Source Oracle #

The first five steps (I-V) are to prepare the Oracle Database for replication and must be executed in an Oracle client. The remaining steps (VI-VIII) are to configure Replicant.

I. Set up Oracle Driver #

Install the appropriate JDBC Driver (Recommended: JDBC Driver 18c and Java 8 compatible ojdbc8 version)
Download ojdbc8.jar from the following link: Oracle JDBC Driver Download
Place the downloaded ojdbc8 jar file into the replicant-cli/lib directory after installing Replicant

II. Setup Oracle User #

Create a new user for Replicant with the following command:

CREATE USER <USERNAME> IDENTIFIED BY <PASSWORD>
DEFAULT TABLESPACE <user-defined-tablesace>
QUOTA unlimited on <user-defined-tablespace>
TEMPORARY TABLESPACE TEMP;

Provide the create session permission:
```
GRANT CREATE SESSION TO <USERNAME>;
```
Grant the select permission for all the tables that are part of the replication:
```
GRANT SELECT ON <TABLENAME> TO <USERNAME>;
```
OR

The select permission can be granted on all of the tables
```
GRANT SELECT ANY TABLE TO <USERNAME>;
```

III. Set up Change Data Capture (CDC) #

Set the destination for the log archive:
```
ALTER SYSTEM SET log_archive_dest = '$PATH_TO_REDO_LOG_FILES' scope=spfile  
```
To use log-based CDC, the Oracle database must be in ARCHIVELOG mode. To check what mode the database is in, use the ARCHIVE LOG LIST command. To set the database in ARCHIVELOG mode, use the following commands:
```
SHUTDOWN IMMEDIATE
STARTUP MOUNT
ALTER DATABASE ARCHIVELOG
ALTER DATABASE OPEN
```
Once the database is in ARCHIVELOG mode, grant the EXECUTE_CATALOG_ROLE role to use the DBMS_LOGMNR package:
```
GRANT EXECUTE_CATALOG_ROLE TO <USERNAME>
```
Provide the following permissions to allow Replicant to access the START_LOGMNR procedure For Oracle 11g:
```
GRANT SELECT ANY TRANSACTION TO <USERNAME>;
```
For Oracle 12C and beyond:
```
GRANT LOGMINING TO <USERNAME>;
```
Provide the following permission to allow Replicant to access v_$logmnr_contents:
```
GRANT SELECT ON v_$logmnr_contents TO <USERNAME>;
GRANT SELECT ON gv$archived_log to $USERNAME;
```
For Oracle 19C and beyond, Replicant requires additional access to v_$logfile:
```
GRANT SELECT ON v_$logfile TO <USERNAME>;
```

Enabling logs #

You have to enable either primary key or all column logging at either the database level or the table level.

If you use table level logging, you must enable it for the CDC heartbeat table as well.

Database level Supplemental logging #

Enable Force Logging:
```
ALTER DATABASE FORCE LOGGING
```

Enable PRIMARY KEY logging:

ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY) COLUMNS

Enable ALL Column logging:

ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS

Table level supplemental logging #

PRIMARY KEY logging

ALTER <TABLE_NAME> ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY) COLUMNS

ALL Column logging

ALTER <TABLE_NAME> ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS

If table level logging is enabled, then force logging should not be enabled. We need force logging for database level logging:
```
ALTER DATABASE FORCE LOGGING
ALTER SYSTEM SWITCH LOGFILE
```

The following additional permissions are required:

GRANT SELECT ON gv_$instance TO $USERNAME;
GRANT SELECT ON gv_$PDBS TO $USERNAME;
GRANT SELECT ON gv_$log TO $USERNAME;
GRANT SELECT ON gv_$database_incarnation to $USERNAME;

Only enable either PRIMARY KEY logging or ALL column logging, not both.

IV. Setup Global Permissions #

Quick Definitions

One Time Access: The granted permission is only required for the initial data load (snapshot) and for reinit operations (snapshots of newly added tables). The permission can be revoked after the necessary operation is complete.
Continuous Access: The granted permission is required throughout the replication process.

