Oracle GoldenGate Best Practices: Active-Active Configuration with DML Auto CDR

Executive Overview

This document is an introduction to Oracle GoldenGate (DIPC remote agent)’s best practices and guidelines for configuring OGG in an active-active environment using the built in functionality of DML Auto Conflict Detection and Resolution (Auto CDR), LOB data type column is also take into consideration.

Prerequisites

· RDBMS is Oracle Database 12.2+

· GoldenGate version 12.3/DIPC agent 18.2.3

· OS: All Oracle GoldenGate supported platforms for Oracle

Introduction

Setting up Conflict Management is key to the OGG bi-direction data sync. Most Active-Active or Multi-Master Systems will have some form of conflict. Conflicts happen due to at least one row being modified on more than one system.

Prior to RDBMS 12.2 and OGG12.2

Tables should contain timestamp columns, or we have to add column onto the table likewise to achieve the same goal. The timestamp column i.e. CHANGE_TS is used for Conflict management and decide resolution of conflict when it happen.

CDR steps are as following:

Datatypes that can be compared are supported:

• NUMERIC

• DATE

• TIMESTAMP

• CHAR/NCHAR

• VARCHAR/NVARCHAR

Typically these data types are used with parameters like COMPARECOLS, GETBEFORECOLS, and in resolution parameters using RESOLVECONFLICT ([USEMIN] | [USEMAX]).

LOGALLSUPCOLS

Extract captures before images for UPDATE operations.

Extract captures before images of supplemental logged columns for both UPDATE and DELETE operations.

GETBEFORECOLS

Ensures certain columns are logged

TABLE option in extract

Example:

GETBEFORECOLS (ON UPDATE ALL, ON DELETE ALL)

TRANSLOGOPTION EXCLUDETAG

• Tag supplied to transaction as it is extracted to prevent receiving replicat from trying to send it back to source

• Classic/Integrated Extract (primary)

• Tag can be any number/letter [0-9 A-Z]

Example:

TRANSLOGOPTION EXCLUDETAG 0294

COMPARECOLS

Used by Replicat to detect and resolve update/delete conflicts

Example:

COMPARECOLS (ON UPDATE ALL, ON DELETE ALL)

Since RDBMS 12.2 and OGG12.3

Timestamp column can be added without effecting the application or code base- leverages invisible columns/RDBMS 12.2 kernel.

Auto CDR makes the conflict management much simpler than before, you also need to meet below prerequisites

· Requires source and target to be Oracle Database 12.2

· Requires Integrated Extract (Classic Extract does not support invisible columns)

· Requires Integrated Replicat or Integrated Parallel Replicat

No Visible Application Changes:

• Easy to enable

• Invisible timestamp columns automatically created and maintained by database kernel

• Delete tombstone log to support updates-delete conflicts (new capability)

• Enables supplemental logging on required columns

• Allows ability to detect conflicts for LOB column changes

• No need to specify CDR/REPERROR parameters

• Last record wins (highest timestamp)

Enable by ADD_AUTO_CDR for LOB columns

SQL> BEGIN

dbms_goldengate_adm.add_auto_cdr(

schema_name => 'HR',

table_name => 'EMPLOYEES');

END;

PL/SQL procedure successfully completed.

The procedure crates an invisible timestamp column to associate with the row, (If no LOB column exist in table). If we have multiple LOB columns, i.e. 2 LOB columns, it will create 2 separate invisible timestamp columns to associate with each LOB columns and one invisible timestamp column associate with the other columns by default.

If we have a test table with below structure:

After enable the Auto CDR by:

SQL> BEGIN

DBMS_GOLDENGATE_ADM.ADD_AUTO_CDR(

schema_name => 'hr',

table_name => 'test');

END;

PL/SQL procedure successfully completed.

We query the ALL_GG_AUTO_CDR_COLUMNS table

SQL>SELECT TABLE_OWNER,

TABLE_NAME,

COLUMN_GROUP_NAME,

COLUMN_NAME,

RESOLUTION_COLUMN

FROM ALL_GG_AUTO_CDR_COLUMNS

ORDER BY TABLE_OWNER, TABLE_NAME;

We can see 3 CDRTS timestamp columns were created, 2 for LOB columns and one for the other columns.

