13 Preparing and Configuring the System for Oracle GoldenGate

Learn about how to prepare the system for running Oracle GoldenGate and how to configure it with your MySQL database.

Topics:

• Database User for Oracle GoldenGate Processes for MySQL
  
• Ensuring Data Availability
  
• Setting Logging Parameters
  
• Adding Host Names
  
• Setting the Session Character Set
  
• Preparing Tables for Processing
  
• Changing the Log-Bin Location
  
• Configuring Bi-Directional Replication
  
• Configuring MySQL for Remote Capture
  
• Configuring a Two-way SSL Connection in MySQL Capture and Delivery
  
• Capturing using a MySQL Replication Slave
  
• Other Oracle GoldenGate Parameters for MySQL
  
• Positioning Extract to a Specific Start Point
  

Database User for Oracle GoldenGate Processes for MySQL

Requirements for the database user for Oracle GoldenGate processes are as follows:

• Create a database user that is dedicated to Oracle GoldenGate. It can be the same user for all of the Oracle GoldenGate processes that must connect to a database:

  • Extract (source database)

  • Replicat (target database)

  • DEFGEN (source or target database)

• To use DDL the MySQL user must have privileges to install the database plug-ins.

• To preserve the security of your data, and to monitor Oracle GoldenGate processing accurately, do not permit other users, applications, or processes to log on as, or operate as, the Oracle GoldenGate database user.

• Keep a record of the database users. They must be specified in the Oracle GoldenGate parameter files with the USERID parameter.

• The Oracle GoldenGate user requires read access to the INFORMATION_SCHEMA database.

• The Oracle GoldenGate user requires the following user privileges.

  Privilege	Source Extract	Target Replicat	Purpose
  SELECT	Yes	Yes	Connect to the database and select object definitions
  REPLICATION SLAVE	Yes	NA	Connect and receive updates from the replication master’s binary log.
  CREATE CREATE VIEW EVENT INSERT UPDATE DELETE	Yes	Yes	Source and target database heartbeat and checkpoint table creation, and data record generation and purging
  DROP	Yes	Yes	Dropping a Replicat checkpoint table or deleting a heartbeat table implementation
  EXECUTE	Yes	Yes	To execute stored procedures.
  INSERT, UPDATE, DELETE on target tables	NA	Yes	Apply replicated DML to target objects
  DDL privileges on target objects (if using DDL support)	NA	Yes	Issue replicated DDL on target objects

• To capture binary log events, an Administrator must provide the following privileges to the Extract user:

  • Read and Execute permissions for the directory where the MySQL configuration file (my.cnf) is located

  • Read permission for the MySQL configuration file (my.cnf)

  • Read and Execute permissions for the directory where the binary logs are located

  • Read and Execute permission for the tmp directory

Ensuring Data Availability

Retain enough binary log data so that if you stop Extract or there is an unplanned outage, Extract can start again from its checkpoints. Extract must have access to the binary log that contains the start of the oldest uncommitted unit of work, and all binary logs thereafter. The recommended retention period is at least 24 hours worth of transaction data, including both active and archived information. You might need to do some testing to determine the best retention time given your data volume and business requirements.

If data that Extract needs during processing was not retained, either in active or backup logs, one of the following corrective actions might be required:

• Alter Extract to capture from a later point in time for which binary log data is available (and accept possible data loss on the target).

• Resynchronize the source and target tables, and then start the Oracle GoldenGate environment over again.

To determine where the Extract checkpoints are, use the INFO EXTRACT command. For more information, see INFO EXTRACT in Command Line Interface Reference for Oracle GoldenGate.

Setting Logging Parameters

To capture from the MySQL transaction logs, the Oracle GoldenGate Extract process must be able to find the index file, which contains the paths of all binary log files.

Extract expects that all of the table columns are in the binary log. As a result, only binlog_row_image set as full is supported and this is the default. Other values of binlog_row_image are not supported.

Note:

Oracle recommends that the binary log is retained for at least 24 hours.

In MySQL 5.7, the server_id option must be specified along with log-bin, otherwise the server will not start. For MySQL 8.0, the server_id is enabled by default.

