1 # Copyright (C) The Arvados Authors. All rights reserved.
3 # SPDX-License-Identifier: AGPL-3.0
5 require_relative '20200501150153_permission_table_constants'
10 def update_permissions perm_origin_uuid, starting_uuid, perm_level, edge_id=nil
11 return if Thread.current[:suppress_update_permissions]
14 # Update a subset of the permission table affected by adding or
15 # removing a particular permission relationship (ownership or a
18 # perm_origin_uuid: This is the object that 'gets' the permission.
19 # It is the owner_uuid or tail_uuid.
21 # starting_uuid: The object we are computing permission for (or head_uuid)
23 # perm_level: The level of permission that perm_origin_uuid gets for starting_uuid.
25 # perm_level is a number from 0-3
29 # or call with perm_level=0 to revoke permissions
31 # check: for testing/debugging, compare the result of the
32 # incremental update against a full table recompute. Throws an
33 # error if the contents are not identical (ie they produce different
38 # Give a change in a specific permission relationship, we recompute
39 # the set of permissions (for all users) that could possibly be
40 # affected by that relationship. For example, if a project is
41 # shared with another user, we recompute all permissions for all
42 # projects in the hierarchy. This returns a set of updated
43 # permissions, which we stash in a temporary table.
45 # Then, for each user_uuid/target_uuid in the updated permissions
46 # result set we insert/update a permission row in
47 # materialized_permissions, and delete any rows that exist in
48 # materialized_permissions that are not in the result set or have
51 # see db/migrate/20200501150153_permission_table.rb for details on
52 # how the permissions are computed.
55 # For changes of ownership, edge_id is starting_uuid. In turns
56 # out most invocations of update_permissions are for changes of
57 # ownership, so make this parameter optional to reduce
59 # For permission links, the uuid of the link object will be passed in for edge_id.
60 edge_id = starting_uuid
63 ActiveRecord::Base.transaction do
65 # "Conflicts with the ROW SHARE, ROW EXCLUSIVE, SHARE UPDATE
66 # EXCLUSIVE, SHARE, SHARE ROW EXCLUSIVE, EXCLUSIVE, and ACCESS
67 # EXCLUSIVE lock modes. This mode allows only concurrent ACCESS
68 # SHARE locks, i.e., only reads from the table can proceed in
69 # parallel with a transaction holding this lock mode."
70 ActiveRecord::Base.connection.execute "LOCK TABLE #{PERMISSION_VIEW} in EXCLUSIVE MODE"
73 # BUG #15160: planner overestimates number of rows in join when there are more than 200 rows coming from CTE
74 # https://www.postgresql.org/message-id/152395805004.19366.3107109716821067806@wrigleys.postgresql.org
76 # For a crucial join in the compute_permission_subgraph() query, the
77 # planner mis-estimates the number of rows in a Common Table
78 # Expression (CTE, this is a subquery in a WITH clause) and as a
79 # result it chooses the wrong join order. The join starts with the
80 # permissions table because it mistakenly thinks
81 # count(materalized_permissions) < count(new computed permissions)
82 # when actually it is the other way around.
84 # Because of the incorrect join order, it choose the wrong join
85 # strategy (merge join, which works best when two tables are roughly
86 # the same size). As a workaround, we can tell it not to use that
87 # join strategy, this causes it to pick hash join instead, which
88 # turns out to be a bit better. However, because the join order is
89 # still wrong, we don't get the full benefit of the index.
91 # This is very unfortunate because it makes the query performance
92 # dependent on the size of the materalized_permissions table, when
93 # the goal of this design was to make permission updates scale-free
94 # and only depend on the number of permissions affected and not the
95 # total table size. In several hours of researching I wasn't able
96 # to find a way to force the correct join order, so I'm calling it
97 # here and I have to move on.
99 # This is apparently addressed in Postgres 12, but I developed &
100 # tested this on Postgres 9.6, so in the future we should reevaluate
101 # the performance & query plan on Postgres 12.
103 # Update: as of 2023-10-13, incorrect merge join behavior is still
104 # observed on at least one major user installation that is using
105 # Postgres 14, so it seems this workaround is still needed.
107 # https://git.furworks.de/opensourcemirror/postgresql/commit/a314c34079cf06d05265623dd7c056f8fa9d577f
109 # Disable merge join for just this query (also local for this transaction), then reenable it.