By enable the Auto CDR, we

• Automatically creates an invisible timestamp column to associate with the row

• Invisible timestamp column automatically maintained

• Automatically enables Delete Tombstone Log Table

• Tombstone table automatically maintained

• Automatically enables all column supplemental logging

Monitoring

We can get the statics for CDR resolution by

GGCSI> stats replicat <group name>,reportcdr

From my test till now, with OGG Version 12.3.0.1.2 OGGCORE_12.3.0.1.0_PLATFORMS_171208.0005_FBO and Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production, LOB CDR resolution stats is NOT show here.

Steps for Implementing OGG in an active-active configuration

Enable Oracle GoldenGate on database

1. Open archive log mode

[Source] [Target]

SQL>shutdown immediate;

SQL>startup mount;

SQL>alter database archivelog;

SQL>alter database open;

SQL>alter system switch logfile;

SQL>archive log list;

SQL> alter PLUGGABLE database all open;

SQL>create user c##ogg identified by ogg;

SQL>GRANT DBA to c##ogg container=all;

SQL> exec dbms_goldengate_auth.grant_admin_privilege('c##ogg',container=>'ALL');

2. Open supplemental log data and force logging

[Source] [Target]

SQL>SELECT supplemental_log_data_min, force_logging FROM v$database;

SQL>alter database add supplemental log data;

SQL>alter database force logging;

SQL>SELECT supplemental_log_data_min, force_logging FROM v$database;

3. Enabling Oracle GoldenGate in the Database

[Source] [Target]

SQL> alter system set enable_goldengate_replication = true scope=both;

5. Create OGG Users

[Source] [Target]

SQL> create user ogg identified by ogg;

SQL>GRANT DBA to ogg;

SQL> BEGIN
  dbms_goldengate_auth.grant_admin_privilege
  (
    grantee => 'c##ogg',
    privilege_type => 'CAPTURE',
    grant_select_privileges => TRUE
  );
END;
/

[Source] [Target]

SQL>BEGIN

dbms_goldengate_auth.grant_admin_privilege

(

grantee => 'c##ogg',

privilege_type => 'APPLY',

grant_select_privileges => TRUE

);

END;

Install Oracle GoldenGate

We use the DIPC remote agent version 18.2.3 in this manual,
just download it and unzip, we can use it.

1. Update the tnsnames.ora

tnsnames.ora

SRC =

(DESCRIPTION =

(ADDRESS_LIST =

(ADDRESS = (PROTOCOL = TCP)(HOST =
192.168.56.106)(PORT = 1521))

)

(CONNECT_DATA =

(SERVICE_NAME = PDBSRC)

)

TGT =

(DESCRIPTION =

(ADDRESS_LIST =

(ADDRESS = (PROTOCOL = TCP)(HOST =
192.168.56.106)(PORT = 1521))

)

(CONNECT_DATA =

(SERVICE_NAME = PDBTGT)

)

ORCL =

(DESCRIPTION =

(ADDRESS_LIST =

(ADDRESS = (PROTOCOL = TCP)(HOST =
192.168.56.106)(PORT = 1521))

)

(CONNECT_DATA =

(SERVICE_NAME = ORCL)

)

2. Update the .bash_profile for OCI

.bash_profile

#
.bash_profile

# Get the
aliases and functions

# User
specific environment and startup programs

ORACLE_HOME=/u01/src/oci; export ORACLE_HOME

export
JAVA_HOME=/usr/java/jdk1.8.0_92

export
JRE_HOME=/usr/java/jdk1.8.0_92/jre

PATH=$JAVA_HOME/bin:$ORACLE_HOME/bin:$PATH
; export PATH

CLASSPATH=$ORACLE_HOME/JRE:$ORACLE_HOME/jlib:$ORACLE_HOME/rdbms/jlib:$JAVA_HOME/lib:

LD_LIBRARY_PATH=$ORACLE_HOME:/lib:/usr/lib; export
LD_LIBRARY_PATH

export
TNS_ADMIN='/u01/src/oci/network/admin/'

3. Testing the Connection

Setting up OGG

OGG Parameters on the Source:

1. Manager:

PORT 8809

2. Extracts:

-- Extract :extsrc

extract
extsrc

userid
c##ogg@orcl,password ogg

exttrail
./dirdat/es

TranLogOptions
Excludetag 00

table
pdbsrc.hr.*;

--Pump: pumsrc

extract
pumsrc

passthru

rmthost
<ip>,mgrport 8919

rmttrail
./dirdat/rs

table
pdbsrc.hr.*;

