Topics:
Parent topic: Using Oracle GoldenGate with MySQL
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 Reference for Oracle GoldenGate
To capture from the MySQL transaction logs, the Oracle GoldenGate Extract process must be able to find the index file. index file in turn contains the paths of all binary log files.
Note:
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.
Extract checks the following parameter settings to get this index file path:
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 database_name@host_name
Where: database_name is the name of the MySQL instance, and host_name is the name or IP address of the local host. 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.
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.
This section describes how to prepare the tables for processing. Table preparation requires these tasks:
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.
Parent topic: Preparing Tables for Processing
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:
Parent topic: Assigning Row Identifiers
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.
Parent topic: Assigning Row Identifiers
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.
Parent topic: Assigning Row Identifiers
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.
Parent topic: Preparing Tables for Processing
Disable triggers, cascade delete constraints, and cascade update constraints 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 or cascade constraint. If the same trigger or constraint gets activated on the target table, it becomes redundant because of the replicated version, and the database returns an error. Consider the following example, where the source tables are emp_src and salary_src and the target tables are emp_targ and salary_targ.
A delete is issued for emp_src.
It cascades a delete to salary_src.
Oracle GoldenGate sends both deletes to the target.
The parent delete arrives first and is applied to emp_targ.
The parent delete cascades a delete to salary_targ.
The cascaded delete from salary_src is applied to salary_targ.
The row cannot be located because it was already deleted in step 5.
Parent topic: Preparing Tables for Processing
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:
log-bin path for the new location.flush master or reset master (based on your MySQL version).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.
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.
Oracle GoldenGate uses SSH tunneling to connect to the AWS Aurora instance using the .pem file and then runs the Oracle GoldenGate MySQL delivery from on-premise.
To set up SSH tunneling for a secure database connection to AWS Aurora MySQL, perform the following tasks:
Task1: Configuring SSH Tunneling
ssh -i your_key.pem -v -f -L local port number:cluster end point:end point port number ec2 host name > mysql_remote_forward.log 2>&1
In the following example, note that the local port number is set to 3308 because the port number 3306 may be used by MySQL that's installed locally.
bash-4.1$ ssh -i "test.pem" -v -N -f -L 3308:test-cluster.cluster-copyxiqzdjjl.us-west-2.rds.amazonaws.com:3306 ec2-user@ec2-52-11-244-17.us-west-2.compute.amazonaws.com > mysql_remote_forward.log 2>&1
ssh -i your_key.pem -v -f -L local port number:cluster end point:end point port number ec2 host name -o command to bypass proxy in double quotes> > mysql_remote_forward.log 2>&1
bash-4.1$ ssh -i "test.pem" -v -N -f -L 3308:test-cluster.cluster-copyxiqzdjjl.us-west-2.rds.amazonaws.com:3306 ec2-user@ec2-52-11-244-17.us-west-2.compute.amazonaws.com -o "ProxyCommand=nc -X connect -x www-proxy.us.oracle.com:80 %h %p" > mysql_remote_forward.log 2>&1
Task 2: Provide the Connection String in the Extract Parameter File
remotedb@127.0.0.1:3308 userid remote-user, password remote-user-password
bash-4.1$ cat ~/.ssh/config ServerAliveInterval 50
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.
Table 13-1 Other Parameters for Oracle GoldenGate for MySQL
| Parameter | Description |
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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 |
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Specifies the DNS name or IP address of the system hosting MySQL to which Replicat must connect. |
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Prevents Replicat from abending when replicated LOB data is too large for a target MySQL |
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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:
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 SOURCEDB dbname@hostname:port, USERID user, PASSWORD password For example: GGSCI> DBLOGIN SOURCEDB mydb@mymachine:3307, USERID myuser, PASSWORD mypassword |
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To enable Replicat to bypass the MySQL connection timeout, configure the following command in a
Where: |
You can position the ADD EXTRACT and ALTER EXTRACT commands to a specific start point in the transaction logs with the following command.
{ADD | ALTER EXTRACT} group, VAM, LOGNUM log_num, LOGPOS log_pos
group is the name of the Oracle GoldenGate Extract group for which the start position is required.
log_num is the log file number. For example, if the required log file name is test.000034, this value is 34. Extract will search for this log file.
log_pos 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 log_pos as 4. The log_pos 0 or 1 are not valid offsets to start reading and processing.
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 and cannot exceed a length of 37. 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.