Extract checks the following parameter settings to get this index file path:

1. 
   
2. Extract TRANLOGOPTIONS parameter with the ALTLOGDEST option. If this parameter specifies a location for the log index file, Extract accepts this location over any default that is specified in the MySQL Server configuration file. When ALTLOGDEST is used, the binary log index file must also be stored in the specified directory. This parameter should be used if the MySQL configuration file does not specify the full index file path name, specifies an incorrect location, or if there are multiple installations of MySQL on the same machine. From Oracle GoldenGate 21c onward, ALTLOGDEST parameter is optional. When ALTLOGDEST is not specified, the binary log index and binary log filepaths will be fetched from the database directly.Please note: The paths thus fetched are also subject to same accessibilitychecks as in the existing process.

   To specify the index file path with TRANLOGOPTIONS with ALTLOGDEST, use the following command format on Windows:

   TRANLOGOPTIONS ALTLOGDEST "C:\Program Files\MySQL\logs\binlog.index"

   On Linux, use this format:

   TRANLOGOPTIONS ALTLOGDEST "/mnt/rdbms/mysql/data/logs/binlog.index" 

   To capture from a remote server or in case of remote capture, you only need to specify the REMOTE option instead of the index file path on the remote server. For remote capture on both Windows and Linux, specify the following in the Extract parameter file:

   TRANLOGOPTIONS ALTLOGDEST REMOTE

3. The MySQL Server configuration file: The configuration file stores default startup options for the MySQL server and clients. On Windows, the name of the configuration file is my.ini. On other platforms, it is my.cnf. In the absence of TRANLOGOPTIONS with ALTLOGDEST, Extract gets information about the location of the log files from the configuration file. However, even with ALTLOGDEST, these Extract parameters must be set correctly:

   • binlog-ignore-db=oggddl: This prevents DDL logging history table entries in the binlog and is set in the my.cnf or my.ini file.

   • log-bin: This parameter is used to enable binary logging. This parameter also specifies the location of the binary log index file and is a required parameter for Oracle GoldenGate, even if ALTLOGDEST is used. If log-bin is not specified, binary logging will be disabled and Extract returns an error.

   • log-bin-index: This parameter specifies the location of the binary log index. If it is not used, Extract assumes that the index file is in the same location as the log files. If this parameter is used and specifies a different directory from the one that contains the binary logs, the binary logs must not be moved once Extract is started.

   • max_binlog_size: This parameter specifies the size, in bytes, of the binary log file.

     Note:

     The server creates a new binary log file automatically when the size of the current log reaches the max_binlog_size value, unless it must finish recording a transaction before rolling over to a new file.

   • binlog_format: This parameter sets the format of the logs. It must be set to the value of ROW, which directs the database to log DML statements in binary format. From Oracle GoldenGate 19c onward, Extract silently ignores the binlog events that are not written in the ROW format instead of abending when it detects a binlog_format other than ROW.

     Note:

     MySQL binary logging does not allow logging to be enabled or disabled for specific tables. It applies globally to all tables in the database.

   • mysql.rds_set_configuration: When capturing from MySQL Amazon RDS instance, you need to call the mysql.rds_set_configuraton stored procedure on MySQL command line, to retain the binary logs for a specific duration. By default, the default value of binlog_retention_hours for MySQL Amazon RDS is set to NULL, which implies that the binary logs are not retained.

     The following example shows the command to preserve the binary log for 24 hours:

     mysql > call mysql.rds_set_configuration('binlog retention hours', 24);

   To locate the configuration file, Extract checks the MYSQL_HOME environment variable: If MYSQL_HOME is set, Extract uses the configuration file in the specified directory. If MYSQL_HOME is not set, Extract queries the information_schema.global_variables table to determine the MySQL installation directory. If a configuration file exists in that directory, Extract uses it.

4. For MariaDB version 10.2 and later, Oracle GoldenGate works in the same way as for MySQL but a new variable needs to be configured in the my.cnf or my.ini file. The variable that needs to be added is "binlog-annotate-row-events=OFF". Restart MariaDB after configuring this variable and then start the Extract process.

