12 Using the Metadata Provider

The Avro Metadata Provider uses Avro schema definition files to retrieve metadata. The Avro schemas are defined using the JSON. For each table mapped in process_name.prm file, a corresponding The Avro schema definition file should be created. More information on defining Avro schemas is found at:

http://avro.apache.org/docs/current/gettingstartedjava.html#Defining+a+schema

Avro Metadata Provider Schema definition syntax:

{"namespace": "[$catalogname.]$schemaname",
"type": "record",
"name": "$tablename",
"fields": [
     {"name": "$col1", "type": "$datatype"},
     {"name": "$col2 ",  "type": "$datatype ", "primary_key":true}, 
     {"name": "$col3", "type": "$datatype ", "primary_key":true}, 
     {"name": "$col4", "type": ["$datatype","null"]}   
   ]
}
 
namespace            - name of catalog/schema being mapped
name                 - name of the table being mapped
fields.name          - array of column names
fields.type          - datatype of the column
fields.primary_key   - indicates the column is part of primary key.

Representing nullable and not nullable columns:

"type":"$datatype" - indicates the column is not nullable, where "$datatype" is the actual datatype.
"type": ["$datatype","null"] - indicates the column is nullable, where "$datatype" is the actual datatype

The file naming convention for Avro schema files accessed by the Avro Metadata Provider must be in the following format:

[$catalogname.]$schemaname.$tablename.mdp.avsc
 
$catalogname    - name of the catalog if exists
$schemaname   - name of the schema
$tablename        - name of the table
.mdp.avsc           -  constant, which should be appended always

Supported Avro Data Types:

• boolean

• bytes

• double

• float

• int

• long

• string

For more information on Avro data types, see https://avro.apache.org/docs/1.7.5/spec.html#schema_primitive.

The Avro schema definitions should be created for all tables mapped in Replicat's parameter file before starting the Replicat process.

There is no additional classpath setting required for Avro Metadata Provider.

The configuration properties of Oracle GoldenGate Avro Metadata Provider are detailed in this section.

This section provides an example for configuring the Avro Metadata Provider. Consider a source with following table:

TABLE GG.TCUSTMER {
     CUST_CODE VARCHAR(4) PRIMARY KEY,
     NAME VARCHAR(100),
     CITY VARCHAR(200),
     STATE VARCHAR(200)
}

Mapping columnCUST_CODE (GG.TCUSTMER) in source to CUST_CODE2 (GG_AVRO.TCUSTMER_AVRO) on target and column CITY (GG.TCUSTMER) in source to CITY2 (GG_AVRO.TCUSTMER_AVRO) on target. Thus, the mapping in process_name.prm file is:

MAP GG.TCUSTMER, TARGET GG_AVRO.TCUSTMER_AVRO, COLMAP(USEDEFAULTS, CUST_CODE2=CUST_CODE, CITY2=CITY);
 

Mapping definition in this example:

• Source schema GG is mapped to target schema GG_AVRO.

• Source column CUST_CODE is mapped to target column CUST_CODE2.

• Source column CITY is mapped to target column CITY2.

• USEDEFAULTS specifies that rest of the columns names are same on both source and target (NAME and STATE columns).

The Avro schema definition file for the preceding example:

File path: /home/ggadp/avromdpGG_AVRO.TCUSTMER_AVRO.mdp.avsc

{"namespace": "GG_AVRO",
"type": "record",
"name": "TCUSTMER_AVRO",
"fields": [
     {"name": "NAME", "type": "string"},
    {"name": "CUST_CODE2",  "type": "string", "primary_key":true},
     {"name": "CITY2", "type": "string"},
     {"name": "STATE", "type": ["string","null"]}
]
}

The configuration in the Java Adapter properties file includes the following:

gg.mdp.type = avro
gg.mdp.schemaFilesPath = /home/ggadp/avromdp

Following is the sample output using delimited text formatter with a semi-colon as the delimiter for the preceding example.

