Edition Based Redefinition - Continuous Database Application Evolution with Oracle Database 11g Release 2

Release 2
Release 3
Base Release
Continuous Database Application Evolution with Oracle Database 11g Release 2
Lucas Jellema
AMIS, The Netherlands

Introducing Oracle 11gR2 Edition Based Redefinitionthe story of the Parallel Application Universes
Release 2
Release 3
Base Release
Lucas Jellema
AMIS, The Netherlands

Availability
Availability = Performance * (Up or Down)
Up = !Down
Down = Unplanned Down + Planned Down
Planned Down???
System Maintenance
Power-supply, Hardware & Network, O/S upgrade
Database patching & Upgrade
Application Upgrades

Maximum Availability Architecture

Application Upgrade
Creation of new objects
Changing existing objects (alter and create or replace)
Add, Modify or Drop columns or constraints
Change packages and stored procedures
Recompile
Drop redundant objects
Convert or migrate data
Resume normal operations
Application is DOWN

Compare with road maintenance

Restructuring A12
Build new road next to current one (A12-B)
Same “functionality” as the old road
At the cut-over moment
Open new A12-B:
Newly arriving traffic travels on temporary road
Close A12 (original)
Cars already on old road keep going

11gR2 Editioning is similar
Application Upgrade:
Prepare new release
Construct the release in parallel to the existing
Operations in existing application ‘edition’ continue normally
From the cut-over point:
Have new sessions operate on new release
Existing sessions can continue to run on existing release

11gR2 Editions introduces a new dimension in the database
Release 3
Release 2
Base Release

Editions introduce or inherit versions of objects
Release 2
Release 3
Base Release

Editions are parallel universes
Database Objects are identified by
Object Type
Schema
Object Name
…. Edition!
(release, application version, stripe, parallel universe id)
Database Sessions run in the context of a specific edition
Using a specific collection of versions of objects

Database sessions run in a specific edition –one version of each object
Release 2
Release 3
Base Release
The database as seen by a sessionrunning in the context of Release 3
3
2
3
B
2
2
3
3
2

Demo of Application Upgrade
Existing base application, in base edition
Create new editon – release_2
Create and Alter database objects
Base application continues running
Cut-over point
New sessions run in release_2 edition
Current sessions continue in base

Some Rules for EBR (Edition Based Redefinition)
Editioning acts on packages, functions, triggers, procedures, views, types and synonyms
Editioning does not apply to tables
Data is not versionend, cloned, migrated
Different incarnations of a table are suggested through editionable views – there is only one table
Applications should never access tables directly!

But wait, there is more
After the release of a new edition – there is no reason why you cannot keep the previous one going for some time
And multiple previous ones!
That means – END OF THE BIG BANG upgrade!
Multiple versions of the application can continue running to suport various user groups (e.g. SaaS)
Without data migration and additional downtime upon later move over of user groups

Parallel Application Versions
Application X
VERSION 1
Application X
VERSION 2
Release 2
Release 3
Base Release

Version 1 on Base Edition

Version 1 on Edition Release 2

Upgrade Base to Release 2
Authors
New columns COUNTRY and BIOGRAPHY
Books
Drop column NUM_OF_PAGES
Modified column ISBN (10 to 20 characters)
New columns LANGUAGE and PUBLICATION_YEAR

Version 2 (on Edition Release 2)

Version 2 on Base Edition

Editions and Tables
Tables cannot be versioned: there is only one definition of a table across all Editions
Data is not versioned: a record exists once and only once
The solution for managing changes to Tables: Editioning Views and Cross Edition Triggers
Editioning Views are defined on base table (no joins)
Editioning Views can have DML triggers defined (just like base table)
Using an editioning view in a query or DML statement does not impact the performance of the query or DML

Editions and Tables
Application A
Application B
Table EMP
SAL
MGR
JOB
ENAME
HIREDATE
COMM

Editions and Tables
Application A
Application B
Editioning View EMP
Table EMP_BASE
SAL
MGR
JOB
ENAME
HIREDATE
COMM

Oracle guarantees:The Execution Plan for a SQL query that uses an Editioning View is identical to that for the same query based directly on the table

Migrate to Editioning Views
Rename Table (for example to <old table name>_BASE)
Constraints continue to refer to the table
Create the Editioning View with the old table name
Using the ‘CREATE OR REPLACE EDITIONING VIEW <view name>’ statement
Reroute privileges – grant on view rather than table
Recompile the triggers on the table
These now become triggers on the Editioning View
Recompile all invalid PL/SQL program units and Views
They now refer to the Editioning View instead of the table
VPD policies are reassigned to the View
Regular auditing and FGA is on the table

Demo
ALTER TABLE EMP RENAME TO EMP_BASE;
CREATE OR REPLACE EDITIONING VIEW EMP
AS
SELECT ...
FROM EMP_BASE
/
DROP TRIGGER EMP_BRI
/
Rem recreate trigger on Editioning View
@<EMP_BRI>.trg
Rem recompile invalid Views and PL/SQL units

Multiple versions of Editioning View
Application A
Application B
Edition R2
Edition R1
Editioning View EMP
Editioning View EMP
Table EMP_BASE
SAL
MGR
JOB
ENAME
HIREDATE
COMM

Application A
Application B
Edition R2
Edition R1
View EMP (1.1)
…* Language
View EMP (1.0)
Table EMP_BASE
SAL
MGR
JOB
ENAME
LANGUAGE
HIREDATE
COMM
Forward CrosseditionTrigger

