- Large objects
The data types that are present in your migration scope can affect performance. Particularly, large objects (LOBs) impact performance and memory consumption. To migrate a LOB value, AWS mainframe modernization service's data replication feature with Precisely requires Primary Key in the table for performing Updates and Deletes. Replicating tables with this datatype has an impact on the memory, so it is important to identify LOB columns in the source and analyze their size.
- Load frequency and transaction size
Load frequency and transactions per second (TPS) influence memory usage. A high number of TPS or data manipulation language (DML) activities leads to high usage of memory. This happens because AWS mainframe modernization service's data replication feature with Precisely caches the changes until they are applied to the target. During CDC, this leads to swapping (writing to the physical disk due to memory overflow), which causes latency.
- Table keys and referential integrity
Information about the keys of the table determines the CDC apply speed that would be done during replication. For long-running transactions, there can be many changes to migrate. In case of transactional apply, replication process might require more memory to store the changes. If you replicate tables without primary keys, Updates and Deletes will fail to apply to and replication job would come to halt. When referential integrity is active between tables during CDC, replication apply process uses transactional apply by default.
Use these metrics to determine if you need the replication instance to be compute optimized or memory optimized.