3. Replicat:

--Replicat: reptgt

replicat
reptgt

userid
ogg@src, password ogg

discardfile
reptgt.dsc, append

NOMAPINVISIBLECOLUMNS

map
pdbtgt.hr.test, target pdbsrc.hr. test;

map
pdbtgt.hr.jobs, target pdbsrc.hr. jobs;

OGG Parameters on the Target:

1. Manager:

PORT
8919

2. Extracts:

Extract exttgt:

extract
exttgt

userid
c##ogg@orcl,password ogg

exttrail
./dirdat/et

TranLogOptions
Excludetag 00

table
pdbtgt.hr.*;

Pump: pumtgt

extract
pumtgt

passthru

rmthost
<ip>,mgrport 8809

rmttrail
./dirdat/rt

table
pdbtgt.hr.*;

3. Replicat:

replicat
repsrc

userid
ogg@tgt, password ogg

discardfile
repsrc.dsc, append

NOMAPINVISIBLECOLUMNS

map
pdbtgt.hr.test, target pdbsrc.hr. test;

map
pdbtgt.hr.jobs, target pdbsrc.hr. jobs;

Adding groups:

Source:

GGCSI> obey Src.oby

--Source OGG
Setup

add extract
extsrc, integrated tranlog, begin now

add exttrail
./dirdat/es, extract extsrc

dblogin
userid c##ogg@orcl password ***

add
schematrandata PDBSRC.HR,allcols

info
trandata PDBSRC.HR.*

add extract
pumsrc, exttrailsource ./dirdat/es

add rmttrail
./dirdat/rs, extract pumsrc

add replicat
reptgt, integrated ,exttrail ./dirdat/rt

Target:

GGCSI>
obey Tgt.oby

----Target
OGG Setup

add extract exttgt,integrated
tranlog, begin now

add exttrail
./dirdat/et, extract exttgt

dblogin
userid c##ogg@orcl password ***

add
schematrandata pdbtgt.hr,allcols

info
trandata pdbtgt.hr.*

add extract
pumtgt, exttrailsource ./dirdat/et

add rmttrail
./dirdat/rt,extract pumtgt

add replicat
repsrc, integrated ,exttrail ./dirdat/rs

Start the processes

Source and Target:

GGSCI>
start mgr !

GGSCI>
start er *

Source:

Target:

Testing Steps for Auto-CDR

In all our test cases below, we took the DML against the
source database firstly and then against target in very short time.

Insert Conflict

Source:

And then on Target:

Query the source again:

Review in GGSCI:

Update Conflict

This time we are going to test a table with LOB data type
column,

INSERT INTO hr.test
VALUES(3,'Pic No.1',bfilename('IMAGE_DIR','1.png')); commit;

What we get on the source and target:

Source:

Target:

Update the LOB value in table:

Source:

update hr.test set
IMAGE =(bfilename('IMAGE_DIR','2.png')),MEMO='PIC #2' where id=3; commit;

Target:

update hr.test set
IMAGE =(bfilename('IMAGE_DIR','3.png')),MEMO='PIC #3' where id=3; commit;

We also query the sample data for those 2 LOB column

For Pic#2:

For Pic#3:

Query source and target we get:

We did not get the CDR stats for LOB columns by running:

stats
<Group_name>,reportcdr

Delete Conflict

1. Run the SQL to delete the record on both source
and target:

delete from
hr.emp where empno=1; commit;

2. Query the result on both databases:

select
EMPNO,SAL,CDRTS$ROW from hr.emp where
empno=1;

No record returns

3. Review in OGG

Source:

Target:

Conclusion

This paper covers the OGG Auto CDR feature which introduced
in version 12.3.

• It
has No Visible Application Changes and more simple to handle.

• It
can handle to detect conflicts for LOB column changes.

• A
Last record wins (with highest timestamp).

If you want to customize the conflict detection resolution
more complex, not only highest timestamp win, you can still try classic CDR. Please
refer to the OGG Administrative Guide for a more extensive view of CDR.

Reference

1. Oracle GoldenGate Best Practices: Active-Active
Configuration with DDL and DML CDR --Tracy West

2. Oracle GoldenGate 12.3: Conflict, Detection and
Resolution –Bobby Curtis

https://www.slideshare.net/BobbyCurtisMBA/goldengate-cdr-from-ukoug-2017

3. CDR Info:
https://docs.oracle.com/goldengate/c1230/gg-winux/GGODB/automatic-conflict-detection-and-resolution2.htm#GGODB-GUID-29EDF7BF-6BD8-4E02-98AB-DDBB4719D038