best of both worlds – application-defined versioning with
complete audit trail of system changes
 Two sets of start/end timestamps defined


Implementation Choices
• User-managed
 Only choice prior to DB2 10
 Typically implemented using triggers to catch “before” version of row
during INSERT/UPDATE/DELETE
► Need application logic to determine if a given series already exists (update old
row + INSERT in same UOW) or not (INSERT only)
 Lots of scope for inconsistency / errors in application code (e.g.
overlapping periods)
► Need audit function to ensure rows are valid, SQL can be horrible
 Lots of scope for performance issues – especially with index design
• DB2-managed
 Designed to avoid the pitfalls above
 Some potential performance gains – see later


Implementing DB2 Temporal Tables
• DBA indicates which tables need temporal support at CREATE/ALTER
time
 Support for UTS, classic partitioned and single table segmented
tablespaces
• For system temporal or bi-temporal tables
 DBA also creates separate history table with identical definition to
base table (same columns, data types, null attributes, etc but no
SYSTEM_TIME specification) and associates with base table via ALTER
 DB2 automatically copies old version of row to history table whenever
row in main table is changed via DELETE or UPDATE
 DB2 automatically UNIONs base and history table as required


Select Extensions
• Elegant extensions to SELECT statement allow historical
perspective to be seen via standard SQL
 Same syntax for SYSTEM_TIME and BUSINESS_TIME
SELECT *
FROM BASE_TABLE
FOR SYSTEM_TIME AS OF :TSTAMP
WHERE CUST_NO = 123

Single - Inclusive/Exclusive

SELECT * SELECT *
FROM BASE_TABLE FROM BASE_TABLE
FOR SYSTEM_TIME BETWEEN :ST_TSTAMP FOR SYSTEM_TIME FROM : ST_TSTAMP
AND :EN_TSTAMP TO : EN_TSTAMP
WHERE CUST_NO = 123 WHERE CUST_NO = 123

Multiple - Inclusive/Inclusive Multiple - Inclusive/Exclusive


Implementing System Temporal
• SYSTEM_TIME row begin column
 TIMESTAMP(12) NOT NULL GENERATED ALWAYS AS ROW BEGIN
 Composed of 9-digit timestamp, plus 3 digits for data sharing member
 DB2 ensures uniqueness of generated values across transactions
 Not updateable by application
• SYSTEM_TIME row end column
 TIMESTAMP(12) NOT NULL GENERATED ALWAYS AS ROW END
 Not updateable by application
• Data types for both begin and end columns must be the same
• INSERT, UPDATE, DELETE use standard syntax, all versioning handled by
DB2
• Query rewrite for SELECT statements to UNION ALL history table


System Temporal DDL
CREATE TABLE CUSTOMER
(
CUST_NO INTEGER NOT NULL,
…
SYS_START TIMESTAMP(12) NOT NULL GENERATED ALWAYS AS ROW BEGIN,
SYS_END TIMESTAMP(12) NOT NULL GENERATED ALWAYS AS ROW END,
SYS_CRT TIMESTAMP(12) NOT NULL GENERATED ALWAYS AS TRANSACTION START ID,
PERIOD SYSTEM_TIME(SYS_START, SYS_END)
);

CREATE TABLE CUSTOMER_HIST
(
…
SYS_START TIMESTAMP(12) NOT NULL,
SYS_END TIMESTAMP(12) NOT NULL
);

ALTER TABLE CUSTOMER ADD VERSIONING USE HISTORY TABLE CUSTOMER_HIST;


Example – System Temporal
System INSERT INTO EMP UPDATE EMP
Event VALUES (321, 20000) WHERE EMPNO = 321
SET SALARY = 25000

T1 T2 Time T3

EmpNo Salary Start_TS End_TS EmpNo Salary Start_TS End_TS
Main 300 10000 T0 31-12-9999 300 10000 T0 31-12-9999
Table
321 20000 T1 31-12-9999 321 25000 T3 31-12-9999

SELECT SALARY EmpNo Salary Start_TS End_TS
FROM EMP = 25000
WHERE EMPNO = 321 321 20000 T1 T3

