Allocating RAM for CDC Replication

When configuring instances of CDC Replication, the default values are used for memory allocation. However, the requirement may fluctuate depending on your replication configuration and the workload of your database. In some cases, it is necessary to allocate more than the minimum RAM in order to improve performance.

Although CDC Replication memory requirements will fluctuate, you must work with your system administrator to ensure the allocated memory for each instance of the product is available at all times. This may involve deployment planning since other applications with memory requirements may be installed on the same server with CDC Replication. Using values other than the defaults or allocating more RAM than is physically available on your server should only be undertaken after considering the impacts on product performance.

CDC Replication source deployments may require additional RAM in the following scenarios:
  • You are replicating large LOB data types with your CDC Replication source deployment. These data types are sent to target while being retrieved from the source database. The target waits until all LOBs (for each record) are received before applying a row. LOBs are stored in memory as long as there is adequate RAM, otherwise they are written to disk on the target.
  • You are replicating "wide" tables with hundreds of columns.
  • You are performing large batch transactions in your source database rather than online transaction processing (OLTP).
With insufficient physically available RAM, you may encounter some of the following performance related issues:
  • A possible performance degradation as the operating system on your server increasingly relies on virtual memory and disk I/O.
  • Additional CPU resources may be consumed as the product spends more time cleaning up memory.
  • Restricted throughput. Replication may be slow or pause due to an increased reliance on virtual memory and disk I/O.
  • Replication may be slow as the product processes smaller units of work to preserve memory.
  • Disk-staging of transactions by the CDC Replication source deployment.
  • Out-of-memory exceptions, time outs, monitoring issues, and configuration issues with command line tools or Management Console.