Provide the following privilege for one time access:
```
GRANT SELECT ON DBA_SEGMENTS TO <USERNAME>;
```

Provide the following continuous access permissions; these are necessary during snapshot as well as continious real-time replication:

GRANT SELECT ON gv_$database TO <USERNAME>;
GRANT SELECT ON gv_$transaction TO <USERNAME>;
GRANT SELECT ON gv_$session TO <USERNAME>;--Not required for replicant release 20.8.13.7 and above

Grant the following continuous access permission for the tables involved in Replication:
```
GRANT FLASHBACK ON <TABLE_NAME> TO <USERNAME>;
```
OR

Enable Flashback for all tables
```
GRANT FLASHBACK ANY TABLE TO <USERNAME>;
```

Provide access to the below system views for schema migration:

GRANT SELECT ON ALL_TABLES TO <USERNAME>;
GRANT SELECT ON ALL_VIEWS TO <USERNAME>;
GRANT SELECT ON ALL_CONSTRAINTS TO <USERNAME>;
GRANT SELECT ON ALL_CONS_COLUMNS TO <USERNAME>;
GRANT SELECT ON ALL_PART_TABLES TO <USERNAME>;
GRANT SELECT ON ALL_PART_KEY_COLUMNS TO <USERNAME>;
GRANT SELECT ON ALL_TAB_COLUMNS TO <USERNAME>;
GRANT SELECT ON SYS.ALL_INDEXES TO <USERNAME>;
GRANT SELECT ON SYS.ALL_IND_COLUMNS TO <USERNAME>;
GRANT SELECT ON SYS.ALL_IND_EXPRESSIONS TO <USERNAME>;

V. Grant Pluggable Database (PDB) Permissions #

Ensure that you are connected as a common user with privileges granted on both CDB$ROOT and PDB

Provide following additional permissions:

GRANT SET CONTAINER TO $USERNAME CONTAINER=ALL;
GRANT SELECT ON DBA_PDBS to <USERNAME> CONTAINER=ALL;

Open pluggable database:

ALTER PLUGGABLE DATABASE $PDB_NAME OPEN READ WRITE FORCE;

The proceeding steps are to set up Replicant. The extracted replicant-cli will be referred to as the $REPLICANT_HOME directory in the proceeding steps.

VI. Set up Connection Configuration #

From $REPLICANT_HOME, navigate to the connection configuration file:
```
vi conf/conn/oracle.yaml
```

Make the necessary changes as follows:

type: ORACLE

host: localhost #Replace localhost with your oracle host name
port: 1521 #Replace the default port number 1521 if needed
service-name: IO #Replace IO with the service name of your Oracle Listener

username: 'REPLICANT' #Replace REPLICANT with your username to connect to Oracle
password: 'Replicant#123' #Replace Replicant#123 with the your user's password

max-connections: 30 #Maximum number of connections replicant can open in Oracle

VII. Setup Filter Configuration #

From $REPLICANT_HOME, navigate to the filter configuration file:
```
vi filter/oracle_filter.yaml
```

In accordance to your replication needs, specify the schema(s)/table(s) which is to be replicated. Use the format explained below:

allow:

  #In this example, data of object type Table in the schema REPLICANT will be replicated
  schema: "REPLICANT"
  types: [TABLE]

  #From the shemca REPLCIANT, only the Orders, Customers, and Returns tables will be replicated.
  #Note: Unless specified, all tables in the schema will be replicated

  allow:
    Orders:
       #Within Orders, only the US and AUS columns will be replicated
       allow: ["US, AUS"]

    Lineitem: #All columns in the table Lineitem  will be replicated without any predicates

    Customers:  
       #Within Customers, only the product and service columns will be replicated as long as they meet the condition C_CUSTKEY < 5000
       allow: ["product", "service"]
       conditions: "C_CUSTKEY < 5000"

Below is the filter file template you must follow:

allow:
  schema: <your_schema_name>
  types: <your_object_type>


  allow:
    your_table_name_1:
      allow: ["your_column_name"]
      conditions: "your_condition"  

    your_table_name_2:

    your_table_name_3:
      allow: ["your_column_name"]
      conditions: "your_condition"

For a detailed explanation of configuration parameters in the filter file, read: Filter Reference

VIII. Set up Extractor Configuration #

For real-time replication, you must create a heartbeat table in the source Oracle.