110 ActiveRecord::Base.connection.exec_query "SET LOCAL enable_mergejoin to false;"
112 ActiveRecord::Base.connection.exec_query %{
113 with temptable_perms as (
114 select * from compute_permission_subgraph($1, $2, $3, $4)),
117 Now that we have recomputed a set of permissions, delete any
118 rows from the materialized_permissions table where (target_uuid,
119 user_uuid) is not present or has perm_level=0 in the recomputed
123 delete from #{PERMISSION_VIEW} where
124 target_uuid in (select target_uuid from temptable_perms) and
125 not exists (select 1 from temptable_perms
126 where target_uuid=#{PERMISSION_VIEW}.target_uuid and
127 user_uuid=#{PERMISSION_VIEW}.user_uuid and
132 Now insert-or-update permissions in the recomputed set. The
133 WHERE clause is important to avoid redundantly updating rows
134 that haven't actually changed.
136 insert into #{PERMISSION_VIEW} (user_uuid, target_uuid, perm_level, traverse_owned)
137 select user_uuid, target_uuid, val as perm_level, traverse_owned from temptable_perms where val>0
138 on conflict (user_uuid, target_uuid) do update
139 set perm_level=EXCLUDED.perm_level, traverse_owned=EXCLUDED.traverse_owned
140 where #{PERMISSION_VIEW}.user_uuid=EXCLUDED.user_uuid and
141 #{PERMISSION_VIEW}.target_uuid=EXCLUDED.target_uuid and
142 (#{PERMISSION_VIEW}.perm_level != EXCLUDED.perm_level or
143 #{PERMISSION_VIEW}.traverse_owned != EXCLUDED.traverse_owned);
145 'update_permissions.select',
152 check_permissions_against_full_refresh
158 def check_permissions_against_full_refresh
159 # No-op except when running tests
160 return unless Rails.env == 'test' and !Thread.current[:no_check_permissions_against_full_refresh] and !Thread.current[:suppress_update_permissions]
162 # For checking correctness of the incremental permission updates.
163 # Check contents of the current 'materialized_permission' table
164 # against a from-scratch permission refresh.
166 q1 = ActiveRecord::Base.connection.exec_query %{
167 select user_uuid, target_uuid, perm_level, traverse_owned from #{PERMISSION_VIEW}
168 order by user_uuid, target_uuid
169 }, "check_permissions_against_full_refresh.permission_table"
171 q2 = ActiveRecord::Base.connection.exec_query %{
172 select pq.origin_uuid as user_uuid, target_uuid, pq.val as perm_level, pq.traverse_owned from (
173 #{PERM_QUERY_TEMPLATE % {:base_case => %{
174 select uuid, uuid, 3, true, true from users
176 :edge_perm => 'edges.val'
177 } }) as pq order by origin_uuid, target_uuid
178 }, "check_permissions_against_full_refresh.full_recompute"
180 if q1.count != q2.count
181 puts "Didn't match incremental+: #{q1.count} != full refresh-: #{q2.count}"
184 if q1.count > q2.count
185 q1.each_with_index do |r, i|
187 puts "+#{r}\n-#{q2[i]}"
192 q2.each_with_index do |r, i|
194 puts "+#{q1[i]}\n-#{r}"
201 def skip_check_permissions_against_full_refresh
202 check_perm_was = Thread.current[:no_check_permissions_against_full_refresh]
203 Thread.current[:no_check_permissions_against_full_refresh] = true
207 Thread.current[:no_check_permissions_against_full_refresh] = check_perm_was
211 def batch_update_permissions
212 check_perm_was = Thread.current[:suppress_update_permissions]
213 Thread.current[:suppress_update_permissions] = true
217 Thread.current[:suppress_update_permissions] = check_perm_was
222 # Used to account for permissions that a user gains by having
223 # can_manage on another user.
225 # note: in theory a user could have can_manage access to a user
226 # through multiple levels, that isn't handled here (would require a
227 # recursive query). I think that's okay because users getting
228 # transitive access through "can_manage" on a user is is rarely/never
229 # used feature and something we probably want to deprecate and remove.
230 USER_UUIDS_SUBQUERY_TEMPLATE = %{
231 select target_uuid from materialized_permissions where user_uuid in (%{user})
232 and target_uuid like '_____-tpzed-_______________' and traverse_owned=true and perm_level >= %{perm_level}