I;GG_AVRO.TCUSTMER_AVRO;2013-06-02 22:14:36.000000;NAME;BG SOFTWARE CO;CUST_CODE2;WILL;CITY2;SEATTLE;STATE;WA

The Oracle GoldenGate for Big Data installation include a sample Replicat configuration file, a sample Java Adapter properties file, and sample Avro schemas at:

GoldenGate_install_directory/AdapterExamples/big-data/metadata_provider/avro

The Avro schema definitions and the mappings in the Replicat configuration file may need to be modified if there is a DDL change in the source database tables. You may want to stop or suspend the Replicat process in the case of a metadata change event. The Replicat process can be stopped by adding the following to the Replicat configuration file (process_name.prm):

DDL INCLUDE ALL, EVENTACTIONS (ABORT)

Alternatively, the Replicat process can be suspended by adding the following to the Replication configuration file.

DDL INCLUDE ALL, EVENTACTIONS (SUSPEND)

Avro bytes data type cannot be used as primary key.

The source to target mapping defined in the Replicat configuration file is static. Oracle GoldenGate 12.2 and later supports DDL propagation and source schema evolution for Oracle Databases as the replication source. However, evolution of the source schemas may be problematic the static mapping configured in the Replicat configuration file.

The JDBC Metadata Provider uses the JDBC Driver provided with your target database. The metadata is retrieved using the JDBC Driver for every target table mapped in the Replicat properties file. Replicat processes use the retrieved target metadata for the column mapping functionality.

You can enable this feature for JDBC Handler by configuring the REPERROR in your Replicat parameter file. In addition, you need to define the error codes specific to your RDBMS JDBC target in the JDBC Handler properties file as follows:

gg.error.duplicateErrorCodes

gg.error.notFoundErrorCodes

gg.error.deadlockErrorCodes 

For example:

#ErrorCode
gg.error.duplicateErrorCodes=1062,1088,1092,1291,1330,1331,1332,1333
gg.error.notFoundErrorCodes=0
gg.error.deadlockErrorCodes=1213

To understand how the various JDBC types are mapped to database-specific SQL types, review the specifics at:

https://docs.oracle.com/javase/6/docs/technotes/guides/jdbc/getstart/mapping.html#table1

The following are the configurable values for the JDBC Metadata Provider. These properties are located in the Java Adapter properties file (not in the Replicat properties file).

This section provides examples for configuring the JDBC Metadata Provider.

MySQL Driver Configuration:

gg.mdp.type=jdbc
gg.mdp.ConnectionUrl=jdbc:oracle:thin:@myhost:1521:orcl
gg.mdp.DriverClassName=oracle.jdbc.driver.OracleDriver
gg.mdp.UserName=username
gg.mdp.Password=password

Netezza Driver Configuration

gg.mdp.type=jdbc
gg.mdp.ConnectionUrl=jdbc:netezza://hostname:port/databaseName
gg.mdp.DriverClassName=org.netezza.Driver
gg.mdp.UserName=username
gg.mdp.Password=password

Oracle OCI Driver configuration:

ggg.mdp.type=jdbc
gg.mdp.ConnectionUrl=jdbc:oracle:oci:@myhost:1521:orcl
gg.mdp.DriverClassName=oracle.jdbc.driver.OracleDriver
gg.mdp.UserName=username
gg.mdp.Password=password

Oracle Teradata Driver configuration:

gg.mdp.type=jdbc
gg.mdp.ConnectionUrl=jdbc:teradata://10.111.11.111/USER=username,PASSWORD=password
gg.mdp.DriverClassName=com.teradata.jdbc.TeraDriver
gg.mdp.UserName=username
gg.mdp.Password=password

Oracle Thin Driver Configuration:

gg.mdp.type=jdbc
gg.mdp.ConnectionUrl=jdbc:mysql://localhost/databaseName?user=username&password=password
gg.mdp.DriverClassName=com.mysql.jdbc.Driver
gg.mdp.UserName=username
gg.mdp.Password=password

Redshift Driver Configuration

gg.mdp.type=jdbc
gg.mdp.ConnectionUrl=jdbc:redshift://hostname:port/databaseName
gg.mdp.DriverClassName=com.amazon.redshift.jdbc42.Driver
gg.mdp.UserName=username
gg.mdp.Password=password

The Hive Metadata Provider uses both Hive JDBC and HCatalog interfaces to retrieve metadata from the Hive metastore. For each table mapped in the process_name.prm file, a corresponding table should be created in Hive.

