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Difficulty: MediumDatabase Migration and Schema Conversion using DMS and SCT

An enterprise organization is migrating a legacy on-premises IBM Db2 LUW database to Amazon RDS for PostgreSQL. A solutions architect has used the AWS Schema Conversion Tool (SCT) to convert the database schema and apply it to the target RDS instance. The architect then creates an AWS Database Migration Service (DMS) replication task with replication type set to 'Full load and ongoing replication'. The full load phase completes successfully, but subsequent source database updates are not reflected in the target database. Which action must the architect perform on the source database to ensure that ongoing changes are successfully captured and replicated?

  1. A
    Install the AWS SCT extractor agent on the source database server and enable direct transaction log forwarding to the DMS replication instance.
  2. Alter the tables on the source Db2 database to enable the DATA CAPTURE CHANGES attribute and ensure write-ahead log archiving is enabled.Answer
  3. C
    Configure the target Amazon RDS for PostgreSQL database to enable logical replication parameters and set rds.logical_replication to 1.
  4. D
    Modify the DMS task settings to increase the transaction log cache size and restart the task with validation enabled.

Answer

Alter the tables on the source Db2 database to enable the DATA CAPTURE CHANGES attribute and ensure write-ahead log archiving is enabled.
For an IBM Db2 LUW database to act as an AWS DMS source for ongoing replication, the tables being replicated must be modified with the DATA CAPTURE CHANGES attribute. This attribute instructs the engine to write additional change details to the transaction logs. Furthermore, log archiving must be turned on to ensure logs are not immediately deleted, allowing AWS DMS sufficient time to read them.

Step-by-Step Solution

1
Diagnose the replication task status showing that the initial full load was successful but ongoing changes are not updating.
Identify that the issue is related to Change Data Capture (CDC) mechanisms failing to read transactional updates from the source engine.
Before performing troubleshooting on the replication instance, verification of source database logging parameters must be completed.
2
Enable the DATA CAPTURE CHANGES attribute on the tables of the source IBM Db2 LUW database.
This writes the complete details of update, insert, and delete operations into the database logs.
AWS DMS requires full log details to accurately replicate changes to a heterogeneous target database engine.
3
Ensure that the source Db2 database is configured for transaction log retention and log archiving.
The log files remain available on the disk for AWS DMS to read and process asynchronously.
If transaction logs are discarded immediately upon transaction commit, AWS DMS cannot read past transactions to catch up.

Key Concept

AWS DMS Change Data Capture (CDC) requires specific engine-dependent logging configurations on the source database (such as supplemental logging, binary logging, or data capture changes) to enable transactional change extraction.
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Database Migration and Schema Conversion using DMS and SCT

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