You now can control the size of the batch of heartbeats that use Oracle Key Vault or OCI KMS (OCI Vault) for centralized key management. The HEARTBEAT_BATCH_SIZE initialization parameter, new with this release, enables you to set the heartbeat batch size. The duration of the heartbeat period defaults to 3 seconds.

This enhancement benefits the situation where you have a very large deployment of PDBs (for example, 1000) that use Oracle Key Vault. By setting the heartbeat batch size, you can stagger the heartbeats across batches of PDBs to ensure that for each batch a heartbeat can be completed for each PDB within the batch during the heartbeat period, and also ensure that PDB keys can be reliably fetched from an Oracle Key Vault server and cached in the persistent state.

For more information see:

https://docs.oracle.com/en/database/oracle/oracle-database/21/asoag/configuring-united-mode2.html#GUID-B4B3CCD1-B10B-4CA8-AA54-57A27AAB58D0