The default Hive configuration starts an embedded and local metastore Derby database. Apache Derby is designed to be an embedded database and only allows a single connection. The single connection limitation of the Derby Database as the Hive Metastore implementation means that it cannot function when working with the Hive Metadata Provider. To overcome this, you must configure Hive with a remote metastore database. More information on configuring Hive with remote metastore database can found at:

https://cwiki.apache.org/confluence/display/Hive/AdminManual+MetastoreAdmin#AdminManualMetastoreAdmin-RemoteMetastoreDatabase

Hive does not support Primary Key semantics, so the metadata retrieved from Hive metastore will not include any primary key definition. Replicat's KEYCOLS parameter should be used to define primary keys when you use the Hive Metadata Provider.

KEYCOLS

The Replicat mapping KEYCOLS parameter must be used to define primary keys in the target schema. The Oracle GoldenGate HBase Handler requires primary keys. Therefore, setting primary keys in the target schema is required when Replicat mapping is employed with HBase as the target.

Additionally, the output of the Avro Formatters includes an Array field to hold the primary column names. If Replicat mapping is employed with the Avro Formatters you should consider using KEYCOLS to identify the primary key columns.

Examples of configuring KEYCOLS is described in Sample Configuration.

Supported Hive Data types:

• BIGINT

• BINARY

• BOOLEAN

• CHAR

• DATE

• DECIMAL

• DOUBLE

• FLOAT

• INT

• SMALLINT

• STRING

• TIMESTAMP

• TINYINT

• VARCHAR

For more information on Hive data types, see https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Types.

A list of supported databases that can be used to configure remote Hive metastore can be found at https://cwiki.apache.org/confluence/display/Hive/AdminManual+MetastoreAdmin#AdminManualMetastoreAdmin-SupportedBackendDatabasesforMetastore.

In the following example, a MySQL database is configured as the Hive metastore using the following properties in the ${HIVE_HOME}/conf/hive-site.xml Hive configuration file:

<property>
         <name>javax.jdo.option.ConnectionURL</name>        
         <value>jdbc:mysql://MYSQL_DB_IP:MYSQL_DB_PORT/DB_NAME?createDatabaseIfNotExist=false</value>
 </property>
 
 <property>
        <name>javax.jdo.option.ConnectionDriverName</name>
        <value>com.mysql.jdbc.Driver</value>
 </property>
 
 <property>
          <name>javax.jdo.option.ConnectionUserName</name>
     <value>MYSQL_CONNECTION_USERNAME</value>
 </property>
 
 <property>
         <name>javax.jdo.option.ConnectionPassword</name>
         <value>MYSQL_CONNECTION_PASSWORD</value>
 </property>

The list of parameters to be configured in the hive-site.xml file for a remote metastore can be found at https://cwiki.apache.org/confluence/display/Hive/AdminManual+MetastoreAdmin#AdminManualMetastoreAdmin-RemoteMetastoreDatabase.

You must configure two things in the gg.classpath configuration variable in order for the Hive Metadata Provider to connect to Hive and run. The first is the hive-site.xml file, which is typically located in the $HIVE_HOME/conf directory. The second are the Hive and HDFS client jars. The client JARs must match the version of Hive that the Hive Metadata Provider is connecting.

