Painless Master Table Alter In Replication Paper # 524

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pr ligence Empowering Intelligence

Painless Master Table Alter In Replication

Paper # 524

Arup Nandapr ligence

Empowering Intelligence

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Question

Two Most Important Objectives of Living Organisms

Surviving

Reproducing!

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Replication Options Revisited

MASTER COPY

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Multi-Master

MASTER COPY

TriggerTrigger

SnapshotLogs

ROW1 ROW1

pushROW2

TriggerTrigger

SnapshotLogs

ROW2

Primary Secondary

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Multi-Master contd.

• Can be Used in Disaster Recovery• Can be SYNCHRONOUS • Secondary Copy Useful for Transactions• Bidirectional Flow of Data _

Changes are PUSHED to secondaryAdvantages

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Multi-Master contd.

• Continuosly Available Link Required• Conflict Resolution Logic Needed• Can Strain the Database _

Disadvantages

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Updateable Snapshot

MASTER SNAPSHOT

TriggerTrigger

SnapshotLogs

ROW1 ROW1

pull

ROW2

TriggerTrigger

SnapshotLogs

ROW2

push

CREATE SNAPSHOT MYSNAP

FOR UPDATE AS

SELECT * FROM MASTER@MAINDB

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Updateble Snapshots contd.

• Changes are PULLED rather than pushedAdvantages• Controlled from Secondary Side• Continuous Link Not Needed• Can be Used in Disaster Recovery _

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Updateable Snapshots contd.

Disadvantages• Conflict Management• Difficult Setup and Administration• Strain on Resources• Cannot be SYNCHRONOUS• Reporting Requirements – Overkill _

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Read Only Snapshot

MASTER SNAPSHOT

TriggerTrigger

SnapshotLogs

ROW1 ROW1

pull

Primary Secondary

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Read Only Snapshots contd.

PULLEDControlled by SecondaryDisadvantages

Cannot be Used in Disaster RecoveryAdvantages• No Conflict Management• Simple Setup• Less Strain on Resources• Continuous Link Not Needed _

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Altering The Master Table

EMPNO ENAME SAL

1 CHARLIE 1000

2 DAN 1500

COMM

100

120

PROD

REPL

Not captured in Refresh Process

EMPNO ENAME SAL COMM

1 CHARLIE 1000 100

2 DAN 1500 120

EMPNO ENAME SAL

1 CHARLIE 1000

2 DAN 1500

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Documented


1 CHARLIE 1000 100

2 DAN 1500 120

PROD

REPL

EMPNO ENAME SAL

1 CHARLIE 1000

2 DAN 1500XDrop the Snasphot

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Documented


1 CHARLIE 1000 100

2 DAN 1500 120

PROD

REPL


1 CHARLIE 1000 100

2 DAN 1500 120

Recreate the Snapshot

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Documented Process

• Drop Snapshot (Snapsite)• Add Column to Master Table (Master)• Create Snapshot (Snapsite)• Refresh Snapshot (Snapsite)

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Problem

• Time Consuming• Rollback Segment Space Needed• ORA-1555• Temporary Segment Space Needed• Space Needed in Target Tablespace

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Database Example

• Schema Owner : ANANDA• Table TEST1

– COL1 CHAR(1)– COL2 CHAR(1)

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Prepping the Master Site

Creating the Snapshot LogAs user ANANDACREATE SNAPSHOT LOG ON TEST1TABLESPACE USER_DATAWITH PRIMARY KEYINCLUDING NEW VALUES;

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Create Repl Group

As REPADMIN UserDBMS_REPCAT. CREATE_MASTER_REPGROUP (GNAME=>'TEST1',QUALIFIER=>'',GROUP_COMMENT=>’TEST SNAPSHOT’

);

Group Name

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Generate Master RepObject

DBMS_REPCAT.CREATE_MASTER_REPOBJECT(GNAME=>'TEST1',

TYPE=>'TABLE', ONAME=>'TEST1', SNAME=>'ANANDA');

Group Name

Table Name

Schema Name

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Generate Repl Support

DBMS_REPCAT.GENERATE_REPLICATION_SUPPORT(SNAME=>'ANANDA',ONAME=>'TEST1',TYPE=>'TABLE',

MIN_COMMUNICATION=>TRUE);

Schema Name

Object Name

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Resume Master Activity

DBMS_REPCAT.RESUME_MASTER_ACTIVITY( GNAME=>'TEST1');

Group Name

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Make the Refresh Group

At Database REPL as user MVADMIN

DBMS_REFRESH.MAKE(NAME=>'MVADMIN.TEST1',NEXT_DATE=>SYSDATE+5/(24*60),INTERVAL=>'SYSDATE+5/(24*60)'

);

Group Name

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Make the Snapshot Group


DBMS_REPCAT.CREATE_SNAPSHOT_REPGROUP(GNAME=>'TEST1',MASTER=>'PROD',PROPAGATION_MODE=> ‘ASYNCHRONOUS’

);

Group Name

Master Database

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Create the Snapshot

At Database REPL as user ANANDA

CREATE SNAPSHOT TEST1REFRESH FASTASSELECT * FROM TEST1@PROD

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Add Snapshot to Group

At Database REPL as user ANANDA

DBMS_REFRESH.ADD (NAME=>'MVADMIN.TEST1',LIST=>'ANANDA.TEST1'