Adding Host Names

Oracle GoldenGate gets the name of the database it is supposed to connect to from the SOURCEDB parameter. A successful connection depends on the localhost entry being properly configured in the system host file. To avoid issues that arise from improper local host configuration, you can use SOURCEDB in the following format:

SOURCEDB dbname@hostname:port, USERID mysqluser, PASSWORD welcome

The dbname is the name of the MySQL instance,hostname is the name or IP address, port is the port number of the MySQL instance. If using an unqualified host name, that name must be properly configured in the DNS database. Otherwise, use the fully qualified host name, for example myhost.company.com.

Setting the Session Character Set

The GGSCI, Extract and Replicat processes use a session character set when connecting to the database. For MySQL, the session character set is taken from the SESSIONCHARSET option of SOURCEDB and TARGETDB. Make certain you specify a session character set in one of these ways when you configure Oracle GoldenGate.

Preparing Tables for Processing

This section describes how to prepare the tables for processing. Table preparation requires these tasks:

• Assigning Row Identifiers
  
• Limiting Row Changes in Tables That Do Not Have a Key
  
• Triggers and Cascade Constraints Considerations
  

Assigning Row Identifiers

Oracle GoldenGate requires some form of unique row identifier on the source and target tables to locate the correct target rows for replicated updates and deletes.

• How Oracle GoldenGate Determines the Kind of Row Identifier to Use
  
• Tables with a Primary Key Derived from a Unique Index
  
• How to Specify Your Own Key for Oracle GoldenGate to Use
  

How Oracle GoldenGate Determines the Kind of Row Identifier to Use

Unless a KEYCOLS clause is used in the TABLE or MAP statement, Oracle GoldenGate selects a row identifier to use in the following order of priority:

1. Primary key
2. First unique key alphanumerically that does not contain a timestamp or non-materialized computed column.
3. If none of the preceding key types exist (even though there might be other types of keys defined on the table) Oracle GoldenGate constructs a pseudo key of all columns that the database allows to be used in a unique key, excluding those that are not supported by Oracle GoldenGate in a key or those that are excluded from the Oracle GoldenGate configuration.

   Note:

   If there are other, non-usable keys on a table or if there are no keys at all on the table, Oracle GoldenGate logs an appropriate message to the report file. Constructing a key from all of the columns impedes the performance of Oracle GoldenGate on the source system. On the target, this key causes Replicat to use a larger, less efficient WHERE clause.

Tables with a Primary Key Derived from a Unique Index

In the absence of a primary key on a table, MySQL will promote a unique index to primary key if the indexed column is NOT NULL. If there are more than one of these not-null indexes, the first one that was created becomes the primary key. To avoid Replicat errors, create these indexes in the same order on the source and target tables.

For example, assume that source and target tables named ggvam.emp each have columns named first, middle, and last, and all are defined as NOT NULL. If you create unique indexes in the following order, Oracle GoldenGate will abend on the target because the table definitions do not match.

Source:

mysql> create unique index uq1 on ggvam.emp(first); 
mysql> create unique index uq2 on ggvam.emp(middle); 
mysql> create unique index uq3 on ggvam.emp(last); 

Target:

mysql> create unique index uq1 on ggvam.emp(last); 
mysql> create unique index uq2 on ggvam.emp(first); 
mysql> create unique index uq3 on ggvam.emp(middle); 

The result of this sequence is that MySQL promotes the index on the source "first" column to primary key, and it promotes the index on the target "last" column to primary key. Oracle GoldenGate will select the primary keys as identifiers when it builds its metadata record, and the metadata will not match. To avoid this error, decide which column you want to promote to primary key, and create that index first on the source and target.

How to Specify Your Own Key for Oracle GoldenGate to Use

If a table does not have one of the preceding types of row identifiers, or if you prefer those identifiers not to be used, you can define a substitute key if the table has columns that always contain unique values. You define this substitute key by including a KEYCOLS clause within the Extract TABLE parameter and the Replicat MAP parameter. The specified key will override any existing primary or unique key that Oracle GoldenGate finds.

