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I am planning a migration from an on-premises Oracle 18c (1.5TB of data, 400TPS) to AWS-hosted databases using AWS Database Migration Service.

According to the official DMS documentation, DMS Binary Reader seems to be the only choice because our database is a PDB instance, and it can handle the REDO logs or the archived logs as the source for Change Data Capture.

I am assuming the archived logs would be a better choice in terms of CDC performance because they are smaller in size than the online REDO logs, but not really sure of other benefits of choosing the archived logs as the CDC source over the REDO logs. Does anyone know?

tsz662
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1 Answers1

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Oracle mining will mine the online redo logs until it gets behind then it will mine the archive logs. You have two options for CDC either Oracle LogMiner or Oracle Binary Reader. In general, use Oracle LogMiner for migrating your Oracle database unless you have one of the following situations:

  • You need to run several migration tasks on the source Oracle database.

  • The volume of changes or the redo log volume on the source Oracle database is high. When using Oracle LogMiner as a source database, the 32 KB buffer limit within LogMiner impacts the performance of change data capture on databases with a high volume of change. For example, the 10GB per hour change rate of a LogMiner source database can exceed DMS change data capture capabilities.

  • Your workload includes UPDATE statements that update only LOB columns. In this case, use Binary Reader. These UPDATE statements aren't supported by Oracle LogMiner.

  • Your source is Oracle version 11 and you perform UPDATE statements on XMLTYPE and LOB columns. In this case, you must use Binary Reader. These statements aren't supported by Oracle LogMiner.

  • You are migrating LOB columns from Oracle 12c. For Oracle 12c, LogMiner doesn't support LOB columns, so in this case use Binary Reader.

Maximouse
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JonC
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  • Deeply sorry for the late reply and thank you for your suggestions. We've chosen BinaryReader due to 1st and 2nd being exactly our case. – tsz662 Mar 17 '21 at 00:20