code: public ManagedBackupShortTermRetentionPolicyInner update(String resourceGroupName, String managedInstanceName, String databaseName, Integer retentionDays) {
          return updateWithServiceResponseAsync(resourceGroupName, managedInstanceName, databaseName, retentionDays).toBlocking().last().body();
      }
docs: Updates a managed database's short term retention policy.
  
  @param resourceGroupName The name of the resource group that contains the resource. You can obtain this value from the Azure Resource Manager API or the portal.
  @param managedInstanceName The name of the managed instance.
  @param databaseName The name of the database.
  @param retentionDays The backup retention period in days. This is how many days Point-in-Time Restore will be supported.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @throws CloudException thrown if the request is rejected by server
  @throws RuntimeException all other wrapped checked exceptions if the request fails to be sent
  @return the ManagedBackupShortTermRetentionPolicyInner object if successful.