1 # Copyright (C) The Arvados Authors. All rights reserved.
3 # SPDX-License-Identifier: AGPL-3.0
5 PERMISSION_VIEW = "materialized_permissions"
6 TRASHED_GROUPS = "trashed_groups"
8 def refresh_permission_view
9 ActiveRecord::Base.transaction do
10 ActiveRecord::Base.connection.execute("LOCK TABLE #{PERMISSION_VIEW}")
11 ActiveRecord::Base.connection.execute("DELETE FROM #{PERMISSION_VIEW}")
12 ActiveRecord::Base.connection.execute %{
13 INSERT INTO #{PERMISSION_VIEW}
14 select users.uuid, g.target_uuid, g.val, g.traverse_owned
15 from users, lateral search_permission_graph(users.uuid, 3) as g where g.val > 0
17 "refresh_permission_view.do"
22 ActiveRecord::Base.connection.execute("LOCK TABLE #{TRASHED_GROUPS}")
23 ActiveRecord::Base.connection.execute("DELETE FROM #{TRASHED_GROUPS}")
24 ActiveRecord::Base.connection.execute("INSERT INTO #{TRASHED_GROUPS} select * from compute_trashed()")
27 def update_permissions perm_origin_uuid, starting_uuid, perm_level, check=false
29 # Update a subset of the permission table affected by adding or
30 # removing a particular permission relationship (ownership or a
33 # perm_origin_uuid: This is the object that 'gets' the permission.
34 # It is the owner_uuid or tail_uuid.
36 # starting_uuid: The object we are computing permission for (or head_uuid)
38 # perm_level: The level of permission that perm_origin_uuid gets for starting_uuid.
40 # perm_level is a number from 0-3
44 # or call with perm_level=0 to revoke permissions
46 # check: for testing/debugging only, compare the result of the
47 # incremental update against a full table recompute. Throws an
48 # error if the contents are not identical (ie they produce different
53 # Give a change in a specific permission relationship, we recompute
54 # the set of permissions (for all users) that could possibly be
55 # affected by that relationship. For example, if a project is
56 # shared with another user, we recompute all permissions for all
57 # projects in the hierarchy. This returns a set of updated
58 # permissions, which we stash in a temporary table.
60 # Then, for each user_uuid/target_uuid in the updated permissions
61 # result set we insert/update a permission row in
62 # materialized_permissions, and delete any rows that exist in
63 # materialized_permissions that are not in the result set or have
66 # see db/migrate/20200501150153_permission_table.rb for details on
67 # how the permissions are computed.
69 # "Conflicts with the ROW EXCLUSIVE, SHARE UPDATE EXCLUSIVE, SHARE
70 # ROW EXCLUSIVE, EXCLUSIVE, and ACCESS EXCLUSIVE lock modes. This
71 # mode protects a table against concurrent data changes."
72 ActiveRecord::Base.connection.execute "LOCK TABLE #{PERMISSION_VIEW} in SHARE MODE"
75 # BUG #15160: planner overestimates number of rows in join when there are more than 200 rows coming from CTE
76 # https://www.postgresql.org/message-id/152395805004.19366.3107109716821067806@wrigleys.postgresql.org
78 # For a crucial join in the compute_permission_subgraph() query, the
79 # planner mis-estimates the number of rows in a Common Table
80 # Expression (CTE, this is a subquery in a WITH clause) and as a
81 # result it chooses the wrong join order. The join starts with the
82 # permissions table because it mistakenly thinks
83 # count(materalized_permissions) < count(new computed permissions)
84 # when actually it is the other way around.
86 # Because of the incorrect join order, it choose the wrong join
87 # strategy (merge join, which works best when two tables are roughly
88 # the same size). As a workaround, we can tell it not to use that
89 # join strategy, this causes it to pick hash join instead, which
90 # turns out to be a bit better. However, because the join order is
91 # still wrong, we don't get the full benefit of the index.
93 # This is very unfortunate because it makes the query performance
94 # dependent on the size of the materalized_permissions table, when
95 # the goal of this design was to make permission updates scale-free
96 # and only depend on the number of permissions affected and not the
97 # total table size. In several hours of researching I wasn't able
98 # to find a way to force the correct join order, so I'm calling it
99 # here and I have to move on.
101 # This is apparently addressed in Postgres 12, but I developed &
102 # tested this on Postgres 9.6, so in the future we should reevaluate
103 # the performance & query plan on Postgres 12.
105 # https://git.furworks.de/opensourcemirror/postgresql/commit/a314c34079cf06d05265623dd7c056f8fa9d577f
107 # Disable merge join for just this query (also local for this transaction), then reenable it.
108 ActiveRecord::Base.connection.exec_query "SET LOCAL enable_mergejoin to false;"
110 temptable_perms = "temp_perms_#{rand(2**64).to_s(10)}"
111 ActiveRecord::Base.connection.exec_query %{
112 create temporary table #{temptable_perms} on commit drop
113 as select * from compute_permission_subgraph($1, $2, $3)
115 'update_permissions.select',
116 [[nil, perm_origin_uuid],
117 [nil, starting_uuid],
120 ActiveRecord::Base.connection.exec_query "SET LOCAL enable_mergejoin to true;"
122 ActiveRecord::Base.connection.exec_delete %{
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
130 "update_permissions.delete"
132 ActiveRecord::Base.connection.exec_query %{
133 insert into #{PERMISSION_VIEW} (user_uuid, target_uuid, perm_level, traverse_owned)
134 select user_uuid, target_uuid, val as perm_level, traverse_owned from #{temptable_perms} where val>0
135 on conflict (user_uuid, target_uuid) do update set perm_level=EXCLUDED.perm_level, traverse_owned=EXCLUDED.traverse_owned;
137 "update_permissions.insert"
139 if check and perm_level>0
140 check_permissions_against_full_refresh
145 def check_permissions_against_full_refresh
147 # For debugging, this checks contents of the
148 # incrementally-updated 'materialized_permission' against a
149 # from-scratch permission refresh.
152 q1 = ActiveRecord::Base.connection.exec_query %{
153 select user_uuid, target_uuid, perm_level, traverse_owned from #{PERMISSION_VIEW}
154 order by user_uuid, target_uuid
155 }, "check_permissions_against_full_refresh.permission_table"
157 q2 = ActiveRecord::Base.connection.exec_query %{
158 select users.uuid as user_uuid, g.target_uuid, g.val as perm_level, g.traverse_owned
159 from users, lateral search_permission_graph(users.uuid, 3) as g where g.val > 0
160 order by users.uuid, target_uuid
161 }, "check_permissions_against_full_refresh.full_recompute"
163 if q1.count != q2.count
164 puts "Didn't match incremental+: #{q1.count} != full refresh-: #{q2.count}"
167 if q1.count > q2.count
168 q1.each_with_index do |r, i|
170 puts "+#{r}\n-#{q2[i]}"
175 q2.each_with_index do |r, i|
177 puts "+#{q1[i]}\n-#{r}"