References:

Explanation
Autonomous Transaction Processing comes with predefined CPU/IO shares assigned to different consumer groups. You can modify these predefined CPU/IO shares if your workload requires different CPU/IO resource allocations.
By default, the CPU/IO shares assigned to the consumer groups TPURGENT, TP, HIGH, MEDIUM, and LOW are 12, 8, 4, 2, and 1, respectively. The shares determine how much CPU/IO resources a consumer group can use with respect to the other consumer groups. With the default settings the consumer group TPURGENT will be able to use 12 times more CPU/IO resources compared to LOW, when needed. The consumer group TP will be able to use 4 times more CPU/IO resources compared to MEDIUM, when needed.

Reference:
https://docs.cloud.oracle.com/en-us/iaas/Content/Network/Tasks/remoteVCNpeering.htm (note)

Pre-authenticated requests provide a way to let users access a bucket or an object without having their own credentials, as long as the request creator has permissions to access those objects. For example, you can create a request that lets an operations support user upload backups to a bucket without owning API keys. Or, you can create a request that lets a business partner update shared data in a bucket without owning API keys.
When you create a pre-authenticated request, a unique URL is generated. Anyone you provide this URL to can access the Object Storage resources identified in the pre-authenticated request, using standard HTTP tools like curl and wget.
Understand the following scope and constraints regarding pre-authenticated requests:
Users can't list bucket contents.
You can create an unlimited number of pre-authenticated requests.
There is no time limit to the expiration date that you can set.
You can't edit a pre-authenticated request. If you want to change user access options in response to changing requirements, you must create a new pre-authenticated request.
The target and actions for a pre-authenticated request are based on the creator's permissions. The request is not, however, bound to the creator's account login credentials. If the creator's login credentials change, a pre-authenticated request is not affected.
You cannot delete a bucket that has a pre-authenticated request associated with that bucket or with an object in that bucket.
Understand the following scope and constraints regarding public access:
Changing the type of access is bi-directional. You can change a bucket's access from public to private or from private to public.
Changing the type of access doesn't affect existing pre-authenticated requests. Existing pre-authenticated requests still work.

A policy is a document that specifies who can access which Oracle Cloud Infrastructure resources that your company has, and how. A policy simply allows a group to work in certain ways with specific types of resources in a particular compartment In general, here's the process an IAM administrator in your organization needs to follow:
Define users, groups, and one or more compartments to hold the cloud resources for your organization.
Create one or more policies, each written in the policy language.
Place users into the appropriate groups depending on the compartments and resources they need to work with.
Provide the users with the one-time passwords that they need in order to access the Console and work with the compartments. For more information,