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  • PowerExchange for CDC and Mainframe 10.5.5
  • All Products

Table of Contents

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  1. Preface
  2. Part 1: PowerExchange CDC Introduction
  3. Part 2: PowerExchange CDC Components
  4. Part 3: PowerExchange CDC Data Sources
  5. Part 4: Change Data Extraction
  6. Part 5: Monitoring and Tuning
  7. Appendix A: DTL__CAPXTIMESTAMP Time Stamps

CDC Guide for Linux, UNIX, and Windows

CDC Guide for Linux, UNIX, and Windows

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Handling Oracle LOB Data

Handling Oracle LOB Data

For Oracle source tables, PowerExchange can process change data from BLOB, CLOB, and NCLOB columns. The maximum row size, which includes data from all columns, that PowerExchange can process is 8 MB. Oracle will write complete LOB data to the redo log when a DML change, such as an Insert or Update, is written to the LOB. PowerExchange Express CDC cannot directly capture Oracle operations that update LOB column data, such as DBMS_LOB subprograms, because Oracle does not log the complete before image of the data to the redo log.
When the ENABLE STORAGE IN ROW attribute enabled in Oracle, LOB data can be stored either fully inline in the row or out-of-line in the LOB file space. PowerExchange can capture only the in-row LOB data or both the in-row and out-of-line LOB data. To capture out-of-line LOB data, set the SUPPORT_LOB_OUT_OF_ROW parameter to Y.
If OPTIONS SUPPORT_LOB_OUT_OF_ROW=N is specified for tables with column BLOB or CLOB datatypes that are defined with the Oracle attribute ENABLE STORAGE IN ROW, PowerExchange can deliver up to 3964 bytes of data to PowerCenter workflows that use a PowerExchange Oracle connection.
Oracle has a maximum column size of 4000 bytes. For LOBs stored in-row, the column contains a 20 byte LOB locator, a 16 byte LOB node and data for a maximum of 3694 bytes. For CLOB data, this data is stored as a double-byte character set, which reduces the maximum size to 1847 characters, even if the column character set is single byte.
If OPTIONS SUPPORT_LOB_OUT_OF_ROW=Y is specified, PowerExchange can deliver up to the LOB_MAX_SIZE value for each LOB column if the total row size is less than 8 MB. Informatica recommends setting LOB_MAX_SIZE to a reasonable value, such as the default value of 8k, to prevent larger LOB files from degrading PowerExchange capture performance.
You can use the PowerExchange-generated DTL__ST
_columnname
 control column with a PowerCenter Expression transformation and unconnected Lookup transformation to retrieve all of the LOB data from BLOB and CLOB columns. The session can then send the data to a target.
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