43 lines
2.1 KiB
SQL
43 lines
2.1 KiB
SQL
/* Copyright 2020 The Matrix.org Foundation C.I.C
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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-- This schema delta alters the schema to enable 'catching up' remote homeservers
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-- after there has been a connectivity problem for any reason.
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-- This stores, for each (destination, room) pair, the stream_ordering of the
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-- latest event for that destination.
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CREATE TABLE IF NOT EXISTS destination_rooms (
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-- the destination in question.
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destination TEXT NOT NULL REFERENCES destinations (destination),
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-- the ID of the room in question
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room_id TEXT NOT NULL REFERENCES rooms (room_id),
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-- the stream_ordering of the event
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stream_ordering BIGINT NOT NULL,
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PRIMARY KEY (destination, room_id)
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-- We don't declare a foreign key on stream_ordering here because that'd mean
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-- we'd need to either maintain an index (expensive) or do a table scan of
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-- destination_rooms whenever we delete an event (also potentially expensive).
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-- In addition to that, a foreign key on stream_ordering would be redundant
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-- as this row doesn't need to refer to a specific event; if the event gets
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-- deleted then it doesn't affect the validity of the stream_ordering here.
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);
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-- This index is needed to make it so that a deletion of a room (in the rooms
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-- table) can be efficient, as otherwise a table scan would need to be performed
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-- to check that no destination_rooms rows point to the room to be deleted.
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-- Also: it makes it efficient to delete all the entries for a given room ID,
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-- such as when purging a room.
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CREATE INDEX IF NOT EXISTS destination_rooms_room_id
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ON destination_rooms (room_id);
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