[jira] [Created] (SENTRY-419) Support reading from the sentry policy service at a consistent point in time

["Lenni Kuff (JIRA)" <ji...@apache.org>]

Lenni Kuff created SENTRY-419:
---------------------------------

             Summary: Support reading from the sentry policy service at a consistent point in time
                 Key: SENTRY-419
                 URL: https://issues.apache.org/jira/browse/SENTRY-419
             Project: Sentry
          Issue Type: Task
            Reporter: Lenni Kuff


It would be very useful for the Sentry Service to support reading the policy metadata at a consistent point in time (read a snapshot). This would allow for better consistency guarantees by clients that cache policy metadata, and would also probably benefit non-cached sentry clients as well.

For example, when a cached client is reading from the Sentry service they typically would implement something along the lines of  (in pseudo-code):
{code}
for(Role role: listRoles()) {
    for (Privilege priv: listPrivileges(role.getName())
       // Process privilege 
}
{code}

Consider the following case where there are two roles - Role A and Role B. 
The client processes all privileges for Role A, but before the client moves to Role B, a  user revokes a privilege from Role A and grants it to Role B.  The client may think that this privilege belongs to both roles., which is a state the sentry policy service has never been in. 

Providing a way to read a consistent snapshot would solve this problem. A bonus would be to support reading an incremental update of the metadata since some previous point in time.



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