Create a heartbeat table in the schema you are going to replicate with the following DDL:

CREATE TABLE "<schema>"."replicate_io_cdc_heartbeat"(
  "timestamp" NUMBER NOT NULL,
  PRIMARY KEY("timestamp"));

Grant INSERT, UPDATE, and DELETE privileges to the user configured for replication
From $REPLICANT_HOME, navigate to the extractor configuration file:
```
vi conf/src/oracle.yaml
```
The configuration file has two parts:
- Parameters related to snapshot mode.
- Parameters related to realtime mode.
Parameters related to snapshot mode #

The following parameters are specific to Oracle as source:
- fetch-create-sql: This option can be used to apply exact create SQL on source to target.
  
  This parameter is available only for Oracle->Oracle pipeline.
- fetch-create-sql-no-constraints: This option is used to split create table SQL and Primary/Unique/Foreign Key constraints as different SQLs. So as part of schema migration we create tables without constraints and after the snapshot is complete the constraints are applied. Application of constraints post snapshot is configured by applier config init-constraint-post-snapshot.
  
  This parameter is available only for Oracle->Oracle pipeline.
- serialize-fetch-createSql: This option is used to fetch create SQL in serialized manner after fetching table schema.
- serialize-fetch-create-sql-no-constraints: This option is used to fetch SQL of Primary/Unique/Foreign Key constraints in serialized manner.
  
  This parameter is available only for Oracle->Oracle pipeline.
The following is a sample configuration for snapshot mode:
```
snapshot:
  threads: 16
  fetch-size-rows: 10_000
  verify-row-count: false
  _fetch-exact-row-count: true
  _traceDBTasks: true
#  inf-number-behavior: EXCEPTION   # EXCEPTION, ROUND, CONVERT_TO_NULL
#  flashback-query: true
#  parallel-query: true
#  fetch-user-roles: true

#   per-table-config:
#   - schema: tpch
#     tables:
#       lineitem1:
#         row-identifier-key: [ORDERKEY, LINENUMBER]
#         extraction-priority: 1 #Higher value is higher priority. Both positive and negative values are allowed. Default priority is 0 if unspecified.
#       lineitem1:
#         row-identifier-key: [ORDERKEY, LINENUMBER]
#        products:
#          per-partition-config:
#          - partition-name: SYS_P461
#            row-count: 0
#          - partition-name: SYS_P462
#            row-count: 0
#          - partition-name: SYS_P463
#            row-count: 1
#          - partition-name: SYS_P464
#            row-count: 3
#        part:
#          row-count: 2000
```
- Supplying split-key in the per-table-config section is not required (and not supported) for Oracle source.
- We strongly recommend that you specify row-identifier-key in per-table-config section for tables not having PK/UK constraints defined on the source Oracle system.
Parameters related to realtime mode #

If you want to operate in realtime mode, you can use the realtime section to specify your configuration. The following Oracle specific parameters are available:
- block-ddl-transaction[v20.09.14.3]: This option blocks fetching logs for DDL operation from Oracle.
- use-current-scn[v20.09.14.8]: In start-postion section, this option allows using current scn value for to start reading realtime operations.
- start-scn[v20.09.14.3]: In start-postion section this option allows using user specified scn value for to start reading realtime operations.
- inter-source-latency-s[v20.10.07.16]: In the start-position section this config option in seconds represents the lag between primary and standby Oracle in case the source-failover feature is enabled.
- stop-inactive-lm-session-after-s[v20.12.04.14]: Check if inactive logminer session after specified seconds and cancel the statement.
- adjust-lm-fetch-size[v21.02.01.2]: Allow adjusting the logimer fetch size if there is a lot of log activity.
- auto-adjust-lm-timeout[v21.04.06.6]: This is a tuning config which will adjust the logminer query timeout based on workload for continuous mine mode.
  
  Default: By default, this parameter is set to false.
- log-miner-dict-file[v21.09.17.6]: If specified, this file will be used as the dictionary for log mining instead of using the online dictionary. The file must be accessible by Oracle.
The following is a sample configuration for realtime mode:
```
realtime:
  threads: 4
  _traceDBTasks: true
  #fetch-size-rows: 0
  #stop-inactive-lm-session-after-s: 2
  heartbeat:
    enable: true
    schema: "tpch"
    interval-ms: 10000
    table-name: replicate_io_cdc_heartbeat

  #start-position:
    #start-scn: 2362927
```

For a detailed explanation of configuration parameters in the extractor file, read: Extractor Reference