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993d90f82b
Switching to a sequence means there's no need to track `last_txn` on the AS state table to generate new TXN IDs. This also means that there is no longer contention between the AS scheduler and AS handler on updates to the `application_services_state` table, which will prevent serialization errors during the complete AS txn transaction.
45 lines
1.6 KiB
Python
45 lines
1.6 KiB
Python
# Copyright 2022 Beeper
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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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Adds a postgres SEQUENCE for generating application service transaction IDs.
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"""
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from synapse.storage.engines import PostgresEngine
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def run_create(cur, database_engine, *args, **kwargs):
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if isinstance(database_engine, PostgresEngine):
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# If we already have some AS TXNs we want to start from the current
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# maximum value. There are two potential places this is stored - the
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# actual TXNs themselves *and* the AS state table. At time of migration
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# it is possible the TXNs table is empty so we must include the AS state
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# last_txn as a potential option, and pick the maximum.
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cur.execute("SELECT COALESCE(max(txn_id), 0) FROM application_services_txns")
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row = cur.fetchone()
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txn_max = row[0]
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cur.execute("SELECT COALESCE(max(last_txn), 0) FROM application_services_state")
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row = cur.fetchone()
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last_txn_max = row[0]
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start_val = max(last_txn_max, txn_max) + 1
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cur.execute(
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"CREATE SEQUENCE application_services_txn_id_seq START WITH %s",
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(start_val,),
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)
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