Limiting Row Changes in Tables That Do Not Have a Key

If a target table does not have a primary key or a unique key, duplicate rows can exist. In this case, Oracle GoldenGate could update or delete too many target rows, causing the source and target data to go out of synchronization without error messages to alert you. To limit the number of rows that are updated, use the DBOPTIONS parameter with the LIMITROWS option in the Replicat parameter file. LIMITROWS can increase the performance of Oracle GoldenGate on the target system because only one row is processed.

Triggers and Cascade Constraints Considerations

Triggers

Disable triggers on the target tables, or alter them to ignore changes made by the Oracle GoldenGate database user. Oracle GoldenGate replicates DML that results from a trigger. If the same trigger gets activated on the target table, then it becomes redundant because of the replicated version, and the database returns an error.

Cascade Constraints Considerations

Cascading updates and deletes captured by Oracle GoldenGate are not logged in binary log, so they are not captured. This is valid for both MySQL and MariaDB. For example, when you run the delete statement in the parent table with a parent child relationship between tables, the cascading deletes (if there are any) happens for child table, but they are not logged in binary log. Only the delete or update record for the parent table is logged in the binary log and captured by Oracle GoldenGate.

See https://mariadb.com/kb/en/replication-and-foreign-keys/ and https://dev.mysql.com/doc/refman/8.0/en/innodb-and-mysql-replication.html for details.

To properly handle replication of cascading operations, it is recommended to disable cascade deletes and updates on the source and code your application to explicitly delete or update the child records prior to modifying the parent record. Alternatively, you must ensure that the target parent table has the same cascade constraints configured as the source parent table, but this could lead to an out-of-sync condition between source and target, especially in cases of bi-directional replication.

Changing the Log-Bin Location

Modifying the binary log location by using the log-bin variable in the MySQL configuration file might result in two different path entries inside the index file, which could result in errors. To avoid any potential errors, change the log-bin location by doing the following:

1. Stop any new DML operations.
2. Let the extract finish processing all of the existing binary logs. You can verify this by noting when the checkpoint position reaches the offset of the last log.
3. After Extract finishes processing the data, stop the Extract group and, if necessary, back up the binary logs.
4. Stop the MySQL database.
5. Modify the log-bin path for the new location.
6. Start the MySQL database.
7. To clean the old log name entries from index file, use flush master or reset master (based on your MySQL version).
8. Start Extract.

Configuring Bi-Directional Replication

In a bi-directional configuration, there are Extract and Replicat processes on both the source and target systems to support the replication of transactional changes on each system to the other system. To support this configuration, each Extract must be able to filter the transactions applied by the local Replicat, so that they are not recaptured and sent back to their source in a continuous loop. Additionally, AUTO_INCREMENT columns must be set so that there is no conflict between the values on each system.

1. Configure Oracle GoldenGate for high availability or active-active replication according to the instructions in the Propagating DDL in Active-Active (Bidirectional) Configurations in Using Oracle GoldenGate for Oracle Database.
2. To filter out Replicat operations in a bi-directional configuration so that the applied operations are not captured and looped back to the source again, take the following steps on each MySQL database:

   • Configure each Replicat process to use a checkpoint table. Replicat writes a checkpoint to this table at the end of each transaction. You can use one global checkpoint table or one per Replicat process See Overview of Replicat in Understanding Oracle GoldenGate.

   • Specify the name of the checkpoint table with the FILTERTABLE option of the TRANLOGOPTIONS parameter in the Extract parameter file. The Extract process will ignore transactions that end with an operation to the specified table, which should only be those of Replicat.

     Note:

     Although optional for other supported databases as a means of enhancing recovery, the use of a checkpoint table is required for MySQL when using bi-directional replication (and likewise, will enhance recovery).

3. Edit the MySQL server configuration file to set the auto_increment_increment and auto_increment_offset parameters to avoid discrepancies that could be caused by the bi-directional operations. The following illustrates these parameters, assuming two servers: ServerA and ServerB.