SELECT SALARY
FROM EMP History Table
FOR SYSTEM TIME AS OF T2 = 20000
WHERE EMPNO = 321


Implementing Business Temporal
• BUSINESS_TIME row begin and row end columns can be defined as either:
 TIMESTAMP(6) NOT NULL
 DATE NOT NULL
• BUSINESS_TIME periods have a check constraint in which end > begin
column
• New optional unique BUSINESS_TIME WITHOUT OVERLAPS index is useful
in having a built-in mechanism for enforcing keys being unique over a
period of time
 Adds start and end columns to index
• UPDATE and DELETE statements have been enhanced to allow updating
and deleting based upon a period of time
 FOR PORTION OF BUSINESS_TIME FROM expression1 TO expression2


FOR PORTION OF…
UPDATE DELETE
Rows Contained
FOR PORTION OF
Business Time Row
Result

Span FROM or TO
FOR PORTION OF
Business Time Row
Result

Span FROM and TO
FOR PORTION OF
Business Time Row
Result


Business Temporal DDL
CREATE TABLE CUSTOMER
(
…
BUS_START TIMESTAMP(6) NOT NULL GENERATED ALWAYS AS ROW BEGIN,
BUS_END TIMESTAMP(6) NOT NULL GENERATED ALWAYS AS ROW END,
PERIOD BUSINESS_TIME(BUS_START, BUS_END)
);

CREATE UNIQUE INDEX CUST_IX
ON CUSTOMER
(
CUST_NO,
BUSINESS_TIME WITHOUT OVERLAPS
);


Topics
• Introduction
• Performance
• Early Experiences
• Further Reading
• Summary


Performance – System Temporal
• Redbook measurement
• Transaction mix of 70% read
(SELECT), 30% write (10% INSERT
+ 20% UPDATE/DELETE)
• Compare:
 Baseline (no history)
 History with triggers
 History with system temporal
• Result: 56% less CPU overhead
using system temporal when
compared to triggers
Source: DB2 10 Performance Topics Redbook


Performance – System Temporal
• Compare, for varying number of
rows
 UPDATE/DELETE with triggers
 UPDATE/DELETE with system
temporal
• Result
 30-39% less CPU overhead using
system temporal for UPDATE
when compared to triggers
 10-19% less CPU for DELETE


Performance – Business Temporal
• Compare performance of UPDATE
which results in two or three rows
being split
 UPDATE with business temporal
 INSERT/UPDATE via stored procedure



Experiences – System Temporal
• System temporal is not a watertight audit strategy
 Can ALTER TABLE to remove history relationship if you have the necessary
authority (no record in SYSCOPY if versioning added or dropped)
• Schema change is painful (e.g. adding a column)
 Need to prevent access, drop versioning, add column to both tables, add
versioning again
 PM31313 addresses this – new function to support ALTER ADD COLUMN and
keep history table in step
• Need to integrate with archival strategy (if you have one…)
• Need to treat base and history table as if they are referentially connected
– backup and recover as a set
• Need to be able to supress history data from being replicated – open PMR
(PM31315)


Experiences – Business Temporal /
General
• Some applications with user-managed temporal functionality
can be ported relatively easily
 As long as DB2 implementation is consistent with your site/application
approach
 DSNZPARM to set inclusive/inclusive or inclusive/exclusive is a
common request
 Benefits must be clear
• Non-temporal UPDATE/DELETE still allowed – care is required
• Limited 3rd party support for SQL extensions


Further Reading
• IBM DB2 10 Home Page
 http://www-01.ibm.com/software/data/db2/zos/db2-10/
• White Paper – DB2 10: A Smarter Database for a Smarter Planet
 https://www14.software.ibm.com/webapp/iwm/web/signup.do?source=sw-
infomgt&S_PKG=wp-z-db2-smarter
 Also available as part of a “flashbook” - ISBN: 1583473610
• DB2 10 for z/OS Performance Topics Redbook (SG24-7942)
• IDUG – International DB2 User Group
 http://www.idug.org/


Topics
• Introduction
• Further Reading
• Summary


Summary
• DB2 10 contains a long list of significant enhancements to improve
performance, scalability and productivity
• Temporal support is an industry first, and offers some compelling
advantages for new applications than need a historical data
perspective
 Improve DBAs and developer productivity
 Reduce errors in application code
 Reduce time-to-market for new applications
 Improve performance by driving function into the database engine
 Improve application consistency
 Support compliance / audit requirements


Time Travelling With DB2 10 For zOS

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