This topic describes the data types and parameters that Oracle Reader supports and how to configure it by using the codeless user interface (UI) and code editor.

Oracle Reader allows you to read data from Oracle. Oracle Reader connects to a remote Oracle database and runs a SELECT statement to select and read data from the database.
Note
  • Relational Database Service (RDS) and Distributed Relational Database Service (DRDS) do not support the Oracle storage engine.
  • Oracle Reader uses the ojdbc7-12.1.0.2.jar driver. For more information about the supported versions of Oracle JDBC drivers, visit Oracle JDBC FAQ.
Specifically, Oracle Reader connects to a remote Oracle database by using Java Database Connectivity (JDBC), generates a SELECT statement based on your configurations, and then sends the statement to the database. The Oracle database runs the statement and returns the result. Then, Oracle Reader assembles the returned data to abstract datasets of custom data types that are supported by Data Integration, and passes the datasets to a writer.
  • Oracle Reader generates the SELECT statement based on the table, column, and where parameters that you have configured, and sends the generated SELECT statement to the Oracle database.
  • If you specify the querySql parameter, Oracle Reader directly sends the value of this parameter to the Oracle database.

Data types

Oracle Reader supports most Oracle data types. Make sure that your data types are supported.

The following table describes the data types that Oracle Reader supports.
Category Oracle data type
Integer NUMBER, ROWID, INTEGER, INT, and SMALLINT
Floating point NUMERIC, DECIMAL, FLOAT, DOUBLE PRECISION, and REAL
String LONG, CHAR, NCHAR, VARCHAR, VARCHAR2, NVARCHAR2, CLOB, NCLOB, CHARACTER, CHARACTER VARYING, CHAR VARYING, NATIONAL CHARACTER, NATIONAL CHAR, NATIONAL CHARACTER VARYING, NATIONAL CHAR VARYING, and NCHAR VARYING
Date and time TIMESTAMP and DATE
Boolean BIT and BOOLEAN
Binary BLOB, BFILE, RAW, and LONG RAW

Parameters

Parameter Description Required Default value
datasource The connection name. It must be the same as the name of the created connection. You can create connections in the code editor. Yes N/A
table The name of the source table. Yes N/A
column The columns to be synchronized from the source table. The columns are described in a JSON array. The default value is [ * ], which indicates all columns.
  • Column pruning is supported. You can select specific columns to export.
  • The column order can be changed. You can configure Oracle Reader to export the specified columns in an order different from that specified in the schema of the table.
  • Constants are supported. The column names must be arranged in JSON format.
    ["id", "1", "'mingya.wmy'", "null", "to_char(a + 1)", "2.3" , "true"]
    • id: a column name.
    • 1: an integer constant.
    • 'mingya.wmy': a string constant, which is enclosed in single quotation marks (' ').
    • null: a null pointer.
    • to_char(a + 1): a function expression.
    • 2.3: a floating-point constant.
    • true: a Boolean value.
  • The column parameter must be specified.
Yes N/A
splitPk The field that is used for data sharding when Oracle Reader reads data. If you specify the splitPk parameter, the table is sharded based on the shard key that is specified by this parameter. Data Integration then runs concurrent threads to synchronize data. This way, data can be synchronized more efficiently.
  • We recommend that you set the splitPk parameter to the primary key of the table. Based on the primary key, data can be well distributed to different shards, but not intensively distributed to specific shards.
  • The splitPk parameter supports data sharding for data types such as integer, string, floating point, and date.
  • If you do not specify the splitPk parameter or leave it empty, Oracle Reader synchronizes data by using a single thread.
No N/A
where The WHERE clause. Oracle Reader generates a SELECT statement based on the table, column, and where parameters that you have configured, and uses the generated SELECT statement to select and read data. For example, set this parameter to row_number().
  • You can use the WHERE clause to synchronize incremental data.
  • If you do not specify the where parameter or leave it empty, all data is read.
No N/A
querySql (available only in the code editor) The SELECT statement that is used for refined data filtering. If you specify this parameter, Data Integration filters data based on this parameter. For example, if you want to join multiple tables for data synchronization, set this parameter to select a,b from table_a join table_b on table_a.id = table_b.id. If you specify the querySql parameter, Oracle Reader ignores the table, column, and where parameters that you have configured. No N/A
fetchSize The number of data records to read at a time. This parameter determines the number of interactions between Data Integration and the database and affects reading efficiency.
Note A value greater than 2048 may lead to out of memory (OOM) during the data synchronization process.
No 1,024

