#
# SPDX-License-Identifier: AGPL-3.0
-require 'update_permissions'
+require '20200501150153_permission_table_constants'
class PermissionTable < ActiveRecord::Migration[5.0]
def up
)
select uuid, trash_at from project_subtree;
$$;
-}
-
- ActiveRecord::Base.connection.execute %{
-create or replace function compute_trashed ()
-returns table (uuid varchar(27), trash_at timestamp)
-STABLE
-language SQL
-as $$
-/* Helper function to populate trashed_groups table. This starts with
- each group owned by a user and computes the subtree under that
- group to find any groups that are trashed.
-*/
-select ps.target_uuid as group_uuid, ps.trash_at from groups,
- lateral project_subtree_with_trash_at(groups.uuid, groups.trash_at) ps
- where groups.owner_uuid like '_____-tpzed-_______________'
-$$;
}
# Now populate the table. For a non-test databse this is the only
# time this ever happens, after this the trash table is updated
# incrementally. See app/models/group.rb#update_trash
- ActiveRecord::Base.connection.execute("INSERT INTO trashed_groups select * from compute_trashed()")
+ refresh_trashed
# The table to store the flattened permissions. This is almost
# exactly the same as the old materalized_permission_view except
# Merge all permission relationships into a single view. This
# consists of: groups (projects) owning things, users owning
- # things, and explicit permission links.
+ # things, users owning themselves, and explicit permission links.
#
- # Fun fact, a SQL view gets inlined into the query where it is
- # used, this enables the query planner to inject constraints, so
- # when using the view we only look up edges we plan to traverse
- # and avoid a brute force computation of all edges.
+ # A SQL view gets inlined into the query where it is used as a
+ # subquery. This enables the query planner to inject constraints,
+ # so we only look up edges we plan to traverse and avoid a brute
+ # force query of all edges.
ActiveRecord::Base.connection.execute %{
create view permission_graph_edges as
select groups.owner_uuid as tail_uuid, groups.uuid as head_uuid, (3) as val from groups
where links.link_class='permission'
}
+ # Code fragment that is used below. This is used to ensure that
+ # the permission edge passed into compute_permission_subgraph
+ # takes precedence over an existing edge in the "edges" view.
override = %{,
case (edges.tail_uuid = perm_origin_uuid AND
edges.head_uuid = starting_uuid)
end
}
+ #
+ # The primary function to compute permissions for a subgraph.
+ # This originally was organized somewhat more cleanly, but this
+ # ran into performance issues due to the query optimizer not
+ # working across function and "with" expression boundaries. So I
+ # had to fall back on using string templates for the repeated
+ # code. I'm sorry.
+
ActiveRecord::Base.connection.execute %{
create or replace function compute_permission_subgraph (perm_origin_uuid varchar(27),
starting_uuid varchar(27),
STABLE
language SQL
as $$
-/* perm_origin_uuid: The object that 'gets' or 'has' the permission.
+
+/* The purpose of this function is to compute the permissions for a
+ subgraph of the database, starting from a given edge. The newly
+ computed permissions are used to add and remove rows from the main
+ permissions table.
+
+ perm_origin_uuid: The object that 'gets' the permission.
starting_uuid: The starting object the permission applies to.
starting_uuid One of 1, 2, 3 for can_read,
can_write, can_manage respectively, or 0 to revoke
permissions.
-
- This function is broken up into a number of clauses, described
- below.
-
- Note on query optimization:
-
- Each clause in a "with" statement is called a "common table
- expression" or CTE.
-
- In Postgres, they are evaluated in sequence and results of each CTE
- is stored in a temporary table. This means Postgres does not
- propagate constraints from later subqueries to earlier subqueries
- when they are CTEs.
-
- This is a problem if, for example, a later subquery chooses 10
- items out of a set of 1000000 defined by an earlier subquery,
- because it will always compute all 1000000 rows even if the query
- on the 1000000 rows could have been constrained. This is why
- permission_graph_edges is a view -- views are inlined so and can be
- optimized using external constraints.
-
- The query optimizer does sort the temporary tables for later use in
- joins.
-
- Final note, this query would have been almost impossible to write
- (and certainly impossible to read) without splitting it up using
- SQL "with" but unfortunately it also stumbles into a frustrating
- Postgres optimizer bug, see
- lib/refresh_permission_view.rb#update_permissions
- for details and a partial workaround.
*/
with
- /* Gets the initial set of objects potentially affected by the
- permission change, using search_permission_graph.