   ServerA:

   auto-increment-increment = 2
   auto-increment-offset = 1
   

   ServerB:

   auto-increment-increment = 2
   auto-increment-offset = 2

Configuring MySQL for Remote Capture

Oracle GoldenGate remote capture for MySQL, Amazon RDS for MySQL, Amazon Aurora MySQL, Azure Database for MySQL are used to capture transaction log data from a database located remotely to the Oracle GoldenGate installation.

Database Server Configuration

For remote capture to work, configure the MySQL server as follows:

1. Grant access permissions to the Oracle GoldenGate remote capture user.

   Run the following statements against the remote database to create the user and grant the permissions needed for remote capture.

   mysql > CREATE USER 'username'@'host' IDENTIFIED BY 'Password'; 
   mysql > GRANT ALL PRIVILEGES ON *.* TO 'username'@'host’ WITH GRANT OPTION; 
   mysql > FLUSH PRIVILEGES;

2. The server_id value of the remote MySQL server should be greater than 0. This value can be verified by issuing the following statement on the MySQL remote server:

   mysql > show variables like ‘server_id’;
   

   If the server_id value is 0, modify the my.cnf configuration file to set to a value greater than 0.

Oracle GoldenGate Configuration

Oracle GoldenGate configuration has the following steps:

1. Provide the remote database's connection information in the Extract's parameter file.

   SOURCEDB [e-mail]:port, USERID username, PASSWORD
   password

2. Add the following parameter to the Extract's parameter file, after the connection information.

   TRANLOGOPTIONS ALTLOGDEST REMOTE

Limitations of Oracle GoldenGate Remote Capture for MySQL

Co-existence of Oracle GoldenGate for MySQL remote capture with the MySQL’s native replication slave is supported with following conditions and limitations:

• The native replication slave should be assigned a different server_id than the currently running slaves. The slave server_id values can be seen using the following MySQL command on the master server.

  mysql> show slave hosts;

  • If the Oracle GoldenGate capture abends with error "A slave with the same server_uuid or server_id as this slave has connected to the master", then change the capture's name and restart the capture.

  • If the native replication slave dies with the error "A slave with the same server_uuid or server_id as this slave has connected to the master", then change the native replication slave’s server_id and restart it.

• Remote capture is supported only on the Linux 64-bit platform and not on Windows. But Oracle GoldenGate remote capture on Linux can capture from a MySQL database running on remote Windows machine.

Configuring a Two-way SSL Connection in MySQL Capture and Delivery

To use the two way SSL in Oracle GoldenGate MySQL capture and delivery, you need to supply the full paths of the certificate authority (ca.pem), the client certificate (client-cert.pem) and the client key (client-key.pem ) files to the capture and delivery.

To know more about generating the certificate files, see:

https://dev.mysql.com/doc/refman/5.7/en/creating-ssl-rsa-files-using-mysql.html

You need to provide these paths in the Extract and Replicat parameter files using the SETENV parameter.

Following are the SETENV environment parameters to set the two-way SSL connection:

• OGG_MYSQL_OPT_SSL_CA: Sets the full path of the certification authority.

• OGG_MYSQL_OPT_SSL_CERT: Sets the full path of the client certificate.

• OGG_MYSQL_OPT_SSL_KEY: Sets the full path of the client key.

In the following example, the MySQL SSL certificate authority, client certificate, and client key paths are set to the Oracle GoldenGate MySQL Extract and Replicat parameter:

SETENV (OGG_MYSQL_OPT_SSL_CA='/var/lib/mysql.pem') 
SETENV (OGG_MYSQL_OPT_SSL_CERT='/var/lib/mysql/client-cert.pem') 
SETENV (OGG_MYSQL_OPT_SSL_KEY='/var/lib/mysql/client-key.pem')

Capturing using a MySQL Replication Slave

You can configure a MySQL replication slave to capture the master's binary log events from the slave.

Typically, the transactions applied by the slave are logged into the relay logs and not into the slave's binlog. For the slave to write transactions in its binlog, that it receives from the master , you must start the replication slave with the log-slave-updates option as 1 in my.cnf in conjunction with the other binary logging parameters for Oracle GoldenGate. After the master's transactions are in the slave's binlog , you can set up a regular Oracle GoldenGate capture on the slave to capture and process the slave's binlog.