Configure Oracle Reader by using the codeless UI

  1. Configure the connections.
    Configure the connections to the source and destination data stores for the sync node.Connections section
    Parameter Description
    Connection The datasource parameter in the preceding parameter description. Select a connection type and select the name of a connection that you have configured in DataWorks.
    Table The table parameter in the preceding parameter description.
    Filter The condition for filtering the data to be synchronized. Oracle Reader cannot filter data based on the limit keyword. The SQL syntax is determined by the selected connection.
    Shard Key The shard key. You can specify a column in the source table as the shard key. We recommend that you use the primary key or an indexed column as the shard key. Only integer fields are supported.
    If data sharding is performed based on the configured shard key, data can be read concurrently. This way, data can be synchronized more efficiently.
    Note The Shard Key parameter is displayed only after you select the connection to the source data store for the sync node.
  2. Configure field mapping. It is equivalent to setting the column parameter in the preceding parameter description.
    Fields in the source table on the left have a one-to-one mapping with fields in the destination table on the right. You can click Add to add a field. To delete a field, move the pointer over the field and click theDelete icon.Mappings section
    GUI element Description
    Map Fields with the Same Name Click Map Fields with the Same Name to establish a mapping between fields with the same name. The data types of the fields must match.
    Map Fields in the Same Line Click Map Fields in the Same Line to establish a mapping between fields in the same row. The data types of the fields must match.
    Delete All Mappings Click Delete All Mappings to remove mappings that have been established.
    Auto Layout Click Auto Layout to sort the fields based on specified rules.
    Change Fields Click the Change Fields icon. In the Change Fields dialog box, you can manually edit the fields in the source table. Each field occupies a row. The first and the last blank rows are included, whereas other blank rows are ignored.
    Add
    • Click Add to add a field. Take note of the following rules when you add a field: You can enter constants. Each constant must be enclosed in single quotation marks (' '), for example, 'abc' and '123'.
    • You can use scheduling parameters such as ${bizdate}.
    • You can enter functions that are supported by relational databases, for example, now() and count(1).
    • Fields that cannot be parsed are indicated by Unidentified.
  3. Configure channel control policies.Channel section
    Parameter Description
    Expected Maximum Concurrency The maximum number of concurrent threads that the sync node uses to read data from or write data to data stores. You can configure the concurrency for the node on the codeless UI.
    Bandwidth Throttling Specifies whether to enable bandwidth throttling. You can enable bandwidth throttling and set a maximum transmission rate to avoid heavy read workload of the source. We recommend that you enable bandwidth throttling and set the maximum transmission rate to a proper value.
    Dirty Data Records Allowed The maximum number of dirty data records allowed.

Configure Oracle Reader by using the code editor

The following example shows how to configure a sync node to read data from an Oracle database.
{
    "type":"job",
    "version":"2.0",// The version number.
    "steps":[
        {
            "stepType":"oracle",
            "parameter":{
                "fetchSize":1024, // The number of data records to read at a time.
                "datasource":"", // The connection name.
                "column":[// The columns to be synchronized from the source table.
                    "id",
                    "name"
                ],
                "where":"",// The WHERE clause.
                "splitPk":"",// The shard key.
                "table":"" // The name of the source table.
            },
            "name":"Reader",
            "category":"reader"
        },
        {
            "stepType":"stream",
            "parameter":{},
            "name":"Writer",
            "category":"writer"
        }
    ],
    "setting":{
        "errorLimit":{
            "record":"0"// The maximum number of dirty data records allowed.
        },
        "speed":{
            "throttle":false,// Specifies whether to enable bandwidth throttling. A value of false indicates that the bandwidth is not throttled. A value of true indicates that the bandwidth is throttled. The maximum transmission rate takes effect only if you set this parameter to true.
            "concurrent":1,// The maximum number of concurrent threads.
        }
    },
    "order":{
        "hops":[
            {
                "from":"Reader",
                "to":"Writer"
            }
        ]
    }
} "to":"Writer"
            }
        ]
    }
}

Usage notes

  • Data synchronization between primary and secondary databases

    A secondary Oracle database can be deployed for disaster recovery. The secondary database continuously synchronizes data from the primary database based on binlogs. Especially when network conditions are unfavorable, data latency between the primary and secondary databases is unavoidable, which can lead to data inconsistency.

  • Concurrency control

    Oracle is a relational database management system (RDBMS), which supports strong consistency for data queries. A database snapshot is created before a sync node starts. Oracle Reader reads data from the database snapshot. Therefore, if new data is written to the database during data synchronization, Oracle Reader cannot obtain the new data.

    Data consistency cannot be ensured when you enable Oracle Reader to run concurrent threads on a single sync node.

    Oracle Reader shards the table based on the splitPk parameter and runs multiple concurrent threads to synchronize data. These concurrent threads belong to different transactions. They read data at different time points. This means that the concurrent threads observe different snapshots.

    Theoretically, the data inconsistency issue is unavoidable if a single sync node includes multiple threads. However, two workarounds can be used:
    • Do not enable concurrent threads in a single sync node. Essentially, do not specify the splitPk parameter. This way, data consistency is ensured although data is synchronized at a low efficiency.
    • Disable writers to ensure that the data is unchanged during data synchronization. For example, lock the table and disable data synchronization between primary and secondary databases. This way, data is efficiently synchronized but your ongoing services may be interrupted.
  • Character encoding

    Oracle Reader uses JDBC, which can automatically convert the encoding of characters. Therefore, you do not need to specify the encoding format.

  • Incremental data synchronization
    Oracle Reader connects to a database by using JDBC and uses a SELECT statement with a WHERE clause to read incremental data.
    • For data in batches, incremental add, update, and delete operations are distinguished by timestamps. The delete operations include logical delete operations. Specify the WHERE clause based on the timestamp. The timestamp must be later than the latest timestamp in the last synchronization.
    • For streaming data, specify the WHERE clause based on the data record ID. The data record ID must be larger than the maximum ID that is involved in the last synchronization.

    If incremental data cannot be distinguished, Oracle Reader cannot perform incremental synchronization but can perform full synchronization only.

  • Syntax validation

    Oracle Reader allows you to specify custom SELECT statements by using the querySql parameter but does not verify the syntax of the custom SELECT statements.