Disk quota for capture components

CDC Replication uses specific components to capture changes from the database log. These components accumulate uncommitted transactions and data changes in memory.

CDC Replication dynamically allocates memory between these components as required and only persists data to disk in the following scenarios:

• An especially large uncommitted transaction is being accumulated.
• A latent subscription. For example, you may know of a subscription or set of subscriptions that will only run periodically which will cause the change log to grow. If sufficient memory to store the data for this latent subscription is not available, the data will be persisted to disk. Also, on shutdown or when this subscription is stopped, CDC Replication persists the data to disk.

You can optionally choose to bound disk space utilization by setting a quota using the mirror_global_disk_quota_mb system parameter. When the disk quota is met, CDC Replication will stop all running subscriptions and generate an event in the Event Log. No data is lost in this scenario.