Other Oracle GoldenGate Parameters for MySQL

The following parameters may be of use in MySQL installations, and might be required if non-default settings are used for the MySQL database. Other Oracle GoldenGate parameters will be required in addition to these, depending on your intended business use and configuration.

Parameter	Description
DBOPTIONS with CONNECTIONPORT port_number	Required to specify to the VAM the TCP/IP connection port number of the MySQL instance to which an Oracle GoldenGate process must connect if MySQL is not running on the default of 3306. DBOPTIONS CONNECTIONPORT 3307
DBOPTIONS with HOST host_id	Specifies the DNS name or IP address of the system hosting MySQL to which Replicat must connect.
DBOPTIONS with ALLOWLOBDATATRUNCATE	Prevents Replicat from abending when replicated LOB data is too large for a target MySQL CHAR, VARCHAR, BINARY or VARBINARY column.
SOURCEDB with USERID and PASSWORD	Specifies database connection information consisting of the database, user name and password to use by an Oracle GoldenGate process that connects to a MySQL database. If MySQL is not running on the default port of 3306, you must specify a complete connection string that includes the port number: SOURCEDB dbname@hostname:port, USERID user, PASSWORD password.Example: SOURCEDB mydb@mymachine:3307, USERID myuser, PASSWORD mypassword If you are not running the MySQL database on port 3306, you must also specify the connection port of the MySQL database in the DBLOGIN command when issuing commands that affect the database through GGSCI: DBLOGIN SOURCEDB dbname@hostname:port, USERID user, PASSWORD password For example: GGSCI> DBLOGIN SOURCEDB mydb@mymachine:3307, USERID myuser, PASSWORD mypassword
SQLEXEC	To enable Replicat to bypass the MySQL connection timeout, configure the following command in a SQLEXEC statement in the Replicat parameter file. SQLEXEC "select CURRENT_TIME();" EVERY n MINUTES Where: n is the maximum interval after which you want Replicat to reconnect. The recommended connection timeout 31536000 seconds (365 days).
Global variable sql_mode	For heartbeattable to work in MySQL 5.7 , MySQL global variable sql_mode should not have NO_ZERO_IN_DATE, NO_ZERO_DATE. In the following example sql_mode includes NO_ZERO_IN_DATE,NO_ZERO_DATE values: mysql> show variables like '%sql_mode%';+---------------+- + | Variable_name | Value | +---------------+------------------------------------------------ + | sql_mode | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_ DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION | +---------------+------------------------------------------------ ----------------------------------------------------------------- + 1 row in set (0.00 sec) These values must be removed by issuing the following command: mysql> Set global sql_mode='ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO _AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION'; Query OK, 0 rows affected, 1 warning (0.00 sec) mysql> show variables like '%sql_mode%'; +---------------+-------------------------------------- -------------------------------------------------+ | Variable_name | Value | +---------------+-------------------------------------- -------------------------------------------------+ | sql_mode | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREA TE_USER,NO_ENGINE_SUBSTITUTION | +---------------+----------------------------------- -------------------------------------------------+ 1 row in set (0.01 sec)

Positioning Extract to a Specific Start Point

You can position the Extract to a specific start point in the transaction logs using the ADD/ALTER EXTRACT commands:

{ADD | ALTER EXTRACT} group, LOGNUM log_num, LOGPOS log_pos

• group is the name of the Oracle GoldenGate Extract group for which the start position is required.

• LOGNUM is the log file number. For example, if the required log file name is test.000034, the LOGNUM value is 34. Extract will search for this log file.

• LOGPOS is an event offset value within the log file that identifies a specific transaction record. Event offset values are stored in the header section of a log record. To position at the beginning of a binlog file, set the LOGPOS as 0.

In MySQL logs, an event offset value can be unique only within a given binary file. The combination of the position value and a log number will uniquely identify a transaction record. Maximum Log number length is 8 bytes unsigned integer and Maximum Log offset length is 8 bytes unsigned integer. Log number and Log offset are separated by a pipe (‘|’) delimiter. Transactional records available after this position within the specified log will be captured by Extract. In addition, you can position an Extract using a timestamp.