Demo
CREATE EDITION R2 AS CHILD OF R1;
ALTER SESSION SET EDITION R2;
SELECT SYS_CONTEXT('Userenv', 'Current_Edition_Name') "Current_Edition" FROM DUAL;
ALTER TABLE EMP_BASE
ADD (LANGUAGE VARCHAR2(2) NULL);
Rem function for deriving value for language
CREATE OR REPLACE FUNCTION
GET_LANGUAGE( p_job in varchar2) return varchar2
is
begin
return case p_job when 'MANAGER' then 'fr'
else 'en' end;
end;

Demo
Rem Create Forward Crossedition Trigger
Rem Applies to DML operations on EMP_BASE from
Rem Earlier Editions
CREATE OR REPLACE TRIGGER EMP_1_1_Fwd_Xed
BEFORE INSERT OR UPDATE ON EMP_BASE
FOR EACH ROW
FORWARD CROSSEDITION
DISABLE
BEGIN
:new.language = get_language(:new.job);
END EMP_1_1_Fwd_Xed;
Rem Enable the Forward Crossedition Trigger
ALTER TRIGGEREMP_1_1_Fwd_Xed ENABLE;

Demo
Rem Use Forward Crossedition trigger to
Rem upgrade existing table records according to new table
Rem version (for large # records use dbms_parallel_execute)
DECLARE
c NUMBER := DBMS_SQL.OPEN_CURSOR();
x NUMBER;
BEGIN
DBMS_SQL.PARSE
( c => c
, Language_Flag => DBMS_SQL.NATIVE
, Statement => 'UPDATE EMP_BASE SET EMPNO = EMPNO'
, Apply_Crossedition_Trigger => 'EMP_1_1_Fwd_Xed'
);
x := DBMS_SQL.EXECUTE(c);
DBMS_SQL.CLOSE_CURSOR(c);
COMMIT;
END;

Upgrade Table Definition
(Create Edition,) Set target Edition for session
Make desired changes to the table
Add columns, modify Columns, … (online redefinition)
Modify the Editioning View in the Edition
To reflect the table as its latest version should look
Perhaps hiding columns you eventually want to drop
(optional) Create Forward Crossedition Trigger on base table to have DML on previous Editions made valid
(optional) Create Reverse Crossedition Trigger on base table to have DML on current Edition synch back

Cross Edition Triggers
If you remove a (mandatory) column from the current Editioning View…
a Reverse Crossedition Trigger ensures that new records get some value in that (invisible) column
If you add a (mandatory) column to the table (and the current Editioning View)…
a Forward Crossedition Trigger ensures that records DMLed through previous Editioning View versions are made valid
(optionally) Apply Forward Crossedition Trigger for all existing records (created in old edition of the table)
Use DBMS_SQL.parse (with parameter Apply_Crossedition_Trigger set to name of trigger)
Use DBMS_PARALLEL_EXECUTE

Application A
Application B
Edition R3
View EMP (1.1)
… (minus ENAME)* Language
o FIRST_NAME
* LAST_NAME
Edition R1
Edition R2
View EMP (1.1)
…* Language
View EMP (1.0)
Table EMP_BASE
Reverse Crossedition Trigger
SAL
MGR
JOB
ENAME
LANGUAGE
FIRSTNAME
LASTNAME
HIREDATE
COMM
Forward CrosseditionTrigger

“Suggested (best) Practices”
Every application (release) sets the Edition it requires when it connects to a session
At the same time it calls dbms_application_info
And sets other Context details
Applications should never access tables – all access should be through views
Only through views can the data structure itself be Editioned
Even triggers should be on the Editioning View

Interesting EBR Tid-Bits
Drop Object in an Edition stops the inheritance from previous Edition. Object no longer is carried forward
Edition can have only one child – no branches (yet)
DBMS_SQL.PARSE can be executed in a specific Edition
Use parameter edition to specify other than current edition
If no explicit edition is set for a session, the default edition is used
ALTER DATABASE DEFAULT EDITION = edition_name;
Hints in queries against Editionable Views are understood in terms of the underlying table
Logical EV column references are correctly mapped

Interesting EBR Tid-Bits
DB Links & Materialized Views currently not editionable
Objects of an editionable type are not editionable when used by a non-editional object
PL/SQL Function used in Function Based Index or the definition of a Materialized View
ADT used as the base type for a column in a table
EBR (online upgrade) benefits from Online Table Redefinition and Fine Grained Dependency tracking
Data Dictionary Views
DBA_/ALL_EDITIONS – editions in the database
DBA_/ALL_OBJECTS – objects (inherited) in current edition
DBA_/ALL_OBJECTS_AE – actual objects across all editions

Summary
11gR2 Editions are parallel, co-existing universes with incarnations of database objects
The new release can be constructed, tested and run in a new edition
The old edition can be switched off at cut-over
Editions also allow long time co-existence of multiple releases of an application
Application Upgrade no longer needs to disrupt the operation through planned downtime
By the way: EBR is available in all DB editions

Conclusion
See our blog for Oracle Database 11gR2 articles (other topics as well)
http://technology.amis.nl/blog
This presentation and the demo scripts are on the blog too
Contact me: lucas.jellema@amis.nl

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Edition Based Redefinition - Continuous Database Application Evolution with Oracle Database 11g Release 2

by Lucas Jellema

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