Rules and guidelines for mapping and mapping tasks
Rules and guidelines for mapping and mapping
tasks
When you configure a mapping and mapping tasks, adhere to the following guidelines:
If you use a custom query in the Source
transformation and configure create target at runtime in the Target
transformation, you must specify the
ExtendedColumnMetadata=true
property in the
Additional Connection Properties
field in the
PostgreSQL connection. The property helps retain the constraints from the source
in the target object.
Ensure that the list of selected
columns, the data types, and the order of the columns that appear in the query
matches the columns, data types, and order in which they appear in the source
object.
When you use the query source type in a
mapping to read from multiple tables, and you configure a join for one or more
tables that have the same column names, the mapping fails.
For example, see
the following SQL query that involves a full outer join between two tables
EMPLOYEE and DEPARTMENT that are part of the SALES.PUBLIC schema, where two
columns have the same name, CITY:
SELECT EMP_ID, NAME, CITY,
DEPT_ID, DEPT_NAME, CITY FROM SALES.PUBLIC.EMPLOYEE FULL OUTER JOIN
SALES.PUBLIC.DEPARTMENT ON EMP_ID = DEPT_ID
To
distinguish the conflicting column names, add aliases that the database can
refer to while joining the tables:
SELECT e.EMP_ID, e.NAME,
e.CITY as ecity,d.DEPT_ID, d.DEPT_NAME, d.CITY as dcity FROM
SALES.PUBLIC.EMPLOYEE e FULL OUTER JOIN SALES.PUBLIC.DEPARTMENT d ON
e.EMP_ID = d.DEPT_ID
When you
configure an SQL override for a PostgreSQL source, partitioning is not
applicable.
To configure
the batch size consider using the following formula:
BatchSize =
(<Threshold Memory in Bytes>)/(3* <Approximate Row Size in
Bytes>)
.
In the formula, the threshold memory in bytes
represents the maximum memory consumption that you want the operation to
consume. The approximate row size is the size of a row, which you can
calculate from the target table field definition.
When you configure a mapping that
includes a column with the JSONB data type in the
Update
Columns
property within the Target transformation, and you
process a large volume of data, the mapping runs significantly slower and
requires a considerable amount of time to process the data.
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