);

Group Name

Object Name

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Generate Repl Support


DBMS_REPCAT.CREATE_SNAPSHOT_REPOBJECT(

GNAME =>'TEST1',SNAME =>'ANANDA',ONAME =>'TEST1',TYPE =>'SNAPSHOT'

)

Group Name

Schema Name

Object Name

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Most Expensive


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Prebuilt Table

PROD

TEST1

SNAPSHOTLOGS

TEST1

EXPORT/IMPORT

SQL*LOADER DIRECT PATH

DIRECT PATH INSERT

CREATE TABLE AS SELECT

REPL

SNAPSHOTLOGS

SNAPSHOT

FAST REFRESH

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Usual Method


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Prebuilt Table

CREATE SNAPSHOT TEST1ON PREBUILT TABLEREFRESH FASTASSELECT * FROM TEST1@PROD

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Needed Changes

• Add a column COL3 CHAR(1)• Modify column COL2 CHAR(1000)

As user ANANDA in PROD Database

ALTER TABLE TEST1 ADD (COL3 CHAR(1);

ALTER TABLE TEST1 MODIFY (COL2 CHAR(1000));

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Snapshot on Prebuilt Table

TEST1TABLE

SNAPSHOT

TEST1 is a TABLECREATE SNASPSHOT TEST1

ON PREBUILT TABLEAS ….

DROP SNASPHOT TEST1TEST1 is a TABLE again!

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SNAPSHOT IS CREATED ON

PREBUILT TABLE

SNAPSHOT IS DROPPED

COL3 IS ADDED TO THE TABLE

SNAPSHOT IS RECREATED ON

THE TABLE

Segment State

COL1 CHAR(1)COL2 CHAR(1)

SNAPSHOT

ROW3

ROW2

ROW1

TEST1

COL3 CHAR(1)

SNAPSHOT

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Segment State Analysis

• Snapshot is Dropped• Segment Reverts to Table• Column Is Added• Snapshot is Recreated• Segment Becomes Snapshot

TIM

E

The state of the segment, i.e. the data is the same

at these two points intime; only the additional

column is different.

Therefore, a FULL Refresh Is NOT Needed!

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Stop Any Refresh

SELECT JOB FROM USER_REFRESH WHERE RNAME = 'TEST1';

EXEC DBMS_JOB.BROKEN(<JOBNUMBER>,TRUE);

COMMIT;SELECT SID FROM

DBA_JOBS_RUNNINGWHERE JOB = <JOBNUMBER>;

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Add the Columns

DROP SNAPSHOT TEST1;Snapshot dropped; Table remains

ALTER TABLE TEST1 ADD (COL4 CHAR(1);

ALTER TABLE TEST1 MODIFY (COL3 CHAR(1000));

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Potential Problem

When a SNAPSHOT is Created on a Master Table, the Snashot Logs Entries are Erased

Need to Capture Snapshot Log EntriesMLOG$_<first 20 Chars of Table Name>

Table Name:THIS_IS_A_LONG_TABLE_NAME

Snap Log Name: MLOG$_THIS_IS_A_LONG_TABLE

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Preserve the LogAs User ANANDACOL PART_TAB_NAME NOPRINT NEW_VALUE PART_TAB_VALSELECT SUBSTR(‘&TABNAME',1,20) PART_TAB_NAMEFROM DUAL/DROP TABLE MLOG_BAK/CREATE TABLE MLOG_BAKASSELECT * FROM MLOG$_&&PART_TAB_VAL.@PROD/

Table to Preserve

Snapshot Log

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Recreate the Snapshot

• Build the Snapshot• Add the Snapshot to the Refresh Group• Build Replication Support for the Group

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Snapshot Log Table

Reinstate the Log Entries

INSERT INTO MLOG$_&&PART_TAB_VAL.@PROD

SELECT * FROM MLOG_BAK/COMMIT/

Table We Preserved the Snapshot Logs In

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Test the Refresh

• Do a Fast Refreshexecute dbms_snapshot.refresh('TEST1','F')

• Re-run the Jobexecute dbms_job.run(<jobnumber>)

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Dare to Compare?Elapsed Time

USUAL APPROACH RECOMMENDED APPROACH

•1m•1m•5m•10 hr•1m•1m

•1m

•5m•1m

•Drop the Snapshot and Table•Add Columns in Master•NO NEED•Recreate the Table•Build the Snapshot•Add the Snapshot to the Refresh Group•Build Replication Support for the Group•NO NEED•Check Refresh

•Drop the Snapshot•Add Columns in Master•Preserve Snapshot Logs •NO NEED•Build the Snapshot•Add the Snapshot to the Refresh Group•Build Replication Support for the Group•Reinstate Logs•Check Refresh

10 hours6 minutes

16 minutes

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Conclusion

• Elapsed Time Reduced As Much As 99%• Resource Utilization Low• All Processes Supported by Oracle• No Data Dictionary Manipluation, No Underscore

Parameters

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Thank You!

Painless Master Table Alter In Replication

Paper # 524by Arup Nanda

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Date post:	10-Jan-2016
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Painless Master Table Alter In Replication Paper # 524

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