Fix background schema updates failing over a large upgrade gap (#15887)

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Shay 2023-07-18 16:59:27 -07:00 committed by GitHub
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Fix background schema updates failing over a large upgrade gap.

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# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from synapse.storage.database import LoggingTransaction
from synapse.storage.engines import BaseDatabaseEngine, PostgresEngine
def run_create(
cur: LoggingTransaction,
database_engine: BaseDatabaseEngine,
) -> None:
"""
An attempt to mitigate a painful race between foreground and background updates
touching the `stream_ordering` column of the events table. More info can be found
at https://github.com/matrix-org/synapse/issues/15677.
"""
# technically the bg update we're concerned with below should only have been added in
# postgres but it doesn't hurt to be extra careful
if isinstance(database_engine, PostgresEngine):
select_sql = """
SELECT 1 FROM background_updates
WHERE update_name = 'replace_stream_ordering_column'
"""
cur.execute(select_sql)
res = cur.fetchone()
# if the background update `replace_stream_ordering_column` is still pending, we need
# to drop the indexes added in 7403, and re-add them to the column `stream_ordering2`
# with the idea that they will be preserved when the column is renamed `stream_ordering`
# after the background update has finished
if res:
drop_cse_sql = """
ALTER TABLE current_state_events DROP CONSTRAINT event_stream_ordering_fkey
"""
cur.execute(drop_cse_sql)
drop_lcm_sql = """
ALTER TABLE local_current_membership DROP CONSTRAINT event_stream_ordering_fkey
"""
cur.execute(drop_lcm_sql)
drop_rm_sql = """
ALTER TABLE room_memberships DROP CONSTRAINT event_stream_ordering_fkey
"""
cur.execute(drop_rm_sql)
add_cse_sql = """
ALTER TABLE current_state_events ADD CONSTRAINT event_stream_ordering_fkey
FOREIGN KEY (event_stream_ordering) REFERENCES events(stream_ordering2) NOT VALID;
"""
cur.execute(add_cse_sql)
add_lcm_sql = """
ALTER TABLE local_current_membership ADD CONSTRAINT event_stream_ordering_fkey
FOREIGN KEY (event_stream_ordering) REFERENCES events(stream_ordering2) NOT VALID;
"""
cur.execute(add_lcm_sql)
add_rm_sql = """
ALTER TABLE room_memberships ADD CONSTRAINT event_stream_ordering_fkey
FOREIGN KEY (event_stream_ordering) REFERENCES events(stream_ordering2) NOT VALID;
"""
cur.execute(add_rm_sql)