+ /* Starting from starting_uuid, determine the set of objects that
+ could be affected by this permission change.
+
+ Note: We don't traverse users unless it is an "identity"
+ permission (permission origin is self).
*/
perm_from_start(perm_origin_uuid, target_uuid, val, traverse_owned) as (
#{PERM_QUERY_TEMPLATE % {:base_case => %{
:override => override
} }),
- /* Finds other inbound edges that grant permissions on the objects
- in perm_from_start, and computes permissions that originate from
- those. This is required to handle the case where there is more
- than one path through which a user gets permission to an object.
- For example, a user owns a project and also shares it can_read
- with a group the user belongs to, adding the can_read link must
- not overwrite the existing can_manage permission granted by
- ownership.
+ /* Find other inbound edges that grant permissions to 'targets' in
+ perm_from_start, and compute permissions that originate from
+ those.
+
+ This is necessary for two reasons:
+
+ 1) Other users may have access to a subset of the objects
+ through other permission links than the one we started from.
+ If we don't recompute them, their permission will get dropped.
+
+ 2) There may be more than one path through which a user gets
+ permission to an object. For example, a user owns a project
+ and also shares it can_read with a group the user belongs
+ to. adding the can_read link must not overwrite the existing
+ can_manage permission granted by ownership.
*/
additional_perms(perm_origin_uuid, target_uuid, val, traverse_owned) as (
#{PERM_QUERY_TEMPLATE % {:base_case => %{
:override => override
} }),
- /* Combines the permissions computed in the first two phases. */
+ /* Combine the permissions computed in the first two phases. */
all_perms(perm_origin_uuid, target_uuid, val, traverse_owned) as (
select * from perm_from_start
union all
Key insights:
- * Permissions are transitive (with some special cases involving
- users, this is controlled by the traverse_owned flag).
+ * For every group, the materialized_permissions lists all users
+ that can access to that group.
- * A user object can only gain permissions via an inbound edge,
- or appearing in the graph.
+ * The all_perms subquery has computed permissions on on a set of
+ objects for all inbound "origins", which are users or groups.
- * The materialized_permissions table includes the permission
- each user has on the tail end of each inbound edge.
+ * Permissions through groups are transitive.
- * The all_perms subquery has permissions for each object in the
- subgraph reachable from certain origin (tail end of an edge).
+ We can infer:
- * Therefore, for each user, we can compute user permissions on
- each object in subgraph by determining the permission the user
- has on each origin (tail end of an edge), joining that with the
- perm_origin_uuid column of all_perms, and taking the least() of
- the origin edge or all_perms val (because of the "least
- permission on the path" rule). If an object was reachable by
- more than one path (appears with more than one origin), we take
- the max() of the computed permissions.
+ 1) The materialized_permissions table declares that user X has permission N on group Y
+ 2) The all_perms result has determined group Y has permission M on object Z
+ 3) Therefore, user X has permission min(N, M) on object Z
- * Finally, because users always have permission on themselves, the
- query also makes sure those permission rows are always
- returned.
+ This allows us to efficiently determine the set of users that
+ have permissions on the subset of objects, without having to
+ follow the chain of permission back up to find those users.
+
+ In addition, because users always have permission on themselves, this
+ query also makes sure those permission rows are always
+ returned.
*/
select v.user_uuid, v.target_uuid, max(v.perm_level), bool_or(v.traverse_owned) from
(select m.user_uuid,
}
#
- # Populate the materialized_permissions by traversing permissions
+ # Populate materialized_permissions by traversing permissions
# starting at each user.
#
- ActiveRecord::Base.connection.execute %{
-INSERT INTO materialized_permissions
- #{PERM_QUERY_TEMPLATE % {:base_case => %{
- select uuid, uuid, 3, true, true from users
-},
-:override => ''
-} }
-}
+ refresh_permissions
end
def down
drop_table :trashed_groups
ActiveRecord::Base.connection.execute "DROP function project_subtree_with_trash_at (varchar, timestamp);"
- ActiveRecord::Base.connection.execute "DROP function compute_trashed ();"
ActiveRecord::Base.connection.execute "DROP function compute_permission_subgraph (varchar, varchar, integer);"
ActiveRecord::Base.connection.execute "DROP function should_traverse_owned(varchar, integer);"
ActiveRecord::Base.connection.execute "DROP view permission_graph_edges;"
projects / arvados.git / blobdiff