Create DB Performance improvements

[tanscorpio7]

Description

In Multi DB mode, as the number of databases increases, so does the time to create the next new DB.
This is because we create three internal roles for each new DB and internally when run the DB subcommands, multiple calls to roles_is_member_of("sysadmin") is made. Now that output of this list contains all the three roles of every db created. This is the major reason for the perfomance degradation of CREATE DB command.

We fix this in three different places.

1. getAvailDbid - this functions makes a call to nextval function, which by default checks for current user's permission and makes a call to roles_is_member_of. Instead we could call the nextval_internal which is the same function but with the additional option of check permissions flag which we will set to false. To double check we can just ensure that the current user is "sysadmin" when getAvailDbid is called. (Currently we only call this when user is sysadmin)

2. Set temporary user when creating schema - when we create the dbo and guest schema for the new database, the create schema function fetches all the roles that current role is member of (recursively) to check if if current role can actually become the target schema owner role. To bypass this we can assume the newdb_dbo role when creating these schemas. In this case all the roles that newdb_dbo is member of will be fetched, but this list is much smaller than sysadmin.

3. Select best grantor - Select best grantor first fetches the roles_list that sysadmin is member of and then start checking for permissions. But sysadmin is always the first to be checked. That is sysadmin is always top of the roles_list.
   We can add a quick check to this. That is, first check if current role is sysadmin and can it give us all the permission needed. If yes, simply return. Note** This does not change any behaviour since this will anyway be done in the first loop after fetching roles_list. We are instead running the first loop before fetching the whole list.

4. Set newdb_dbo user when creating sysdatabases view in new db

Create DB	After	Before
DBs10	2ms	5ms
DBs500	3ms	163ms
DBs1000	4ms	740ms
DBs3000	9ms	NA(~18secs)

Engine PR: babelfish-for-postgresql/postgresql_modified_for_babelfish#234

Extension PR: #1899

Issues Resolved

BABEL-3869

Signed-off-by: Tanzeel Khan [email protected]

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[shalinilohia50]

Could you please mention how much improvement we have observed after these changes?