1. Create hive-site.xml file with the following properties:

   <configuration>
   <!-- Mandatory Property --> 
   <property>
   <name>hive.metastore.uris</name>
   <value>thrift://HIVE_SERVER_HOST_IP:9083</value>
   <property>
    
   <!-- Optional Property. Default value is 5 -->
   <property>
   <name>hive.metastore.connect.retries</name>
   <value>3</value>
   </property>
    
   <!-- Optional Property. Default value is 1 -->
   <property>
   <name>hive.metastore.client.connect.retry.delay</name>
   <value>10</value>
   </property>
    
   <!-- Optional Property. Default value is 600 seconds -->
   <property>
   <name>hive.metastore.client.socket.timeout</name>
   <value>50</value>
   </property>
   
    </configuration>
   

   Note:

   For example, if the hive-site.xml file is created in the /home/user/oggadp/dirprm directory, then gg.classpath entry is gg.classpath=/home/user/oggadp/dirprm/

2. The default location of the Hive and HDFS client jars are the following directories:

   HIVE_HOME/hcatalog/share/hcatalog/*
   HIVE_HOME/lib/*
   HIVE_HOME/hcatalog/share/webhcat/java-client/*
   HADOOP_HOME/share/hadoop/common/*
   HADOOP_HOME/share/hadoop/common/lib/*
   HADOOP_HOME/share/hadoop/mapreduce/*
   

   Configure the gg.classpath exactly as shown in the preceding step. Creating a path to the hive-site.xml should contain the path with no wildcard appended. The inclusion of the * wildcard in the path to the hive-site.xml file causes it not to be picked up. Conversely, creating a path to the dependency JARs should include the * wildcard character to include all of the JAR files in that directory in the associated classpath. Do not use *.jar.

The configuration properties of the Hive Metadata Provider are detailed in this section.

The following is an example for configuring the Hive Metadata Provider. Consider a source with following table:

TABLE GG.TCUSTMER {
     CUST_CODE VARCHAR(4)   PRIMARY KEY,
     NAME VARCHAR(100),
     CITY VARCHAR(200),
     STATE VARCHAR(200)}

The example maps the column CUST_CODE (GG.TCUSTMER) in the source to CUST_CODE2 (GG_HIVE.TCUSTMER_HIVE) on the target and column CITY (GG.TCUSTMER) in the source to CITY2 (GG_HIVE.TCUSTMER_HIVE)on the target.

Mapping configuration in the process_name.prm file:

MAP GG.TCUSTMER, TARGET GG_HIVE.TCUSTMER_HIVE, COLMAP(USEDEFAULTS, CUST_CODE2=CUST_CODE, CITY2=CITY) KEYCOLS(CUST_CODE2); 

The mapping definition for this example is:

• Source schema GG is mapped to target schema GG_HIVE

• Source column CUST_CODE is mapped to target column CUST_CODE2

• Source column CITY is mapped to target column CITY2

• USEDEFAULTS specifies that rest of the columns names are same on both source and target (NAME and STATE columns).

• KEYCOLS is used to specify that CUST_CODE2 should be treated as primary key.

Since primary keys cannot be specified in Hive DDL, the KEYCOLS parameter is used to specify the primary keys.

Create schema and tables in Hive for the preceding example:

To start the Hive CLI type the following command:

HIVE_HOME/bin/hive

To create a schema, GG_HIVE, in Hive, use the following command:

hive> create schema gg_hive;
OK
Time taken: 0.02 seconds

To create a table TCUSTMER_HIVE in GG_HIVE database type the following command:

hive> CREATE EXTERNAL TABLE `TCUSTMER_HIVE`(
    >   "CUST_CODE2" VARCHAR(4),
    >   "NAME" VARCHAR(30),
    >   "CITY2" VARCHAR(20),
    >   "STATE" STRING);
OK
Time taken: 0.056 seconds

Configuration in the .properties file can be like the following:

gg.mdp.type=hive
gg.mdp.connectionUrl=jdbc:hive2://HIVE_SERVER_IP:10000/gg_hive
gg.mdp.driverClassName=org.apache.hive.jdbc.HiveDriver

Following is the sample output using delimited text formatter with a comma as the delimiter for the preceding example.

I;GG_HIVE.TCUSTMER_HIVE;2015-10-07T04:50:47.519000;cust_code2;WILL;name;BG SOFTWARE CO;city2;SEATTLE;state;WA

A sample Replicat configuration file, Java Adapter properties file, and a Hive create table SQL script are included with the installation, and located at:

GoldenGate_install_directory/AdapterExamples/big-data/metadata_provider/hive

The Hive server can be secured using Kerberos Authentication. Refer to the Hive documentation for your specific Hive release for instructions on how to secure the Hive server. The Hive Metadata Provider can connect to a Kerberos secured Hive server.

The HDFS core-site.xml and hive-site.xml should be in handler's classpath.

Enable the following properties in core-site.xml:

<property>
<name>hadoop.security.authentication</name>
<value>kerberos</value> 
</property>
 
<property> 
<name>hadoop.security.authorization</name> 
<value>true</value> 
</property>

Enable the following properties in hive-site.xml

<property>
<name>hive.metastore.sasl.enabled</name>
<value>true</value>
</property>
 
<property>
<name>hive.metastore.kerberos.keytab.file</name>
<value>/path/to/keytab</value> <!-- Change this value -->
</property>
 
<property>
<name>hive.metastore.kerberos.principal</name>
<value>Kerberos Principal</value> <!-- Change this value -->
</property>
 
<property>
   <name>hive.server2.authentication</name>
    <value>KERBEROS</value>
</property>
 
<property>
   <name>hive.server2.authentication.kerberos.principal</name>
    <value>Kerberos Principal</value> <!-- Change this value -->
</property>
 
<property>
    <name>hive.server2.authentication.kerberos.keytab</name>
    <value>/path/to/keytab</value> <!-- Change this value -->
</property>

Tables in Hive metastore should be updated/altered/created manually if there is a change in source database tables. You may wish to abort or suspend the Replicat process in the case of a metadata change event. The Replicat process can be aborted by adding the following to the Replicat configuration file (process_name.prm):

DDL INCLUDE ALL, EVENTACTIONS (ABORT)

Alternatively, the Replicat process can be suspended by adding the following to the Replication configuration file (process_name.prm):

DDL INCLUDE ALL, EVENTACTIONS (SUSPEND)

Columns with binary data type cannot be used as primary key.

The source to target mapping defined in the Replicat configuration file is static. Oracle GoldenGate 12.2 and later supports DDL propagation and source schema evolution for Oracle Databases as the replication source. However, evolution of the source schemas may be problematic the static mapping configured in the Replicat configuration file.

The most common problems encountered are the Java classpath issues. The Hive Metadata Provider requires certain Hive and HDFS client libraries to be resolved in its classpath as a prerequisite.

The required client JAR directories are listed in Classpath Configuration. Hive and HDFS client jars do not ship with Oracle GoldenGate for Big Data product. The client JARs should be the same version as the Hive version to which Hive Metadata Provider is connecting.

To establish a connection to the Hive server, the hive-site.xml file must be in the classpath.

The Replicat process will abend with a "Table metadata resolution exception" if the mapped target table does not exist in Hive.

For example, consider the following mapping:

MAP GG.TCUSTMER, TARGET GG_HIVE.TCUSTMER_HIVE, COLMAP(USEDEFAULTS, CUST_CODE2=CUST_CODE, CITY2=CITY) KEYCOLS(CUST_CODE2);

The preceding mapping requires a table called TCUSTMER_HIVE to be created in schema GG_HIVE in the Hive metastore. Failure to create the GG_HIVE.TCUSTMER_HIVE table in Hive will result in following exception:

ERROR [main) - Table Metadata Resolution Exception
Unable to retrieve table matadata. Table : GG_HIVE.TCUSTMER_HIVE
NoSuchObjectException(message:GG_HIVE.TCUSTMER_HIVE table not found)